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- PostgreSQL için Sıkça Sorulan Sorular (SSS)
-
-Son güncelleme : 19 Mayıs 2003 Pazartesi - 03:05:21
-
-Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us
-<mailto:pgman@candle.pha.pa.us>)
-
-Çeviren : Devrim GÜNDÜZ (devrim@gunduz.org <mailto:devrim@gunduz.org>)
-Nicolai Tufar (ntufar@yahoo.com <mailto:ntufar@yahoo.com>)
-
-Bu belgenin en güncel hali,
-http://www.PostgreSQL.org/docs/faqs/FAQ_turkish.html ve
-http://www.gunduz.org/seminer/pg/FAQ_turkish adreslerinde görülebilir.
-
-Platforma özel sorularınız,http://www.PostgreSQL.org/docs/index.html
-adresinde yanıtlanır..
-
-------------------------------------------------------------------------
-
-
- Genel Sorular
-
-1.1 <#1.1>) PostgreSQL nedir? Nasıl okunur?
-1.2 <#1.2>) PostgreSQL' in hakları nedir?
-1.3 <#1.3>) PostgreSQL, hangi Unix platformlarında çalısır?
-1.4 <#1.4>) Hangi Unix olmayan uyarlamaları bulunmaktadır?
-1.5 <#1.5>) PostgreSQL'i nereden indirebilirim?
-1.6 <#1.6>) Desteği nereden alabilirim?
-1.7 <#1.7>) En son sürümü nedir?
-1.8 <#1.8>) Hangi belgelere ulasabilirim?
-1.9 <#1.9>) Bilinen hatalar ya da eksik özelliklere nereden ulasabilirim?
-1.10 <#1.10>) Nasıl SQL öğrenebilirim?
-1.11 <#1.11>) PostgreSQL 2000 yılına uyumlu mudur?
-1.12 <#1.12>) Geliştirme takımına nasıl katılabilirim??
-1.13 <#1.13>) Bir hata raporunu nasıl gönderebilirim?
-1.14 <#1.14>) PostgreSQL, diger VTYS(DBMS lerle nasıl karşılaştırılabilir?
-1.15 <#1.15>) PostgreSQL'e maddi açıdan nasıl destek olabilirim?
-
-
- Kullanıcı/istemci Soruları
-
-2.1 <#2.1>) Are there ODBC drivers for PostgreSQL?
-2.2 <#2.2>) What tools are available for using PostgreSQL with Web pages?
-2.3 <#2.3>) Does PostgreSQL have a graphical user interface?
-2.4 <#2.4>) What languages are available to communicate with PostgreSQL?
-
-
- Administrative Questions
-
-3.1 <#3.1>) How do I install PostgreSQL somewhere other than
-//usr/local/pgsql/?
-3.2 <#3.2>) When I start /postmaster/, I get a /Bad System Call/ or core
-dumped message. Why?
-3.3 <#3.3>) When I try to start /postmaster/, I get /IpcMemoryCreate/
-errors. Why?
-3.4 <#3.4>) When I try to start /postmaster/, I get /IpcSemaphoreCreate/
-errors. Why?
-3.5 <#3.5>) How do I control connections from other hosts?
-3.6 <#3.6>) How do I tune the database engine for better performance?
-3.7 <#3.7>) What debugging features are available?
-3.8 <#3.8>) Why do I get /"Sorry, too many clients"/ when trying to connect?
-3.9 <#3.9>) What is in the /pgsql_tmp/ directory?
-3.10 <#3.10>) Why do I need to do a dump and restore to upgrade
-PostgreSQL releases?
-
-
- Operational Questions
-
-4.1 <#4.1>) What is the difference between binary cursors and normal
-cursors?
-4.2 <#4.2>) How do I SELECT only the first few rows of a query?
-4.3 <#4.3>) How do I get a list of tables or other things I can see in
-/psql/?
-4.4 <#4.4>) How do you remove a column from a table?
-4.5 <#4.5>) What is the maximum size for a row, a table, and a database?
-4.6 <#4.6>) How much database disk space is required to store data from
-a typical text file?
-4.7 <#4.7>) How do I find out what tables, indexes, databases, and users
-are defined?
-4.8 <#4.8>) My queries are slow or don't make use of the indexes. Why?
-4.9 <#4.9>) How do I see how the query optimizer is evaluating my query?
-4.10 <#4.10>) What is an R-tree index?
-4.11 <#4.11>) What is the Genetic Query Optimizer?
-4.12 <#4.12>) How do I perform regular expression searches and
-case-insensitive regular expression searches? How do I use an index for
-case-insensitive searches?
-4.13 <#4.13>) In a query, how do I detect if a field is NULL?
-4.14 <#4.14>) What is the difference between the various character types?
-4.15.1 <#4.15.1>) How do I create a serial/auto-incrementing field?
-4.15.2 <#4.15.2>) How do I get the value of a SERIAL insert?
-4.15.3 <#4.15.3>) Don't /currval()/ and /nextval()/ lead to a race
-condition with other users?
-4.15.4 <#4.15.4>) Why aren't my sequence numbers reused on transaction
-abort? Why are there gaps in the numbering of my sequence/SERIAL column?
-4.16 <#4.16>) What is an OID? What is a TID?
-4.17 <#4.17>) What is the meaning of some of the terms used in PostgreSQL?
-4.18 <#4.18>) Why do I get the error /"ERROR: Memory exhausted in
-AllocSetAlloc()"/?
-4.19 <#4.19>) How do I tell what PostgreSQL version I am running?
-4.20 <#4.20>) Why does my large-object operations get /"invalid large
-obj descriptor"/?
-4.21 <#4.21>) How do I create a column that will default to the current
-time?
-4.22 <#4.22>) Why are my subqueries using |IN| so slow?
-4.23 <#4.23>) How do I perform an outer join?
-4.24 <#4.24>) How do I perform queries using multiple databases?
-4.25 <#4.25>) How do I return multiple rows or columns from a function?
-4.26 <#4.26>) Why can't I reliably create/drop temporary tables in
-PL/PgSQL functions?
-4.27 <#4.27>) What replication options are available?
-4.28 <#4.28>) What encryption options are available?
-
-
- Extending PostgreSQL
-
-5.1 <#5.1>) I wrote a user-defined function. When I run it in /psql/,
-why does it dump core?
-5.2 <#5.2>) How can I contribute some nifty new types and functions to
-PostgreSQL?
-5.3 <#5.3>) How do I write a C function to return a tuple?
-5.4 <#5.4>) I have changed a source file. Why does the recompile not see
-the change?
-------------------------------------------------------------------------
-
-
- General Questions
-
-
- 1.1) What is PostgreSQL? How is it pronounced?
-
-PostgreSQL is pronounced /Post-Gres-Q-L/.
-
-PostgreSQL is an enhancement of the POSTGRES database management system,
-a next-generation DBMS research prototype. While PostgreSQL retains the
-powerful data model and rich data types of POSTGRES, it replaces the
-PostQuel query language with an extended subset of SQL. PostgreSQL is
-free and the complete source is available.
-
-PostgreSQL development is performed by a team of developers who all
-subscribe to the PostgreSQL development mailing list. The current
-coordinator is Marc G. Fournier (scrappy@PostgreSQL.org
-<mailto:scrappy@PostgreSQL.org>). (See section 1.6 <#1.6> on how to
-join). This team is now responsible for all development of PostgreSQL.
-
-The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many
-others have contributed to the porting, testing, debugging, and
-enhancement of the code. The original Postgres code, from which
-PostgreSQL is derived, was the effort of many graduate students,
-undergraduate students, and staff programmers working under the
-direction of Professor Michael Stonebraker at the University of
-California, Berkeley.
-
-The original name of the software at Berkeley was Postgres. When SQL
-functionality was added in 1995, its name was changed to Postgres95. The
-name was changed at the end of 1996 to PostgreSQL.
-
-
- 1.2) What is the copyright on PostgreSQL?
-
-PostgreSQL is subject to the following COPYRIGHT:
-
-PostgreSQL Data Base Management System
-
-Portions copyright (c) 1996-2002, PostgreSQL Global Development Group
-Portions Copyright (c) 1994-6 Regents of the University of California
-
-Permission to use, copy, modify, and distribute this software and its
-documentation for any purpose, without fee, and without a written
-agreement is hereby granted, provided that the above copyright notice
-and this paragraph and the following two paragraphs appear in all copies.
-
-IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
-FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
-INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
-DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF
-THE POSSIBILITY OF SUCH DAMAGE.
-
-THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
-INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
-AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
-ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS
-TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
-
-The above is the BSD license, the classic open-source license. It has no
-restrictions on how the source code may be used. We like it and have no
-intention of changing it.
-
-
- 1.3) What Unix platforms does PostgreSQL run on?
-
-In general, a modern Unix-compatible platform should be able to run
-PostgreSQL. The platforms that had received explicit testing at the time
-of release are listed in the installation instructions.
-
-
- 1.4) What non-Unix ports are available?
-
-*Client*
-
-It is possible to compile the /libpq/ C library, psql, and other
-interfaces and client applications to run on MS Windows platforms. In
-this case, the client is running on MS Windows, and communicates via
-TCP/IP to a server running on one of our supported Unix platforms. A
-file /win32.mak/ is included in the distribution for making a Win32
-/libpq/ library and /psql/. PostgreSQL also communicates with ODBC clients.
-
-*Server*
-
-The database server can run on Windows NT and Win2k using Cygwin, the
-Cygnus Unix/NT porting library. See /pgsql/doc/FAQ_MSWIN/ in the
-distribution or the MS Windows FAQ at
-http://www.PostgreSQL.org/docs/faqs/text/FAQ_MSWIN
-<http://www.PostgreSQL.org/docs/faqs/text/FAQ_MSWIN>.
-
-A native port to MS Win NT/2000/XP is currently being worked on. For
-more details on the current status of PostgreSQL on Windows see
-http://techdocs.postgresql.org/guides/Windows
-<http://techdocs.postgresql.org/guides/Windows>.
-
-There is also a Novell Netware 6 port at http://forge.novell.com.
-
-
- 1.5) Where can I get PostgreSQL?
-
-The primary anonymous ftp site for PostgreSQL is
-ftp://ftp.PostgreSQL.org/pub. For mirror sites, see our main web site.
-
-
- 1.6) Where can I get support?
-
-The main mailing list is: pgsql-general@PostgreSQL.org
-<mailto:pgsql-general@PostgreSQL.org>. It is available for discussion of
-matters pertaining to PostgreSQL. To subscribe, send mail with the
-following lines in the body (not the subject line):
-
- subscribe
- end
-
-to pgsql-general-request@PostgreSQL.org
-<mailto:pgsql-general-request@PostgreSQL.org>.
-
-There is also a digest list available. To subscribe to this list, send
-email to: pgsql-general-digest-request@PostgreSQL.org
-<mailto:pgsql-general-digest-request@PostgreSQL.org> with a body of:
-
- subscribe
- end
-
-Digests are sent out to members of this list whenever the main list has
-received around 30k of messages.
-
-The bugs mailing list is available. To subscribe to this list, send
-email to pgsql-bugs-request@PostgreSQL.org
-<mailto:pgsql-bugs-request@PostgreSQL.org> with a body of:
-
- subscribe
- end
-
-There is also a developers discussion mailing list available. To
-subscribe to this list, send email to
-pgsql-hackers-request@PostgreSQL.org
-<mailto:pgsql-hackers-request@PostgreSQL.org> with a body of:
-
- subscribe
- end
-
-Additional mailing lists and information about PostgreSQL can be found
-via the PostgreSQL WWW home page at:
-
- http://www.PostgreSQL.org
-
-There is also an IRC channel on EFNet and OpenProjects, channel
-/#PostgreSQL/. I use the Unix command |irc -c '#PostgreSQL' "$USER"
-irc.phoenix.net.|
-
-A list of commercial support companies is available at
-http://www.ca.PostgreSQL.org/users-lounge/commercial-support.html.
-
-
- 1.7) What is the latest release?
-
-The latest release of PostgreSQL is version 7.3.3.
-
-We plan to have major releases every four months.
-
-
- 1.8) What documentation is available?
-
-Several manuals, manual pages, and some small test examples are included
-in the distribution. See the //doc/ directory. You can also browse the
-manuals online at http://www.PostgreSQL.org/docs.
-
-There are two PostgreSQL books available online at
-http://www.PostgreSQL.org/docs/awbook.html and
-http://www.commandprompt.com/ppbook/. There is a list of PostgreSQL
-books available for purchase at http://www.ca.PostgreSQL.org/books/.
-There is also a collection of PostgreSQL technical articles at
-http://techdocs.PostgreSQL.org/.
-
-/psql/ has some nice \d commands to show information about types,
-operators, functions, aggregates, etc.
-
-Our web site contains even more documentation.
-
-
- 1.9) How do I find out about known bugs or missing features?
-
-PostgreSQL supports an extended subset of SQL-92. See our TODO
-<http://developer.PostgreSQL.org/todo.php> list for known bugs, missing
-features, and future plans.
-
-
- 1.10) How can I learn SQL?
-
-The PostgreSQL book at http://www.PostgreSQL.org/docs/awbook.html
-teaches SQL. There is another PostgreSQL book at
-http://www.commandprompt.com/ppbook.
-<http://www.commandprompt.com/ppbook/> There is a nice tutorial at
-http://www.intermedia.net/support/sql/sqltut.shtm,
-<http://www.intermedia.net/support/sql/sqltut.shtm> at
-http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM,
-<http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM>
-and at http://sqlcourse.com. <http://sqlcourse.com/>
-
-Another one is "Teach Yourself SQL in 21 Days, Second Edition" at
-http://members.tripod.com/er4ebus/sql/index.htm
-
-Many of our users like /The Practical SQL Handbook/, Bowman, Judith S.,
-et al., Addison-Wesley. Others like /The Complete Reference SQL/, Groff
-et al., McGraw-Hill.
-
-
- 1.11) Is PostgreSQL Y2K compliant?
-
-Yes, we easily handle dates past the year 2000 AD, and before 2000 BC.
-
-
- 1.12) How do I join the development team?
-
-First, download the latest source and read the PostgreSQL Developers
-documentation on our web site, or in the distribution. Second, subscribe
-to the /pgsql-hackers/ and /pgsql-patches/ mailing lists. Third, submit
-high quality patches to pgsql-patches.
-
-There are about a dozen people who have commit privileges to the
-PostgreSQL CVS archive. They each have submitted so many high-quality
-patches that it was impossible for the existing committers to keep up,
-and we had confidence that patches they committed were of high quality.
-
-
- 1.13) How do I submit a bug report?
-
-Please visit the PostgreSQL BugTool page at
-http://www.PostgreSQL.org/bugs/bugs.php, which gives guidelines and
-directions on how to submit a bug report.
-
-Also check out our ftp site ftp://ftp.PostgreSQL.org/pub to see if there
-is a more recent PostgreSQL version or patches.
-
-
- 1.14) How does PostgreSQL compare to other DBMSs?
-
-There are several ways of measuring software: features, performance,
-reliability, support, and price.
-
-*Features*
- PostgreSQL has most features present in large commercial DBMSs, like
- transactions, subselects, triggers, views, foreign key referential
- integrity, and sophisticated locking. We have some features they do
- not have, like user-defined types, inheritance, rules, and
- multi-version concurrency control to reduce lock contention.
-
-*Performance*
- PostgreSQL has performance similar to other commercial and open
- source databases. it is faster for some things, slower for others.
- In comparison to MySQL or leaner database systems, we are slower on
- inserts/updates because of transaction overhead. Of course, MySQL
- does not have any of the features mentioned in the /Features/
- section above. We are built for reliability and features, though we
- continue to improve performance in every release. There is an
- interesting Web page comparing PostgreSQL to MySQL at
- http://openacs.org/philosophy/why-not-mysql.html
- <http://openacs.org/philosophy/why-not-mysql.html>
-
-*Reliability*
- We realize that a DBMS must be reliable, or it is worthless. We
- strive to release well-tested, stable code that has a minimum of
- bugs. Each release has at least one month of beta testing, and our
- release history shows that we can provide stable, solid releases
- that are ready for production use. We believe we compare favorably
- to other database software in this area.
-
-*Support*
- Our mailing lists provide contact with a large group of developers
- and users to help resolve any problems encountered. While we cannot
- guarantee a fix, commercial DBMSs do not always supply a fix either.
- Direct access to developers, the user community, manuals, and the
- source code often make PostgreSQL support superior to other DBMSs.
- There is commercial per-incident support available for those who
- need it. (See FAQ section 1.6 <#1.6>.)
-
-*Price*
- We are free for all use, both commercial and non-commercial. You can
- add our code to your product with no limitations, except those
- outlined in our BSD-style license stated above.
-
-
- 1.15) How can I financially assist PostgreSQL?
-
-PostgreSQL has had a first-class infrastructure since we started in
-1996. This is all thanks to Marc Fournier, who has created and managed
-this infrastructure over the years.
-
-Quality infrastructure is very important to an open-source project. It
-prevents disruptions that can greatly delay forward movement of the project.
-
-Of course, this infrastructure is not cheap. There are a variety of
-monthly and one-time expenses that are required to keep it going. If you
-or your company has money it can donate to help fund this effort, please
-go to http://store.pgsql.com/shopping/ and make a donation.
-
-Although the web page mentions PostgreSQL, Inc, the "contributions" item
-is solely to support the PostgreSQL project and does not fund any
-specific company. If you prefer, you can also send a check to the
-contact address.
-
-------------------------------------------------------------------------
-
-
- User Client Questions
-
-
- 2.1) Are there ODBC drivers for PostgreSQL?
-
-There are two ODBC drivers available, PsqlODBC and OpenLink ODBC.
-
-You can download PsqlODBC from
-http://gborg.postgresql.org/project/psqlodbc/projdisplay.php
-<http://gborg.postgresql.org/project/psqlodbc/projdisplay.php>.
-
-OpenLink ODBC can be gotten from http://www.openlinksw.com
-<http://www.openlinksw.com/>. It works with their standard ODBC client
-software so you'll have PostgreSQL ODBC available on every client
-platform they support (Win, Mac, Unix, VMS).
-
-They will probably be selling this product to people who need
-commercial-quality support, but a freeware version will always be
-available. Please send questions to postgres95@openlink.co.uk
-<mailto:postgres95@openlink.co.uk>.
-
-
- 2.2) What tools are available for using PostgreSQL with Web pages?
-
-A nice introduction to Database-backed Web pages can be seen at:
-http://www.webreview.com
-
-For Web integration, PHP is an excellent interface. It is at
-http://www.php.net.
-
-For complex cases, many use the Perl interface and CGI.pm or mod_perl.
-
-
- 2.3) Does PostgreSQL have a graphical user interface?
-
-Yes, there are several graphical interfaces to PostgreSQL available.
-These include PgAccess http://www.pgaccess.org
-<http://www.pgaccess.org>), PgAdmin II (http://www.pgadmin.org,
-Win32-only), RHDB Admin (http://sources.redhat.com/rhdb/ ) and Rekall (
-http://www.thekompany.com/products/rekall/
-<http://www.thekompany.com/products/rekall/>, proprietary). There is
-also PHPPgAdmin ( http://phppgadmin.sourceforge.net/
-<http://phppgadmin.sourceforge.net/>), a web-based interface to PostgreSQL.
-
-See http://techdocs.postgresql.org/guides/GUITools for a more detailed list.
-
-
- 2.4) What languages are able to communicate with PostgreSQL?
-
-Most popular programming languages contain an interface to PostgreSQL.
-Check your programming language's list of extension modules.
-
-The following interfaces are included in the PostgreSQL distribution:
-
- * C (libpq)
- * Embedded C (ecpg)
- * Java (jdbc)
- * Python (PyGreSQL)
- * TCL (libpgtcl)
-
-Additional interfaces are available at http://gborg.postgresql.org in
-the /Drivers/Interfaces/ section.
-
-------------------------------------------------------------------------
-
-
- Administrative Questions
-
-
- 3.1) How do I install PostgreSQL somewhere other than
- //usr/local/pgsql/?
-
-Specify the /--prefix/ option when running /configure/.
-
-
- 3.2) When I start /postmaster/, I get a /Bad System Call/ or
- core dumped message. Why?
-
-It could be a variety of problems, but first check to see that you have
-System V extensions installed in your kernel. PostgreSQL requires kernel
-support for shared memory and semaphores.
-
-
- 3.3) When I try to start /postmaster/, I get /IpcMemoryCreate/
- errors. Why?
-
-You either do not have shared memory configured properly in your kernel
-or you need to enlarge the shared memory available in the kernel. The
-exact amount you need depends on your architecture and how many buffers
-and backend processes you configure for /postmaster/. For most systems,
-with default numbers of buffers and processes, you need a minimum of ~1
-MB. See the PostgreSQL Administrator's Guide
-<http://www.PostgreSQL.org/docs/view.php?version=current&idoc=1&file=kernel-resources.html>
-for more detailed information about shared memory and semaphores.
-
-
- 3.4) When I try to start /postmaster/, I get
- /IpcSemaphoreCreate/ errors. Why?
-
-If the error message is /IpcSemaphoreCreate: semget failed (No space
-left on device)/ then your kernel is not configured with enough
-semaphores. Postgres needs one semaphore per potential backend process.
-A temporary solution is to start /postmaster/ with a smaller limit on
-the number of backend processes. Use /-N/ with a parameter less than the
-default of 32. A more permanent solution is to increase your kernel's
-SEMMNS and SEMMNI parameters.
-
-Inoperative semaphores can also cause crashes during heavy database access.
-
-If the error message is something else, you might not have semaphore
-support configured in your kernel at all. See the PostgreSQL
-Administrator's Guide for more detailed information about shared memory
-and semaphores.
-
-
- 3.5) How do I control connections from other hosts?
-
-By default, PostgreSQL only allows connections from the local machine
-using Unix domain sockets. Other machines will not be able to connect
-unless you add the /-i/ flag to /postmaster/, *and* enable host-based
-authentication by modifying the file /$PGDATA/pg_hba.conf/ accordingly.
-This will allow TCP/IP connections.
-
-
- 3.6) How do I tune the database engine for better performance?
-
-Certainly, indexes can speed up queries. The EXPLAIN command allows you
-to see how PostgreSQL is interpreting your query, and which indexes are
-being used.
-
-If you are doing many INSERTs, consider doing them in a large batch
-using the COPY command. This is much faster than individual INSERTS.
-Second, statements not in a BEGIN WORK/COMMIT transaction block are
-considered to be in their own transaction. Consider performing several
-statements in a single transaction block. This reduces the transaction
-overhead. Also, consider dropping and recreating indexes when making
-large data changes.
-
-There are several tuning options. You can disable /fsync()/ by starting
-/postmaster/ with a /-o -F/ option. This will prevent /fsync()/s from
-flushing to disk after every transaction.
-
-You can also use the /postmaster/ /-B/ option to increase the number of
-shared memory buffers used by the backend processes. If you make this
-parameter too high, the /postmaster/ may not start because you have
-exceeded your kernel's limit on shared memory space. Each buffer is 8K
-and the default is 64 buffers.
-
-You can also use the backend /-S/ option to increase the maximum amount
-of memory used by the backend process for temporary sorts. The /-S/
-value is measured in kilobytes, and the default is 512 (i.e. 512K).
-
-You can also use the CLUSTER command to group data in tables to match an
-index. See the CLUSTER manual page for more details.
-
-
- 3.7) What debugging features are available?
-
-PostgreSQL has several features that report status information that can
-be valuable for debugging purposes.
-
-First, by running /configure/ with the --enable-cassert option, many
-/assert()/s monitor the progress of the backend and halt the program
-when something unexpected occurs.
-
-Both /postmaster/ and /postgres/ have several debug options available.
-First, whenever you start /postmaster/, make sure you send the standard
-output and error to a log file, like:
-
- cd /usr/local/pgsql
- ./bin/postmaster >server.log 2>&1 &
-
-This will put a server.log file in the top-level PostgreSQL directory.
-This file contains useful information about problems or errors
-encountered by the server. /Postmaster/ has a /-d/ option that allows
-even more detailed information to be reported. The /-d/ option takes a
-number that specifies the debug level. Be warned that high debug level
-values generate large log files.
-
-If /postmaster/ is not running, you can actually run the /postgres/
-backend from the command line, and type your SQL statement directly.
-This is recommended *only* for debugging purposes. Note that a newline
-terminates the query, not a semicolon. If you have compiled with
-debugging symbols, you can use a debugger to see what is happening.
-Because the backend was not started from /postmaster/, it is not running
-in an identical environment and locking/backend interaction problems may
-not be duplicated.
-
-If /postmaster/ is running, start /psql/ in one window, then find the
-PID of the /postgres/ process used by /psql/. Use a debugger to attach
-to the /postgres/ PID. You can set breakpoints in the debugger and issue
-queries from /psql/. If you are debugging /postgres/ startup, you can
-set PGOPTIONS="-W n", then start /psql/. This will cause startup to
-delay for /n/ seconds so you can attach to the process with the
-debugger, set any breakpoints, and continue through the startup sequence.
-
-The /postgres/ program has /-s, -A/, and /-t/ options that can be very
-useful for debugging and performance measurements.
-
-You can also compile with profiling to see what functions are taking
-execution time. The backend profile files will be deposited in the
-/pgsql/data/base/dbname/ directory. The client profile file will be put
-in the client's current directory. Linux requires a compile with
-/-DLINUX_PROFILE/ for proper profiling.
-
-
- 3.8) Why do I get /"Sorry, too many clients"/ when trying to
- connect?
-
-You need to increase /postmaster/'s limit on how many concurrent backend
-processes it can start.
-
-The default limit is 32 processes. You can increase it by restarting
-/postmaster/ with a suitable /-N/ value or modifying /postgresql.conf/.
-
-Note that if you make /-N/ larger than 32, you must also increase /-B/
-beyond its default of 64; /-B/ must be at least twice /-N/, and probably
-should be more than that for best performance. For large numbers of
-backend processes, you are also likely to find that you need to increase
-various Unix kernel configuration parameters. Things to check include
-the maximum size of shared memory blocks, SHMMAX; the maximum number of
-semaphores, SEMMNS and SEMMNI; the maximum number of processes, NPROC;
-the maximum number of processes per user, MAXUPRC; and the maximum
-number of open files, NFILE and NINODE. The reason that PostgreSQL has a
-limit on the number of allowed backend processes is so your system won't
-run out of resources.
-
-
- 3.9) What is in the /pgsql_tmp/ directory?
-
-This directory contains temporary files generated by the query executor.
-For example, if a sort needs to be done to satisfy an ORDER BY and the
-sort requires more space than the backend's /-S/ parameter allows, then
-temporary files are created here to hold the extra data.
-
-The temporary files are usually deleted automatically, but might remain
-if a backend crashes during a sort. A stop and restart of the
-/postmaster/ will remove files from those directories.
-
-
- 3.10) Why do I need to do a dump and restore to upgrade between
- major PostgreSQL releases?
-
-The PostgreSQL team makes only small changes between minor releases, so
-upgrading from 7.2 to 7.2.1 does not require a dump and restore.
-However, major releases (e.g. from 7.2 to 7.3) often change the internal
-format of system tables and data files. These changes are often complex,
-so we don't maintain backward compatability for data files. A dump
-outputs data in a generic format that can then be loaded in using the
-new internal format.
-
-In releases where the on-disk format does not change, the /pg_upgrade/
-script can be used to upgrade without a dump/restore. The release notes
-mention whether /pg_upgrade/ is available for the release.
-
-------------------------------------------------------------------------
-
-
- Operational Questions
-
-
- 4.1) What is the difference between binary cursors and normal
- cursors?
-
-See the DECLARE manual page for a description.
-
-
- 4.2) How do I SELECT only the first few rows of a query?
-
-See the FETCH manual page, or use SELECT ... LIMIT....
-
-The entire query may have to be evaluated, even if you only want the
-first few rows. Consider using a query that has an ORDER BY. If there is
-an index that matches the ORDER BY, PostgreSQL may be able to evaluate
-only the first few records requested, or the entire query may have to be
-evaluated until the desired rows have been generated.
-
-
- 4.3) How do I get a list of tables or other things I can see in
- /psql/?
-
-You can read the source code for /psql/ in file
-/pgsql/src/bin/psql/describe.c/. It contains SQL commands that generate
-the output for psql's backslash commands. You can also start /psql/ with
-the /-E/ option so it will print out the queries it uses to execute the
-commands you give.
-
-
- 4.4) How do you remove a column from a table?
-
-This functionality was added in release 7.3 with ALTER TABLE DROP
-COLUMN. In earlier versions, you can do this:
-
- BEGIN;
- LOCK TABLE old_table;
- SELECT ... -- select all columns but the one you want to remove
- INTO TABLE new_table
- FROM old_table;
- DROP TABLE old_table;
- ALTER TABLE new_table RENAME TO old_table;
- COMMIT;
-
-
- 4.5) What is the maximum size for a row, a table, and a database?
-
-These are the limits:
-
- Maximum size for a database? unlimited (4 TB databases exist)
- Maximum size for a table? 16 TB
- Maximum size for a row? 1.6TB
- Maximum size for a field? 1 GB
- Maximum number of rows in a table? unlimited
- Maximum number of columns in a table? 250-1600 depending on column types
- Maximum number of indexes on a table? unlimited
-
-Of course, these are not actually unlimited, but limited to available
-disk space and memory/swap space. Performance may suffer when these
-values get unusually large.
-
-The maximum table size of 16 TB does not require large file support from
-the operating system. Large tables are stored as multiple 1 GB files so
-file system size limits are not important.
-
-The maximum table size and maximum number of columns can be increased if
-the default block size is increased to 32k.
-
-
- 4.6) How much database disk space is required to store data from
- a typical text file?
-
-A PostgreSQL database may require up to five times the disk space to
-store data from a text file.
-
-As an example, consider a file of 100,000 lines with an integer and text
-description on each line. Suppose the text string avergages twenty bytes
-in length. The flat file would be 2.8 MB. The size of the PostgreSQL
-database file containing this data can be estimated as 6.4 MB:
-
- 36 bytes: each row header (approximate)
- 24 bytes: one int field and one text field
- + 4 bytes: pointer on page to tuple
- ----------------------------------------
- 64 bytes per row
-
- The data page size in PostgreSQL is 8192 bytes (8 KB), so:
-
- 8192 bytes per page
- ------------------- = 128 rows per database page (rounded down)
- 64 bytes per row
-
- 100000 data rows
- -------------------- = 782 database pages (rounded up)
- 128 rows per page
-
-782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4 MB)
-
-Indexes do not require as much overhead, but do contain the data that is
-being indexed, so they can be large also.
-
-NULLs are stored in bitmaps, so they use very little space.
-
-
- 4.7) How do I find out what tables, indexes, databases, and
- users are defined?
-
-/psql/ has a variety of backslash commands to show such information. Use
-\? to see them. There are also system tables beginning with /pg_/ that
-describe these too. Also, /psql -l/ will list all databases.
-
-Also try the file /pgsql/src/tutorial/syscat.source/. It illustrates
-many of the SELECTs needed to get information from the database system
-tables.
-
-
- 4.8) My queries are slow or don't make use of the indexes. Why?
-
-Indexes are not automatically used by every query. Indexes are only used
-if the table is larger than a minimum size, and the query selects only a
-small percentage of the rows in the table. This is because the random
-disk access caused by an index scan can be slower than a straight read
-through the table, or sequential scan.
-
-To determine if an index should be used, PostgreSQL must have statistics
-about the table. These statistics are collected using VACUUM ANALYZE, or
-simply ANALYZE. Using statistics, the optimizer knows how many rows are
-in the table, and can better determine if indexes should be used.
-Statistics are also valuable in determining optimal join order and join
-methods. Statistics collection should be performed periodically as the
-contents of the table change.
-
-Indexes are normally not used for ORDER BY or to perform joins. A
-sequential scan followed by an explicit sort is usually faster than an
-index scan of a large table.
-
-However, LIMIT combined with ORDER BY often will use an index because
-only a small portion of the table is returned. In fact, though MAX() and
-MIN() don't use indexes, it is possible to retrieve such values using an
-index with ORDER BY and LIMIT:
-
- SELECT col
- FROM tab
- ORDER BY col [ DESC ]
- LIMIT 1;
-
-If you believe the optimizer is incorrect in choosing a sequential scan,
-use |SET enable_seqscan TO 'off'| and run tests to see if an index scan
-is indeed faster.
-
-When using wild-card operators such as LIKE or /~/, indexes can only be
-used in certain circumstances:
-
- * The beginning of the search string must be anchored to the start
- of the string, i.e.
- o LIKE patterns must not start with /%/.
- o /~/ (regular expression) patterns must start with /^/.
- * The search string can not start with a character class, e.g. [a-e].
- * Case-insensitive searches such as ILIKE and /~*/ do not utilise
- indexes. Instead, use functional indexes, which are described in
- section 4.12 <#4.12>.
- * The default /C/ locale must be used during /initdb/.
-
-
- 4.9) How do I see how the query optimizer is evaluating my query?
-
-See the EXPLAIN manual page.
-
-
- 4.10) What is an R-tree index?
-
-An R-tree index is used for indexing spatial data. A hash index can't
-handle range searches. A B-tree index only handles range searches in a
-single dimension. R-trees can handle multi-dimensional data. For
-example, if an R-tree index can be built on an attribute of type
-/point/, the system can more efficiently answer queries such as "select
-all points within a bounding rectangle."
-
-The canonical paper that describes the original R-tree design is:
-
-Guttman, A. "R-trees: A Dynamic Index Structure for Spatial Searching."
-Proceedings of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.
-
-You can also find this paper in Stonebraker's "Readings in Database
-Systems".
-
-Built-in R-trees can handle polygons and boxes. In theory, R-trees can
-be extended to handle higher number of dimensions. In practice,
-extending R-trees requires a bit of work and we don't currently have any
-documentation on how to do it.
-
-
- 4.11) What is the Genetic Query Optimizer?
-
-The GEQO module speeds query optimization when joining many tables by
-means of a Genetic Algorithm (GA). It allows the handling of large join
-queries through nonexhaustive search.
-
-
- 4.12) How do I perform regular expression searches and
- case-insensitive regular expression searches? How do I use an
- index for case-insensitive searches?
-
-The /~/ operator does regular expression matching, and /~*/ does
-case-insensitive regular expression matching. The case-insensitive
-variant of LIKE is called ILIKE.
-
-Case-insensitive equality comparisons are normally expressed as:
-
- SELECT *
- FROM tab
- WHERE lower(col) = 'abc';
-
-This will not use an standard index. However, if you create a functional
-index, it will be used:
-
- CREATE INDEX tabindex ON tab (lower(col));
-
-
- 4.13) In a query, how do I detect if a field is NULL?
-
-You test the column with IS NULL and IS NOT NULL.
-
-
- 4.14) What is the difference between the various character types?
-
-Type Internal Name Notes
---------------------------------------------------
-VARCHAR(n) varchar size specifies maximum length, no padding
-CHAR(n) bpchar blank padded to the specified fixed length
-TEXT text no specific upper limit on length
-BYTEA bytea variable-length byte array (null-byte safe)
-"char" char one character
-
-You will see the internal name when examining system catalogs and in
-some error messages.
-
-The first four types above are "varlena" types (i.e., the first four
-bytes on disk are the length, followed by the data). Thus the actual
-space used is slightly greater than the declared size. However, these
-data types are also subject to compression or being stored out-of-line
-by TOAST, so the space on disk might also be less than expected.
-
-VARCHAR(n) is best when storing variable-length strings and it limits
-how long a string can be. TEXT is for strings of unlimited length, with
-a maximum of one gigabyte.
-
-CHAR(n) is for storing strings that are all the same length. CHAR(n)
-pads with blanks to the specified length, while VARCHAR(n) only stores
-the characters supplied. BYTEA is for storing binary data, particularly
-values that include NULL bytes. All the types described here have
-similar performance characteristics.
-
-
- 4.15.1) How do I create a serial/auto-incrementing field?
-
-PostgreSQL supports a SERIAL data type. It auto-creates a sequence and
-index on the column. For example, this:
-
- CREATE TABLE person (
- id SERIAL,
- name TEXT
- );
-
-is automatically translated into this:
-
- CREATE SEQUENCE person_id_seq;
- CREATE TABLE person (
- id INT4 NOT NULL DEFAULT nextval('person_id_seq'),
- name TEXT
- );
- CREATE UNIQUE INDEX person_id_key ON person ( id );
-
-See the /create_sequence/ manual page for more information about
-sequences. You can also use each row's /OID/ field as a unique value.
-However, if you need to dump and reload the database, you need to use
-/pg_dump/'s /-o/ option or COPY WITH OIDS option to preserve the OIDs.
-
-
- 4.15.2) How do I get the value of a SERIAL insert?
-
-One approach is to retrieve the next SERIAL value from the sequence
-object with the /nextval()/ function /before/ inserting and then insert
-it explicitly. Using the example table in 4.15.1 <#4.15.1>, an example
-in a pseudo-language would look like this:
-
- new_id = execute("SELECT nextval('person_id_seq')");
- execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')");
-
-You would then also have the new value stored in |new_id| for use in
-other queries (e.g., as a foreign key to the |person| table). Note that
-the name of the automatically created SEQUENCE object will be named
-</table/>_</serialcolumn/>_/seq/, where /table/ and /serialcolumn/ are
-the names of your table and your SERIAL column, respectively.
-
-Alternatively, you could retrieve the assigned SERIAL value with the
-/currval()/ function /after/ it was inserted by default, e.g.,
-
- execute("INSERT INTO person (name) VALUES ('Blaise Pascal')");
- new_id = execute("SELECT currval('person_id_seq')");
-
-Finally, you could use the OID <#4.16> returned from the INSERT
-statement to look up the default value, though this is probably the
-least portable approach. In Perl, using DBI with Edmund Mergl's DBD::Pg
-module, the oid value is made available via /$sth->{pg_oid_status}/
-after /$sth->execute()/.
-
-
- 4.15.3) Don't /currval()/ and /nextval()/ lead to a race
- condition with other users?
-
-No. /currval()/ returns the current value assigned by your backend, not
-by all users.
-
-
- 4.15.4) Why aren't my sequence numbers reused on transaction
- abort? Why are there gaps in the numbering of my sequence/SERIAL
- column?
-
-To improve concurrency, sequence values are given out to running
-transactions as needed and are not locked until the transaction
-completes. This causes gaps in numbering from aborted transactions.
-
-
- 4.16) What is an OID? What is a TID?
-
-OIDs are PostgreSQL's answer to unique row ids. Every row that is
-created in PostgreSQL gets a unique OID. All OIDs generated during
-/initdb/ are less than 16384 (from /include/access/transam.h/). All
-user-created OIDs are equal to or greater than this. By default, all
-these OIDs are unique not only within a table or database, but unique
-within the entire PostgreSQL installation.
-
-PostgreSQL uses OIDs in its internal system tables to link rows between
-tables. These OIDs can be used to identify specific user rows and used
-in joins. It is recommended you use column type OID to store OID values.
-You can create an index on the OID field for faster access.
-
-OIDs are assigned to all new rows from a central area that is used by
-all databases. If you want to change the OID to something else, or if
-you want to make a copy of the table, with the original OIDs, there is
-no reason you can't do it:
-
- CREATE TABLE new_table(old_oid oid, mycol int);
- SELECT old_oid, mycol INTO new FROM old;
- COPY new TO '/tmp/pgtable';
- DELETE FROM new;
- COPY new WITH OIDS FROM '/tmp/pgtable';
-
-OIDs are stored as 4-byte integers, and will overflow at 4 billion. No
-one has reported this ever happening, and we plan to have the limit
-removed before anyone does.
-
-TIDs are used to identify specific physical rows with block and offset
-values. TIDs change after rows are modified or reloaded. They are used
-by index entries to point to physical rows.
-
-
- 4.17) What is the meaning of some of the terms used in PostgreSQL?
-
-Some of the source code and older documentation use terms that have more
-common usage. Here are some:
-
- * table, relation, class
- * row, record, tuple
- * column, field, attribute
- * retrieve, select
- * replace, update
- * append, insert
- * OID, serial value
- * portal, cursor
- * range variable, table name, table alias
-
-A list of general database terms can be found at:
-http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary/glossary.html
-
-
- 4.18) Why do I get the error /"ERROR: Memory exhausted in
- AllocSetAlloc()"/?
-
-You probably have run out of virtual memory on your system, or your
-kernel has a low limit for certain resources. Try this before starting
-/postmaster/:
-
- ulimit -d 262144
- limit datasize 256m
-
-Depending on your shell, only one of these may succeed, but it will set
-your process data segment limit much higher and perhaps allow the query
-to complete. This command applies to the current process, and all
-subprocesses created after the command is run. If you are having a
-problem with the SQL client because the backend is returning too much
-data, try it before starting the client.
-
-
- 4.19) How do I tell what PostgreSQL version I am running?
-
-From /psql/, type |SELECT version();|
-
-
- 4.20) Why does my large-object operations get /"invalid large
- obj descriptor"/?
-
-You need to put |BEGIN WORK| and |COMMIT| around any use of a large
-object handle, that is, surrounding |lo_open| ... |lo_close.|
-
-Currently PostgreSQL enforces the rule by closing large object handles
-at transaction commit. So the first attempt to do anything with the
-handle will draw /invalid large obj descriptor/. So code that used to
-work (at least most of the time) will now generate that error message if
-you fail to use a transaction.
-
-If you are using a client interface like ODBC you may need to set
-|auto-commit off.|
-
-
- 4.21) How do I create a column that will default to the current
- time?
-
-Use /CURRENT_TIMESTAMP/:
-
-|CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
-|
-
-
- 4.22) Why are my subqueries using |IN| so slow?
-
-Currently, we join subqueries to outer queries by sequentially scanning
-the result of the subquery for each row of the outer query. If the
-subquery returns only a few rows and the outer query returns many rows,
-|IN| is fastest. To speed up other queries, replace |IN| with |EXISTS|:
-
- SELECT *
- FROM tab
- WHERE col IN (SELECT subcol FROM subtab);
-
-to:
-
- SELECT *
- FROM tab
- WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col);
-
-For this to be fast, |subcol| should be an indexed column. This
-preformance problem will be fixed in 7.4.
-
-
- 4.23) How do I perform an outer join?
-
-PostgreSQL supports outer joins using the SQL standard syntax. Here are
-two examples:
-
- SELECT *
- FROM t1 LEFT OUTER JOIN t2 ON (t1.col = t2.col);
-
-or
-
- SELECT *
- FROM t1 LEFT OUTER JOIN t2 USING (col);
-
-These identical queries join t1.col to t2.col, and also return any
-unjoined rows in t1 (those with no match in t2). A RIGHT join would add
-unjoined rows of t2. A FULL join would return the matched rows plus all
-unjoined rows from t1 and t2. The word OUTER is optional and is assumed
-in LEFT, RIGHT, and FULL joins. Ordinary joins are called INNER joins.
-
-In previous releases, outer joins can be simulated using UNION and NOT
-IN. For example, when joining /tab1/ and /tab2/, the following query
-does an /outer/ join of the two tables:
-
- SELECT tab1.col1, tab2.col2
- FROM tab1, tab2
- WHERE tab1.col1 = tab2.col1
- UNION ALL
- SELECT tab1.col1, NULL
- FROM tab1
- WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2)
- ORDER BY col1
-
-
- 4.24) How do I perform queries using multiple databases?
-
-There is no way to query a database other than the current one. Because
-PostgreSQL loads database-specific system catalogs, it is uncertain how
-a cross-database query should even behave.
-
-/contrib/dblink/ allows cross-database queries using function calls. Of
-course, a client can make simultaneous connections to different
-databases and merge the results on the client side.
-
-
- 4.25) How do I return multiple rows or columns from a function?
-
-In 7.3, you can easily return multiple rows or columns from a function,
-http://techdocs.postgresql.org/guides/SetReturningFunctions
-<http://techdocs.postgresql.org/guides/SetReturningFunctions>.
-
-
- 4.26) Why can't I reliably create/drop temporary tables in
- PL/PgSQL functions?
-
-PL/PgSQL caches function contents, and an unfortunate side effect is
-that if a PL/PgSQL function accesses a temporary table, and that table
-is later dropped and recreated, and the function called again, the
-function will fail because the cached function contents still point to
-the old temporary table. The solution is to use EXECUTE for temporary
-table access in PL/PgSQL. This will cause the query to be reparsed every
-time.
-
-
- 4.27) What replication options are available?
-
-There are several master/slave replication options available. These
-allow only the master to make database changes and the slave can only do
-database reads. The bottom of
-http://gborg.PostgreSQL.org/genpage?replication_research
-<http://gborg.PostgreSQL.org/genpage?replication_research> lists them. A
-multi-master replication solution is being worked on at
-http://gborg.PostgreSQL.org/project/pgreplication/projdisplay.php.
-
-
- 4.28) What encryption options are available?
-
- * /contrib/pgcrypto/ contains many encryption functions for use in
- SQL queries.
- * The only way to encrypt transmission from the client to the server
- is by using /hostssl/ in /pg_hba.conf/.
- * Database user passwords are automatically encrypted when stored in
- version 7.3. In previous versions, you must enable the option
- /PASSWORD_ENCRYPTION/ in /postgresql.conf/.
- * The server can run using an encrypted file system.
-
-------------------------------------------------------------------------
-
-
- Extending PostgreSQL
-
-
- 5.1) I wrote a user-defined function. When I run it in /psql/,
- why does it dump core?
-
-The problem could be a number of things. Try testing your user-defined
-function in a stand-alone test program first.
-
-
- 5.2) How can I contribute some nifty new types and functions to
- PostgreSQL?
-
-Send your extensions to the /pgsql-hackers/ mailing list, and they will
-eventually end up in the /contrib// subdirectory.
-
-
- 5.3) How do I write a C function to return a tuple?
-
-In versions of PostgreSQL beginning with 7.3, table-returning functions
-are fully supported in C, PL/PgSQL, and SQL. See the Programmer's Guide
-for more information. An example of a table-returning function defined
-in C can be found in /contrib/tablefunc/.
-
-
- 5.4) I have changed a source file. Why does the recompile not
- see the change?
-
-The /Makefiles/ do not have the proper dependencies for include files.
-You have to do a /make clean/ and then another /make/. If you are using
-GCC you can use the /--enable-depend/ option of /configure/ to have the
-compiler compute the dependencies automatically.
-
+ + PostgreSQL için Sıkça Sorulan Sorular (SSS) + +Son güncelleme : 26 Temmuz 2003 Cumartesi - 18:32:11 + +Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us +<mailto:pgman@candle.pha.pa.us>) + +Çevirenler : Devrim Gündüz (devrim@gunduz.org <mailto:devrim@gunduz.org>) +Nicholas Morris Tufar (ntufar@yahoo.com <mailto:ntufar@yahoo.com>) +Volkan Yazıcı (volkany@celiknet.com <mailto:volkany@celiknet.com>) + +Bu belgenin en güncel hali, +http://www.PostgreSQL.org/docs/faqs/FAQ_turkish.html +<http://www.postgresql.org/docs/faqs/FAQ_turkish.html> ve +http://www.gunduz.org/seminer/pg/FAQ_turkish adreslerinde görülebilir. + +Platforma özel sorularınız, http://www.PostgreSQL.org/docs/index.html +<http://www.postgresql.org/docs/index.html> adresinde yanıtlanır. + +------------------------------------------------------------------------ + + + Genel Sorular + +1.1 <#1.1>) PostgreSQL nedir? Nasıl okunur? +1.2 <#1.2>) PostgreSQL' in hakları nedir? +1.3 <#1.3>) PostgreSQL, hangi Unix platformlarında çalısır? +1.4 <#1.4>) Hangi Unix olmayan uyarlamaları bulunmaktadır? +1.5 <#1.5>) PostgreSQL'i nereden indirebilirim? +1.6 <#1.6>) Desteği nereden alabilirim? +1.7 <#1.7>) En son sürümü nedir? +1.8 <#1.8>) Hangi belgelere ulaşabilirim? +1.9 <#1.9>) Bilinen hatalar ya da eksik özelliklere nereden ulasabilirim? +1.10 <#1.10>) Nasıl SQL öğrenebilirim? +1.11 <#1.11>) PostgreSQL 2000 yılına uyumlu mudur? +1.12 <#1.12>) Geliştirme takımına nasıl katılabilirim?? +1.13 <#1.13>) Bir hata raporunu nasıl gönderebilirim? +1.14 <#1.14>) PostgreSQL, diğer VTYS(DBMS) lerle nasıl karşılaştırılabilir? +1.15 <#1.15>) PostgreSQL'e maddi açıdan nasıl destek olabilirim? + + + Kullanıcı/istemci Soruları + +2.1 <#2.1>) PostgreSQL için ODBC sürücüleri var mı ? +2.2 <#2.2>) PostgreSQL'i web sayfalarında kullanabilmek için hangi +araçlar bulunmaktadır ? +2.3 <#2.3>) PostgreSQL'in grafik kullanıcı arabirimi var mıdır? +2.4 <#2.4>) PostgreSQL ile iletişimi kurabilmek için hangi dilleri +kullanabilirim? + + + Yönetimsel Sorular + +3.1 <#3.1>) PostgreSQL'i //usr/local/pgsql/ dizininden başka dizinlere +nasıl kurabilirim?? +3.2 <#3.2>) /Postmaster/'ı başlattığımda /Bad System Call/ ya da core +dumped mesajı alıyorum. Neden? +3.3 <#3.3>) /Postmaster/'ı başlattığımda, /IpcMemoryCreate/ hatası +alıyorum. Neden? +3.4 <#3.4>) /Postmaster/, başlattığımda, /IpcSemaphoreCreate hatası/ +alıyorum. Neden? +3.5 <#3.5>) Diğer bilgisayarların benim PostgreSQL veritabanı sunucuma +bağlantılarını nasıl kontrol edebilirim? +3.6 <#3.6>) Veritabanı motorunu daha iyi başarım icin nasıl ayarlayabilirim? +3.7 <#3.7>) Hangi hata ayıklama özellikleri bulunmaktadır? +3.8 <#3.8>) Bağlanmaya çalışırken, neden "/Sorry, too many clients/" +hatasını alıyorum? +3.9 <#3.9>) /pgsql_tmp/dizinin içindeki dosyalar nelerdir? +3.10 <#3.10>) PostgreSQL sürümlerini yükselmek için neden bir +dump/reload işlemi gerçekleştirmek zorundayım? + + + İşletimsel Sorular + +4.1 <#4.1>) Binary cursor ve normal cursor arasındaki fark nedır? +4.2 <#4.2>)Sorgunun sadece ilk birkaç satırını nasıl SELECT edebilirim? +4.3 <#4.3>) /psql/'in içinde gördügüm tablolarin ya da diğer şeylerin +listesini nasıl alabilirim? +4.4 <#4.4>)Bir tablodan bir kolonu nasıl kaldırabilirim? +4.5 <#4.5>)Bir satır, tablo ve veritabanı icin en fazla büyüklük nedir? +4.6 <#4.6>) Tipik bir metin dosyasındaki veriyi saklamak için ne kadar +disk alanı gereklidir? +4.7 <#4.7>) Veritabanında hangi tablo ya da indexlerin tanımlandıgını +nasil görebilirim? +4.8 <#4.8>) Sorgularım cok yavas, ya da indexlerimi kullanmiyorlar. Neden? +4.9 <#4.9>) Query-optimizer in sorgularımı nasıl değerlendirdigini, +işleme soktuğunu nasıl görebilirim? +4.10 <#4.10>) R-tree index nedir? +4.11 <#4.11>) Genetic Query Optimizer nedir? +4.12 <#4.12>) Düzenli ifade (Regular Expression) aramalarını ve +büyük/küçük harfe duyarsız aramaları nasil yapabilirim? Bu büyük(küçük +harfe duyarlı aramalar için indeksi nasil kullanabilirim? +4.13 <#4.13>) Bir sorguda, bir alanın NULL olduğunu nasıl ortaya +çıkarabilirim? +4.14 <#4.14>) Çesitli karakter tipleri arasındaki farklar nelerdir? +4.15.1 <#4.15.1>) Nasıl serial/otomatik artan(auto-incrementing) bir +alan yaratabilirim? +4.15.2 <#4.15.2>) Serial girişinin değerini nasıl alabilirim? +4.15.3 <#4.15.3>) /currval()/ ve /nextval()/ diğer kullanıcılara sorun +yaratmaz mı?> +4.15.4 <#4.15.4>) Neden sequence sayıların transaction işleminin +iptalinden sonra yeniden kullanılıyor? Neden sequence/SERIAL kolonumdaki +sayılarda atlamalar oluyor? +4.16 <#4.16>) OID nedir? TID nedir? +4.17 <#4.17>) PostgreSQL' de kullanılan bazı terimlerin anlamları nelerdi? +4.18 <#4.18>) Neden /"ERROR: Memory exhausted in AllocSetAlloc()"/ +hatasını alıyorum? +4.19 <#4.19>) Hangi PostgreSQL sürümünü çalıstırdığımı nasıl görebilirim?? +4.20 <#4.20>) Neden large-object işlemlerim, /"invalid large obj +descriptor"/ hatasını veriyor? +4.21 <#4.21>) Şu andaki zamanı öntanımlı değer olarak kabul eden kolonu +nasıl yaratırım? +4.22 <#4.22>) Neden |IN| kullanan subquerylerim çok yavaş? +4.23 <#4.23>) Outer join işlemini nasıl yapabilirim? +4.24 <#4.24>) Aynı anda birden fazla veritabanında nasıl işlem yapabilirim? +4.25 <#4.25>) Bir fonksiyondan nasıl çoklu satır ya da kolon +döndürebilirim?? +4.26 <#4.26>) Neden Pl/PgSQL fonksiyonları içinden güvenli bir şekilde +tablo yaratma/kaldırma işlemlerini yapamıyoruz? +4.27 <#4.27>) Hangi replikasyon seçenekleri bulunmaktadır? +4.28"D <#4.28>) Hangi şifreleme seçenekleri bulunmaktadır? + + + PostgreSQL Özelliklerini Genişletmek + +5.1 <#5.1>) Kullanıcı-tanımlı bir fonksiyon yazdım. /psql/'de +çalıştırdığım zaman neden core dump ediyor? +5.2 <#5.2>) PostgreSQL'e nasıl yeni veri tipleri/fonksiyonlar ekleyebilirim? +5.3 <#5.3>) Bir tuple döndürmek için bir C fonksiyonunu nasıl yazarım? +5.4 <#5.4>) Bir kaynak dosyasında değisiklik yaptım. Yeniden derlememe +rağmen değişiklik geçerli olmuyor. Neden?? +------------------------------------------------------------------------ + + + Genel Sorular + + + 1.1) PostgreSQL nedir? Nasıl okunur? + +PostgreSQL, /Post-Gres-Q-L/. olarak okunur + +PostgreSQL, yeni-nesil VTYS araştırma prototipi olan POSTGRES veritabanı +yönetim sisteminin geliştirilmesidir. POSTGRES' in zengin veri tiplerini +ve güçlü veri modelini tutarken, SQL'in geliştirilmis alt kümesi olan +PostQuel dilini kullanır. PostgreSQL ücretsizdir ve kaynak kodu açık +dağıtılır. + +PostgreSQL, PostgreSQL geliştirme listesine üye olan bir Internet +geliştirici takımı tarafından geliştirilir. Şu andaki koordinatör, Marc +G. Fournier (scrappy@PostgreSQL.org <mailto:scrappy@PostgreSQL.org>). +(Bu takıma nasıl katılacagınızı öğrenmek için 1.6 <#1.6> numaralı +maddeyi okuyunuz.) Bu takım, tüm PostgreSQL gelişiminden sorumludur. + +PostgreSQL 1.01 sürümünün yazarları Andrew Yu ve Jolly Chen idi. +Bunların dışında bir kaç kisi de uyarlama, hata ayıklama ve kodun +geliştirilmesi için çalısmıştı. PostgreSQL'in türedigi orijinal Postgres +kodu, lisans, lisansüstü ve akademisyenler tarafından, Professor Michael +Stonebraker ) University of California, Berkeley) koordinatörlügünde +yazılmıstır. + +Berkley'deki yazılımın adı Postgres idi. SQL uyumluluğu 1995'te +eklenince, adı Postgres 95 oldu. 1996 yılının sonlarında adı PostgreSQL +olarak değiştirildi. + + + 1.2) PostgreSQL'in hakları nedir? + +PostgreSQL Data Base Management System + +Portions copyright (c) 1996-2002, PostgreSQL Global Development Group +Portions Copyright (c) 1994-6 Regents of the University of California + +Permission to use, copy, modify, and distribute this software and its +documentation for any purpose, without fee, and without a written +agreement is hereby granted, provided that the above copyright notice +and this paragraph and the following two paragraphs appear in all copies. + +IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY +FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, +INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS +DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF +THE POSSIBILITY OF SUCH DAMAGE. + +THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES, +INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY +AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS +ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS +TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS. + +Üstteki metin klasik açık-kod lisansı olan BSD lisansıdır. Kaynak kodun +nasıl kullanılabileceğine dair sınırlamaları yoktur. Bu lisansı +seviyoruz. Değiştirme niyetimiz bulunmamaktadır. + + + 1.3) PostgreSQL, hangi Unix platforlarında çalısır? + +Genel olarak, modern bir Unix-uyumlu platform PostgreSQL'i +çalıştıracaktır. Ayrıntılı bilgi için kurulum belgelerine bakabilirsiniz. + + + 1.4) Hangi Unix olmayan uyarlamaları bulunmaktadır? + +*İstemci* + +libpq C kütüphanesini, psql ve diger arabirimleri ve binary dosyaları, +MS Windows ortamlarında çalısması için derlemeniz mümkündür. Bu örnekte +istemcide MS Windows çalısıyor ve desteklenen Unix platformlarından +birinde çalısan PostgreSQL sunucuna TCP/IP ile baglanmaktadır. Dağıtım +içindeki win31.mak dosyası ile, Win32 libpg kütüphanesi ve psql +yaratabilirsiniz. PostgreSQL aynı zamanda ODBC istemcileri ile +haberlesebilmektedir. + +*Sunucu* + +Veritabanı sunuucsu Cygwin kullanarak Windows NT, 2K ya da XP üzerinde +calistirilabilir. Dagıtım içindeki pgsql/doc/FAQ_MSWıN dosyasını ya da +web sitemizdeki MS Windows FAQ'u inceleyebilirsiniz. + +Doğal Windows NT/2000/XP portu için şu anda çalışmalar devam etmektedir. +Windows sürümü hakkında güncel bilgi için, +http://techdocs.postgresql.org/guides/Windows adresini ziyaret +edebilirsiniz. + +Ayrıca, http://forge.novell.com adresinde Novell Netware 6 portu +bulunmaktadır. + + + 1.5) PostgreSQL'i nereden indirebilirim? + +PostgreSQL için ana anonim ftp sitesi ftp://ftp.PostgreSQL.org/pub' dur. +Yansılar için, ana web sayfamıza bakabilirsiniz. + + + 1.6) Nereden destek alabilirim? + +Ana e-posta listesi : pgsql-general@PostgreSQL.org. PostgreSQL +konusundaki tartısmalara açıktır. Üye olmak için, asagıdaki satırları +e-postanizin body kısmına (konu kısmına degil) yazıp, +pgsql-general-request@PostgreSQL.org adresine gönderin: + +subscribe +end + +Aynı zamanda, bir digest listesi bulunmaktadır. Bu listeye üye olmak +için, pgsql-general-digest-request@PostgreSQL.org adresine, body kısmında + +subscribe +end + +yazan bir e-posta atmanız yeterli olacaktır. + +Digest postalar, ana liste 30k civarında e-postaya ulastiginda üyelere +gönderilmektedir. + +Buglar için bir e-posta listesi bulunmaktadır. Bu listeye üye olmak +için, email to pgsql-bugs-request@PostgreSQL.org adresine, body kısmında + +subscribe +end + +yazan bir e-posta atmanız yeterli olacaktır. + +Aynı zamanda, gelistiriciler için tartısma listesi bulunmaktadır. Bu +listeye üye olmak için, pgsql-hackers-request@PostgreSQL.org adresine, +body kısmında + +subscribe +end + +yazan bir e-posta atmanız yeterli olacaktır. + +Bunun dısındaki e-posta listelerine ve PostgreSQL hakkında bilgiye, +PostgreSQL WWW ana sayfasından ulasabilirsiniz: + +http://www.PostgreSQL.org + +Aynı zamanda, EFNet üzerinde, #PostgreSQL adlı bir ıRC kanalı +bulunmaktadır. Bunun için, irc -c '#PostgreSQL' "$USER" irc.phoenix.net +Unix komutunu kullanabilirsiniz. + +Ticari destek veren firmaların listesine + +http://www.postgresql.org/users-lounge/commercial-support.html + +adresinden ulasabilirsiniz. + + + 1.7) En son sürüm nedir? + +PostgreSQL'in son sürümü 7.3.3'tür. + +Her 4 ayda major release çıkarılması planlanmaktadır. + + + 1.8) Hangi belgelere ulasabilirim? + +Dağıtımın icinde, kitapciklar, kitapcik sayfalari ve bazi küçük örnekler +verilmektedir. /doc dizinine bakınız. Ayrica, bu el kitapçıklarını +online olarak http://www.PostgreSQL.org/docs/ adresinden inceleyebilirsiniz. + +http://www.PostgreSQL.org/docs/awbook.html ve +http://www.commandprompt.com/ppbook adreslerinde PostgreSQL kitapları +bulunmaktadır. PostgreSQL kitablarının listesine, +http://www.ca.PostgreSQL.org/books/ adresinden ulaşaiblirsiniz. Ayrıca, +PostgreSQL konusundaki teknik makalelere de +http://techdocs.PostgreSQL.org/ adresinden ulaşabilirsiniz. + +psql'in, \d ile baslayan veri tipler, operatorler, fonksiyonlar, +aggregateler, vb. ile ilgili güzel komutları vardır. + +Web sitemiz daha fazla belgeyi içermektedir. + + + 1.9) Bilinen hatalar ya da eksik özelliklere nereden ulasabilirim? + +PostgreSQL SQL-92 uyumlugugu icindedir, standartlardan fazla da +özellikleri bulunmaktadır. Bilinen hatalar, eksik özellikler ve gelecek +ile ilgili planlar için TODO listesine bakınız. + + + 1.10) Nasıl SQL öğrenebilirim? + +http:/www.PostgreSQL.org/docs/awbook.html adresindeki kitap SQL +ögretecektir. http://www.commandprompt.com/ppbook adresinde de bir baska +PostgreSQL kitabı bulunmaktadır. + +http://www.intermedia.net/support/sql/sqltut.shtm, +http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM +http://sqlcourse.com ve http://sqlcourse2.com adreslerinde de güzel +belgeler bulunmaktadır. + +Bir başkası da, http://members.tripod.com/er4ebus/sql/index.htm +adresinde bulunan "Teach Yourself SQL in 21 Days, Second Edition" kitabıdır. + +Bazı kullanıcılarımız da şu kitabı önermektedirler: The Practical SQL +Handbook, Bowman, Judith S., et al.,Addison-Wesley. Others like The +Complete Reference SQL, Groff et al., McGraw-Hill. + + + 1.11) PostgreSQL 2000 yılına uyumlu mudur? + +Evet. + + + 1.12) Gelistirme takımına nasıl katılabilirim? + +Öncelikle, en son kaynak kodunu indirin ve web sitemizdeki ya da +dagıtımın içindeki PostgreSQL Developer belgesini okuyun. Ardindan, +pgsql-hackers ve pgsql-patches listelerine üye olun. Üçüncü olarak da, +pgsql-pacthes listesine yüksek kalitede yamalar gönderin. + +PostgreSQL CVS arsivine erisim izni olan, 10 kadar gelistirici +bulunmaktadir. Hepsi defalarca, diger kisilerin yaptigindan cok daha +yüksek-kaliteli patchler gondermislerdir. Ayrica biz de bu +gelistiricilerin ekledikleri yamalarin yüksek kalitede olduguna güveniyoruz. + + + 1.13) Bir hata raporunu nasıl gönderebilirim? + +PostgreSQL BugTool sayfasina gidiniz. O sayfada bir bug bildirmek icin +neleri yapmanız gerektigi anlatilmistir. + +Ayrıca, ftp://ftp.PostgreSQL.org/pub ftp adresimizde, yeni bir +PostgreSQL sürümü ya da yamasi olup olmadigini kontrol ediniz. + + + 1.14) PostgreSQL, diger DBMS'lerle nasıl karsilastırılabilir? + +Bir yazilimin gücünü ölçmek için çesitli yollar vardir: Yazilimin +özellikleri, basarımı, güvenilirligi, destegi ve ücreti. + +Özellikler: + +PostgreSQL mevcut büyük ticari veritabanlarinin, transaction, subselect, +trigger, view, foreign key referential integrity ve sophisticated +locking gibi (user-defined types), rules, inheritance ve lock +cakısmalarini düsürmek icin multi-version uyumluluk özellikleri +bulunmaktadir. + +Performans (Başarım): + +PostgreSQL, diğer ticari ve açık kaynak kodlu veritabanlarıyla yakın +başarımı sağlar. Bazı açılardan daha hızlıdır, diğer açılardan da +yavaştır. MySQL ya da daha zayıf veritabanları ile +karşılaştırıldığında,insert/update islemlerinde, transaction bazlı +çalıstığımız için daha yavaşız. MySQL, yukarıdaki "Özellikler" kısmında +belirtilenlerden hiç birine sahip değildir. Biz, başarımımızı her +sürümde arttırsak da, esneklik ve gelişmiş özellikler için yapılanmıs +durumdayız . PostgreSQL'i MySQL ile karşılaştıran şu web sitesine +bakabilirsiniz: http://openacs.org/why-not-mysql.html + +Güvenilirlik: + +DBMSlerin güvenilir olması gerketigi, yoksa degerleri olmayacagini +düsünüyoruz Çok iyi test edilmis, dengeli çalısan minimum sayıda hata +içeren kod sunmaya çalısıyoruz. Her bir sürüm en az 1 aylık beta +testlerinden geçirilmektedir. Sürüm geçmişine bakarsanız, üretime hazır, +dengeli ve kararlı kodlar sundugumuzu görebilirsiniz. Bu alanda, diger +veritabanı yaZılımlarına üstünlügümüz olduguna inanmaktayız + +Destek: + +E-posta listemiz, olusan herhangi bir sorunu çözebilecek büyük sayıda +kullanıcı ve gelistirici grubunu içerir. Sorununuz için, en az bir +ticari veritabanı kadar rahat çözüm bulabilirsiniz. Gelistiricilere, +kullanıcı grubuna, belgelere ve kaynak koda direk olarak erisebilme, +PostgreSQL destegini, diger DBMSlere göre daha önemli kılar. Gereksinimi +olanlara, ticari destek verilebilir. (Destek için 1.6 bölümüne bakınız.) + +Fiyat: + +Ticari ve ticari olmayan tüm kullanımlarınız için PostgreSQL +ücretsizdir. Kodumuzu, yukarıda belirtilen BSD-stili lisanstaki +sınırlamalar hariç, ürününüzün içine ekleyebilirsiniz. + + + 1.15) PostgreSQL'e maddi açıdan nasıl destek olabilirim? + +PostgreSQL, 1996 yılından beri 1.sınıf altyapıya ashiptir. Bunun için, +yıllar boyu çalısıp bu altyapıyı olusturup yöneten Marc Fournier'e +tesekkürler. + +Bir açık kaynak kodlu proje için, kaliteli altyapı çok önemlidir. Bu +altyapı, projenin kesilmesini önler ve projenin ilerlemesini hızlandırır. + +Tabii ki bu altyapı ucuz degildir. ıslerin yürümesi için çeşitli yılık +ve anlık harcamalarımız olmaktadır. Eger siz ya da sirketinizin bu +çabamıza bagısta bulunabilecek parası varsa, lütfen +http://www.pgsql.com/pg_goodies adresine gidiniz ve bagısta, hibede +bulununuz. + +Web sayfasının PostgreSQL, ınc.' den bahsetmesine ragmen, "katkıda +bulunanlar" (contributors) maddesi sadece PostgreSQL projesini +desteklemek içindir ve belirli bir sirketin para kaynagı degildir. +isterseniz, baglantı adresine bir çek gönderebilirsiniz. + +------------------------------------------------------------------------ + + + Kullanıcı/istemci Soruları + + + 2.1) PostgreSQL icin ODBC sürücüleri var mı? + +iki tane ODBC sürücüsü bulunmaktadır: PsqlODBC ve OpenLink ODBC. + +PsqlODBC'i http://gborg.postgresql.org/project/psqlodbc/projdisplay.php +adresinden indirebilirsiniz. + +OpenLink ODBC http://www.openlinksw.com adresinden alınabilir.Bu sürücü, +kendi standart ODBC istemci yazılımı ile çalıstığından, destekledikleri +her platformda (Win, Mac, Unix, VMS) PostgreSQL ODBC bulunmalidir. + +Ücretsiz sürümü olmakla beraber, ticari kalitede destek almak +isteyenlere satmak isteyeceklerdir. Sorularınızı lütfen +postgres95@openlink.co.uk adresine gönderiniz. + + + 2.2) PostgreSQL'i web sayfalarında kullanabilmek için hangi + araçlar bulunmaktadır? + +http://www.webreview.com adresinde, arka planda veritabanı çalıstıran +Web sayfaları için giris seviyesinde bilgi bulunmaktadır. + +Web ile bütünlesme için, PHP mükemmel bir arabirim sunar. http://www.php.net + +Karmaşık sorunlar için, çoğu kisi Perl arabirimini ve CGI.pm ya da +mod_perl kullanır. + + + 2.3) PostgreSQL'in grafik kullanıcı arabirimi var mıdır? + +Çeşitli grafik arabirimlerimiz bulunmaktadır. Bunların arasında, +PgAccess (http://www.pgaccess.org), PgAdmin II (http://www.pgadmin.org, +sadece Win32 için), RHDB Admin (http://sources.redhat.com/rhdb/ ) ve +Rekall (http://www.thekompany.com/products/rekall/) bulunmaktadır. +Ayrıca, PostgreSQL için web tabanlı bir arabirim olan PHPPgAdmin ( +http://phppgadmin.sourceforge.net/ ) bulunmaktadır. + +Daha ayrıntılı liste için http://techdocs.postgresql.org/guides/GUITools +adresine bakabilirsiniz. + + + 2.4) PostgreSQL ile iletişimi kurabilmek için hangi dilleri + kullanabilirim? + + * C (libpq) + * Embedded C (ecpg) + * Java (jdbc) + * Python (PyGreSQL) + * TCL (libpgtcl) + +Diğerleri için, http://gborg.postgresql.org adresindeki +Drivers/Interfaces bölümüne bakabilirsiniz. + +------------------------------------------------------------------------ + + + Yönetimsel Sorular + + + 3.1) PostgreSQL'i, /usr/local/pgsql dizininden baska dizinlere + nasıl kurabilirim? + +configure betigini çalıstırırken, --prefix seçenegini veriniz. + + + 3.2) postmaster'i baslattıgımda, a Bad System Call ya da core + dumped mesajı alıyorum. Neden? + +Bunun birçok nedeni olabilir. Ancak ilk kontrol edilmesi gereken sey, +çekirdeginize System V uzantılarının kurulu olup olmadıgını kontrol +etmek olabilir. PostgreSQL shared memory ve semaphores için çekirdek +destegine gereksinim duyar. + + + 3.3) postmaster'i baslattıgımda, a ıpcMemoryCreate hatası + alıyorum. Neden? + +Ya çekirdeginizde shared memory desteginiz düzgünce +yapılandırılmamıstır, ya da çekirdeginizdeki mevcut shared memory +miktarını büyütmeniz gerekecektir. Gereksinim duyacagınız miktar, +mimarinize ve postmaster için ayarladıgınız tampon ile backend islemi +sayısına baglıdır. Tüm sistemler için, tamponlar ve islemlerde öntanımlı +sayılarla, ~ 1MB kadar yere gereksinmeniz olacaktir.PostgreSQL +Administrator's Guide' a, shared memory ve semaphorelar hakkındaki +ayrıntılı bilgi için bakabilirsiniz. + + + 3.4) postmaster'i baslattıgımda, a ıpcSemaphoreCreate hatası + alıyorum. Neden? + +Eger hata, "ıpcSemaphoreCreate: semget failed (No space left on device)" +ise, çekirdeginiz yeterli semaphore ile yapılandırılmamıs demektir. +Postgres, her bir potansiyel backend için bir semaphore gereksinmesi +duyar. Geçici bir çözüm, postmasterı backend islemleri için daha az +miktarda sınırla baslatmak olabilir. -N i varsaılan deger olan 32'den +küçük bir degerle baslatınız. Daha kalıcı bir çözüm, çekirdeğinizin +SEMMNS ve SEMMNI parametrelerini yükseltmek olacaktır. + +Çalışmayan semaphorelar ağır veritabanı islemlerinde çökme yaratabilirler. + +Eger hata mesajınız baska birsey ise, çekirdeginizde semaphore destegini +yapılandırmamıs olabilirsiniz. Shared memory ve semaphorelar hakkındaki +daha ayrıntılı bilgi için PostgreSQL Administrator's Guide'a bakabilirsiniz. + + + 3.5) Diger bilgisayarların benim PostgreSQL veritabanı sunucuma + baglantılarını nasıl kontrol edebilirim? + +Ön tanımlı olarak, PostgreSQL sadece yerel makineden Unix domain sockets +kullanarak baglanılmasına izin verir. Diger makineler, postmaster'a -i +etiketini geçirmezseniz ve $PGDATA_pg_hba.conf dosyasını düzenleyerek +host-based authentication'a olanak vermezseniz, baglantı yapamayacaklardır. + + + 3.6) Veritabani motorunu daha iyi basarim icin nasil + ayarlayabilirim? + +Indexler sorguları hızlandırabilir. EXPLAIN komutu, PostgreSQL'in +sorgunuzu nasıl yorumladığını ve hangi indexleri kullandigini görmenize +izin verir. + +Eğer cok fazla INSERT islemi yapiyorsaniz, bunları büyük bir toplu islem +dosyasi kullanıp COPY komutu ile veritabanina girmeyi deneyiniz. Bu, +tekil ıNSERTlerden daha hızlıdır. ikinci olarak, BEGıN WORK/COMMıT +transaction blogu içinde olmayan ifadeler kendi transactionlarindaymis +gibi düsünülür. Çoklu ifadeleri tek bir transaction bloğu içinde +yapabilirsiniz. Bu, transaction overheadini düşürecektir. Tek bir +transaction bloğu içinde birden çok ifadeyi çalıştırmayı +deneyebilirsiniz. Bu, transaction overhead ini düşürür. + +Çeşitli ayarlama seçenekleri mevcuttur. fsync() işlemini, postmaster'ı +-o -F seçeneği ile başlatarak devre dışı bırakabilirsiniz. Bu işlem, +fsync()'lerin her transactiondan sonra diske flush etmesini engelleyecektir. + +Aynı zamanda, postmaster'i -B seçeneği ile başlatıp, backend işlemleri +tarafından kullanılan shared memorf buffers sayılarını +arttırabilirsiniz. Eger bu parametreyi çok yüksek tutarsanız, +çekirdeğinizin shared memory bölgesindeki limiti aşma olasılığınız +yüzünden postmaster başlayamayabilir. Her bir tampon (buffer) 8K'dır. +Öntanımlı sayı ise 64 tampondur. + +Aynı şekilde, backend'in -S seçeneğini geçici sıralamalar için backend +süreçleri tarafından kullanılacak hafızayı arttırmak amacıyla +kullanabilirsiniz. -S seçeneği kilobayt cinsinden değer alır ve ön +tanımlı değeri 512'dir (512 K) + +Tablolardaki veriyi bir indekse eşlemek amacıyla gruplama için CLUSTER +komutunu kullanabilirsiniz. Ayrıntılı bilgi için CLUSTER komutunun +yardım sayfasına bakabilirsiniz. + + + 3.7) Hangi hata ayıklama özellikleri bulunmaktadır? + +PostgreSQL, hata ayıklama amacıyla kullanılabilecek durum bilgisi rapor +eden çeşitli özeliklere sahiptir. + +Öncelikle, configure betiğini --enable-cassert seçeneğiyle +çalıştırırsanız, bir çok assert() backend calışmasını gözlemler ve +beklenmeyen bir durumda programı durdurur. + +Postmaster ve postgres çeşitli hata ayıklama seçeneklerine sahiptir. +Öncelikle, postmaster'i başlattığınızda, standart çıktıyı ve hataları +bir log dosyasına yönlendirdiğinize emin olun: + +cd /usr/local/pgsql +./bin/postmaster >server.log 2>&1 & + +Bu işlem PostgreSQL ana dizinine server.log dosyası yerleştirecektir. Bu +dosya sunucunun yaşadığı sorunlar ya da hatalar hakkında yararlı +bilgiler içerir. -d seçeneği, hata ayıklama seviyesini belirten bir +rakam ile kullanılır. Yüksek hata ayıklama seviyelerinin büyük log +dosyaları oluşturacağını unutmayınız. + +Eğer postmaster çalışmıyorsa, postgres backend'ini komut satırından +çalıştırabilir ve SQL ifadenizi direk olarak yazabilirsiniz. Bu sadece +hata ayıklama amacıyla önerilir. Burada, noktalı virgülün değil de yeni +bir satırın sorguyu sonlandırdığını unutmayınız. Eğer hata ayıklama +sembolleri ile derlediyseniz, ne olduğunu görmek için bir hata +ayıklayıcı kullanabilirsiniz. backend postmasterdan başlatılmadığından, +eşdeğer bir ortamda çalışmamaktadır ve locking/backend etkileşim +sorunları artabilir. + +Eğer postmaster çalışıyorsa, bir pencerede psql'i çalıştırın ve psql +tarafından kullanılan postgres sürecinin süreç numarasını (PID) bulun. +Postgres süreci ile ilişkilendirmek için bir hata ayıklarıcı kullanın. +Sorguları psql aracılığı ile çalıştırabilirsiniz. Eğer postgres +başlangıcında hata ayıklamak istiyorsanız, PGOPTIONS="-W n" seçeneğini +ayarlayabilir ve psql'i başlatabilirsiniz. Bu işlem, başlangıcın n +saniye kadar gecikmesini sağlayacaktır; böylece hata ayıklayıcıyı sürece +ilişkilendirdikten sonra başlangıç sürecinin devam etmesini +sağlayabilirsiniz. + +postgres programı hata ayıklama ve başarım ölçümleri için -s, -A ve -t +seçeneklerine sahiptir. + + + 3.8) Baglanmaya çalısıken, neden "Sorry, too many clients" + hatasını alıyorum? + +Postmaster'in eşzamanlı olarak başlatabileceği backend süreçleri +sınırlarını arttırmanız gerekmektedir. + +Ön tanımlı değer 32 süreçtir. Bunu, postmaster'i uygun -N değeri ile ya +da postgresql.conf dosyasını düzenleyerek yeniden başlatmakla +arttırabilirsiniz. + +Eğer -N değerini 32'den büyük yapacaksanız, aynı zamanda -B değerini de +değiştirmeniz gerektiğini unutmayın. -B -N'nin en az 2 katı kadar +olmalıdır; daha iyi başarım için bu sayıyı daha da arttırmalısınız. +Yüksek sayıdaki backend süreçleri için, çeşitli çekirdek yapılandırma +parametrelerini arttırmanız gerekecektir. Yapılması gerekenler, SHMMAX, +SEMMNS, SEMMNI, NPROC, MAXUPRC ve açılabilecek dosyaların maksimum +sayısı olan NFILE ve NINODE değerlerini karıştırmaktır. Bunun nedeni, +PostgreSQL'in izin verilen backend süreçlerinin sayısı üzerinde bir +sınırı olmasıdır. Böylelikle sistem kaynaklarının dışına çıkılmayacaktır. + +PostgreSQL'in 6.5 sürümüne kadar, en fazla backend sayısı 64 idi ve bunu +değiştirmek için include/storage/sinvaladt.h dosyası içindeki +MaxBAckendid sabitini değiştirdek sonra yazılımı yeniden derlemek +gerekiyordu. + + + 3.9) pgsql_tmp dizinin içindeki dosyalar nelerdir? + +Sorgu çalıstırıcı (query executer) tarafından yaratılan geçici +dosyalardır. Örnegin, bir sıralama ORDER BY ile yapilacaksa ve sıralama +backend'in -s parametresinin izin verdiginden daha fazla alana +gereksinim duyuyorsa, ekstra veriyi tutmak için geçici dosyalar yaratılır. + +Geçici dosyalar, eger sıralama sırasında backend göçmezse otomatik +olarak silinecektir. Eger çalısan durumda bir backendiniz yoksa, +pg_tempNNN.NN dosyalarını silmeniz güvenlidir.. + + + 3.10) PostgreSQL sürümlerini yükselmek için neden bir + dump/reload işlemi gerçekleştirmek zorundayım? + +PostgreSQL takımı ara sürümlerde sadece küçük değişiklikler yapmaktadır; +bu yüzden 7.2 sürümünden 7.2.1'e yükseltmek dump/restore işlemi +gerekmemektedir. Ancak, esas sürümlerde (örnek: 7.2'den 7.3'e) +çoğunlukla sistem tablolarının ve veri dosyalarının iç yapısı +değiştirilir. Bu değişiklikler çoğunlukla karmaşıktır; dolayısıyla veri +dosyalarının geriye dönük uyumluluğu işlemlerini yapmıyoruz. Dump +işlemi, veriyi genel biçimde alacağından yeniden yükleme esnasında veri, +yeni iç biçime uygun şekilde yerleştirilecektir. + +Disk biçiminin değişmediği sürümlerde, pg_upgrade betiği güncellemenin +bir dump/restore gerektirmeden yapılmasını sağlayacaktır. pg_upgrade +betiğinin o sürüm için bulunup bulunmadığını sürüm notları içinde +bulabilirsiniz. + +------------------------------------------------------------------------ + + + İşletimsel Sorular + + + 4.1) Binary cursor ve normal cursor arasindaki fark nedir? + +DECLARE yardım sayfasina bakiniz. + + + 4.2) Sorgunun sadece ilk birkaç satırını nasil SELECT edebilirim? + +FETCH yardım sayfasina bakiniz, aya da SELECT ... LIMIT.... kullanınız. + +The entire query may have to be evaluated, even if you only want the +first few rows. Consider a query that has an ORDER BY. ıf there is an +index that matches the ORDER BY, PostgreSQL may be able to evaluate only +the first few records requested, or the entire query may have to be +evaluated until the desired rows have been generated. + + + 4.3) psql'in içinde gördügüm tablolarin ya da diger seylerin + listesini nasil alabilirim? + +pgsql/src/bin/psql/describe.c içindeki psql kaynak kodunu +okuyabilirsiniz. Bu kod, psql'in \ ile baslayan komutlarının çıktısını +olusturan SQL komutlarini içerir. Aynı zamanda, psql'i -E seçeneği ile +başlatıp, verdiğiniz komutları çalıştırmak için yaptığı sorguların +çıktılarını görebilirsiniz. + + + 4.4) Bir tablodan bir kolonu nasıl kaldırabilirim? + +Bu özellik (ALTER TABLE DROP COLUMN) 7.3 sürümü ile gelmiştir. Eski +sürümlerde aşağıdakileri uygulamalısınız: + +BEGIN; +LOCK TABLE old_table; +SELECT ... -- select all columns but the one you want to remove +INTO TABLE new_table +FROM old_table; +DROP TABLE old_table; +ALTER TABLE new_table RENAME TO old_table; +COMMIT; + + + + 4.5) Bir satır, tablo ve veritabanı icin en fazla büyüklük nedir? + +Sınırlar: + +Veritabani icin en fazla büyüklük nedir? +Sınırsız (4 TB'lık veritabanı bulunmaktadır) + +Bir tablo icin en fazla büyüklük nedir? +16 TB + +Bir satır için en fazla büyüklük nedir? +1.6 TB + +Bir alan için en fazla büyüklük nedir? +1 GB + +Tabloda en fazla satır sayısı kaçtır? +Sınırsız + +Bir tabloda olabilecek en fazla kolon sayısı kaçtır? +Kolon tiplerine bağlı olarak 250-1600 + +Bir tabloda olabilecek en fazla index sayısı kaçtır? +sınırsız + +These are the limits: + + Maximum size for a database? unlimited (4 TB databases exist) + Maximum size for a table? 16 TB + Maximum size for a row? 1.6TB + Maximum size for a field? 1 GB + Maximum number of rows in a table? unlimited + Maximum number of columns in a table? 250-1600 depending on column types + Maximum number of indexes on a table? unlimited + +Of course, these are not actually unlimited, but limited to available +disk space and memory/swap space. Performance may suffer when these +values get unusually large. + +The maximum table size of 16 TB does not require large file support from +the operating system. Large tables are stored as multiple 1 GB files so +file system size limits are not important. + +The maximum table size and maximum number of columns can be increased if +the default block size is increased to 32k. + + + 4.6) How much database disk space is required to store data from + a typical text file? + +A PostgreSQL database may require up to five times the disk space to +store data from a text file. + +As an example, consider a file of 100,000 lines with an integer and text +description on each line. Suppose the text string avergages twenty bytes +in length. The flat file would be 2.8 MB. The size of the PostgreSQL +database file containing this data can be estimated as 6.4 MB: + + 36 bytes: each row header (approximate) + 24 bytes: one int field and one text field + + 4 bytes: pointer on page to tuple + ---------------------------------------- + 64 bytes per row + + The data page size in PostgreSQL is 8192 bytes (8 KB), so: + + 8192 bytes per page + ------------------- = 128 rows per database page (rounded down) + 64 bytes per row + + 100000 data rows + -------------------- = 782 database pages (rounded up) + 128 rows per page + +782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4 MB) + +Indexes do not require as much overhead, but do contain the data that is +being indexed, so they can be large also. + +NULLs are stored in bitmaps, so they use very little space. + + + 4.7) How do I find out what tables, indexes, databases, and + users are defined? + +/psql/ has a variety of backslash commands to show such information. Use +\? to see them. There are also system tables beginning with /pg_/ that +describe these too. Also, /psql -l/ will list all databases. + +Also try the file /pgsql/src/tutorial/syscat.source/. It illustrates +many of the SELECTs needed to get information from the database system +tables. + + + 4.8) My queries are slow or don't make use of the indexes. Why? + +Indexes are not automatically used by every query. Indexes are only used +if the table is larger than a minimum size, and the query selects only a +small percentage of the rows in the table. This is because the random +disk access caused by an index scan can be slower than a straight read +through the table, or sequential scan. + +To determine if an index should be used, PostgreSQL must have statistics +about the table. These statistics are collected using VACUUM ANALYZE, or +simply ANALYZE. Using statistics, the optimizer knows how many rows are +in the table, and can better determine if indexes should be used. +Statistics are also valuable in determining optimal join order and join +methods. Statistics collection should be performed periodically as the +contents of the table change. + +Indexes are normally not used for ORDER BY or to perform joins. A +sequential scan followed by an explicit sort is usually faster than an +index scan of a large table. + +However, LIMIT combined with ORDER BY often will use an index because +only a small portion of the table is returned. In fact, though MAX() and +MIN() don't use indexes, it is possible to retrieve such values using an +index with ORDER BY and LIMIT: + + SELECT col + FROM tab + ORDER BY col [ DESC ] + LIMIT 1; + +If you believe the optimizer is incorrect in choosing a sequential scan, +use |SET enable_seqscan TO 'off'| and run tests to see if an index scan +is indeed faster. + +When using wild-card operators such as LIKE or /~/, indexes can only be +used in certain circumstances: + + * The beginning of the search string must be anchored to the start + of the string, i.e. + o LIKE patterns must not start with /%/. + o /~/ (regular expression) patterns must start with /^/. + * The search string can not start with a character class, e.g. [a-e]. + * Case-insensitive searches such as ILIKE and /~*/ do not utilise + indexes. Instead, use functional indexes, which are described in + section 4.12 <#4.12>. + * The default /C/ locale must be used during /initdb/. + + + 4.9) How do I see how the query optimizer is evaluating my query? + +See the EXPLAIN manual page. + + + 4.10) What is an R-tree index? + +An R-tree index is used for indexing spatial data. A hash index can't +handle range searches. A B-tree index only handles range searches in a +single dimension. R-trees can handle multi-dimensional data. For +example, if an R-tree index can be built on an attribute of type +/point/, the system can more efficiently answer queries such as "select +all points within a bounding rectangle." + +The canonical paper that describes the original R-tree design is: + +Guttman, A. "R-trees: A Dynamic Index Structure for Spatial Searching." +Proceedings of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57. + +You can also find this paper in Stonebraker's "Readings in Database +Systems". + +Built-in R-trees can handle polygons and boxes. In theory, R-trees can +be extended to handle higher number of dimensions. In practice, +extending R-trees requires a bit of work and we don't currently have any +documentation on how to do it. + + + 4.11) What is the Genetic Query Optimizer? + +The GEQO module speeds query optimization when joining many tables by +means of a Genetic Algorithm (GA). It allows the handling of large join +queries through nonexhaustive search. + + + 4.12) How do I perform regular expression searches and + case-insensitive regular expression searches? How do I use an + index for case-insensitive searches? + +The /~/ operator does regular expression matching, and /~*/ does +case-insensitive regular expression matching. The case-insensitive +variant of LIKE is called ILIKE. + +Case-insensitive equality comparisons are normally expressed as: + + SELECT * + FROM tab + WHERE lower(col) = 'abc'; + +This will not use an standard index. However, if you create a functional +index, it will be used: + + CREATE INDEX tabindex ON tab (lower(col)); + + + 4.13) In a query, how do I detect if a field is NULL? + +You test the column with IS NULL and IS NOT NULL. + + + 4.14) What is the difference between the various character types? + +Type Internal Name Notes +-------------------------------------------------- +VARCHAR(n) varchar size specifies maximum length, no padding +CHAR(n) bpchar blank padded to the specified fixed length +TEXT text no specific upper limit on length +BYTEA bytea variable-length byte array (null-byte safe) +"char" char one character + +You will see the internal name when examining system catalogs and in +some error messages. + +The first four types above are "varlena" types (i.e., the first four +bytes on disk are the length, followed by the data). Thus the actual +space used is slightly greater than the declared size. However, these +data types are also subject to compression or being stored out-of-line +by TOAST, so the space on disk might also be less than expected. + +VARCHAR(n) is best when storing variable-length strings and it limits +how long a string can be. TEXT is for strings of unlimited length, with +a maximum of one gigabyte. + +CHAR(n) is for storing strings that are all the same length. CHAR(n) +pads with blanks to the specified length, while VARCHAR(n) only stores +the characters supplied. BYTEA is for storing binary data, particularly +values that include NULL bytes. All the types described here have +similar performance characteristics. + + + 4.15.1) How do I create a serial/auto-incrementing field? + +PostgreSQL supports a SERIAL data type. It auto-creates a sequence and +index on the column. For example, this: + + CREATE TABLE person ( + id SERIAL, + name TEXT + ); + +is automatically translated into this: + + CREATE SEQUENCE person_id_seq; + CREATE TABLE person ( + id INT4 NOT NULL DEFAULT nextval('person_id_seq'), + name TEXT + ); + CREATE UNIQUE INDEX person_id_key ON person ( id ); + +See the /create_sequence/ manual page for more information about +sequences. You can also use each row's /OID/ field as a unique value. +However, if you need to dump and reload the database, you need to use +/pg_dump/'s /-o/ option or COPY WITH OIDS option to preserve the OIDs. + + + 4.15.2) How do I get the value of a SERIAL insert? + +One approach is to retrieve the next SERIAL value from the sequence +object with the /nextval()/ function /before/ inserting and then insert +it explicitly. Using the example table in 4.15.1 <#4.15.1>, an example +in a pseudo-language would look like this: + + new_id = execute("SELECT nextval('person_id_seq')"); + execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')"); + +You would then also have the new value stored in |new_id| for use in +other queries (e.g., as a foreign key to the |person| table). Note that +the name of the automatically created SEQUENCE object will be named +</table/>_</serialcolumn/>_/seq/, where /table/ and /serialcolumn/ are +the names of your table and your SERIAL column, respectively. + +Alternatively, you could retrieve the assigned SERIAL value with the +/currval()/ function /after/ it was inserted by default, e.g., + + execute("INSERT INTO person (name) VALUES ('Blaise Pascal')"); + new_id = execute("SELECT currval('person_id_seq')"); + +Finally, you could use the OID <#4.16> returned from the INSERT +statement to look up the default value, though this is probably the +least portable approach. In Perl, using DBI with Edmund Mergl's DBD::Pg +module, the oid value is made available via /$sth->{pg_oid_status}/ +after /$sth->execute()/. + + + 4.15.3) Don't /currval()/ and /nextval()/ lead to a race + condition with other users? + +No. /currval()/ returns the current value assigned by your backend, not +by all users. + + + 4.15.4) Why aren't my sequence numbers reused on transaction + abort? Why are there gaps in the numbering of my sequence/SERIAL + column? + +To improve concurrency, sequence values are given out to running +transactions as needed and are not locked until the transaction +completes. This causes gaps in numbering from aborted transactions. + + + 4.16) What is an OID? What is a TID? + +OIDs are PostgreSQL's answer to unique row ids. Every row that is +created in PostgreSQL gets a unique OID. All OIDs generated during +/initdb/ are less than 16384 (from /include/access/transam.h/). All +user-created OIDs are equal to or greater than this. By default, all +these OIDs are unique not only within a table or database, but unique +within the entire PostgreSQL installation. + +PostgreSQL uses OIDs in its internal system tables to link rows between +tables. These OIDs can be used to identify specific user rows and used +in joins. It is recommended you use column type OID to store OID values. +You can create an index on the OID field for faster access. + +OIDs are assigned to all new rows from a central area that is used by +all databases. If you want to change the OID to something else, or if +you want to make a copy of the table, with the original OIDs, there is +no reason you can't do it: + + CREATE TABLE new_table(old_oid oid, mycol int); + SELECT old_oid, mycol INTO new FROM old; + COPY new TO '/tmp/pgtable'; + DELETE FROM new; + COPY new WITH OIDS FROM '/tmp/pgtable'; + +OIDs are stored as 4-byte integers, and will overflow at 4 billion. No +one has reported this ever happening, and we plan to have the limit +removed before anyone does. + +TIDs are used to identify specific physical rows with block and offset +values. TIDs change after rows are modified or reloaded. They are used +by index entries to point to physical rows. + + + 4.17) What is the meaning of some of the terms used in PostgreSQL? + +Some of the source code and older documentation use terms that have more +common usage. Here are some: + + * table, relation, class + * row, record, tuple + * column, field, attribute + * retrieve, select + * replace, update + * append, insert + * OID, serial value + * portal, cursor + * range variable, table name, table alias + +A list of general database terms can be found at: +http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary/glossary.html + + + 4.18) Why do I get the error /"ERROR: Memory exhausted in + AllocSetAlloc()"/? + +You probably have run out of virtual memory on your system, or your +kernel has a low limit for certain resources. Try this before starting +/postmaster/: + + ulimit -d 262144 + limit datasize 256m + +Depending on your shell, only one of these may succeed, but it will set +your process data segment limit much higher and perhaps allow the query +to complete. This command applies to the current process, and all +subprocesses created after the command is run. If you are having a +problem with the SQL client because the backend is returning too much +data, try it before starting the client. + + + 4.19) How do I tell what PostgreSQL version I am running? + +From /psql/, type |SELECT version();| + + + 4.20) Why does my large-object operations get /"invalid large + obj descriptor"/? + +You need to put |BEGIN WORK| and |COMMIT| around any use of a large +object handle, that is, surrounding |lo_open| ... |lo_close.| + +Currently PostgreSQL enforces the rule by closing large object handles +at transaction commit. So the first attempt to do anything with the +handle will draw /invalid large obj descriptor/. So code that used to +work (at least most of the time) will now generate that error message if +you fail to use a transaction. + +If you are using a client interface like ODBC you may need to set +|auto-commit off.| + + + 4.21) How do I create a column that will default to the current + time? + +Use /CURRENT_TIMESTAMP/: + +|CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP ); +| + + + 4.22) Why are my subqueries using |IN| so slow? + +Currently, we join subqueries to outer queries by sequentially scanning +the result of the subquery for each row of the outer query. If the +subquery returns only a few rows and the outer query returns many rows, +|IN| is fastest. To speed up other queries, replace |IN| with |EXISTS|: + + SELECT * + FROM tab + WHERE col IN (SELECT subcol FROM subtab); + +to: + + SELECT * + FROM tab + WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col); + +For this to be fast, |subcol| should be an indexed column. This +preformance problem will be fixed in 7.4. + + + 4.23) How do I perform an outer join? + +PostgreSQL supports outer joins using the SQL standard syntax. Here are +two examples: + + SELECT * + FROM t1 LEFT OUTER JOIN t2 ON (t1.col = t2.col); + +or + + SELECT * + FROM t1 LEFT OUTER JOIN t2 USING (col); + +These identical queries join t1.col to t2.col, and also return any +unjoined rows in t1 (those with no match in t2). A RIGHT join would add +unjoined rows of t2. A FULL join would return the matched rows plus all +unjoined rows from t1 and t2. The word OUTER is optional and is assumed +in LEFT, RIGHT, and FULL joins. Ordinary joins are called INNER joins. + +In previous releases, outer joins can be simulated using UNION and NOT +IN. For example, when joining /tab1/ and /tab2/, the following query +does an /outer/ join of the two tables: + + SELECT tab1.col1, tab2.col2 + FROM tab1, tab2 + WHERE tab1.col1 = tab2.col1 + UNION ALL + SELECT tab1.col1, NULL + FROM tab1 + WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2) + ORDER BY col1 + + + 4.24) How do I perform queries using multiple databases? + +There is no way to query a database other than the current one. Because +PostgreSQL loads database-specific system catalogs, it is uncertain how +a cross-database query should even behave. + +/contrib/dblink/ allows cross-database queries using function calls. Of +course, a client can make simultaneous connections to different +databases and merge the results on the client side. + + + 4.25) How do I return multiple rows or columns from a function? + +In 7.3, you can easily return multiple rows or columns from a function, +http://techdocs.postgresql.org/guides/SetReturningFunctions +<http://techdocs.postgresql.org/guides/SetReturningFunctions>. + + + 4.26) Why can't I reliably create/drop temporary tables in + PL/PgSQL functions? + +PL/PgSQL caches function contents, and an unfortunate side effect is +that if a PL/PgSQL function accesses a temporary table, and that table +is later dropped and recreated, and the function called again, the +function will fail because the cached function contents still point to +the old temporary table. The solution is to use EXECUTE for temporary +table access in PL/PgSQL. This will cause the query to be reparsed every +time. + + + 4.27) What replication options are available? + +There are several master/slave replication options available. These +allow only the master to make database changes and the slave can only do +database reads. The bottom of +http://gborg.PostgreSQL.org/genpage?replication_research +<http://gborg.postgresql.org/genpage?replication_research> lists them. A +multi-master replication solution is being worked on at +http://gborg.PostgreSQL.org/project/pgreplication/projdisplay.php +<http://gborg.postgresql.org/project/pgreplication/projdisplay.php>. + + + 4.28) What encryption options are available? + + * /contrib/pgcrypto/ contains many encryption functions for use in + SQL queries. + * The only way to encrypt transmission from the client to the server + is by using /hostssl/ in /pg_hba.conf/. + * Database user passwords are automatically encrypted when stored in + version 7.3. In previous versions, you must enable the option + /PASSWORD_ENCRYPTION/ in /postgresql.conf/. + * The server can run using an encrypted file system. + +------------------------------------------------------------------------ + + + Extending PostgreSQL + + + 5.1) I wrote a user-defined function. When I run it in /psql/, + why does it dump core? + +The problem could be a number of things. Try testing your user-defined +function in a stand-alone test program first. + + + 5.2) How can I contribute some nifty new types and functions to + PostgreSQL? + +Send your extensions to the /pgsql-hackers/ mailing list, and they will +eventually end up in the /contrib// subdirectory. + + + 5.3) Bir tuple döndürmek için bir C fonksiyonunu nasıl yazarım? + +PostgreSQL 7.3 sürümü ile birlikte, C, PL/PgSQL ve SQL kullanılarak +tablo-döndüren fonksiyonlar tamamen desteklenmektedir. Ayrıntılı bilgi +için "Programmer's Guide" a bakabilrisiniz. Bir örneği +/contrib/tablefunc/ içinde bulabilirsiniz. + + + 5.4) Bir kaynak dosyasında değişiklik yaptım. Yeniden derlememe + rağmen değişiklik geçerli olmuyor. Neden? + +/Makefile'lar/ include dosyaları için tam bir bağımlılık içermezler. +Öncelikle /make clean/, ardından da baska bir /make/ işlemi yapmanız +gerekir. GCC kullanıyorsaniz, /configure/ betiğinin /--enable-depend/ +seçeneğini, derleyicinin bağımlılıkları otomatik olarak hesaplaması için +kullanabilirsiniz. + |