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Diffstat (limited to 'doc/FAQ')
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1 files changed, 22 insertions, 20 deletions
@@ -1,15 +1,15 @@ Frequently Asked Questions (FAQ) for PostgreSQL - Last updated: Tue Dec 17 23:56:27 EST 2002 + Last updated: Fri Feb 14 09:03:00 EST 2003 Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us) The most recent version of this document can be viewed at - http://www.PostgreSQL.org/docs/faq-english.html. + http://www.ca.PostgreSQL.org/docs/faq-english.html. Platform-specific questions are answered at - http://www.PostgreSQL.org/users-lounge/docs/faq.html. + http://www.ca.PostgreSQL.org/users-lounge/docs/faq.html. _________________________________________________________________ General Questions @@ -242,11 +242,11 @@ Unix command irc -c '#PostgreSQL' "$USER" irc.phoenix.net. A list of commercial support companies is available at - http://www.PostgreSQL.org/users-lounge/commercial-support.html. + http://www.ca.PostgreSQL.org/users-lounge/commercial-support.html. 1.7) What is the latest release? - The latest release of PostgreSQL is version 7.3.1. + The latest release of PostgreSQL is version 7.3.2. We plan to have major releases every four months. @@ -255,7 +255,7 @@ Several manuals, manual pages, and some small test examples are included in the distribution. See the /doc directory. You can also browse the manual online at - http://www.PostgreSQL.org/users-lounge/docs/. + http://www.ca.PostgreSQL.org/users-lounge/docs/. There are two PostgreSQL books available online at http://www.PostgreSQL.org/docs/awbook.html and @@ -586,10 +586,6 @@ that PostgreSQL has a limit on the number of allowed backend processes is so your system won't run out of resources. - In PostgreSQL versions prior to 6.5, the maximum number of backends - was 64, and changing it required a rebuild after altering the - MaxBackendId constant in include/storage/sinvaladt.h. - 3.9) What is in the pgsql_tmp directory? This directory contains temporary files generated by the query @@ -749,6 +745,10 @@ 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 @@ -820,10 +820,10 @@ Type Internal Name Notes -------------------------------------------------- -"char" char 1 character -CHAR(n) bpchar blank padded to the specified fixed length 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 +"char" char one character BYTEA bytea variable-length byte array (null-byte safe) You will see the internal name when examining system catalogs and in @@ -834,13 +834,15 @@ BYTEA bytea variable-length byte array (null-byte safe) 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. - - CHAR(n) is best when storing strings that are usually the same length. - VARCHAR(n) is best when storing variable-length strings but it limits + 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, - maximum 1 gigabyte. BYTEA is for storing binary data, particularly - values that include NULL bytes. These types have similar performance - characteristics. + 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. These types have similar + performance characteristics. 4.15.1) How do I create a serial/auto-incrementing field? @@ -1009,8 +1011,8 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP ); FROM tab WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col); - For this to be fast, subcol should be an indexed column. We hope to - fix this limitation in a future release. + 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? |