path: root/doc/TODO.detail/java

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Date: Sat, 03 Feb 2001 10:46:24 +0000
To: Alex Pilosov <alex@pilosoft.com>, tomasz konefal <twkonefal@yahoo.ca>
From: Peter Mount <peter@retep.org.uk>
Subject: Re: [HACKERS] TODO list:  Allow Java server-side programming
Cc: pgsql-hackers@postgresql.org
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At 14:57 02/02/01 -0500, Alex Pilosov wrote:
>On Fri, 2 Feb 2001, tomasz konefal wrote:
>
> >   could someone please clarify what "Allow Java
> > server-side programming" actually means?  what are the
> > limitations of using java and jdbc with pgsql?
>
>It means to embed Java interpreter inside postgres, and allow writing
>stored procedures and triggers in Java.

Thats correct. Basically you are talking of something like PL/Java. The 
Java side would be simple, but its linking the JVM to the backend that's 
the problem.

It's been a while since I delved into the backend, but unless it's changed 
from fork() to threading, I don't really see this happening, unless someone 
who knows C that well knows of a portable way of communicating between two 
processes - other than RMI. If that could be solved, then you could use JNI 
to interface the JVM.

I know some people think this would slow the backend down, but it's only 
the instanciation of the JVM thats slow, hence the other reason fork() is 
holding this back. Ideally you would want the JVM to be running with 
PostMaster, and then each backend can then use the JVM as and when necessary.

Obviously you wouldn't want a JVM in every installation, but there are a 
lot of good reasons to have this capability. For example, as part of the 
course I did this week, we used Tomcat (Servlet/JSP/Web server). Now 
there's no reason why Tomcat could run within the same JVM. JBoss is 
another good example (EJB Server). The JBoss team have actually got Tomcat 
to run within the same JVM. Doesn't hinder performance at all, but does 
reduce the memory footprint.

This is a good future thing to look into (why not for 8.0 ;-) ). If we 
could find an _optional_ way of hooking the backend direct into the JVM, we 
could get PostgreSQL into a lot of new areas. It also would make things 
like CORBA etc a doddle.

PS: I'm writing down notes of the course to go onto the JDBC web site this 
weekend, so there's some nice things for EJB, RMI, Corba etc.

More later, Peter


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Date: Sat, 3 Feb 2001 17:56:33 +0100 (CET)
From: Peter Eisentraut <peter_e@gmx.net>
To: Peter Mount <peter@retep.org.uk>
cc: Alex Pilosov <alex@pilosoft.com>, tomasz konefal <twkonefal@yahoo.ca>,
        <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] TODO list:  Allow Java server-side programming
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Peter Mount writes:

> Thats correct. Basically you are talking of something like PL/Java. The
> Java side would be simple, but its linking the JVM to the backend that's
> the problem.

I've tried that recently, here's how it looks as far as Linux JVMs go:

* Kaffe has a very polluted name space.  Calls to its own functions get
resolved to PostgreSQL, and vice versa.  Crash and burn result.  The Kaffe
folks have admitted that this should be fixed but I didn't look farther
yet.

* The Sun/Blackdown JVM didn't work at all (not even 'java -version')
until I upgraded my libc.  Then a simple test run crashes with an "error
external to JVM"; at first it looked like a segfault when referencing a
string constant.  In gdb I saw myself faced with about 10 threads running
when nothing was going on yet, at which point I was too exhausted to
proceed.

* IBM's offering didn't work at all.  I don't recall the problem anymore
but I think it didn't even link correctly.

So currently I don't see how this could become a mainstream project, let
alone across platforms.

> I know some people think this would slow the backend down, but it's only
> the instanciation of the JVM thats slow, hence the other reason fork() is
> holding this back. Ideally you would want the JVM to be running with
> PostMaster, and then each backend can then use the JVM as and when necessary.

But how do the other languages cope?  Starting up a new Perl for each
backend can't be so cheap either.

-- 
Peter Eisentraut      peter_e@gmx.net       http://yi.org/peter-e/


From pgsql-hackers-owner+M4154@postgresql.org Sat Feb  3 12:37:02 2001
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Date: Sat, 3 Feb 2001 12:36:01 -0500 (EST)
From: Alex Pilosov <alex@pilosoft.com>
To: Peter Mount <peter@retep.org.uk>
cc: Alex Pilosov <alex@pilosoft.com>, tomasz konefal <twkonefal@yahoo.ca>,
        pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] TODO list:  Allow Java server-side programming
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On Sat, 3 Feb 2001, Peter Mount wrote:

> It's been a while since I delved into the backend, but unless it's
> changed from fork() to threading, I don't really see this happening,
> unless someone who knows C that well knows of a portable way of
> communicating between two processes - other than RMI. If that could be
> solved, then you could use JNI to interface the JVM.
There are many ways one can do this:
a) each backend will have a JVM linked in (shared object). This is the
way perl/tcl/ruby is embedded, and it works pretty nice. But, Java
['s memory requirement] sucks, therefore, this may not be the optimal
way.

> I know some people think this would slow the backend down, but it's
> only the instanciation of the JVM thats slow, hence the other reason
> fork() is holding this back. Ideally you would want the JVM to be
> running with PostMaster, and then each backend can then use the JVM as
> and when necessary.
b) since JVM is threaded, it may be more efficient to have a dedicated
process running JVM, and accepting some sort of IPC connections from
postgres processes. The biggest problem here is SPI, there aren't a good
way for that JVM to talk back to database.

c) temporarily, to have quick working code, you can reach java using hacks
using programming languages already built into postgres. Both TCL (tcl
blend) and Perl (JPL and another hack which name escapes me) are able to
execute java code. SPI is possible, I think both of these bindings are
two-way (you can go perl-java-perl-java). Might be worth a quick try?
-alex
 


From pgsql-hackers-owner+M4164@postgresql.org Sun Feb  4 04:23:42 2001
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To: Peter Mount <peter@retep.org.uk>
CC: Alex Pilosov <alex@pilosoft.com>, tomasz konefal <twkonefal@yahoo.ca>,
        pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] TODO list:  Allow Java server-side programming
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Peter Mount wrote:
> 
> At 14:57 02/02/01 -0500, Alex Pilosov wrote:
> >On Fri, 2 Feb 2001, tomasz konefal wrote:
> >
> > >   could someone please clarify what "Allow Java
> > > server-side programming" actually means?  what are the
> > > limitations of using java and jdbc with pgsql?
> >
> >It means to embed Java interpreter inside postgres, and allow writing
> >stored procedures and triggers in Java.
> 
> Thats correct. Basically you are talking of something like PL/Java. The
> Java side would be simple, but its linking the JVM to the backend that's
> the problem.
> 
> It's been a while since I delved into the backend, but unless it's changed
> from fork() to threading,

Someone posted here recently his port/tweaks of backend so that it used 
threads instead of fork(). IIRC it was done to be used inside a java 
client in an embedded system.

----------------
Hannu

From pgsql-hackers-owner+M4168@postgresql.org Sun Feb  4 06:54:27 2001
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To: Peter Eisentraut <peter_e@gmx.net>
From: Peter Mount <peter@retep.org.uk>
Subject: Re: [HACKERS] TODO list:  Allow Java server-side programming
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At 17:56 03/02/01 +0100, Peter Eisentraut wrote:
>Peter Mount writes:
>
> > Thats correct. Basically you are talking of something like PL/Java. The
> > Java side would be simple, but its linking the JVM to the backend that's
> > the problem.
>
>I've tried that recently, here's how it looks as far as Linux JVMs go:

[snip]


>So currently I don't see how this could become a mainstream project, let
>alone across platforms.

I don't think it would be, but it would be a good side-project. Over time 
the various JVM's should become better to interface with.


> > I know some people think this would slow the backend down, but it's only
> > the instanciation of the JVM thats slow, hence the other reason fork() is
> > holding this back. Ideally you would want the JVM to be running with
> > PostMaster, and then each backend can then use the JVM as and when 
> necessary.
>
>But how do the other languages cope?  Starting up a new Perl for each
>backend can't be so cheap either.

But a lot cheaper than Java.

Peter


From pgsql-hackers-owner+M4169@postgresql.org Sun Feb  4 06:57:24 2001
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Date: Sun, 04 Feb 2001 11:54:20 +0000
To: Alex Pilosov <alex@pilosoft.com>
From: Peter Mount <peter@retep.org.uk>
Subject: Re: [HACKERS] TODO list:  Allow Java server-side programming
Cc: Alex Pilosov <alex@pilosoft.com>, tomasz konefal <twkonefal@yahoo.ca>,
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At 12:36 03/02/01 -0500, Alex Pilosov wrote:
>On Sat, 3 Feb 2001, Peter Mount wrote:

[snip]


> > I know some people think this would slow the backend down, but it's
> > only the instanciation of the JVM thats slow, hence the other reason
> > fork() is holding this back. Ideally you would want the JVM to be
> > running with PostMaster, and then each backend can then use the JVM as
> > and when necessary.
>b) since JVM is threaded, it may be more efficient to have a dedicated
>process running JVM, and accepting some sort of IPC connections from
>postgres processes. The biggest problem here is SPI, there aren't a good
>way for that JVM to talk back to database.

That was my other idea, but it is the IPC thats problematical. You would 
still need to do some native api to implement some messaging system between 
the two.

However, at the other extreme there is RPC, which is possible now, but 
would be a lot slower.


>c) temporarily, to have quick working code, you can reach java using hacks
>using programming languages already built into postgres. Both TCL (tcl
>blend) and Perl (JPL and another hack which name escapes me) are able to
>execute java code. SPI is possible, I think both of these bindings are
>two-way (you can go perl-java-perl-java). Might be worth a quick try?

Might be one way to go...

Peter

>-alex
>


From pgsql-jdbc-owner+M884@postgresql.org Wed Jun 27 13:36:09 2001
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From: "Dave Cramer" <Dave@micro-automation.net>
To: "'Barry Lind'" <barry@xythos.com>
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Subject: [JDBC] RE: Todo/missing? (was Re: [ADMIN] High memory usage [PATCH])
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Barry,

The getXXXFunctions aren't implemented
Some of the other functions are correct for version 7.1 but not for
previous versions. Ie. The row length, etc. I think the driver should
get the version and determine what is correct for each version. 

I think this is incorrect. 
  public boolean supportsSelectForUpdate() throws SQLException
  {
    // XXX-Not Implemented
    return false;
  }

There are a number of things here which are hard coded, and possible
wrong.

I started to work on this, but since I am going on vacation next week I
have a number of fires to get down to a slow burn before I go.

Dave

-----Original Message-----
From: Barry Lind [mailto:barry@xythos.com] 
Sent: June 26, 2001 9:22 PM
To: Dave Cramer
Cc: pgsql-jdbc@postgresql.org
Subject: Re: Todo/missing? (was Re: [ADMIN] High memory usage [PATCH])

Dave,

Can you give a little more detail on what you mean by 'Improved 
DatabaseMetaData'?  What specific areas are currently lacking?

thanks,
--Barry


>>On Mon, Jun 25, 2001 at 10:56:18PM -0400, Dave Cramer wrote:
>>
>>>I have to agree, we need to compile a todo list. 
>>>
>>>Mine would include:
>>>
>>>1) Comprehensive test suite. This may be available already.
>>>2) Updateable resultSet
>>>3) Improved DatabaseMetaData
>>>4) Compatible blob support
>>>
> 
> Added to official PostgreSQL TODO:
> 
> * JDBC
>         * Comprehensive test suite. This may be available already.    
>         * Updateable resultSet     
>         * Improved DatabaseMetaData     
>         * Compatible blob support    
> 
> 




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TIP 4: Don't 'kill -9' the postmaster

From pgsql-jdbc-owner+M968@postgresql.org Sun Jul  8 18:59:29 2001
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Date: Mon, 9 Jul 2001 00:55:37 +0200 (CEST)
From: Peter Eisentraut <peter_e@gmx.net>
To: <pgsql-jdbc@postgresql.org>
Subject: [JDBC] To do list for DatabaseMetaData
Message-ID: <Pine.LNX.4.30.0107090041240.677-100000@peter.localdomain>
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Status: OR

Since DatabaseMetaData seems to have been a subject of interest lately I
have composed a list of concrete things that need to be done there.

The spec of DatabaseMetaData is here:
http://java.sun.com/j2se/1.3/docs/api/java/sql/DatabaseMetaData.html

All the functions listed in the spec and not listed below I have recently
checked and updated for correctness and compliance.  Thus, this list is
complete.  Functions marked with '?' I have not checked yet.

If someone wants to tackle some of the getThings() functions, a
description of the system catalogs is in the Developer's Guide.  Also note
that some functions currently incorrectly handle the case of null patterns
vs. "" patterns vs. "%" patterns.

At least two parameters obtained by a DatabaseMetaData method are
user-tunable on the server side.  The only way to get at those numbers
currently is to use SHOW and parse the NOTICE: it sends back (which is
impossible in the days of internationalized messages), so a nice
side-project would be to implement a get_config_variable(text) returns
text (better names possible) function to allow easier access.

Now the list:

allProceduresAreCallable()		not all procedures listed are
					callable (triggers, in/out)
allTablesAreSelectable()		should this check access
					privileges or what?
getSQLKeywords()			outdated, could be automated like
					keywords.sgml
getNumericFunctions()			decide what exactly is a "numeric function"?
getStringFunctions()			ditto
getSystemFunctions()			ditto
getTimeDateFunctions()			ditto
getExtraNameCharacters()		server allows \200 to \377, how
					does this fit in with Unicode?
getMaxColumnNameLength()		32 is hard-coded here, maybe query server
getMaxColumnsInIndex()			this should be detected from server
getMaxColumnsInTable()			this limit is probably shaky
getMaxConnections()			could query the server for this
					(SHOW, see above)
getMaxCursorNameLength()		32 hard-coded
getMaxSchemaNameLength()		will be 32 when done
getMaxProcedureNameLength()		32 hard-coded
getMaxCatalogNameLength()		should be NAMEDATALEN
doesMaxRowSizeIncludeBlobs()		since we don't have blobs, should
					this throw an exception?
getMaxStatements()			questionable, see comment there
getMaxTableNameLength()			32 hard-coded
getMaxUserNameLength()			32 hard-coded
getDefaultTransactionIsolation()	This is configurable in 7.2.
					(SHOW, see above)
getProcedures()				missing catalog (database) and
					remarks columns
getProcedureColumns()			only dummy implementation
getTables()				fails to handle pre-7.1 servers
					(relkind 'v')
getSchemas()				This should throw an exception.
getTableTypes()				?
getColumns()				?
getColumnPrivileges()			not implemented
getTablePrivileges()			not implemented
getBestRowIdentifier()			only dummy implementation
getVersionColumns()			not implemented
getPrimaryKeys()			?
getImportedKeys()			?
getExportedKeys()			not implemented
getCrossReference()			not implemented
getTypeInfo()				?
getIndexInfo()				?
getUDTs()				?


-- 
Peter Eisentraut   peter_e@gmx.net   http://funkturm.homeip.net/~peter


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