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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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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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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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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
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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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From pgsql-general-owner+M14602@postgresql.org Sat Sep  1 00:50:49 2001
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From: "Robert J. Sanford, Jr." <rsanford@nolimitsystems.com>
To: <pgsql-general@postgresql.org>
Subject: Re: [GENERAL] PL/java?
Date: Fri, 31 Aug 2001 23:02:04 -0500
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note - i don't work for any of the companies whose products
are mentioned below. i have performed evaluations of these
products and the support provided when attempting to determine
what platform my company's systems should run on. unfortunately,
i did not choose orion and i am suffering for it now...

some goober blathered thusly:
> Have you ever actually used Java on an enterprise-level 
> application?  Ever see the Tomcat webserver?  It uses
> 100MB of memory, drives the load on our server up to 8,
> and doesn't serve nearly as fast apache. Do you really
> want that in your database?

first - don't complain about java because you or someone
in your group/department/company made a poor decision on
what tools to use. that's like complaining about mexican
food when the only experience you have is eating an out-
dated frozen burrito from the 7-11 freezer.

when looking at the performance of java you have to take
a look at two things - first you have to compare various
java implementations against each other and then you have
to compare the best java implementations against native
c/c++ code. the following link does that. the java tests
include tomcat, orion, websphere, and resin. jrun and
weblogic were originally included in the testing but
were both removed at their companies' request.

the tests also compare orion vs microsoft asp running on
win2k and iis5. all tests run on the same hardware.

what i believe these tests clearly demonstrate is that
java is not the problem, the implementation applications
based on java is. i also do not believe that tomcat is
a fair representation of java performance in that it is
intended to be a reference implementation. as such, the
code base should sacrifice performance for clarity.

http://www.orionserver.com/benchmarks/benchmark.html


while not in the benchmark i would also like to
recommend jetty as an app server. it is an opensource,
100% java web and application server. in its base form
it is "just" a web, servlet, and jsp engine. it does,
however, have contributed code providing integration
with other j2ee opensource projects such as the JBoss
EJB engine.

you can find the jetty home page at:
   http://jetty.mortbay.com/

and then they blathered some more:
> Compare the speed of Oracle 8 with 8i if you don't
> believe me.  The stability is also much worse.  Ever
> see a JVM on any platform that didn't crash if you
> looked at it cockeyed?  Ever really trust the garbage
> collection?  I don't.  I've found a memory leak in IBM 
> developed java libraries.  Gotta restart that app
> every once in a while to reclaim system resources it
> gobbled up and never gave back.

some mention was made regarding the performance of
the oracle8i application server. well, oracle has
realized that their performance was sub-optimal and
rectified the situation by licensing the orion server
for oracle9i. while money and politics most certainly
play a part in any licensing arrangement they must
also realize that making customers happy through the
performance of their applications will lead to more
money. the link to the press release is below.

http://www.oracle.com/corporate/press/index.html?759347.html

all of that being said...

i don't think that the person that started this thread
did anything wrong by making the request they did. that
is what opensource is all about - contributions, even
just contributions of ideas, are welcomed. even so, there
are several options that i see for getting it implemented:
1) its an open source project so implement it yourself.
   while i have never worked on modifying the code base
   i am extremely confident that the current developers
   will be more than willing to give you advice and
   pointers.
2) if #1 is not feasible either because you don't have
   the time, the inclination, or the experience then
   you can write a contract that will pay one of the
   postgres developers to implement it for you.
3) if that isn't feasible you can try to get a volunteer
   to do so.
4) if that isn't feasible then you either have to live
   with what you have, go elsewhere, or be quiet.

to the person that blathered thusly in response to the
request for java:
> Merits of the language notwithstanding, I'd rather
> not have a buggy, still under development
> (depreciating everything under the sun with every
> new iteration) JVM parasite in my DB.

informed and intelligent debate is good. given that i
believe such to be true, i would request that you
refrain from blathering such vitriol and uninformed
nonsense. not only is it for the good of the people
on the list who don't want to hear it but it will
also do you good by not telling everyone out there
that you are a very silly person that doesn't deal
with logic and/or facts.

to everyone else on the list - if we all contribute
a penny we could probably buy enough burritos from
7-11 to make sure that his hands and mouth are busy
for a good long while.

rjsjr



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From pgsql-general-owner+M14597@postgresql.org Fri Aug 31 23:23:15 2001
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Date: Fri, 31 Aug 2001 22:35:23 -0400 (EDT)
From: Alex Pilosov <alex@pilosoft.com>
To: Alex Knight <knight@phunc.com>
cc: pgsql-general@postgresql.org
Subject: [WAY OT] Re: [GENERAL] PL/java?
In-Reply-To: <MAEFKNDLAHNIFMAIEGHJCEKJCDAA.knight@phunc.com>
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On Fri, 31 Aug 2001, Alex Knight wrote:

> It is generally wiser to split the webservers from the appservers;
> that will save on memory footprints from each respectively. That alone
> can give each machine a specific task to accomplish... generally more
> efficiently. But I would assume you know this.

And it is wise to split database from middleware, and not try to saddle
PostgreSQL with requirements to support Java in-process. _IF_ java stored
procedures are implemented, it should be via something like a) oracle's
extproc (start a separate process to load the function) b) some of perl
java tools (they start a jdk in a separate process and communicate with it
using RMI).


Problem with java-pgsql integration is the threads model: Java really
really wants threads. Postgres doesn't do threads. So if most simple way
is attempted, you will incur overhead of starting up JVM for each backend
(a few seconds as opposed to milliseconds) and non-shared 30M of memory
per backend (as opposed to currently <3 megs of non-shared memory per
backend).

> Using something like WebLogic, WebSphere, or Orion would be a wiser
> approach. For the company with the low budget, Orion is only something
> like $2000, and it has full J2EE support, including EJBs, etc. Try
> finding that kind of richness in Tomcat. Also, Orion takes up only
> 40-50mb at start, which is really fairly reasonable; ram is cheap
> anyways... a server that has to perform complicated algorithms to a
> large audience but has hardly any ram shouldn't be on the internet
> anyways; unless it can handle it.

_ONLY_ 40-50Mb?! Egads, I'm hard pressed to find any other piece of
(non-windows, non-java) software that takes 40-50M just to start up!

I worked with both CrapLogic and CrapSphere. Weblogic takes 20-60 seconds
to start up on P3-800, that, IMHO, is ridiculous. 

It is not only issue of memory, its easy to throw memory at the problem,
its an issue of _incremental use_ of memory. As you scale 

> I feel that you don't really have enough experience with _java_ to
> judge it accurately. Frankly, the JVM is quite small nowadays,
> considering the amount of base classes that sit in memory much of the
> time. And the JVMs are really much faster these days. Java is still
> slow for 2 reasons: 1) Developers who don't optimize their code as
> they write it, 2) Bytecode interpretation is and probably never will
> be as fast as something like C/C++. But it certainly isn't the JVM
> itself slowing it down because of some "extended memory" that it lives
> in. Any reasonable server should have absolutely no problems if the
> jvm is implemented _properly_ (which many packages do not do), etc. If
> you're comparing Java to perl, yes, certainly it's a bit more of a
> beast, but perl quite simply can't keep up in speed and feature
> richness (when was the last time you secured your perl code in a
> redistributable fashion?)
_WHY_ the heck do all base classes need to be in memory all the time? Why
are they so huge? Libc is _far far_ smaller, and libstdc++ is tiny
compared to all the java standard library. 

You know what the answer to it is: Because they are ALL written in java,
as opposed to more sane languages like perl which handcode their "standard
libraries" or the most important pieces of them in C. 

Perl is far faster than java in about any practical application I did.
Again, the issue is not speed of JVM versus PP (perl virtual machine), if
you did number crunching in perl and java, they would probably be at par.
Its an issue of standard libraries. They are _horribly slow_. Perl's
hashtables are a very nice piece of optimized C code. Java's hashtables
are written in Java. Need I say more? Java's AWT was a dog. Swing is a dog
and a half, because they reimplemented all the things that are commonly
done in C in Java.

> The only mistake the developers can make is poorly implementing the
> jvm, but most certainly not Java itself. I've been working on
> architecting and building enterprise level sites and applications for
> nearly 8 years now, and I've seen too many people try to implement
> perl cgi websites for enterprise sites and watch them choke and crawl
> to their knees because of poor system resource handling, lack of
> scalability, etc... I most certainly don't consider a single webserver
> with an appserver and tiny database to be enterprise level either (not
> that I'm inferring you said it was).
You cannot compare a perl CGI script and a J2EE server. Its like comparing
a webserver you wrote yourself vs apache! There are application servers
(or more closely, code libraries) for perl that match what J2EE provides. 

--
Alex Pilosov            | http://www.acedsl.com/home.html
CTO - Acecape, Inc.     | AceDSL:The best ADSL in the world
325 W 38 St. Suite 1005 | (Stealth Marketing Works! :)
New York, NY 10018      |


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From pgsql-hackers-owner+M14652=candle.pha.pa.us=pgman@postgresql.org Thu Oct 25 22:24:44 2001
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* tweekie <None@news.tht.net> wrote:
|
| I asked this question a while back but got no response - is there any way of 
| creating a Java stored procedure in a postgres database ? I can see that 
| there is a built-in PL/sql type of environment and a python one but it would  
| be nice if I could migrate Java stored procedures in an Oracle database into  
| postgres.
| 
| Any comments?


It would rock ;-) An Hungarian guy just sent a mail indicating that he
had a first prototype version of something with Kaffe up and running.
But I believe there is a lot of issues to be solved, especially
threading issues...

-- 
Gunnar Rønning - gunnar@polygnosis.com
Senior Consultant, Polygnosis AS, http://www.polygnosis.com/

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From pgsql-general-owner+M18147=candle.pha.pa.us=pgman@postgresql.org Mon Dec  3 13:53:24 2001
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Hi!

A few months ago I asked if anyone started working on PL/JAVA, the 
ansver was no. Now I started to write a java stored procedure language 
and environment for PostgreSQL. Some code is already working, and it is 
geting interresting. So, I would like to ask you to write me your ideas, 
suggestions, etc for this environment.
The source code will be available under GPL when it is worth for 
distributing it (this will take for a while).
thanks.

Laszlo Hornyak


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cc: Laszlo Hornyak <hornyakl@freemail.hu>, pgsql-general@postgresql.org,
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Subject: Re: [GENERAL] java stored procedures
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From: Doug McNaught <doug@wireboard.com>
Date: 04 Dec 2001 12:58:47 -0500
In-Reply-To: Barry Lind's message of "Tue, 04 Dec 2001 08:44:50 -0800"
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Barry Lind <barry@xythos.com> writes:

> Having one jvm that all the postgres backend processes communicate with makes
> the whole feature much more complicated, but is necessary in my opinion.

Agreed.  Also, the JVM is a multithreaded app, and running it inside a
non-threaded program (the backend) might cause problems. 

> Then the question becomes how does the jvm process interact with the database
> since they are two different processes.  You will need some sort of
> interprocess communication between the two to execute sql statements.  This
> could be accomplished by using the existing jdbc driver.  But the bigest
> problem here is getting the transaction semantics right.  How does a sql
> statement being run by a java stored procedure get access to the same
> connection/transaction as the original client?  What you don't want happening
> is that sql issued in a stored java procedure executes in a different
> transaction as the caller, what would rollback of the stored function call
> mean in that case?

I think you would have to to expose the SPI layer to Java running in a
separate process, either using an RMI server written in C or a custom
protocol over a TCP socket (Java of course can't do Unix sockets).
This raises some thorny issues of authentication and security but I
don't think they're insurmountable.  You could, for example, create a
cryptographically strong "cookie" in the backend when a Java function
is called.  The cookie would be passed to the Java function when it
gets invoked, and then must be passed back to the SPI layer in order
for the latter to accept the call.  A bit clunky but should be safe as
far as I can see.

The cookie would be needed anyhow, I think, in order for the SPI layer 
to be able to find the transaction that the Java function was
originally invoked in.

You could make the SPI layer stuff look like a normal JDBC driver to
user code--PL/Perl does this kind of thing with the Perl DBI
interface.

-Doug
-- 
Let us cross over the river, and rest under the shade of the trees.
   --T. J. Jackson, 1863

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From pgsql-jdbc-owner+M2545@postgresql.org Tue Dec  4 12:49:03 2001
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Date: Tue, 04 Dec 2001 08:44:50 -0800
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To: Laszlo Hornyak <hornyakl@freemail.hu>
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Subject: Re: [JDBC] [GENERAL] java stored procedures
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Laszlo,

I think it would help a lot if you could take a little time to write 
down what your planned architecture for a pljava would be.  It then 
becomes much easier for myself and probably others reading these lists 
to make suggestions on ways to improve what you are planning (or 
possible problems with your strategy).  Without knowing what exactly you 
are thinking of doing it is difficult to comment.

But let me try throwing out a few thoughts about how I think this should 
be done.

First question is how will the jvm be run?  Since postgres is a 
multiprocess implementation (i.e. each connection has a separate process 
on the server) and since java is a multithreaded implementation (i.e. 
one process supporting multiple threads), what should the pljava 
implementation look like?  I think there should be a single jvm process 
for the entire db server that each postgresql process connects to 
through sockets/rmi.  It will be too expensive to create a new jvm 
process for each postgresql connection (expensive in both terms of 
memory and cpu, since the startup time for the jvm is significant and it 
requires a lot of memory).

Having one jvm that all the postgres backend processes communicate with 
makes the whole feature much more complicated, but is necessary in my 
opinion.

Then the question becomes how does the jvm process interact with the 
database since they are two different processes.  You will need some 
sort of interprocess communication between the two to execute sql 
statements.  This could be accomplished by using the existing jdbc 
driver.  But the bigest problem here is getting the transaction 
semantics right.  How does a sql statement being run by a java stored 
procedure get access to the same connection/transaction as the original 
client?  What you don't want happening is that sql issued in a stored 
java procedure executes in a different transaction as the caller, what 
would rollback of the stored function call mean in that case?

I am very interested in hearing what your plans are for pl/java.  I 
think this is a very difficult project, but one that would be very 
useful and welcome.

thanks,
--Barry




Laszlo Hornyak wrote:

> Hi!
> 
> I am such a lame in the licensing area. As much as I know, BSD license 
> is more free than GPL. I think it is too early to think about licensing, 
> but it`s ok, you won :), when it will be ready(or it will seem to get 
> closer to a working thing, currently it looks more like a interresting 
> test), I will ask you if you want to distribute it with Postgres, and if 
> you say yes, the license will be the same as Postgresql`s license. 
> Anyway is this neccessary when it is the part of the distribution?
> Is this ok for you?
> 
> thanks,
> Laszlo Hornyak
> 
> ps: still waiting for your ideas, suggestions, etc :) I am not memeber 
> of the mailing list, please write me dirrectly!
> 
> Barry Lind wrote:
> 
>> Laszlo,
>>
>> In my mind it would be more useful if this code was under the same 
>> license as the rest of postgresql.  That way it could become part of 
>> the product as opposed to always being a separate component.  (Just 
>> like plpgsql, pltcl and the other procedural languages).
>>
>> thanks,
>> --Barry
>>
>>
> 
> 



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From pgsql-jdbc-owner+M2555@postgresql.org Thu Dec  6 10:16:31 2001
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From: Laszlo Hornyak <hornyakl@freemail.hu>
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Subject: Re: [JDBC] [GENERAL] java stored procedures
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Hi!

Barry Lind wrote:

> Laszlo,
>
> I think it would help a lot if you could take a little time to write 
> down what your planned architecture for a pljava would be.  It then 
> becomes much easier for myself and probably others reading these lists 
> to make suggestions on ways to improve what you are planning (or 
> possible problems with your strategy).  Without knowing what exactly 
> you are thinking of doing it is difficult to comment. 

>
>
> But let me try throwing out a few thoughts about how I think this 
> should be done.
>
> First question is how will the jvm be run?  Since postgres is a 
> multiprocess implementation (i.e. each connection has a separate 
> process on the server) and since java is a multithreaded 
> implementation (i.e. one process supporting multiple threads), what 
> should the pljava implementation look like?  I think there should be a 
> single jvm process for the entire db server that each postgresql 
> process connects to through sockets/rmi.  It will be too expensive to 
> create a new jvm process for each postgresql connection (expensive in 
> both terms of memory and cpu, since the startup time for the jvm is 
> significant and it requires a lot of memory). 

I absolutely agree. OK, it`s done.

So, a late-night-brainstorming here:
What I would like to see in PL/JAVA is the object oriented features, 
that makes postgresql nice. Creating a new table creates a new class in 
the java side too. Instantiating an object of the newly created class 
inserts a row into the table. In postgresql tables can be inherited, and 
this could be easyly done by pl/java too. I think this would look nice.
But this is not the main feature. Why I would like to see a nice java 
procedural language inside postgres is java`s advanced communication 
features (I mean CORBA, jdbc, other protocols). This is the sugar in the 
caffe.

I am very far from features like this.
PL/JAVA now:
-there is a separate process running java (kaffe). this process creates 
a sys v message queue, that holds requests. almost forgot, a shared 
memory segment too. I didn`t find better way to tell postgres the 
informations about the java process.
-the java request_handler function on the server side attaches to the 
shared memory, reads the key of the message queue., attaches to it, 
sends the data of the function, and a signal for the pl/java. after, it 
is waiting for a signal from the java thread.
-when java thread receives the signal, it reads the message(s) from the 
queue, and starts some actions. When done it tells postgres with a 
signal that it is ready, and it can come for its results. This will be 
rewritten see below problems.
-And postgres is runing, while java is waiting for postgres to say 
something.

Threading on the java process side is not done yet, ok, it is not that 
hard, I will write it, if it will be realy neccessary.

The problems, for now:
I had a very simple system, that passed a very limited scale of argument 
types, with a very limited quantity of parameters (int, varchar, bool). 
Postgres has limits for the argument count too, but not for types. It 
had too much limits, so I am working (or to tell the truth now only 
thinking) on a new type handling that fits the felxibility of 
Postgresql`s type flexibility. For this I will have to learn a lot about 
Postgres`s type system. This will be my program this weekend. :)

thanks,
Laszlo Hornyak


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From pgsql-jdbc-owner+M2549@postgresql.org Tue Dec  4 22:34:48 2001
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Laszlo,


> I am very far from features like this.
> PL/JAVA now:
> -there is a separate process running java (kaffe). this process creates 
> a sys v message queue, that holds requests. almost forgot, a shared 
> memory segment too. I didn`t find better way to tell postgres the 
> informations about the java process.


Does the mechanism you are planning support running any JVM?  In my 
opionion Kaffe isn't good enough to be widely useful.  I think you 
should be able to plugin whatever jvm is best on your platform, which 
will likely be either the Sun or IBM JVMs.

Also, can you explain this a little bit more.  How does the jvm process 
get started? (I would hope that the postgresql server processes would 
start it when needed, as opposed to requiring that it be started 
separately.)  How does the jvm access these shared memory structures? 
Since there aren't any methods in the java API to do such things that I 
am aware of.

> -the java request_handler function on the server side attaches to the 
> shared memory, reads the key of the message queue., attaches to it, 
> sends the data of the function, and a signal for the pl/java. after, it 
> is waiting for a signal from the java thread.


I don't understand how you do this in java?  I must not be understanding 
  something correctly here.

> -when java thread receives the signal, it reads the message(s) from the 
> queue, and starts some actions. When done it tells postgres with a 
> signal that it is ready, and it can come for its results. This will be 
> rewritten see below problems.


Are signals the best way to accomplish this?

> -And postgres is runing, while java is waiting for postgres to say 
> something.


But in reality if the postgres process is executing a stored function it 
needs to wait for the result of that function call before continuing 
doesn't it?

> 
> Threading on the java process side is not done yet, ok, it is not that 
> hard, I will write it, if it will be realy neccessary.


Agreed, this is important.

> 
> The problems, for now:
> I had a very simple system, that passed a very limited scale of argument 
> types, with a very limited quantity of parameters (int, varchar, bool). 
> Postgres has limits for the argument count too, but not for types. It 
> had too much limits, so I am working (or to tell the truth now only 
> thinking) on a new type handling that fits the felxibility of 
> Postgresql`s type flexibility. For this I will have to learn a lot about 
> Postgres`s type system. This will be my program this weekend. :)


Shouldn't this code use all or most of the logic found in the FE/BE 
protocol?  Why invent and code another mechanism to transfer data when 
one already exists.  (I will admit that the current FE/BE mechanism 
isn't the ideal choice, but it seems easier to reuse what exists for now 
and improve on it later).


> 
> thanks,
> Laszlo Hornyak
> 

You didn't mention how you plan to deal with the transaction symantics. 
  So what happens when the pl/java function calls through jdbc back to 
the server to insert some data?  That should happen in the same 
transaction as the caller correct?

thanks,
--Barry


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From: Laszlo Hornyak <hornyakl@freemail.hu>
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Subject: Re: [JDBC] [GENERAL] java stored procedures
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Hi!

Barry Lind wrote:

> Does the mechanism you are planning support running any JVM?  In my 
> opionion Kaffe isn't good enough to be widely useful.  I think you 
> should be able to plugin whatever jvm is best on your platform, which 
> will likely be either the Sun or IBM JVMs.

Ok, I also had problems with caffe, but it may work. I like it becouse 
it is small (the source is about 6M). As much as I know Java VM`s has a 
somewhat standard native interface called JNI. I use this to start the 
VM, and communicate with it. If you think I should change I will do it, 
but it may take a long time to get the new VM. For then I have to run kaffe.

> Also, can you explain this a little bit more.  How does the jvm 
> process get started? (I would hope that the postgresql server 
> processes would start it when needed, as opposed to requiring that it 
> be started separately.)  How does the jvm access these shared memory 
> structures? Since there aren't any methods in the java API to do such 
> things that I am aware of.

JVM does not. 'the java process' does with simple posix calls. I use 
debian potatoe, on any other posix system it should work, on any other 
somewhat posix compatible system it may work, I am not sure...

>
> I don't understand how you do this in java?  I must not be 
> understanding  something correctly here.

My failure.
The 'java request_handler' is not a java function, it is the C 
call_handler in the Postgres side, that is started when a function of 
language 'pljava' is called.
I made some failure in my previous mail. At home I named the pl/java 
language pl/pizza (something that is not caffe, but well known enough 
:). The application has two running binaries:
-pizza (which was called 'java process' last time) This is a small C 
program that uses JNI to start VM and call java methods.
-plpizza.so the shared object that contains the call_handler function.


>
>
>> -when java thread receives the signal, it reads the message(s) from 
>> the queue, and starts some actions. When done it tells postgres with 
>> a signal that it is ready, and it can come for its results. This will 
>> be rewritten see below problems.
>
>
>
> Are signals the best way to accomplish this? 

I don`t know if it is the best, it is the only way I know :)
Do you know any other ways?

>
>
>> -And postgres is runing, while java is waiting for postgres to say 
>> something.
>
> But in reality if the postgres process is executing a stored function 
> it needs to wait for the result of that function call before 
> continuing doesn't it? 

Surely, this is done. How could Postgres tell the result anyway ? :)

>
>>
>> Threading on the java process side is not done yet, ok, it is not 
>> that hard, I will write it, if it will be realy neccessary.
>
> Agreed, this is important.
>
> Shouldn't this code use all or most of the logic found in the FE/BE 
> protocol?  Why invent and code another mechanism to transfer data when 
> one already exists.  (I will admit that the current FE/BE mechanism 
> isn't the ideal choice, but it seems easier to reuse what exists for 
> now and improve on it later). 

Well, I am relatively new to Postgres, and I don`t know these protocols. 
In the weekend I will start to learn it, and in Sunday or Monday I maybe 
I will understand it, if not, next weekend..

>
> You didn't mention how you plan to deal with the transaction 
> symantics.  So what happens when the pl/java function calls through 
> jdbc back to the server to insert some data?  That should happen in 
> the same transaction as the caller correct? 

I don`t think this will be a problem, I have ideas for this. Idea mean: 
I know how I will start it, it may be good, or it may be fataly stupid 
idea, it will turn out when I tried it. Simply: The same way plpizza 
tells pizza the request, pizza can talk back to plpizza. This is planed 
to work with similar mechanism I described last time (shm+signals).

Monday I will try to send a little pieces of code to make thing clear, ok?

thanks,
Laszlo Hornyak


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Laszlo,

I have cc'ed the hackers mail list since that group of developers is 
probably better able than I to make suggestions on the best interprocess 
communication mechanism to use for this.  See 
http://archives2.us.postgresql.org/pgsql-general/2001-12/msg00092.php 
for background on this thread.

I also stopped cc'ing the general list, since this is getting too 
detailed for most of the members on that list.

Now to your mail:

Laszlo Hornyak wrote:

> Hi!
> 
> Barry Lind wrote:
> 
>> Does the mechanism you are planning support running any JVM?  In my 
>> opionion Kaffe isn't good enough to be widely useful.  I think you 
>> should be able to plugin whatever jvm is best on your platform, which 
>> will likely be either the Sun or IBM JVMs.
> 
> 
> Ok, I also had problems with caffe, but it may work. I like it becouse 
> it is small (the source is about 6M). As much as I know Java VM`s has a 
> somewhat standard native interface called JNI. I use this to start the 
> VM, and communicate with it. If you think I should change I will do it, 
> but it may take a long time to get the new VM. For then I have to run 
> kaffe.
> 


This seems like a reasonable approach and should work across different 
JVMs.  It would probably be a good experiment to try this with the Sun 
or IBM jvm at some point to verify.  What I was afraid of was that you 
were hacking the Kaffe code to perform the integration which would limit 
this solution to only using Kaffe.


>> Also, can you explain this a little bit more.  How does the jvm 
>> process get started? (I would hope that the postgresql server 
>> processes would start it when needed, as opposed to requiring that it 
>> be started separately.)  How does the jvm access these shared memory 
>> structures? Since there aren't any methods in the java API to do such 
>> things that I am aware of.
> 
> 
> JVM does not. 'the java process' does with simple posix calls. I use 
> debian potatoe, on any other posix system it should work, on any other 
> somewhat posix compatible system it may work, I am not sure...
> 
>>
>> I don't understand how you do this in java?  I must not be 
>> understanding  something correctly here.
> 
> 
> My failure.
> The 'java request_handler' is not a java function, it is the C 
> call_handler in the Postgres side, that is started when a function of 
> language 'pljava' is called.
> I made some failure in my previous mail. At home I named the pl/java 
> language pl/pizza (something that is not caffe, but well known enough 
> :). The application has two running binaries:
> -pizza (which was called 'java process' last time) This is a small C 
> program that uses JNI to start VM and call java methods.
> -plpizza.so the shared object that contains the call_handler function.
> 


Just a suggestion:  PL/J might be a good name, since as you probably 
know it can't be called pl/java because of the trademark restrictions on 
the word 'java'.

I am a little concerned about the stability and complexity of having 
this '-pizza' program be responsible for handling the calls on the java 
side.  My concern is that this will need to be a multithreaded program 
since multiple backends will concurrently be needing to interact with 
multiple java threads through this one program.  It might be simpler if 
each postgres process directly communicated to a java thread via a tcpip 
socket.  Then the "-pizza" program would only need to be responsible for 
starting up the jvm and creating java threads and sockets for a postgres 
process (it would perform a similar role to postmaster for postgres 
client connections).


> 
>>
>>
>>> -when java thread receives the signal, it reads the message(s) from 
>>> the queue, and starts some actions. When done it tells postgres with 
>>> a signal that it is ready, and it can come for its results. This will 
>>> be rewritten see below problems.
>>
>>
>>
>>
>> Are signals the best way to accomplish this? 
> 
> 
> I don`t know if it is the best, it is the only way I know :)
> Do you know any other ways?
> 


I don't know, but hopefully someone on the hackers list will chip in 
here with a comment.


>>
>>>
>>> Threading on the java process side is not done yet, ok, it is not 
>>> that hard, I will write it, if it will be realy neccessary.
>>
>>
>> Agreed, this is important.
>>
>> Shouldn't this code use all or most of the logic found in the FE/BE 
>> protocol?  Why invent and code another mechanism to transfer data when 
>> one already exists.  (I will admit that the current FE/BE mechanism 
>> isn't the ideal choice, but it seems easier to reuse what exists for 
>> now and improve on it later). 
> 
> 
> Well, I am relatively new to Postgres, and I don`t know these protocols. 
> In the weekend I will start to learn it, and in Sunday or Monday I maybe 
> I will understand it, if not, next weekend..
> 
>>
>> You didn't mention how you plan to deal with the transaction 
>> symantics.  So what happens when the pl/java function calls through 
>> jdbc back to the server to insert some data?  That should happen in 
>> the same transaction as the caller correct? 
> 
> 
> I don`t think this will be a problem, I have ideas for this. Idea mean: 
> I know how I will start it, it may be good, or it may be fataly stupid 
> idea, it will turn out when I tried it. Simply: The same way plpizza 
> tells pizza the request, pizza can talk back to plpizza. This is planed 
> to work with similar mechanism I described last time (shm+signals).
> 


OK, so the same backend process that called the function gets messaged 
to process the sql.  This should work.  However it means you will need a 
special version of the jdbc driver that uses this shm+signals 
communication mechanism instead of what the current jdbc driver does. 
This is something I would be happy to help you with.



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