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Re: [INTERFACES] libpq and multi-threading on Linux?

From: Peter T Mount <peter(at)retep(dot)org(dot)uk>
To: Michael Olivier <molivier(at)yahoo(dot)com>
Cc: pgsql interfaces <pgsql-interfaces(at)postgresql(dot)org>
Subject: Re: [INTERFACES] libpq and multi-threading on Linux?
Date: 1999-02-15 19:50:31
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Lists: pgsql-interfaces
On Mon, 15 Feb 1999, Michael Olivier wrote:

> Peter - thanks for your response -- see comments below.
> ---Peter T Mount <peter(at)retep(dot)org(dot)uk> wrote:
> >
> > On Wed, 10 Feb 1999, Michael Olivier wrote:
> > 
> > > Hi folks,
> > > 
> > > I apologize in advance if I have overlooked docs, but I haven't been
> > > able to find a discussion of how PostGreSQL via libpq on Linux fares
> > > with pthreads. Can someone point me to docs if available, or
> otherwise
> > > enlighten me? How well does it work and what are the important
> design
> > > issues to consider?
> > > 
> > > I'm expecting to create a pool of db connections to use within a
> > > long-running process, which will create a new thread for each
> incoming
> > > request from a client. I've found just a very little bit about PG
> > > being multi-processing, but not how it will interact with a
> > > multi-threaded client. I appreciate your comments.
> > 
> > Take a look on how I got the JDBC driver to handle multi-threading.
> OK, great -- how do I get this? From looking at your web site, I can
> see downloadable jdbc6.4.jar, but I'm not doing Java work so don't
> have a way to access this - looks like an archive.

I should have said look at the source. The .jar files on my site contain
just the pre-compiled .class files.

Oh, you can use any zip tool to expand a jar file.

> Can you send me the source file(s) or post a URL?

It's under the src/interfaces/jdbc directory in the main source tree.

> > At certain points, the driver obtains a lock on the network connection
> > before sending a query, and releases the lock when the query has
> finished
> > (ie: all results have been returned in to the ResultSet).
> Is this so several threads can share one connection, or so that
> Postgresql doesn't get screwed up with different threads using
> different connections? I think you're saying the former, but I'm not
> sure.

It's the former. Usually most people only run one connection per thread,
but just in case, the locking of the connection gives us some protection.

> I'm looking at allocating one connection per thread, so I need
> this clarified, i.e., do I need to do locking of some sort or will it
> work for me that each thread has a unique DB connection?

What you need is a pool of connections. In the current development source,
there is an example of a pool of connections in the JDBC-CORBA example.
It's under src/interfaces/jdbc/example/corba

> > I'm not sure if this is what you were after.
> Yes, it's getting at it. Thanks.

       Peter T Mount peter(at)retep(dot)org(dot)uk
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