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Re: Allow pooled connections to list all prepared queries

From: David Brown <dave(at)spoonguard(dot)org>
To: Kris Jurka <books(at)ejurka(dot)com>
Cc: PostgreSQL Global Development Group <pgsql-patches(at)postgresql(dot)org>,Charlie Peck <charliep(at)cs(dot)earlham(dot)edu>
Subject: Re: Allow pooled connections to list all prepared queries
Date: 2004-12-27 19:12:20
Message-ID: 20041227191220.GA19378@lan.spoonguard.org (view raw or flat)
Thread:
Lists: pgsql-patches
On Mon, Dec 27, 2004 at 01:03:08PM -0500, Kris Jurka wrote:
>has not prepared.  So I don't see why, simply because it's in a pool, that 
>it forgets what's been prepared.

The connection (the open socket to Postgres) doesn't forget anything.  If 
you have multiple machines sharing a connection pool, though, there may not 
be any guarantee that the same client-side connection object (in your 
example, the proxy object) will always be associated with the same 
underlying connection (the open socket to Postgres).

Multiple machines connecting through a single connection pooling server need 
some way to communicate the state of a particular connection between 
themselves ("state", in this case, being the list of prepared queries).  
This information could be tracked by the connection pool, it could be 
tracked by the clients and shared through some back channel, or it could 
just be exposed via SQL (since Postgres already has it in a convenient 
format).

The patch provides a way to inspect the list of prepared queries on a 
connection, via SQL. It'd be up to the client to avoid this round-trip when 
it isn't necessary (e.g. the single-server or single-process cases you've 
mentioned, where keeping and sharing the list of prepared statements is 
cheap).

At a bare minimum, it'd at least be convenient for humans to be able to 
connect to a pool and look at what's been prepared. There was no way to do 
this before.

- Dave


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