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Re: Possible bug in ECPGlib thread-safety (Postgres 7.4)...

From: Lee Kindness <lkindness(at)csl(dot)co(dot)uk>
To: Philip Yarra <philip(at)utiba(dot)com>
Cc: "Demetres Pantermalis" <dpant(at)intracom(dot)gr>,<pgsql-interfaces(at)postgresql(dot)org>, Lee Kindness <lkindness(at)csl(dot)co(dot)uk>
Subject: Re: Possible bug in ECPGlib thread-safety (Postgres 7.4)...
Date: 2003-12-05 09:19:51
Message-ID: 16336.19895.354907.412172@kelvin.csl.co.uk (view raw or flat)
Thread:
Lists: pgsql-interfaces
Philip Yarra writes:
 > Unlike the libpq C interface, there is no "connection" variable maintained in 
 > ECPG... instead, ECPG internally maintains a global list of open connections. 
 > When a client application issues an EXEC SQL, a connection is retrieved from 
 > the list, and the SQL statement is executed on that connection. The first 
 > connection in the list is the "default" connection, so if you don't specify a 
 > named connection using "AT conn_name" ECPG grabs the first connection in the 
 > list.
 > 
 > I'm pretty sure what happens when you issue EXEC SQL SET CONNECTION is that it 
 > sets the the default connection, so each of your threads would simply have 
 > shuffled the default connection. Then when each thread attempts to EXEC SQL 
 > they grab the same connection... whichever connection was made the default by 
 > the last thread to issue EXEC SQL SET CONNECTION.
 > 
 > I believe this behaviour is consistent with other DBMS implementations of 
 > embedded SQL, but I'm shooting from the hip.

Not sure on the consistency, that's one thing ESQL/C rarely is!

Anyway you're right regarding the SET CONNECTION behaviour. However
it'd be fairly simple to change things such that each thread keeps
track of its "current" connection (set by connecting and SET
CONNECTION) by using thread local storage.

It'd be a definite improvement over having to specify the connection
on each call!

I'll probably do this at some point, but since i'm off to India on
Monday for the rest of December it'll not be till the New Year at the
earliest!

L.

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Subject: PyGreSQL on Cygwin installation
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