FreeTDS Development Group

["Federico Alves" <sales AT minixel.com>]

I am having discussion on the Asterisk Developer's List about a bug that
forces me to use Perl and AGI and not the Connection-Pooling mechanism.
Tilghman says that my interpretation of the issue is wrong. The facts are:
using Perl I can open a connection, execute a query, close it and thus I can
have dozens, possibly hundreds of simultaneous queries to the SQL. Using
Asterisk's ODBC sharing mechanism, it chokes to death and after a few
queries per second, Asterisk starts to slow down and "constipate", many
queries are queued and just a few are executed. I blame Asterisk and
Tilghman blames Freetds. Frediano Ziglio was involved in debugging this
issue with Digium's Steve Murphy, but it never worked. It would be great if
Frediano or somebody with advanced knowledge of the Asterisk code would
intervene. Just send me your comments and I will post them to the List or
kindly signup for the Asterisk Developer's List.
Federico

On Saturday 07 February 2009 14:25:30 Venefax wrote:
> I did not test it. I don't think that the driver has anything to do 
> with this. If you read carefully what has been written you may achieve 
> the same conclusion.
> a) Freetds allows me to execute 100+ simultaneous queries to the 
> database, on separate channels. Open Connection, Execute, Close
Connection.
> b) Asterisk slows down to a halt in the same scenario. The difference 
> is that the connections are never closed, are "pooled".

If you believe that reconnecting for every single query would make a
difference, that is a very easy change.  However, given the single-engine-
multi-instance aspect, I doubt this will have a positive effect.  But I'd be
happy to code it, if you're willing to test it.

> If you compare a) to b), there is no way to blame the driver. This 
> absolutely absurd. The driver opens a connection and keeps a list of 
> open connections in its internal structure. It is a black box. This 
> black box does in fact work as expected, because at the same second I 
> may have dozens of independent queries being processed using Perl.

I think you're revealing a fundamental lack of understanding about the
codebase.  The only way that I could see a relevant comparison is if your
Perl process was multi-threaded, running Fast AGI, and running multiple
queries without ever shutting down.  As it stands, I believe that you're
running multiple Perl instances, which means that you aren't testing FreeTDS
for concurrent queries, the way Asterisk runs.  As a result, your
determination that the driver is not at fault is sorely lacking.

> I think that a portion of the sharing mechanism inside Asterisk's ODBC 
> technology is keeping a lock longer than necessary.

You're free to think whatever you like; the difference here is that the
entire codebase is open source, so all are welcome to look and determine for
themselves if any part is holding any lock for longer than necessary.  I've
reviewed the codebase multiple times, and I've found nothing to backup such
a claim.

--
Tilghman

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