Subject: PostgreSQL, and ODBC statement handles

From: Reza Taheri <[email-masked]>
Date: Wed, 3 May 2017 23:41:33 +0000

I am running a benchmark (TPCx-V) with a single process on the client system handing all the load. Each connection to the server is in a separate thread with its own connection to PGSQL, and its own connection handle and statement handle.  I am facing a contention problem with ODBC on the client side. strace and perf top show we are serializing over what appears to be accesses to the ODBC statement handle. Contention goes away if I use multiple processes instead of multiple threads within a process.

I suppose I don't understand the concept of "handles" well, but I am surprised that all the threads get the same connection handle number and the same statement handle number. Does that mean some data structure is shared between the different threads? Is there a way to force different statement handles (or handle numbers???) for different threads within one process? I have asked this question on the ODBC mailing list, and they suggested it could be something in the postgresql driver. I can provide detailed performance data, but maybe someone can help me figure out what might be a very basic configuration or parameter setting problem. I am running the following RPMs on RHEL 7.1:
postgresql93-9.3.5-2PGDG.rhel7.x86_64
postgresql93-odbc-09.03.0300-1PGDG.rhel7.x86_64
unixODBC-2.3.1-10.el7.x86_64

Thanks,
Reza

---

From: Tom Lane <[email-masked]>
Date: Thu, 04 May 2017 00:12:49 -0400

Reza Taheri <[email-masked]> writes:
> I am running a benchmark (TPCx-V) with a single process on the client
> system handing all the load. Each connection to the server is in a
> separate thread with its own connection to PGSQL, and its own connection
> handle and statement handle.  I am facing a contention problem with ODBC
> on the client side. strace and perf top show we are serializing over
> what appears to be accesses to the ODBC statement handle. Contention
> goes away if I use multiple processes instead of multiple threads within
> a process.

No idea about the answer to this, but I suggest that you might find
help on the pgsql-odbc list, if no one answers here.

			regards, tom lane

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