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Psycopg website

Psycopg2 hung queries

Reported by Psycopg website | June 23rd, 2012 @ 02:44 PM

Submitted by: anoop

We have a python program which uses psycopg2 to make a connection every 2 seconds to postgresql-9.0 and batch insert/update records. The connection is closed after use.

It's part of a server software which run continuously for months. Some times the query processes is getting stuck (for ever) in pgWaitTimed.

But pg_stat_activity on postgresql indicates that no query is running.

StackTrace
-----------
>> pqWaitTimed
>> PQgetResult

The processes has to be restarted to fix the issue.

Comments and changes to this ticket

  • Josh Berkus

    Josh Berkus June 28th, 2012 @ 09:19 PM

    I'm seeing the exact same problem in a multithreaded Python application. It makes and drops connections rapidfire for a few minutes, then hangs. GDB indicates the hang is in psycopg2.

    We have a 100% reproduceable test case for this on our test environment; let me know what you want to trace etc. in order to diagnose this.

  • Daniele Varrazzo

    Daniele Varrazzo June 28th, 2012 @ 09:51 PM

    • State changed from “new” to “open”

    Josh, are you using the latest, 2.4.5? There have been a few multithread bug fixed in that version.

    Anoop, from your tag I see you are using 2.4.1: can you try updating and repeat your test?

    Josh, a stack trace would be a start. Are you creating one cursor per connection or many cursors? Is the same connection used by different threads from the different cursors? (which should work, but here is where a bug may lurk). Is the same cursor used by different threads? (which is not to be done).

    It would be killer if you could synthesize your test case into something that you can provide us.

    Thank you.

  • Daniele Varrazzo

    Daniele Varrazzo June 28th, 2012 @ 10:07 PM

    Josh, another possible source of help: try compiling and running psycopg with debug info (setting PSYCOPG_DEBUG in setup.cfg and running the program with the PSYCOPG_DEBUG env variable set). You will have plenty of debug info on stderr.

  • Josh Berkus

    Josh Berkus June 28th, 2012 @ 10:21 PM

    Daniele,

    The original bug isn't mine, I'm just adding to it because it seems to be the exact same symptoms. It's Anoop's bug originally.

    I am using 2.4.5.

    We'll enable the trace and get back to you.

  • Daniele Varrazzo

    Daniele Varrazzo April 20th, 2013 @ 01:36 AM

    • State changed from “open” to “invalid”

    Closing for lack of further information and tests.

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Psycopg is the most used PostgreSQL adapter for the Python programming language. At the core it fully implements the Python DB API 2.0 specifications. Several extensions allow access to many of the features offered by PostgreSQL.

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