Open Stack

On 07/14/2014 10:41 AM, Mike Bayer wrote:
>
> On Jul 14, 2014, at 12:29 PM, Chris Friesen <chris.friesen at windriver.com> wrote:
>
>> On 07/09/2014 05:17 AM, Ihar Hrachyshka wrote:
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>>> Hi all,
>>>
>>> Multiple projects are suffering from db lock timeouts due to deadlocks
>>> deep in mysqldb library that we use to interact with mysql servers. In
>>> essence, the problem is due to missing eventlet support in mysqldb
>>> module, meaning when a db lock is encountered, the library does not
>>> yield to the next green thread, allowing other threads to eventually
>>> unlock the grabbed lock, and instead it just blocks the main thread,
>>> that eventually raises timeout exception (OperationalError).
>>>
>>> The failed operation is not retried, leaving failing request not
>>> served. In Nova, there is a special retry mechanism for deadlocks,
>>> though I think it's more a hack than a proper fix.
>>
>> This may be a bit of a tangent to the original discussion, but does anyone know where we stand with postgres and eventlets?  Is pyscopg2 susceptible to the same problems as mysqldb?
>
> if psycopg2 is in use, the set_wait_callback() extension must be enabled.
>
> see http://initd.org/psycopg/docs/extensions.html#psycopg2.extensions.set_wait_callback and https://bitbucket.org/zzzeek/green_sqla/src/2732bb7ea9d06b9d4a61e8cd587a95148ce2599b/green_sqla/psyco_gevent.py?at=default for an example use taken from psycopg2 developers.

Can you elaborate a bit?  It's my understanding that sqlalchemy will use 
psycopg2 for connection strings like:

sql_connection = postgresql://

is that correct?


Assuming this is the case, do we need to do something extra to set up 
the extension above and beyond what is already in the 
openstack/sqlalchemy/eventlet codebase?  Is this documented somewhere?

Chris