Add python stack trace to SQL comment strings

[aeva black]

It would be helpful to inject a pseudo-stack-trace showing the relevant parts of the python call stack into a SQL comment string in each database query. This could be used for debugging transactional issues (my current focus), or other debugging tasks. It could also be aggregated by pt-query-digest to analyze database activity coming from different sections of the nova code.

This can be done by monkey-patching the database driver when the sql_connection_debug option is set at a certain level.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/8070

[aeva black (tenbrae)]

To enable the above code in devstack, add this to your localrc:

EXTRA_OPTS=(sql_connection_debug=20)

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/8070
Committed: http://github.com/openstack/nova/commit/ad0031c7fbfd0461b4b804b3a75a48212d5c9e9f
Submitter: Jenkins
Branch: master

commit ad0031c7fbfd0461b4b804b3a75a48212d5c9e9f
Author: Devananda van der Veen <email address hidden>
Date: Fri Jun 1 12:54:22 2012 -0700

    implement sql-comment-string stack traces

    Implements solution for bug 1007648.

    Add python stack traces to all sql comment strings so that someone
    looking at database query logs can immediately see what code
    generated each query. This is especially powerful when combined
    with pt-query-digest to get per-file or per-method aggregates.

    Change-Id: Ieda5cf4d70cc2643d27fb00efb48de14ca2abe52