PostgreSQL writes several following logs during the problem which I never
saw before 9.2.3:
LOG: process 4793 acquired ExclusiveLock on extension of relation 305605 of database 16396 after 2348.675 ms
The key here is not that it is an ExclusiveLock, but rather than it is the relation extension lock. I don't think the extension lock is ever held across user-code, or transaction boundaries, or anything like that. It is held over some small IOs. So if it blocked on that for over 2 seconds, you almost surely have some serious IO congestion.
And this particular message is probably more a symptom of that congestion than anything else.
You said you rolled back to 9.2.2 and the stalling is still there. Are you still seeing the log message, or are you now seeing silently stalls? Did you roll back all other changes that were made at the same time as the upgrade to 9.2.3 (kernel versions, filesystem changes/versions, etc.)?
Cheers,
Jeff
