From: | "Simon Riggs" <simon(at)2ndquadrant(dot)com> |
---|---|
To: | "Bruce Momjian" <bruce(at)momjian(dot)us> |
Cc: | "Jeremy Haile" <jhaile(at)fastmail(dot)fm>, <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: URGENT: Out of disk space pg_xlog |
Date: | 2006-12-29 18:18:18 |
Message-ID: | 1167416298.3903.230.camel@silverbirch.site |
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Thread: | |
Lists: | pgsql-performance |
On Sat, 2006-12-23 at 13:13 -0500, Bruce Momjian wrote:
> The bottom line is that we know of now cases where a long-running
> transaction would delay recycling of the WAL files, so there is
> certainly something not understood here.
We can see from all of this that a checkpoint definitely didn't occur.
Tom's causal chain was just one way that could have happened, there
could well be others.
I've noticed previously that a checkpoint can be starved out when trying
to acquire the CheckpointStartLock. I've witnessed a two minute delay
plus in obtaining the lock in the face of heavy transactions.
If wal_buffers is small enough, WAL write rate high enough and the
transaction rate high enough, a long queue can form for the
WALWriteLock, which ensures that the CheckpointStartLock would queue
indefinitely.
I've tried implementing a queueable shared lock for the
CheckpointStartLock. That helps the checkpoint, but it harms performance
of other transactions waiting to commit, so I let that idea go.
--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com
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