On Tue, Nov 22, 2011 at 9:21 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Nov 22, 2011 at 3:23 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> Some time ago, I changed GetOldestXmin() to ignore procs in other
>> databases resulting in a potentially later xmin.
>> GetSnapshotData() was not touched when that happened, even though the
>> comments say "...This is the same computation done by
>> GetOldestXmin(true, true)." The transam/README file says it stronger
>> "GetSnapshotData also performs an oldest-xmin calculation (which had
>> match GetOldestXmin's)". Doh.
>> As a result, VACUUM ignores procs in other databases, whereas HOT does
>> not. That means we aren't cleaning up as much as we could do when
>> running multiple databases. If its OK for VACUUM, then it must be OK
>> for HOT cleanup also.
>> Attached patch ignores procs in other databases during
>> GetSnapshotData() when IsMVCCSnapshot(), using similar coding to
>> Any doubters?
> I think this is unsafe for shared catalogs.
I think so too. Thats why it uses IsMVCCSnapshot() to confirm when it
is safe to do so.
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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