On 30.08.2013 21:07, Heikki Linnakangas wrote:
On 30.08.2013 19:01, Andres Freund wrote:
For the logical decoding patch I added support for pegging
RecentGlobalXmin (and GetOldestXmin) to a lower value. To avoid causing
undue bloat& cpu overhead (hot pruning is friggin expensive) I split
RecentGlobalXmin into RecentGlobalXmin and RecentGlobalDataXmin where
the latter is the the xmin horizon used for non-shared, non-catalog
tables. That removed almost all overhead I could measure.
During that I was tinkering with the idea of reusing that split to
vacuum/prune user tables in a per db fashion. In a very quick and hacky
test that sped up the aggregate performance of concurrent pgbenches in
different databases by about 30%. So, somewhat worthwile ;).
The problem with that is that GetSnapshotData, which computes
RecentGlobalXmin, only looks at the PGXACT structures and not PGPROC
which contains the database oid. This is a recently added optimization
which made GetSnapshotData() quite a bit faster& scalable which is
important given the frequency it's called at.
Hmm, so you're creating a version of GetSnapshotData() that only takes
into account backends in the same backend?
I mean, only takes account backends in the same database?
- Heikki
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