On 09/30/2011 12:28 PM, Andrew Shved wrote:
I have a set up where most of the data located in partitions of the
large table and that data never changes. The only table that really
changes is current day's partition. The problem is that transaction
wraparound vacuum generates a lot of traffic quite frequently on
partitions that never changed (technically read only). This is
especially a problem with streaming replication due to enormous
amounts of logging activity that is being generated. Is there a way
to limit or eliminate those frequent vacuum. Something akin to oralce
read only tablespace or a way to set frozen transaction xid on a
partition level? Basically anything to make it less frequent
especially when there is zero activity on those tables after initial
loads.
There's not really a good answer to this yet. Write-once data is common
enough that I'd like to see some accelerated paths for adding it
appear. I'm not aware of anyone working in that direction right now though.
Normally writes in PostgreSQL can result in blocks being written out
many times:
-pg_xlog image
-Initial write to data block on disk
-Write(s) to update hint bits
-Initial VACUUM
-XID wraparound VACUUM FREEZE
If you aggressively run VACUUM FREEZE yourself, setting
vacuum_freeze_min_age and possibly autovacuum_freeze_max_age to lower
values than the defaults, you might avoid some number of these multiple
writes, which are wasted from your perspective. Aim to commit and
freeze as fast as possible afterwards, avoiding some of the intermediate
writes you might otherwise see. That's the best that can be done
without some hacking on the server code.
--
Greg Smith 2ndQuadrant US g...@2ndquadrant.com Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us
