On 03/04/13 08:44, dben...@whitepages.com wrote:
The following bug has been logged on the website:
Bug reference: 8034
Logged by: Devin Ben-Hur
Email address: dben...@whitepages.com
PostgreSQL version: 9.2.3
Operating system: Ubuntu Precise
Description:
When a very large shared buffer pool (~480GB) is used with postgresql,
pg_buffercache contrib module gets an allocation error trying to Allocate
NBuffers worth of BufferCachePagesRec records:
https://github.com/postgres/postgres/blob/REL9_2_3/contrib/pg_buffercache/pg_buffercache_pages.c#L101-L102
The requested allocation exceeds the 1GB limitation imposed by
AllocSizeIsValid macro:
https://github.com/postgres/postgres/blob/REL9_2_3/src/include/utils/memutils.h#L40-L43
Reproduce:
1) acquire server with half terabyte of memory
2) tweak OS settings to allow large shared memory
3) set postgresql.conf: shared_buffers = 400GB
4) CREATE EXTENSION pg_buffercache;
5) SELECT * FROM pg_buffercache LIMIT 1;
Yes indeed - however I'm not sure this is likely to be encountered in
any serious configuration. The general rule for sizing shared buffers is:
shared_buffers = min(0.25 * RAM, 8G)
Now there has been some discussion about how settings bigger than 8G
make sense in some cases...but I'm not aware of any suggestions that
sizes in the hundreds of G make sense.
However it would be nice if pg_buffercache *could* work with bigger
sizes if they make sense at any time. Someone who understands the
memory allocation system better than I do will need to comment about how
that might work :-)
Cheers
Mark
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