On Thu, Oct 6, 2016 at 4:40 PM, Jeff Janes <jeff.janes@gmail.com> wrote:
> Scale factor 3000 obviously doesn't fit in shared_buffers. But does it fit
> in RAM? That is, are the backends doing real IO, or they just doing fake IO
> to the kernel's fs cache?
That's a good question.
[rhaas@hydra ~]$ free -g total used free shared buffers cached
Mem: 61 26 34 0 0 24
-/+ buffers/cache: 2 58
Swap: 19 4 15
rhaas=# select pg_size_pretty(pg_relation_size('pgbench_accounts'));pg_size_pretty
----------------38 GB
(1 row)
rhaas=# select pg_size_pretty(pg_database_size(current_database()));pg_size_pretty
----------------44 GB
(1 row)
That's pretty tight, especially since I now notice Andres also left a
postmaster running on this machine back in April, with
shared_buffers=8GB. 44GB for this database plus 8GB for
shared_buffers plus 8GB for the other postmaster's shared_buffers
leaves basically no slack, so it was probably doing quite a bit of
real I/O, especially after the database got a bit of bloat.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
