Re: pgbench vs. wait events

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