Re: Question about buffers_alloc in pg_stat_bgwriter view for monitoring

Am 28.03.2018 um 23:38 schrieb Alvar Freude:
> Hi all,
>
> Can someone tell me, what the value of buffers_alloc in the pg_stat_bgwriter view (https://www.postgresql.org/docs/current/static/monitoring-stats.html#PG-STAT-BGWRITER-VIEW) is exactly? Is this the amount of shared buffers used by the bgwriter?

As I had to research that anyway, there's no reason not to write this
down here as well... (probably simplified, but I'm quite confident the
information is correct ;-):

Whenever a buffer is allocated, a global counter is incremented (see
"StrategyGetBuffer" in storage/buffer/freelist.c. That counter is used
by the BGWriter to determine its own wakeup/hibernate strategy, and
on-the-fly written to the global stats.

Thus, buffer_alloc is the global count of buffers allocated in the
cluster. That it appears in the bgwriter statistics is more or less
coincidental.

Best regards,
--
Gunnar "Nick" Bluth
RHCE/SCLA

Mobil +49 172 8853339
Email: gunnar(dot)bluth(at)pro-open(dot)de
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