Re: spinlocks storm bug

On 2013-12-06 07:22:27 +0100, Pavel Stehule wrote:
> I have a report of critical bug (database is temporary unavailability ..
> restart is necessary).

> PostgreSQL 9.2.4,
> 24 CPU
> 140G RAM
> SSD disc for all
>
>
> Database is under high load. There is a few databases with very high number
> of similar simple statements. When application produce higher load, then
> number of active connection is increased to 300-600 about.
>
> In some moment starts described event - there is a minimal IO, all CPU are
> on 100%.
>
> Perf result shows:
> 354246.00 93.0% s_lock
> /usr/lib/postgresql/9.2/bin/postgres
> 10503.00 2.8% LWLockRelease
> /usr/lib/postgresql/9.2/bin/postgres
> 8802.00 2.3% LWLockAcquire

> We try to limit a connection to 300, but I am not sure if this issue is not
> related to some Postgres bug.

We've seen this issue repeatedly now. None of the times it turned out to
be a bug, but just limitations in postgres' scalability. If you can I'd
strongly suggest trying to get postgres binaries compiled with
-fno-omit-frame-pointer installed to check which locks are actually
conteded.
My bet is BufMappingLock.

There's a CF entry about changing our lwlock implementation to scale
better...

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services