Re: Patch: fix lock contention for HASHHDR.mutex

From: Aleksander Alekseev <a(dot)alekseev(at)postgrespro(dot)ru>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Patch: fix lock contention for HASHHDR.mutex
Date: 2015-12-17 16:03:42
Message-ID: 20151217190342.07e4533a@fujitsu
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> It'd really like to see it being replaced by a queuing lock
> (i.e. lwlock) before we go there. And then maybe partition the
> freelist, and make nentries an atomic.

I believe I just implemented something like this (see attachment). The
idea is to partition PROCLOCK hash table manually into NUM_LOCK_
PARTITIONS smaller and non-partitioned hash tables. Since these tables
are non-partitioned spinlock is not used and there is no lock

On 60-core server we gain 3.5-4 more TPS according to benchmark
described above. As I understand there is no performance degradation in
other cases (different CPU, traditional pgbench, etc).

If this patch seems to be OK I believe we could consider applying the
same change not only to PROCLOCK hash table.

Attachment Content-Type Size
shard-proclock-hash-table.patch text/x-patch 13.5 KB

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