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Re: CLOG contention, part 2

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: CLOG contention, part 2
Date: 2012-02-28 18:11:38
Message-ID: (view raw or flat)
Lists: pgsql-hackers
On Mon, Feb 27, 2012 at 4:03 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> So please use a scale factor that the hardware can cope with.

OK.  I tested this out on Nate Boley's 32-core AMD machine, using
scale factor 100 and scale factor 300. I initialized it with Simon's
patch, which should have the effect of rendering the entire table
unhinted and giving each row a different XID.  I used my usual
configuration settings for that machine, which are: shared_buffers =
8GB, maintenance_work_mem = 1GB, synchronous_commit = off,
checkpoint_segments = 300, checkpoint_timeout = 15min,
checkpoint_completion_target = 0.9, wal_writer_delay = 20ms.  I did
three runs on master, as of commit
9bf8603c7a9153cada7e32eb0cf7ac1feb1d3b56, and three runs with the
clog_history_v4 patch applied.  The command to initialize the database

~/install/clog-contention/bin/pgbench -i -I -s $scale

The command to run the test was:

~/install/clog-contention/bin/pgbench -l -T 1800 -c 32 -j 32 -n

Executive Summary: The patch makes things way slower at scale factor
300, and possibly slightly slower at scale factor 100.

Detailed Results:

resultslp.clog_history_v4.32.100.1800:tps = 14286.049637 (including
connections establishing)
resultslp.clog_history_v4.32.100.1800:tps = 13532.814984 (including
connections establishing)
resultslp.clog_history_v4.32.100.1800:tps = 13972.987301 (including
connections establishing)
resultslp.clog_history_v4.32.300.1800:tps = 5061.650470 (including
connections establishing)
resultslp.clog_history_v4.32.300.1800:tps = 4871.126457 (including
connections establishing)
resultslp.clog_history_v4.32.300.1800:tps = 5861.124177 (including
connections establishing)
resultslp.master.32.100.1800:tps = 13420.777222 (including connections
resultslp.master.32.100.1800:tps = 14912.336257 (including connections
resultslp.master.32.100.1800:tps = 14505.718977 (including connections
resultslp.master.32.300.1800:tps = 14766.984548 (including connections
resultslp.master.32.300.1800:tps = 14783.026190 (including connections
resultslp.master.32.300.1800:tps = 14567.504887 (including connections

I don't know whether this is just a bug or whether there's some more
fundamental problem with the approach.

Robert Haas
The Enterprise PostgreSQL Company

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