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Re: restore time: sort_mem vs. checkpoing_segments

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Vivek Khera <khera(at)kcilink(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: restore time: sort_mem vs. checkpoing_segments
Date: 2003-09-23 13:59:01
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Vivek Khera wrote:
> And the winner is... checkpoint_segments.
> Restore of a significanly big database (~19.8GB restored) shows nearly
> no time difference depending on sort_mem when checkpoint_segments is
> large.  There are quite a number of tables and indexes.  The restore
> was done from a pg_dump -Fc dump of one database.
> All tests with 16KB page size, 30k shared buffers, sort_mem=8192, PG
> 7.4b2 on FreeBSD 4.8.
> 3 checkpoint_segments restore time: 14983 seconds
> 50 checkpoint_segments restore time: 11537 seconds
> 50 checkpoint_segments, sort_mem 131702 restore time: 11262 seconds

With the new warning about too-frequent checkpoints, people have actual
feedback to encourage them to increase checkpoint_segments.  One issue
is that it is likely to recommend increasing checkpoint_segments during
restore, even if there is no value to it being large during normal
server operation.  Should that be decumented?

  Bruce Momjian                        |
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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