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Re: Why is restored database faster?

From: David Shadovitz <david(at)shadovitz(dot)com>
To: 'Dennis Bjorklund' <db(at)zigo(dot)dhs(dot)org>,"'shridhar_daithankar(at)persistent(dot)co(dot)in'" <shridhar_daithankar(at)persistent(dot)co(dot)in>,"'neilc(at)samurai(dot)com'" <neilc(at)samurai(dot)com>
Cc: "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Why is restored database faster?
Date: 2003-12-18 03:54:45
Message-ID: 01C3C4D7.A7F88280.david@shadovitz.com (view raw or flat)
Thread:
Lists: pgsql-performance
Dennis, Shridhar, and Neil,

Thanks for your input.  Here are my responses:

I ran VACUUM FULL on the table in question.  Although that did reduce "Pages" 
and "UnUsed", the "SELECT *" query is still much slower on this installation 
than in the new, restored one.

  Old server:
 # VACUUM FULL abc;
  VACUUM
  # VACUUM VERBOSE abc;
  NOTICE: --Relation abc--
 NOTICE: Pages 1526: Changed 0, Empty 0; Tup 91528; Vac 0, Keep 0, UnUsed 32.
     Total CPU 0.07s/0.52u sec elapsed 0.60 sec.
 VACUUM

  New server:
 # VACUUM VERBOSE abc;
  NOTICE: --Relation abc--
  NOTICE: Pages 1526: Changed 0, Empty 0; Tup 91528; Vac 0, Keep 0, UnUsed 0.
    Total CPU 0.02s/0.00u sec elapsed 0.02 sec.
 VACUUM

max_fsm_pages is at its default value, 10000.

People don't have the practice of dumping and restoring just for the purpose of 
improving performance, do they?

Neil asked how much disk space the database directory takes on each machine. 
 What directory is of interest?  The whole thing takes up about 875 MB on each 
machine.

-David 

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Next:From: Shridhar DaithankarDate: 2003-12-18 06:47:12
Subject: Re: Why is restored database faster?
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Subject: Re: Adding RAM: seeking advice & warnings of hidden "gotchas"

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