Script to compute random page cost

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org>
Subject: Script to compute random page cost
Date: 2002-09-09 05:05:49
Message-ID: 200209090505.g8955nq14584@candle.pha.pa.us
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-hackers

Because we have seen many complains about sequential vs index scans, I
wrote a script which computes the value for your OS/hardware
combination.

Under BSD/OS on one SCSI disk, I get a random_page_cost around 60. Our
current postgresql.conf default is 4.

What do other people get for this value?

Keep in mind if we increase this value, we will get a more sequential
scans vs. index scans.

One flaw in this test is that it randomly reads blocks from different
files rather than randomly reading from the same file. Do people have a
suggestion on how to correct this? Does it matter?

--
Bruce Momjian | http://candle.pha.pa.us
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

Attachment Content-Type Size
unknown_filename text/plain 2.2 KB

Responses

Browse pgsql-hackers by date

  From Date Subject
Next Message Joe Conway 2002-09-09 05:31:26 Re: Schemas not available for pl/pgsql %TYPE....
Previous Message Stephan Szabo 2002-09-09 04:53:41 Re: Proposal: Solving the "Return proper effected tuple