| 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 |
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| 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
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