| From: | Curt Sampson <cjs(at)cynic(dot)net> |
|---|---|
| To: | pgsql-admin(at)postgresql(dot)org |
| Subject: | Re: Are statistics gathered on function indexes? |
| Date: | 2002-06-28 09:49:39 |
| Message-ID: | Pine.NEB.4.43.0206281845210.6613-100000@angelic.cynic.net |
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| Lists: | pgsql-admin |
The vast majority of the cost of using an index is due to reading
the data blocks in the table in a random order, rathern than
sequentially, right? Rather than making estimates of the selectivity
of an index when you search for 'W%', why not actually start the
index lookup and count how many you get? If you know you want to
do a table scan if you have more than, say, 500 rows that match
'W%', you'd only have to read a few index pages to determine whether
or not there are more than 500 rows, right?
Or am I on crack here?
cjs
--
Curt Sampson <cjs(at)cynic(dot)net> +81 90 7737 2974 http://www.netbsd.org
Don't you know, in this new Dark Age, we're all light. --XTC
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