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BRIN cost estimate

From: Alvaro Herrera <alvherre(at)2ndQuadrant(dot)com>
To: Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: BRIN cost estimate
Date: 2015-11-16 13:52:39
Message-ID: 20151116135239.GV614468@alvherre.pgsql (view raw, whole thread or download thread mbox)
Thread:
Lists: pgsql-hackers
Somebody wrote to me a few days ago that the BRIN cost estimation is
rather poor.  One immediately obvious issue which I think is easily
fixed is the correlation estimate, which is currently hardcoded to 1.  

Since a BRIN scan always entails a scan of the relation in physical
order, it's simple to produce a better estimate for that, per the
attached patch.  (Note: trying to run this on expression indexes will
cause a crash.  I need to complete that part ...)

There are other improvements we've been discussing, but I'm unclear that
I will have time to study them to get a useful patch quickly enough.  If
somebody else wants to mess with this, please get in touch.

Thoughts?

-- 
Álvaro Herrera                            33.5S 70.5W

Attachment: brin-correlation.patch
Description: text/x-diff (3.2 KB)

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