| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Josh Berkus <josh(at)agliodbs(dot)com> |
| Cc: | Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Richard Huxton <dev(at)archonet(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>, Jeff Davis <pgsql(at)j-davis(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Stats for multi-column indexes |
| Date: | 2007-03-20 17:49:06 |
| Message-ID: | 15589.1174412946@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Josh Berkus <josh(at)agliodbs(dot)com> writes:
>> Actually, I think you don't particularly need stats for that in most
>> cases --- if the planner simply took note that the FK relationship
>> exists, it would know that each row of the FK side joins to exactly
>> one row of the PK side, which in typical cases is sufficient.
> Is it? What about the other direction?
I recall that we had decided at the Greenplum meeting last year that
we could use a better heuristic if we noted that a join was being done
on an FK-and-PK combination, but I don't recall the details right at
the moment. Did anyone take notes?
regards, tom lane
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