Tom Lane wrote:
> John A Meinel <john(at)arbash-meinel(dot)com> writes:
>>What I don't understand is that the planner is actually estimating that
>>joining against the new table is going to *increase* the number of
> It evidently thinks that incidentid in the k_r table is pretty
> nonunique. We really need to look at the statistics data to
> see what's going on.
> regards, tom lane
Okay, sure. What about doing this, then:
SELECT recordtext FROM eventactivity
JOIN (SELECT DISTINCT incidentid FROM k_r JOIN k_b USING (incidentid)
WHERE k_r.id = ?? AND k_b.id = ??)
Since I assume that eventactivity is the only table with "recordtext",
and that you don't get any columns from k_r and k_b, meaning it would be
pointless to get duplicate incidentids.
I may be misunderstanding what the query is trying to do, but depending
on what is in k_r and k_b, is it possible to use a UNIQUE INDEX rather
than just an index on incidentid?
There is also the possibility of
SELECT recordtext FROM eventactivtity
JOIN (SELECT incidentid FROM k_r WHERE k_r.id = ??
UNION SELECT incidentid FROM k_b WHERE k_b.id = ??)
But both of these would mean that you don't actually want columns from
k_r or k_b, just a unique list of incident ids.
But first, I agree, we should make sure the pg_stats values are reasonable.
In response to
pgsql-performance by date
|Next:||From: Alison Winters||Date: 2005-07-14 23:42:12|
|Subject: Re: lots of updates on small table|
|Previous:||From: Tom Lane||Date: 2005-07-14 23:30:02|
|Subject: Re: slow joining very large table to smaller ones |