| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Peter Geoghegan <pg(at)heroku(dot)com> |
| Cc: | Daniel Newman <dtnewman(at)gmail(dot)com>, danielnewman(at)umich(dot)edu, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-bugs <pgsql-bugs(at)postgresql(dot)org> |
| Subject: | Re: BUG #14210: filter by "=" constraint doesn't work when hash index is present on a column |
| Date: | 2016-06-27 20:22:25 |
| Message-ID: | 5399.1467058945@sss.pgh.pa.us |
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| Lists: | pgsql-bugs |
Peter Geoghegan <pg(at)heroku(dot)com> writes:
> I like this idea. Should I write a patch?
BTW, while you're at it: it strikes me that the threshold should be
either min(NBuffers, maintenance_work_mem) or
min(NLocBuffer, maintenance_work_mem), depending on whether we're
talking about a regular or temp table/index. That is, there's a
pre-existing bug here that when NLocBuffer is a good deal less than
NBuffers (which is the typical case nowadays) you'll get a lot of
thrashing between local buffers and kernel cache, if the index isn't
quite big enough to trigger the sorting code. This might not manifest
as actual I/O, but it's not the intended behavior either.
regards, tom lane
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