| From: | "Lawrence, Ramon" <ramon(dot)lawrence(at)ubc(dot)ca> |
|---|---|
| To: | "Bruce Momjian" <bruce(at)momjian(dot)us> |
| Cc: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, <pgsql-hackers(at)postgresql(dot)org>, "Michael Henderson" <mikecubed(at)gmail(dot)com> |
| Subject: | Re: Potential Join Performance Issue |
| Date: | 2009-01-08 03:44:03 |
| Message-ID: | 6EEA43D22289484890D119821101B1DF2C1864@exchange20.mercury.ad.ubc.ca |
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| Thread: | |
| Lists: | pgsql-hackers |
> Has this been completed? TODO item?
> > > I'd be more inclined to deal with the issue by trying to establish
a
> > > "safety margin" in the estimate of whether the hash will go
> > multi-batch.
> > > IOW we should disuse_physical_tlist if the hash is estimated to be
> > close to but still within one batch.
I do not know how this issue was resolved. It is an issue that is very
important for multi-batch hash joins. The simplest resolution is to
disable physical_tlist on the outer relation for hash joins of more than
one batch. However, as discussed in the thread, more sophisticated
solutions are also viable.
--
Ramon Lawrence
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