| From: | Markus Wanner <markus(at)bluegap(dot)ch> |
|---|---|
| To: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
| Cc: | Kevin Grittner <kgrittn(at)ymail(dot)com>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Yuri Levinsky <yuril(at)celltick(dot)com>, PostgreSQL-Dev <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Hash partitioning. |
| Date: | 2013-06-26 15:55:37 |
| Message-ID: | 51CB0EF9.60802@bluegap.ch |
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| Lists: | pgsql-hackers |
On 06/26/2013 05:46 PM, Heikki Linnakangas wrote:
> We could also allow a large query to search a single table in parallel.
> A seqscan would be easy to divide into N equally-sized parts that can be
> scanned in parallel. It's more difficult for index scans, but even then
> it might be possible at least in some limited cases.
So far reading sequentially is still faster than hopping between
different locations. Purely from the I/O perspective, that is.
For queries where the single CPU core turns into a bottle-neck and which
we want to parallelize, we should ideally still do a normal, fully
sequential scan and only fan out after the scan and distribute the
incoming pages (or even tuples) to the multiple cores to process.
Regards
Markus Wanner
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