From: | Markus Wanner <markus(at)bluegap(dot)ch> |
---|---|
To: | Yuri Levinsky <yuril(at)celltick(dot)com> |
Cc: | ktm(at)rice(dot)edu, 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>, PostgreSQL-Dev <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Hash partitioning. |
Date: | 2013-06-26 14:47:09 |
Message-ID: | 51CAFEED.5060606@bluegap.ch |
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Lists: | pgsql-hackers |
On 06/26/2013 04:10 PM, Yuri Levinsky wrote:
> You typically don't want to use b-tree index when yo select
> more when ~1-2% of your data.
Agreed. Indices on columns with very low selectivity don't perform well.
(Postgres knows that and uses a sequential scan based on selectivity
estimates. Being able to eliminate entire partitions from such a seq
scan would certainly be beneficial, yes.)
In the Postgres world, though, I think CLUSTERing might be the better
approach to solve that problem. (Note: this has nothing to do with
distributed systems in this case.) I'm not sure what the current status
of auto clustering or optimized scans on such a permanently clustered
table is, though.
The minmax indices proposed for 9.4 might be another feature worth
looking at.
Both of these approaches may eventually provide a more general and more
automatic way to speed up scans on large portions of a relation, IMO.
Regards
Markus Wanner
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