Re: Hash partitioning.

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