Re: On partitioning

From: "Amit Langote" <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: "'Robert Haas'" <robertmhaas(at)gmail(dot)com>, "'Amit Kapila'" <amit(dot)kapila16(at)gmail(dot)com>
Cc: "'Andres Freund'" <andres(at)2ndquadrant(dot)com>, "'Alvaro Herrera'" <alvherre(at)2ndquadrant(dot)com>, "'Bruce Momjian'" <bruce(at)momjian(dot)us>, "'Pg Hackers'" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: On partitioning
Date: 2014-12-09 02:38:05
Message-ID: 002d01d01359$290cb4a0$7b261de0$
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> From: Robert Haas [mailto:robertmhaas(at)gmail(dot)com]
> On Sat, Dec 6, 2014 at 2:59 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> wrote:
> >> I guess you could list or hash partition on multiple columns, too.
> >
> > How would you distinguish values in list partition for multiple
> > columns? I mean for range partition, we are sure there will
> > be either one value for each column, but for list it could
> > be multiple and not fixed for each partition, so I think it will not
> > be easy to support the multicolumn partition key for list
> > partitions.
> I don't understand. If you want to range partition on columns (a, b),
> you say that, say, tuples with (a, b) values less than (100, 200) go
> here and the rest go elsewhere. For list partitioning, you say that,
> say, tuples with (a, b) values of EXACTLY (100, 200) go here and the
> rest go elsewhere. I'm not sure how useful that is but it's not
> illogical.

In case of list partitioning, 100 and 200 would respectively be one of the values in lists of allowed values for a and b. I thought his concern is whether this "list of values for each column in partkey" is as convenient to store and manipulate as range partvalues.


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