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Re: Transparent table partitioning in future version of PG?

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: david(at)lang(dot)hm
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, henk de wit <henk53602(at)hotmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Transparent table partitioning in future version of PG?
Date: 2009-05-08 16:47:42
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Thu, May 7, 2009 at 10:52 PM,  <david(at)lang(dot)hm> wrote:
>>> Hopefully, notions of partitioning won't be directly tied to chunking of
>>> data for parallel query access. Most queries access recent data and
>>> hence only a single partition (or stripe), so partitioning and
>>> parallelism and frequently exactly orthogonal.
>> Yes, I think those things are unrelated.
> I'm not so sure (warning, I am relativly inexperianced in this area)
> it sounds like you can take two basic approaches to partition a database
> 1. The Isolation Plan
> 2. The Load Balancing Plan

Well, even if the table is not partitioned at all, I don't see that it
should preclude parallel query access.  If I've got a 1 GB table that
needs to be sequentially scanned for rows meeting some restriction
clause, and I have two CPUs and plenty of I/O bandwidth, ISTM it
should be possible to have them each scan half of the table and
combine the results.  Now, this is not easy and there are probably
substantial planner and executor changes required to make it work, but
I don't know that it would be particularly easier if I had two 500 MB
partitions instead of a single 1 GB table.

IOW, I don't think you should need to partition if all you want is
load balancing.  Partitioning should be for isolation, and load
balancing should happen when appropriate, whether there is
partitioning involved or not.


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