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Re: Performance Improvement by reducing WAL for Update Operation

From: Amit Kapila <amit(dot)kapila(at)huawei(dot)com>
To: "'Heikki Linnakangas'" <hlinnakangas(at)vmware(dot)com>
Cc: <simon(at)2ndquadrant(dot)com>, "'Alvaro Herrera'" <alvherre(at)2ndquadrant(dot)com>, <noah(at)leadboat(dot)com>, <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Performance Improvement by reducing WAL for Update Operation
Date: 2013-01-30 15:02:23
Message-ID: 002c01cdfefa$d0305540$7090ffc0$@kapila@huawei.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tuesday, January 29, 2013 7:42 PM Amit Kapila wrote:
> On Tuesday, January 29, 2013 3:53 PM Heikki Linnakangas wrote:
> > On 29.01.2013 11:58, Amit Kapila wrote:
> > > Can there be another way with which current patch code can be made
> > better,
> > > so that we don't need to change the encoding approach, as I am
> having
> > > feeling that this might not be performance wise equally good.
> >
> > The point is that I don't want to heap_delta_encode() to know the
> > internals of pglz compression. You could probably make my patch more
> > like yours in behavior by also passing an array of offsets in the new
> > tuple to check, and only checking for matches as those offsets.
> 
> I think it makes sense, because if we have offsets of both new and old
> tuple, we
> can internally use memcmp to compare columns and use same algorithm for
> encoding.
> I will change the patch according to this suggestion.

I have modified the patch as per above suggestion.
Apart from passing new and old tuple offsets, I have passed bitmaplength
also, as we need
to copy the bitmap of new tuple as it is into Encoded WAL Tuple.

Please see if such API design is okay?

I shall update the README and send the performance/WAL Reduction data for
modified patch tomorrow.

With Regards,
Amit Kapila.


Attachment: wal_update_changes_v10.patch
Description: application/octet-stream (34.3 KB)

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