From: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
---|---|
To: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Mike Blackwell <mike(dot)blackwell(at)rrd(dot)com> |
Subject: | Re: Performance Improvement by reducing WAL for Update Operation |
Date: | 2014-02-05 15:36:05 |
Message-ID: | CAA4eK1+mxUY+QKNUcMzK+8WOmChwsqekSheav5fEeFtSQon_AA@mail.gmail.com |
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On Wed, Feb 5, 2014 at 8:50 PM, Heikki Linnakangas
<hlinnakangas(at)vmware(dot)com> wrote:
> On 02/05/2014 04:48 PM, Amit Kapila wrote:
>>
>> I have done one test where there is a large suffix match, but
>> not large enough that it can compress more than 75% of string,
>> the CPU overhead with wal-update-prefix-suffix-encode-1.patch is
>> not much, but there is no I/O reduction as well.
>
>
> Hmm, it's supposed to compress if you save at least 25%, not 75%. Apparently
> I got that backwards in the patch...
Okay I think that is right, may be I can change the that check to see the
difference, but in general isn't it going to loose compression in much more
cases like if there is less than 25% match in prefix/suffix, but
more than 50% match in between the string.
While debugging, I noticed that it compresses less than history table
approach for general cases when internally update is done like for
Truncate table.
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com
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