Re: Performance Improvement by reducing WAL for Update Operation

On Wed, Feb 5, 2014 at 8:50 PM, Heikki Linnakangas
 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