Re: [REVIEW] Re: Compression of full-page-writes

On Thu, Dec 11, 2014 at 11:34 AM, Bruce Momjian <bruce@momjian.us> wrote:
>> compression = 'on'  : 1838 secs
>>             = 'off' : 1701 secs
>>
>> Different is around 140 secs.
>
> OK, so the compression took 2x the cpu and was 8% slower.  The only
> benefit is WAL files are 35% smaller?

Compression didn't take 2x the CPU.  It increased user CPU from 354.20
s to 562.67 s over the course of the run, so it took about 60% more
CPU.

But I wouldn't be too discouraged by that.  At least AIUI, there are
quite a number of users for whom WAL volume is a serious challenge,
and they might be willing to pay that price to have less of it.  Also,
we have talked a number of times before about incorporating Snappy or
LZ4, which I'm guessing would save a fair amount of CPU -- but the
decision was made to leave that out of the first version, and just use
pg_lz, to keep the initial patch simple.  I think that was a good
decision.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company