On Fri, Dec 12, 2014 at 11:12 AM, Andres Freund <andres@anarazel.de> wrote:
> On 2014-12-12 11:08:52 -0500, Robert Haas wrote:
>> Unless I'm missing something, this test is showing that FPW
>> compression saves 298MB of WAL for 17.3 seconds of CPU time, as
>> against master. And compressing the whole record saves a further 1MB
>> of WAL for a further 13.39 seconds of CPU time. That makes
>> compressing the whole record sound like a pretty terrible idea - even
>> if you get more benefit by reducing the lower boundary, you're still
>> burning a ton of extra CPU time for almost no gain on the larger
>> records. Ouch!
>
> Well, that test pretty much doesn't have any large records besides FPWs
> afaics. So it's unsurprising that it's not beneficial.
"Not beneficial" is rather an understatement. It's actively harmful,
and not by a small margin.
--
Robert Haas
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