WAL CPU overhead/optimization (was Master-slave visibility order)

On 2013-08-30 01:10:40 +0300, Ants Aasma wrote:
> On Fri, Aug 30, 2013 at 12:33 AM, Andres Freund <andres@2ndquadrant.com> wrote:
> > FWIW, WAL is still the major bottleneck for INSERT heavy workloads. The
> > per CPU overhead actually minimally increased (at least in my tests), it
> > just scales noticeably better than before.
> 
> Interesting. Do you have any insight what is behind the CPU overhead?
> Maybe the solution is to make WAL insertion cheap enough to not
> matter. That won't be easy, but neither are the alternatives.

Funnily by far the biggest thing I have seen in benchmarks is the CRC32
computation. I plan to brush up my ~3 year old CRC32 reimplementation
patch sometime, but afair you had a much better one?

I have some doubts about weakening the hash function by also using FNV
or similar here, so I'd first like to try how much of a difference a
better CRC32 implementation can make with the current XLogInsert()
implementation.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
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