Re: Enable data checksums by default

Re: Tom Lane 2019-03-22 <4368(dot)1553270842(at)sss(dot)pgh(dot)pa(dot)us>
> Christoph Berg <myon(at)debian(dot)org> writes:
> > I think, the next step in that direction would be to enable data
> > checksums by default. They make sense in most setups,
>
> Well, that is exactly the point that needs some proof, not just
> an unfounded assertion.

I run a benchmark with checksums disabled/enabled. shared_buffers is
512kB to make sure almost any read will fetch the page from the OS
cache; scale factor is 50 (~750MB) to make sure the whole cluster fits
into RAM.

model name: Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz (8 threads)
alter system set shared_buffers = '512kB';
pgbench -s 50 -i
pgbench -P 5 -M prepared -c 8 -j 8 -T 60 --select-only

without checksums:
tps = 96893.627255 (including connections establishing)
tps = 97570.587793 (including connections establishing)
tps = 97455.484419 (including connections establishing)
tps = 97533.668801 (including connections establishing)
average: 97363

with checksums:
tps = 91942.502487 (including connections establishing)
tps = 92390.556925 (including connections establishing)
tps = 92956.923271 (including connections establishing)
tps = 92914.205047 (including connections establishing)
average: 92551

select 92551.0/97363;
0.9506

So the cost is 5% in this very contrived case. In almost any other
setting, the cost would be lower, I'd think.

Christoph