Re: To Tom Lane 2019-03-26 <20190326151446.GG3829@msg.df7cb.de>
> 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.
[...]
> So the cost is 5% in this very contrived case. In almost any other
> setting, the cost would be lower, I'd think.
(That was on 12devel, btw.)
That was about the most extreme OLTP read-only workload. After
thinking about it some more, I realized that exercising large seqscans
might be an even better way to test it because of less per-query
overhead.
Same setup again, shared_buffers = 16 (128kB), jit = off,
max_parallel_workers_per_gather = 0:
select count(bid) from pgbench_accounts;
no checksums: ~456ms
with checksums: ~489ms
456.0/489 = 0.9325
The cost of checksums is about 6.75% here.
Christoph
