Re: To Tom Lane 2019-03-26 <20190326151446.gg3...@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
