Re: Checksums by default?

On 1/23/17 1:30 AM, Amit Kapila wrote:
> On Sun, Jan 22, 2017 at 3:43 PM, Tomas Vondra
> <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>>
>> That being said, I'm ready to do some benchmarking on this, so that we have
>> at least some numbers to argue about. Can we agree on a set of workloads
>> that we want to benchmark in the first round?
>>
>
> I think if we can get data for pgbench read-write workload when data
> doesn't fit in shared buffers but fit in RAM, that can give us some
> indication. We can try by varying the ratio of shared buffers w.r.t
> data. This should exercise the checksum code both when buffers are
> evicted and at next read. I think it also makes sense to check the
> WAL data size for each of those runs.

I tried testing this (and thought I sent an email about it but don't see
it now :/). Unfortunately, on my laptop I wasn't getting terribly
consistent runs; I was seeing +/- ~8% TPS. Sometimes checksumps appeared
to add ~10% overhead, but it was hard to tell.

If someone has a more stable (is in, dedicated) setup, testing would be
useful.

BTW, I ran the test with small (default 128MB) shared_buffers, scale 50
(800MB database), sync_commit = off, checkpoint_timeout = 1min, to try
and significantly increase the rate of buffers being written out.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
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