Re: [HACKERS] 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.vondra@2ndquadrant.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
Data in Trouble? Get it in Treble! http://BlueTreble.com
855-TREBLE2 (855-873-2532)