Re: Will higher shared_buffers improve tpcb-like benchmarks?

From: Saurabh Nanda <saurabhnanda(at)gmail(dot)com>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: pgsql-performance(at)lists(dot)postgresql(dot)org
Subject: Re: Will higher shared_buffers improve tpcb-like benchmarks?
Date: 2019-01-29 18:10:53
Message-ID: CAPz=2oH+ZkXMHTX68fCLPgTHzJWEkm2rj2mAUeravg+iGJdumQ@mail.gmail.com
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>
> That is likely correct, but the data will likely be stored in the OS file
> cache, so reading it from there will still be pretty fast.
>

Right -- but increasing shared_buffers won't increase my TPS, right? Btw, I
just realised that irrespective of shared_buffers, my entire DB is already
in memory (DB size=30GB, RAM=64GB). I think the following output from iotop
confirms this. All throughout the benchmarking (client=1,4,8,12,24,48,96),
the *disk read* values remain zero!

Total DISK READ : 0.00 B/s | Total DISK WRITE : 73.93 M/s
Actual DISK READ: 0.00 B/s | Actual DISK WRITE: 43.69 M/s

Could this explain why my TPS numbers are not changing no matter how much I
fiddle with the Postgres configuration?

If my hypothesis is correct, increasing the pgbench scale to get a 200GB
database would immediately show different results, right?

-- Saurabh.

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