From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Michael <rmichael@edgeofthenet.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: Slow ext'd query via client native implementation vs. libpq & simple psql
Date: Wed, 11 Mar 2020 18:54:16 -0400
Message-ID: <6262.1583967256@sss.pgh.pa.us> (raw)
In-Reply-To: <CABR0jERv5L7U0eYyNxv3ZES9HbJj9r2KPK3_=oPMBXTbTC+oXw@mail.gmail.com>
References: <CABR0jERv5L7U0eYyNxv3ZES9HbJj9r2KPK3_=oPMBXTbTC+oXw@mail.gmail.com>
Richard Michael <rmichael@edgeofthenet.org> writes:
> On PG 12.2, I am analyzing a performance problem when using a client
> (Elixir/postgrex) querying via the extended query protocol. I am comparing
> with
> psql and a C program. Logs for all three follow this short explanation.
Hmm, your auto-explain log entries show all three queries having
server-side execution times of a couple dozen msec. It seems like
the excess time must be involved in transmitting the data to the
client. So I guess I'd be looking at whether the client is really
slow at absorbing data for some reason.
IIRC, auto-explain's 'actual time' for the top-level query node does not
count the time to format data or transmit it to the client. Still, we
have an upper bound of ~80 msec for that to happen with the libpq client,
and there's no obvious reason why it'd be different for the other client.
[ thinks for a bit... ] You might double check that those two clients
are using the same client_encoding setting. 400ms doing encoding
conversion seems excessive, but there aren't that many other possibilities
for the I/O time to be different.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, rmichael@edgeofthenet.org
Subject: Re: Slow ext'd query via client native implementation vs. libpq & simple psql
In-Reply-To: <6262.1583967256@sss.pgh.pa.us>
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