Re: optimizing pg_upgrade's once-in-each-database steps

From: Nathan Bossart <nathandbossart(at)gmail(dot)com>
To: Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
Cc: Ilya Gladyshev <ilya(dot)v(dot)gladyshev(at)gmail(dot)com>, Daniel Gustafsson <daniel(at)yesql(dot)se>, Robert Haas <robertmhaas(at)gmail(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: optimizing pg_upgrade's once-in-each-database steps
Date: 2024-08-10 15:35:46
Message-ID: ZreI0vpZoQfoocDq@nathan
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On Sat, Aug 10, 2024 at 10:17:27AM -0500, Nathan Bossart wrote:
> On Fri, Aug 09, 2024 at 04:06:16PM -0400, Corey Huinker wrote:
>>> Furthermore, most of the callbacks should do almost nothing for a given
>>> upgrade, and since pg_upgrade runs on the server, client/server round-trip
>>> time should be pretty low.
>>
>> To my mind, that makes pipelining make more sense, you throw out N queries,
>> most of which are trivial, and by the time you cycle back around and start
>> digesting result sets via callbacks, more of the queries have finished
>> because they were waiting on the query ahead of them in the pipeline, not
>> waiting on a callback to finish consuming its assigned result set and then
>> launching the next task query.
>
> My assumption is that the "waiting for a callback before launching the next
> query" time will typically be pretty short in practice. I could try
> measuring it...

Another option might be to combine all the queries for a task into a single
string and then send that in one PQsendQuery() call. That may be a simpler
way to eliminate the time between queries.

--
nathan

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