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From: Fabien COELHO <[email protected]>
To: Thomas Munro <[email protected]>
Cc: PostgreSQL Developers <[email protected]>
Subject: Re: pgbench with libevent?
Date: Mon, 14 Aug 2023 12:09:52 +0200 (CEST)
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+hUKGK8St8+hJ1kb1fygEzNwgJunVyBL-+1pg-6W+JJPmOnyA@mail.gmail.com>
References: <[email protected]>
	<[email protected]>
	<CA+hUKGK8St8+hJ1kb1fygEzNwgJunVyBL-+1pg-6W+JJPmOnyA@mail.gmail.com>


Hello Thomas,

>>> Pgbench is managing clients I/Os manually with select or poll. Much of this
>>> could be managed by libevent.
>>
>> Or maybe libuv (used by nodejs?).
>>
>> From preliminary testing libevent seems not too good at fine grain time
>> management which are used for throttling, whereas libuv advertised that it
>> is good at it, although what it does is yet to be seen.
>
> Do you think our WaitEventSet stuff could be good here, if made
> frontend-friendly?

Interesting question.

AFAICS, the answer is that it could indeed probably fit the task, but it 
would require significant work to make it thread-compatible, and to 
untangle it from IsUnderPosmaster/postmaster death, memory context, 
elog/ereport, and other back-end specific stuff.

If you remove all that with a clean abstraction (quite a task), then once 
done the question could be why not use libevent/libuv/… in the backend 
instead of maintaining more or less the same thing inside postgres?

So ISTM that as far as pgbench is concerned it would be much simpler to 
use libevent/libuv/… directly if the pros are enough and the cons not 
redhibitory, and provided that the needed detailed features are really 
there.

-- 
Fabien.

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