From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bruce Momjian <bruce@momjian.us>
cc: Yugo NAGATA <nagata@sraoss.co.jp>,
        Alvaro Herrera <alvherre@alvh.no-ip.org>, pgsql-hackers@postgresql.org
Subject: Re: Question about non-blocking mode in libpq
In-reply-to: <ZUGwJY1qmzUMgk0Y@momjian.us>
References: <20210719231129.b2ab655c0d0e80545274c86f@sraoss.co.jp> <202107201605.b3hmz4g6uqqz@alvherre.pgsql> <20210721101509.7e70e0f801a4457a2f6a6174@sraoss.co.jp> <ZUEyKtrtl3IoTwWW@momjian.us> <2604997.1698775114@sss.pgh.pa.us> <ZUFuyJtiEXRQE8zi@momjian.us> <2666892.1698801066@sss.pgh.pa.us> <ZUGwJY1qmzUMgk0Y@momjian.us>
Comments: In-reply-to Bruce Momjian <bruce@momjian.us>
	message dated "Tue, 31 Oct 2023 21:55:49 -0400"
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Date: Tue, 31 Oct 2023 22:16:07 -0400
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Bruce Momjian <bruce@momjian.us> writes:
> On Tue, Oct 31, 2023 at 09:11:06PM -0400, Tom Lane wrote:
>> What I'm objecting to is removal of the bit about "if they need to be
>> called again".  That provides a hint that retry is the appropriate
>> response to a failure.  Admittedly, it's not 100% clear, but your
>> version makes it 0% clear.

> I thought the original docs said you had to re-call on failure (it would
> not block but it would fail if it could not be sent), while we are now
> saying that it will be queued in the input buffer.

For these functions in nonblock mode, failure means "we didn't queue it".

> Is retry really something we need to mention now?  If out of memory is
> our only failure case now ("unable to enlarge the buffer because OOM"),
> is retry really a realistic option?

Well, ideally the application would do something to alleviate the
OOM problem before retrying.  I don't know if we want to go so far
as to discuss that.  I do object to giving the impression that
failure is impossible, which I think your proposed wording does.

An orthogonal issue with your latest wording is that it's unclear
whether *unsuccessful* calls to these functions will block.

			regards, tom lane