From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Nitin Jadhav <nitinjadhavpostgres@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@anarazel.de>
Cc: Stephen Frost <sfrost@snowman.net>
Cc: Magnus Hagander <magnus@hagander.net>
Cc: Thomas Munro <thomas.munro@gmail.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: when the startup process doesn't (logging startup delays)
Date: Wed, 29 Sep 2021 14:36:14 -0300
Message-ID: <202109291736.w3lzq4prep3p@alvherre.pgsql> (raw)
In-Reply-To: <CAMm1aWae1qaxQC+83VZd0NVpzO==n3cxMoqedZvU=TWpmo-uSg@mail.gmail.com>
So, I've wondered about this part all along:
> +/*
> + * Calculates the timestamp at which the next timer should expire and enables
> + * the timer accordingly.
> + */
> +static void
> +reset_startup_progress_timeout(TimestampTz now)
> +{
> + TimestampTz next_timeout;
> +
> + next_timeout = TimestampTzPlusMilliseconds(scheduled_startup_progress_timeout,
> + log_startup_progress_interval);
> + if (next_timeout < now)
> + {
> + /*
> + * Either the timeout was processed so late that we missed an
> + * entire cycle or system clock was set backwards.
> + */
> + next_timeout = TimestampTzPlusMilliseconds(now, log_startup_progress_interval);
> + }
> +
> + enable_timeout_at(STARTUP_PROGRESS_TIMEOUT, next_timeout);
Why is it that we set the next timeout to fire not at "now + interval"
but at "when-it-should-have-fired-but-didn't + interval"? As a user, if
I request a message to be logged every N milliseconds, and one
of them is a little bit delayed, then (assuming I set it to 10s) I still
expect the next one to occur at now+10s. I don't expect the next at
"now+5s" if one is delayed 5s.
In other words, I think this function should just be
enable_timeout_after(STARTUP_PROGRESS_TIMEOUT, log_startup_progress_interval);
This means you can remove the scheduled_startup_progress_timeout
variable.
--
Álvaro Herrera 39°49'30"S 73°17'W — https://www.EnterpriseDB.com/
"No hay ausente sin culpa ni presente sin disculpa" (Prov. francés)
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To: pgsql-hackers@postgresql.org
Cc: alvherre@alvh.no-ip.org, nitinjadhavpostgres@gmail.com, robertmhaas@gmail.com, pryzby@telsasoft.com, michael@paquier.xyz, bharath.rupireddyforpostgres@gmail.com, tgl@sss.pgh.pa.us, andres@anarazel.de, sfrost@snowman.net, magnus@hagander.net, thomas.munro@gmail.com
Subject: Re: when the startup process doesn't (logging startup delays)
In-Reply-To: <202109291736.w3lzq4prep3p@alvherre.pgsql>
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