Date: Thu, 30 Aug 2018 23:23:54 -0700
From: Michael Paquier <michael@paquier.xyz>
To: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Cc: cyberdemn@gmail.com, pgsql-hackers@postgresql.org,
	alvherre@2ndquadrant.com, 9erthalion6@gmail.com,
	pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #15346: Replica fails to start after the crash
Message-ID: <20180831062354.GK15446@paquier.xyz>
References: <20180830185705.GF15446@paquier.xyz>
 <20180831.094846.52751456.horiguchi.kyotaro@lab.ntt.co.jp>
 <20180831014855.GJ15446@paquier.xyz>
 <20180831.145206.05203037.horiguchi.kyotaro@lab.ntt.co.jp>
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On Fri, Aug 31, 2018 at 02:52:06PM +0900, Kyotaro HORIGUCHI wrote:
> The patch inhibits turning off updateMinRecoveryPoint on other
> than the startup process running crash-recovery except at the end
> of XLogNeedsFlush.

Yes that's a matter of safety, as I put into the truck any modules which
may use XLogFlush().  And that maps with the old code, so there is no
more surprise.

> Even if any other processes than the startup calls the function
> during crash recovery, they don't have a means to turn on
> updateMinRecoveryPoint again. Actually the only process that
> calls the function during crash recovery is the startup. bwriter
> and checkpointer doesn't. Hot-standby backends come after
> crash-recvery ends. After all, we just won't have an invalid
> minRecoveryPoint value there, and updateMinRecoverypoint must be
> true.

Yes, until a recovery point is reached only the startup process could
call that.  Now I would imagine that we could have a background worker
as well which is spawned when the postmaster starts, and calls those
code paths...

> +	/*
> +	 * No other process than the startup doesn't reach here before crash
> +	 * recovery ends. So minRecoveryPoint must have a valid value here.
> +	 */
> +	Assert(minRecoveryPoint != InvalidXLogRecPtr);

...  And that would invalidate your assertion here.
--
Michael

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