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Date: Sun, 10 Feb 2019 21:13:49 -0800
From: Noah Misch <noah@leadboat.com>
To: pgsql-hackers@postgresql.org
Subject: Re: Spurious "apparent wraparound" via SimpleLruTruncate() rounding
Message-ID: <20190211051349.GA952299@rfd.leadboat.com>
References: <20190202083822.GC32531@gust.leadboat.com>
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On Sat, Feb 02, 2019 at 03:38:22AM -0500, Noah Misch wrote:
> The main consequence is the false alarm.  A prudent DBA will want to react to
> true wraparound, but no such wraparound has occurred.  Also, we temporarily
> waste disk space in pg_xact.  This feels like a recipe for future bugs.  The
> fix I have in mind, attached, is to change instances of
> ctl->PagePrecedes(FIRST_PAGE_OF_SEGMENT, ROUNDED_cutoffPage) to
> ctl->PagePrecedes(LAST_PAGE_OF_SEGMENT, cutoffPage).  I'm inclined not to
> back-patch this; does anyone favor back-patching?

To avoid wasting more of anyone's time: that patch is bad; I'll update this
thread when I have something better.