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Re: strange nbtree corruption report

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Noah Misch <noah(at)leadboat(dot)com>
Cc: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: strange nbtree corruption report
Date: 2011-11-22 03:43:23
Message-ID: 1189.1321933403@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Noah Misch <noah(at)leadboat(dot)com> writes:
> Just a suspicion ... when looking at the B-tree page reclamation algorithm, I
> had a thought that the logic in _bt_page_recyclable() was obsolete as of the
> introduction (in 8.3) of xid-free read-only transactions.  A transaction
> without a persistent xid does not hold back RecentXmin, so how could waiting
> for a RecentXmin window to pass prove that no scan still holds a link to the
> page?  Similarly, running VACUUMs do not hold back RecentXmin.

Uh, sure they do.  It's their advertised snapshot xmin that counts, not
their own xid (if any).

			regards, tom lane

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