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pgsql: Don't throw a warning if vacuum sees PD_ALL_VISIBLE flag seton

From: Heikki Linnakangas <heikki(dot)linnakangas(at)iki(dot)fi>
To: pgsql-committers(at)postgresql(dot)org
Subject: pgsql: Don't throw a warning if vacuum sees PD_ALL_VISIBLE flag seton
Date: 2011-03-08 19:00:22
Message-ID: E1Px28s-0007aF-5J@gemulon.postgresql.org (view raw or flat)
Thread:
Lists: pgsql-committers
Don't throw a warning if vacuum sees PD_ALL_VISIBLE flag set on a page that
contains newly-inserted tuples that according to our OldestXmin are not
yet visible to everyone. The value returned by GetOldestXmin() is conservative,
and it can move backwards on repeated calls, so if we see that contradiction
between the PD_ALL_VISIBLE flag and status of tuples on the page, we have to
assume it's because an earlier vacuum calculated a higher OldestXmin value,
and all the tuples really are visible to everyone.

We have received several reports of this bug, with the "PD_ALL_VISIBLE flag
was incorrectly set in relation ..." warning appearing in logs. We were
finally able to hunt it down with David Gould's help to run extra diagnostics
in an environment where this happened frequently.

Also reword the warning, per Robert Haas' suggestion, to not imply that the
PD_ALL_VISIBLE flag is necessarily at fault, as it might also be a symptom
of corruption on a tuple header.

Backpatch to 8.4, where the PD_ALL_VISIBLE flag was introduced.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/93d888232e80e4d676e24fe93ae6d27459d966be

Modified Files
--------------
src/backend/commands/vacuumlazy.c   |   20 ++++++++++++++++++--
src/backend/storage/ipc/procarray.c |   12 ++++++++++++
2 files changed, 30 insertions(+), 2 deletions(-)

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Next:From: Heikki LinnakangasDate: 2011-03-08 19:06:48
Subject: pgsql: Fix overly strict assertion inSummarizeOldestCommittedSxact().
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Subject: pgsql: Adjust CHAR() doc mention of pattern matching issues fortrailin

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