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pgsql: Fix SPGiST vacuum algorithm to handle concurrent tuple motionpr

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: pgsql-committers(at)postgresql(dot)org
Subject: pgsql: Fix SPGiST vacuum algorithm to handle concurrent tuple motionpr
Date: 2012-03-12 20:10:39
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Lists: pgsql-committers
Fix SPGiST vacuum algorithm to handle concurrent tuple motion properly.

A leaf tuple that we need to delete could get moved as a consequence of an
insertion happening concurrently with the VACUUM scan.  If it moves from a
page past the current scan point to a page before, we'll miss it, which is
not acceptable.  Hence, when we see a leaf-page REDIRECT that could have
been made since our scan started, chase down the redirection pointer much
as if we were doing a normal index search, and be sure to vacuum every page
it leads to.  This fixes the issue because, if the tuple was on page N at
the instant we start our scan, we will surely find it as a consequence of
chasing the redirect from page N, no matter how much it moves around in
between.  Problem noted by Takashi Yamamoto.



Modified Files
src/backend/access/spgist/README      |   21 +++
src/backend/access/spgist/spgvacuum.c |  231 +++++++++++++++++++++++++++++++--
2 files changed, 242 insertions(+), 10 deletions(-)

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