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pgsql: Prevent index-only scans from returning wrong answers underHot

From: Robert Haas <rhaas(at)postgresql(dot)org>
To: pgsql-committers(at)postgresql(dot)org
Subject: pgsql: Prevent index-only scans from returning wrong answers underHot
Date: 2012-04-27 00:03:16
Message-ID: (view raw or whole thread)
Lists: pgsql-committers
Prevent index-only scans from returning wrong answers under Hot Standby.

The alternative of disallowing index-only scans in HS operation was
discussed, but the consensus was that it was better to treat marking
a page all-visible as a recovery conflict for snapshots that could still
fail to see XIDs on that page.  We may in the future try to soften this,
so that we simply force index scans to do heap fetches in cases where
this may be an issue, rather than throwing a hard conflict.



Modified Files
src/backend/access/heap/heapam.c        |   18 ++++++++++++++++--
src/backend/access/heap/visibilitymap.c |    9 ++++++---
src/backend/commands/vacuumlazy.c       |   11 +++++++++--
src/include/access/heapam.h             |    2 +-
src/include/access/htup.h               |    3 ++-
src/include/access/visibilitymap.h      |    2 +-
src/include/access/xlog_internal.h      |    2 +-
7 files changed, 36 insertions(+), 11 deletions(-)

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