pgsql: Don't clear btpo_cycleid during _bt_vacuum_one_page.

Don't clear btpo_cycleid during _bt_vacuum_one_page.

When "vacuuming" a single btree page by removing LP_DEAD tuples, we are not
actually within a vacuum operation, but rather in an ordinary insertion
process that could well be running concurrently with a vacuum. So clearing
the cycleid is incorrect, and could cause the concurrent vacuum to miss
removing tuples that it needs to remove. This is a longstanding bug
introduced by commit e6284649b9e30372b3990107a082bc7520325676 of
2006-07-25. I believe it explains Maxim Boguk's recent report of index
corruption, and probably some other previously unexplained reports.

In 9.0 and up this is a one-line fix; before that we need to introduce a
flag to tell _bt_delitems what to do.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/593a9631a7947ab95903e87e24786d7e469cc988

Modified Files
--------------
src/backend/access/nbtree/nbtpage.c | 7 +++----
1 files changed, 3 insertions(+), 4 deletions(-)