pgsql: Fix off-by-one error in calculating subtrans/multixact truncatio - Mailing list pgsql-committers

Fix off-by-one error in calculating subtrans/multixact truncation point.

If there were no subtransactions (or multixacts) active, we would calculate
the oldestxid == next xid. That's correct, but if next XID happens to be
on the next pg_subtrans (pg_multixact) page, the page does not exist yet,
and SimpleLruTruncate will produce an "apparent wraparound" warning. The
warning is harmless in this case, but looks very alarming to users.

Backpatch to all supported versions. Patch and analysis by Thomas Munro.

Branch
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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/84330d0c1fd3dd76f95ce82dd5856a9de52b5b23

Modified Files
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src/backend/access/transam/multixact.c |   14 ++++++++++----
src/backend/access/transam/subtrans.c  |    7 ++++++-
src/include/access/multixact.h         |    1 +
3 files changed, 17 insertions(+), 5 deletions(-)