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_0_STABLE
Details
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http://git.postgresql.org/pg/commitdiff/40ad7822019a2cf8b9e0d5bd770490af7b56e652
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(-)