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_4_STABLE
Details
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http://git.postgresql.org/pg/commitdiff/b7551339dfde58682dfd9f32f6cea27491da6463
Modified Files
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src/backend/access/transam/multixact.c | 12 ++++++++++--
src/backend/access/transam/subtrans.c | 7 ++++++-
2 files changed, 16 insertions(+), 3 deletions(-)
