Back-patch contrib/vacuumlo's new -l (limit) option into 9.0 and 9.1.
Since 9.0, removing lots of large objects in a single transaction risks
exceeding max_locks_per_transaction, because we merged large object removal
into the generic object-drop mechanism, which takes out an exclusive lock
on each object to be dropped. This creates a hazard for contrib/vacuumlo,
which has historically tried to drop all unreferenced large objects in one
transaction. There doesn't seem to be any correctness requirement to do it
that way, though; we only need to drop enough large objects per transaction
to amortize the commit costs.
To prevent a regression from pre-9.0 releases wherein vacuumlo worked just
fine, back-patch commits b69f2e36402aaa222ed03c1769b3de6d5be5f302 and
64c604898e812aa93c124c666e8709fff1b8dd26, which break vacuumlo's deletions
into multiple transactions with a user-controllable upper limit on the
number of objects dropped per transaction.
Tim Lewis, Robert Haas, Tom Lane
contrib/vacuumlo/vacuumlo.c | 145 ++++++++++++++++++++++++++++++++++---------
doc/src/sgml/vacuumlo.sgml | 24 ++++++--
2 files changed, 135 insertions(+), 34 deletions(-)
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