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pgsql: Back-patch contrib/vacuumlo's new -l (limit) option into 9.0and

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: pgsql-committers(at)postgresql(dot)org
Subject: pgsql: Back-patch contrib/vacuumlo's new -l (limit) option into 9.0and
Date: 2012-03-21 17:05:41
Message-ID: E1SAOyj-0001Fd-4i@gemulon.postgresql.org (view raw or flat)
Thread:
Lists: pgsql-committers
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

Branch
------
REL9_1_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/5bd06e619c82c3b2e29fed40aae5fc39a9620908

Modified Files
--------------
contrib/vacuumlo/vacuumlo.c |  143 ++++++++++++++++++++++++++++++++++--------
doc/src/sgml/vacuumlo.sgml  |   22 ++++++-
2 files changed, 133 insertions(+), 32 deletions(-)

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