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Overdue code review for transaction-level advisory locks patch.

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Commit 62c7bd31c8 had assorted problems, most
visibly that it broke PREPARE TRANSACTION in the presence of session-level
advisory locks (which should be ignored by PREPARE), as per a recent
complaint from Stephen Rees.  More abstractly, the patch made the
LockMethodData.transactional flag not merely useless but outright
dangerous, because in point of fact that flag no longer tells you anything
at all about whether a lock is held transactionally.  This fix therefore
removes that flag altogether.  We now rely entirely on the convention
already in use in lock.c that transactional lock holds must be owned by
some ResourceOwner, while session holds are never so owned.  Setting the
locallock struct's owner link to NULL thus denotes a session hold, and
there is no redundant marker for that.

PREPARE TRANSACTION now works again when there are session-level advisory
locks, and it is also able to transfer transactional advisory locks to the
prepared transaction, but for implementation reasons it throws an error if
we hold both types of lock on a single lockable object.  Perhaps it will be
worth improving that someday.

Assorted other minor cleanup and documentation editing, as well.

Back-patch to 9.1, except that in the 9.1 branch I did not remove the
LockMethodData.transactional flag for fear of causing an ABI break for
any external code that might be examining those structs.
This commit is contained in:
Tom Lane
2012-05-04 17:43:27 -04:00
parent 1715ff1128
commit 71b9549d05
6 changed files with 266 additions and 208 deletions
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10
src/backend/storage/lmgr/proc.c
View File

@@ -697,9 +697,12 @@ LockErrorCleanup(void)
* ProcReleaseLocks() -- release locks associated with current transaction
* at main transaction commit or abort
*
* At main transaction commit, we release all locks except session locks.
* At main transaction commit, we release standard locks except session locks.
* At main transaction abort, we release all locks including session locks.
*
* Advisory locks are released only if they are transaction-level;
* session-level holds remain, whether this is a commit or not.
*
* At subtransaction commit, we don't release any locks (so this func is not
* needed at all); we will defer the releasing to the parent transaction.
* At subtransaction abort, we release all locks held by the subtransaction;
@@ -713,10 +716,9 @@ ProcReleaseLocks(bool isCommit)
return;
/* If waiting, get off wait queue (should only be needed after error) */
LockErrorCleanup();
/* Release locks */
/* Release standard locks, including session-level if aborting */
LockReleaseAll(DEFAULT_LOCKMETHOD, !isCommit);
/* Release transaction level advisory locks */
/* Release transaction-level advisory locks */
LockReleaseAll(USER_LOCKMETHOD, false);
}