database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-08-19 23:22:23 +03:00
Code Activity

Repair two related errors in heap_lock_tuple: it was failing to recognize

Browse Source 
cases where we already hold the desired lock "indirectly", either via
membership in a MultiXact or because the lock was originally taken by a
different subtransaction of the current transaction.  These cases must be
accounted for to avoid needless deadlocks and/or inappropriate replacement of
an exclusive lock with a shared lock.  Per report from Clarence Gardner and
subsequent investigation.
This commit is contained in:
Tom Lane
2006-11-17 18:00:15 +00:00
parent b6b5aa102b
commit 4f335a3d7f
4 changed files with 115 additions and 46 deletions
Download Patch File Download Diff File Expand all files Collapse all files

51
src/backend/access/transam/multixact.c
View File

@@ -42,7 +42,7 @@
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/access/transam/multixact.c,v 1.21 2006/10/04 00:29:49 momjian Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/multixact.c,v 1.22 2006/11/17 18:00:15 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -366,7 +366,6 @@ bool
MultiXactIdIsRunning(MultiXactId multi)
{
TransactionId *members;
TransactionId myXid;
int nmembers;
int i;
@@ -380,12 +379,14 @@ MultiXactIdIsRunning(MultiXactId multi)
return false;
}
/* checking for myself is cheap */
myXid = GetTopTransactionId();
/*
* Checking for myself is cheap compared to looking in shared memory,
* so first do the equivalent of MultiXactIdIsCurrent(). This is not
* needed for correctness, it's just a fast path.
*/
for (i = 0; i < nmembers; i++)
{
if (TransactionIdEquals(members[i], myXid))
if (TransactionIdIsCurrentTransactionId(members[i]))
{
debug_elog3(DEBUG2, "IsRunning: I (%d) am running!", i);
pfree(members);
@@ -416,6 +417,44 @@ MultiXactIdIsRunning(MultiXactId multi)
return false;
}
/*
* MultiXactIdIsCurrent
* Returns true if the current transaction is a member of the MultiXactId.
*
* We return true if any live subtransaction of the current top-level
* transaction is a member. This is appropriate for the same reason that a
* lock held by any such subtransaction is globally equivalent to a lock
* held by the current subtransaction: no such lock could be released without
* aborting this subtransaction, and hence releasing its locks. So it's not
* necessary to add the current subxact to the MultiXact separately.
*/
bool
MultiXactIdIsCurrent(MultiXactId multi)
{
bool result = false;
TransactionId *members;
int nmembers;
int i;
nmembers = GetMultiXactIdMembers(multi, &members);
if (nmembers < 0)
return false;
for (i = 0; i < nmembers; i++)
{
if (TransactionIdIsCurrentTransactionId(members[i]))
{
result = true;
break;
}
}
pfree(members);
return result;
}
/*
* MultiXactIdSetOldestMember
* Save the oldest MultiXactId this transaction could be a member of.