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-rw-r--r--src/backend/commands/vacuum.c28
1 files changed, 16 insertions, 12 deletions
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 75b0ca9..329c73d 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -1532,6 +1532,8 @@ vac_update_datfrozenxid(void)
/*
* We must seqscan pg_class to find the minimum Xid, because there is no
* index that can help us here.
+ *
+ * See vac_truncate_clog() for the race condition to prevent.
*/
relation = table_open(RelationRelationId, AccessShareLock);
@@ -1540,7 +1542,9 @@ vac_update_datfrozenxid(void)
while ((classTup = systable_getnext(scan)) != NULL)
{
- Form_pg_class classForm = (Form_pg_class) GETSTRUCT(classTup);
+ volatile FormData_pg_class *classForm = (Form_pg_class) GETSTRUCT(classTup);
+ TransactionId relfrozenxid = classForm->relfrozenxid;
+ TransactionId relminmxid = classForm->relminmxid;
/*
* Only consider relations able to hold unfrozen XIDs (anything else
@@ -1550,8 +1554,8 @@ vac_update_datfrozenxid(void)
classForm->relkind != RELKIND_MATVIEW &&
classForm->relkind != RELKIND_TOASTVALUE)
{
- Assert(!TransactionIdIsValid(classForm->relfrozenxid));
- Assert(!MultiXactIdIsValid(classForm->relminmxid));
+ Assert(!TransactionIdIsValid(relfrozenxid));
+ Assert(!MultiXactIdIsValid(relminmxid));
continue;
}
@@ -1570,34 +1574,34 @@ vac_update_datfrozenxid(void)
* before those relations have been scanned and cleaned up.
*/
- if (TransactionIdIsValid(classForm->relfrozenxid))
+ if (TransactionIdIsValid(relfrozenxid))
{
- Assert(TransactionIdIsNormal(classForm->relfrozenxid));
+ Assert(TransactionIdIsNormal(relfrozenxid));
/* check for values in the future */
- if (TransactionIdPrecedes(lastSaneFrozenXid, classForm->relfrozenxid))
+ if (TransactionIdPrecedes(lastSaneFrozenXid, relfrozenxid))
{
bogus = true;
break;
}
/* determine new horizon */
- if (TransactionIdPrecedes(classForm->relfrozenxid, newFrozenXid))
- newFrozenXid = classForm->relfrozenxid;
+ if (TransactionIdPrecedes(relfrozenxid, newFrozenXid))
+ newFrozenXid = relfrozenxid;
}
- if (MultiXactIdIsValid(classForm->relminmxid))
+ if (MultiXactIdIsValid(relminmxid))
{
/* check for values in the future */
- if (MultiXactIdPrecedes(lastSaneMinMulti, classForm->relminmxid))
+ if (MultiXactIdPrecedes(lastSaneMinMulti, relminmxid))
{
bogus = true;
break;
}
/* determine new horizon */
- if (MultiXactIdPrecedes(classForm->relminmxid, newMinMulti))
- newMinMulti = classForm->relminmxid;
+ if (MultiXactIdPrecedes(relminmxid, newMinMulti))
+ newMinMulti = relminmxid;
}
}