Fix memory leak in LogStandbySnapshot().

The array allocated by GetRunningTransactionLocks() needs to be pfree'd
when we're done with it.  Otherwise we leak some memory during each
checkpoint, if wal_level = hot_standby.  This manifests as memory bloat
in the checkpointer process, or in bgwriter in versions before we made
the checkpointer separate.

Reported and fixed by Naoya Anzai.  Back-patch to 9.0 where the issue
was introduced.

In passing, improve comments for GetRunningTransactionLocks(), and add
an Assert that we didn't overrun the palloc'd array.

diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 1a5481177adb2851370b033c686461ceb130338c..1db951d1fbcc16f853928aab22653933fe7911fd 100644 (file)
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -879,16 +879,11 @@ LogStandbySnapshot(void)
 
    /*
     * Get details of any AccessExclusiveLocks being held at the moment.
-    *
-    * XXX GetRunningTransactionLocks() currently holds a lock on all
-    * partitions though it is possible to further optimise the locking. By
-    * reference counting locks and storing the value on the ProcArray entry
-    * for each backend we can easily tell if any locks need recording without
-    * trying to acquire the partition locks and scanning the lock table.
     */
    locks = GetRunningTransactionLocks(&nlocks);
    if (nlocks > 0)
        LogAccessExclusiveLocks(nlocks, locks);
+   pfree(locks);
 
    /*
     * Log details of all in-progress transactions. This should be the last

diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index e9afc7c0093e6af9e2011ddaf91cc9ef9e44f0b0..1020756ae343ce44daf1ab624bfb36d857c83eb6 100644 (file)
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -2360,18 +2360,26 @@ GetLockStatusData(void)
 }
 
 /*
- * Returns a list of currently held AccessExclusiveLocks, for use
- * by GetRunningTransactionData().
+ * Returns a list of currently held AccessExclusiveLocks, for use by
+ * LogStandbySnapshot().  The result is a palloc'd array,
+ * with the number of elements returned into *nlocks.
+ *
+ * XXX This currently takes a lock on all partitions of the lock table,
+ * but it's possible to do better.  By reference counting locks and storing
+ * the value in the ProcArray entry for each backend we could tell if any
+ * locks need recording without having to acquire the partition locks and
+ * scan the lock table.  Whether that's worth the additional overhead
+ * is pretty dubious though.
  */
 xl_standby_lock *
 GetRunningTransactionLocks(int *nlocks)
 {
+   xl_standby_lock *accessExclusiveLocks;
    PROCLOCK   *proclock;
    HASH_SEQ_STATUS seqstat;
    int         i;
    int         index;
    int         els;
-   xl_standby_lock *accessExclusiveLocks;
 
    /*
     * Acquire lock on the entire shared lock data structure.
@@ -2428,6 +2436,8 @@ GetRunningTransactionLocks(int *nlocks)
        }
    }
 
+   Assert(index <= els);
+
    /*
     * And release locks.  We do this in reverse order for two reasons: (1)
     * Anyone else who needs more than one of the locks will be trying to lock