diff options
| -rw-r--r-- | src/backend/storage/lmgr/lmgr.c | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index fe9889894bb..fb07aa633b9 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -557,6 +557,7 @@ XactLockTableWait(TransactionId xid, Relation rel, ItemPointer ctid, LOCKTAG tag; XactLockTableWaitInfo info; ErrorContextCallback callback; + bool first = true; /* * If an operation is specified, set up our verbose error context @@ -590,7 +591,26 @@ XactLockTableWait(TransactionId xid, Relation rel, ItemPointer ctid, if (!TransactionIdIsInProgress(xid)) break; - xid = SubTransGetParent(xid); + + /* + * If the Xid belonged to a subtransaction, then the lock would have + * gone away as soon as it was finished; for correct tuple visibility, + * the right action is to wait on its parent transaction to go away. + * But instead of going levels up one by one, we can just wait for the + * topmost transaction to finish with the same end result, which also + * incurs less locktable traffic. + * + * Some uses of this function don't involve tuple visibility -- such + * as when building snapshots for logical decoding. It is possible to + * see a transaction in ProcArray before it registers itself in the + * locktable. The topmost transaction in that case is the same xid, + * so we try again after a short sleep. (Don't sleep the first time + * through, to avoid slowing down the normal case.) + */ + if (!first) + pg_usleep(1000L); + first = false; + xid = SubTransGetTopmostTransaction(xid); } if (oper != XLTW_None) @@ -607,6 +627,7 @@ bool ConditionalXactLockTableWait(TransactionId xid) { LOCKTAG tag; + bool first = true; for (;;) { @@ -622,7 +643,12 @@ ConditionalXactLockTableWait(TransactionId xid) if (!TransactionIdIsInProgress(xid)) break; - xid = SubTransGetParent(xid); + + /* See XactLockTableWait about this case */ + if (!first) + pg_usleep(1000L); + first = false; + xid = SubTransGetTopmostTransaction(xid); } return true; |