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https://github.com/postgres/postgres.git
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Use the standard lock manager to establish priority order when there
is contention for a tuple-level lock. This solves the problem of a would-be exclusive locker being starved out by an indefinite succession of share-lockers. Per recent discussion with Alvaro.
This commit is contained in:
Tom Lane
parent
47458f8c2f
commit
93b2477278
@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.188 2005/04/28 21:47:10 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.189 2005/04/30 19:03:32 tgl Exp $
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*
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*
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* INTERFACE ROUTINES
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@ -1209,12 +1209,13 @@ heap_delete(Relation relation, ItemPointer tid,
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ItemPointer ctid, CommandId cid,
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Snapshot crosscheck, bool wait)
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{
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HTSU_Result result;
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TransactionId xid = GetCurrentTransactionId();
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ItemId lp;
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HeapTupleData tp;
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PageHeader dp;
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Buffer buffer;
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HTSU_Result result;
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bool have_tuple_lock = false;
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Assert(ItemPointerIsValid(tid));
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@ -1243,20 +1244,36 @@ l1:
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TransactionId xwait;
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uint16 infomask;
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/* must copy state data before unlocking buffer */
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xwait = HeapTupleHeaderGetXmax(tp.t_data);
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infomask = tp.t_data->t_infomask;
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LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
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/*
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* Acquire tuple lock to establish our priority for the tuple
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* (see heap_lock_tuple). LockTuple will release us when we are
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* next-in-line for the tuple.
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*
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* If we are forced to "start over" below, we keep the tuple lock;
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* this arranges that we stay at the head of the line while
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* rechecking tuple state.
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*/
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if (!have_tuple_lock)
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{
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LockTuple(relation, &(tp.t_self), ExclusiveLock);
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have_tuple_lock = true;
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}
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/*
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* Sleep until concurrent transaction ends. Note that we don't care
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* if the locker has an exclusive or shared lock, because we need
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* exclusive.
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*/
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/* must copy state data before unlocking buffer */
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xwait = HeapTupleHeaderGetXmax(tp.t_data);
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infomask = tp.t_data->t_infomask;
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if (infomask & HEAP_XMAX_IS_MULTI)
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{
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/* wait for multixact */
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LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
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MultiXactIdWait((MultiXactId) xwait);
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LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
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@ -1283,7 +1300,6 @@ l1:
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else
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{
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/* wait for regular transaction to end */
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LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
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XactLockTableWait(xwait);
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LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
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@ -1335,6 +1351,8 @@ l1:
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*ctid = tp.t_data->t_ctid;
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LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
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ReleaseBuffer(buffer);
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if (have_tuple_lock)
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UnlockTuple(relation, &(tp.t_self), ExclusiveLock);
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return result;
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}
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@ -1406,6 +1424,12 @@ l1:
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WriteBuffer(buffer);
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/*
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* Release the lmgr tuple lock, if we had it.
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*/
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if (have_tuple_lock)
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UnlockTuple(relation, &(tp.t_self), ExclusiveLock);
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return HeapTupleMayBeUpdated;
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}
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@ -1476,6 +1500,7 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
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ItemPointer ctid, CommandId cid,
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Snapshot crosscheck, bool wait)
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{
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HTSU_Result result;
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TransactionId xid = GetCurrentTransactionId();
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ItemId lp;
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HeapTupleData oldtup;
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@ -1486,7 +1511,7 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
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already_marked;
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Size newtupsize,
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pagefree;
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HTSU_Result result;
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bool have_tuple_lock = false;
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Assert(ItemPointerIsValid(otid));
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@ -1522,20 +1547,36 @@ l2:
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TransactionId xwait;
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uint16 infomask;
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/* must copy state data before unlocking buffer */
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xwait = HeapTupleHeaderGetXmax(oldtup.t_data);
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infomask = oldtup.t_data->t_infomask;
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LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
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/*
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* Acquire tuple lock to establish our priority for the tuple
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* (see heap_lock_tuple). LockTuple will release us when we are
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* next-in-line for the tuple.
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*
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* If we are forced to "start over" below, we keep the tuple lock;
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* this arranges that we stay at the head of the line while
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* rechecking tuple state.
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*/
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if (!have_tuple_lock)
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{
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LockTuple(relation, &(oldtup.t_self), ExclusiveLock);
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have_tuple_lock = true;
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}
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/*
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* Sleep until concurrent transaction ends. Note that we don't care
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* if the locker has an exclusive or shared lock, because we need
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* exclusive.
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*/
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/* must copy state data before unlocking buffer */
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xwait = HeapTupleHeaderGetXmax(oldtup.t_data);
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infomask = oldtup.t_data->t_infomask;
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if (infomask & HEAP_XMAX_IS_MULTI)
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{
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/* wait for multixact */
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LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
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MultiXactIdWait((MultiXactId) xwait);
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LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
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@ -1562,7 +1603,6 @@ l2:
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else
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{
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/* wait for regular transaction to end */
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LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
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XactLockTableWait(xwait);
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LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
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@ -1614,6 +1654,8 @@ l2:
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*ctid = oldtup.t_data->t_ctid;
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LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
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ReleaseBuffer(buffer);
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if (have_tuple_lock)
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UnlockTuple(relation, &(oldtup.t_self), ExclusiveLock);
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return result;
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}
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@ -1803,6 +1845,12 @@ l2:
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*/
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CacheInvalidateHeapTuple(relation, newtup);
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/*
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* Release the lmgr tuple lock, if we had it.
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*/
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if (have_tuple_lock)
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UnlockTuple(relation, &(oldtup.t_self), ExclusiveLock);
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return HeapTupleMayBeUpdated;
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}
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@ -1847,17 +1895,53 @@ simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
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/*
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* heap_lock_tuple - lock a tuple in shared or exclusive mode
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*
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* NOTES: because the shared-memory lock table is of finite size, but users
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* could reasonably want to lock large numbers of tuples, we do not rely on
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* the standard lock manager to store tuple-level locks over the long term.
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* Instead, a tuple is marked as locked by setting the current transaction's
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* XID as its XMAX, and setting additional infomask bits to distinguish this
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* usage from the more normal case of having deleted the tuple. When
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* multiple transactions concurrently share-lock a tuple, the first locker's
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* XID is replaced in XMAX with a MultiTransactionId representing the set of
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* XIDs currently holding share-locks.
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*
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* When it is necessary to wait for a tuple-level lock to be released, the
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* basic delay is provided by XactLockTableWait or MultiXactIdWait on the
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* contents of the tuple's XMAX. However, that mechanism will release all
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* waiters concurrently, so there would be a race condition as to which
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* waiter gets the tuple, potentially leading to indefinite starvation of
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* some waiters. The possibility of share-locking makes the problem much
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* worse --- a steady stream of share-lockers can easily block an exclusive
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* locker forever. To provide more reliable semantics about who gets a
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* tuple-level lock first, we use the standard lock manager. The protocol
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* for waiting for a tuple-level lock is really
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* LockTuple()
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* XactLockTableWait()
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* mark tuple as locked by me
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* UnlockTuple()
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* When there are multiple waiters, arbitration of who is to get the lock next
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* is provided by LockTuple(). However, at most one tuple-level lock will
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* be held or awaited per backend at any time, so we don't risk overflow
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* of the lock table. Note that incoming share-lockers are required to
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* do LockTuple as well, if there is any conflict, to ensure that they don't
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* starve out waiting exclusive-lockers. However, if there is not any active
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* conflict for a tuple, we don't incur any extra overhead.
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*/
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HTSU_Result
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heap_lock_tuple(Relation relation, HeapTuple tuple, Buffer *buffer,
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CommandId cid, LockTupleMode mode)
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{
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TransactionId xid;
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HTSU_Result result;
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ItemPointer tid = &(tuple->t_self);
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ItemId lp;
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PageHeader dp;
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HTSU_Result result;
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TransactionId xid;
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uint16 new_infomask;
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LOCKMODE tuple_lock_type;
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bool have_tuple_lock = false;
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tuple_lock_type = (mode == LockTupleShared) ? ShareLock : ExclusiveLock;
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*buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
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LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
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@ -1879,94 +1963,121 @@ l3:
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}
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else if (result == HeapTupleBeingUpdated)
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{
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if (mode == LockTupleShared &&
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(tuple->t_data->t_infomask & HEAP_XMAX_SHARED_LOCK))
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result = HeapTupleMayBeUpdated;
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TransactionId xwait;
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uint16 infomask;
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/* must copy state data before unlocking buffer */
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xwait = HeapTupleHeaderGetXmax(tuple->t_data);
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infomask = tuple->t_data->t_infomask;
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LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
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/*
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* Acquire tuple lock to establish our priority for the tuple.
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* LockTuple will release us when we are next-in-line for the
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* tuple. We must do this even if we are share-locking.
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*
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* If we are forced to "start over" below, we keep the tuple lock;
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* this arranges that we stay at the head of the line while
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* rechecking tuple state.
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*/
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if (!have_tuple_lock)
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{
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LockTuple(relation, tid, tuple_lock_type);
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have_tuple_lock = true;
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}
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if (mode == LockTupleShared && (infomask & HEAP_XMAX_SHARED_LOCK))
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{
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/*
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* Acquiring sharelock when there's at least one sharelocker
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* already. We need not wait for him/them to complete.
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*/
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LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
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/*
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* Make sure it's still a shared lock, else start over. (It's
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* OK if the ownership of the shared lock has changed, though.)
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*/
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if (!(tuple->t_data->t_infomask & HEAP_XMAX_SHARED_LOCK))
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goto l3;
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}
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else if (infomask & HEAP_XMAX_IS_MULTI)
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{
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/* wait for multixact to end */
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MultiXactIdWait((MultiXactId) xwait);
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LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
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/*
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* If xwait had just locked the tuple then some other xact
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* could update this tuple before we get to this point.
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* Check for xmax change, and start over if so.
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*/
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if (!(tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
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!TransactionIdEquals(HeapTupleHeaderGetXmax(tuple->t_data),
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xwait))
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goto l3;
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/*
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* You might think the multixact is necessarily done here, but
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* not so: it could have surviving members, namely our own xact
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* or other subxacts of this backend. It is legal for us to
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* lock the tuple in either case, however. We don't bother
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* changing the on-disk hint bits since we are about to
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* overwrite the xmax altogether.
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*/
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}
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else
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{
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TransactionId xwait;
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uint16 infomask;
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/* wait for regular transaction to end */
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XactLockTableWait(xwait);
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LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
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/*
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* Sleep until concurrent transaction ends.
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* xwait is done, but if xwait had just locked the tuple then
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* some other xact could update this tuple before we get to
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* this point. Check for xmax change, and start over if so.
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*/
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if ((tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
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!TransactionIdEquals(HeapTupleHeaderGetXmax(tuple->t_data),
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xwait))
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goto l3;
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/* must copy state data before unlocking buffer */
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xwait = HeapTupleHeaderGetXmax(tuple->t_data);
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infomask = tuple->t_data->t_infomask;
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if (infomask & HEAP_XMAX_IS_MULTI)
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/* Otherwise we can mark it committed or aborted */
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if (!(tuple->t_data->t_infomask & (HEAP_XMAX_COMMITTED |
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HEAP_XMAX_INVALID)))
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{
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/* wait for multixact */
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LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
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MultiXactIdWait((MultiXactId) xwait);
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LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
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/*
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* If xwait had just locked the tuple then some other xact
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* could update this tuple before we get to this point.
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* Check for xmax change, and start over if so.
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*/
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if (!(tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
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!TransactionIdEquals(HeapTupleHeaderGetXmax(tuple->t_data),
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xwait))
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goto l3;
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/*
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* You might think the multixact is necessarily done here, but
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* not so: it could have surviving members, namely our own xact
|
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* or other subxacts of this backend. It is legal for us to
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* lock the tuple in either case, however. We don't bother
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* changing the on-disk hint bits since we are about to
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* overwrite the xmax altogether.
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*/
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if (TransactionIdDidCommit(xwait))
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tuple->t_data->t_infomask |= HEAP_XMAX_COMMITTED;
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else
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tuple->t_data->t_infomask |= HEAP_XMAX_INVALID;
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SetBufferCommitInfoNeedsSave(*buffer);
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}
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else
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{
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/* wait for regular transaction to end */
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LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
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XactLockTableWait(xwait);
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LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);
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/*
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* xwait is done, but if xwait had just locked the tuple then
|
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* some other xact could update this tuple before we get to
|
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* this point. Check for xmax change, and start over if so.
|
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*/
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if ((tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
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!TransactionIdEquals(HeapTupleHeaderGetXmax(tuple->t_data),
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xwait))
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goto l3;
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/* Otherwise we can mark it committed or aborted */
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if (!(tuple->t_data->t_infomask & (HEAP_XMAX_COMMITTED |
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HEAP_XMAX_INVALID)))
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{
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if (TransactionIdDidCommit(xwait))
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tuple->t_data->t_infomask |= HEAP_XMAX_COMMITTED;
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else
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tuple->t_data->t_infomask |= HEAP_XMAX_INVALID;
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SetBufferCommitInfoNeedsSave(*buffer);
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}
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}
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/*
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* We may lock if previous xmax aborted, or if it committed
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* but only locked the tuple without updating it.
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*/
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if (tuple->t_data->t_infomask & (HEAP_XMAX_INVALID |
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HEAP_IS_LOCKED))
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result = HeapTupleMayBeUpdated;
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else
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result = HeapTupleUpdated;
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}
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/*
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* We may lock if previous xmax aborted, or if it committed
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* but only locked the tuple without updating it. The case where
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* we didn't wait because we are joining an existing shared lock
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* is correctly handled, too.
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*/
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if (tuple->t_data->t_infomask & (HEAP_XMAX_INVALID |
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HEAP_IS_LOCKED))
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result = HeapTupleMayBeUpdated;
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else
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result = HeapTupleUpdated;
|
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}
|
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|
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if (result != HeapTupleMayBeUpdated)
|
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{
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ItemPointerData newctid = tuple->t_data->t_ctid;
|
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Assert(result == HeapTupleSelfUpdated || result == HeapTupleUpdated);
|
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tuple->t_self = tuple->t_data->t_ctid;
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LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
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if (have_tuple_lock)
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UnlockTuple(relation, tid, tuple_lock_type);
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/* can't overwrite t_self (== *tid) until after above Unlock */
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tuple->t_self = newctid;
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return result;
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}
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@ -2142,6 +2253,13 @@ l3:
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WriteNoReleaseBuffer(*buffer);
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|
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/*
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* Now that we have successfully marked the tuple as locked, we can
|
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* release the lmgr tuple lock, if we had it.
|
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*/
|
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if (have_tuple_lock)
|
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UnlockTuple(relation, tid, tuple_lock_type);
|
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|
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return HeapTupleMayBeUpdated;
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}
|
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|
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|
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@ -8,7 +8,7 @@
|
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*
|
||||
*
|
||||
* IDENTIFICATION
|
||||
* $PostgreSQL: pgsql/src/backend/storage/lmgr/lmgr.c,v 1.72 2005/04/29 22:28:24 tgl Exp $
|
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* $PostgreSQL: pgsql/src/backend/storage/lmgr/lmgr.c,v 1.73 2005/04/30 19:03:33 tgl Exp $
|
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*
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*-------------------------------------------------------------------------
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*/
|
||||
@ -339,6 +339,46 @@ UnlockPage(Relation relation, BlockNumber blkno, LOCKMODE lockmode)
|
||||
LockRelease(LockTableId, &tag, GetTopTransactionId(), lockmode);
|
||||
}
|
||||
|
||||
/*
|
||||
* LockTuple
|
||||
*
|
||||
* Obtain a tuple-level lock. This is used in a less-than-intuitive fashion
|
||||
* because we can't afford to keep a separate lock in shared memory for every
|
||||
* tuple. See heap_lock_tuple before using this!
|
||||
*/
|
||||
void
|
||||
LockTuple(Relation relation, ItemPointer tid, LOCKMODE lockmode)
|
||||
{
|
||||
LOCKTAG tag;
|
||||
|
||||
SET_LOCKTAG_TUPLE(tag,
|
||||
relation->rd_lockInfo.lockRelId.dbId,
|
||||
relation->rd_lockInfo.lockRelId.relId,
|
||||
ItemPointerGetBlockNumber(tid),
|
||||
ItemPointerGetOffsetNumber(tid));
|
||||
|
||||
if (!LockAcquire(LockTableId, &tag, GetTopTransactionId(),
|
||||
lockmode, false))
|
||||
elog(ERROR, "LockAcquire failed");
|
||||
}
|
||||
|
||||
/*
|
||||
* UnlockTuple
|
||||
*/
|
||||
void
|
||||
UnlockTuple(Relation relation, ItemPointer tid, LOCKMODE lockmode)
|
||||
{
|
||||
LOCKTAG tag;
|
||||
|
||||
SET_LOCKTAG_TUPLE(tag,
|
||||
relation->rd_lockInfo.lockRelId.dbId,
|
||||
relation->rd_lockInfo.lockRelId.relId,
|
||||
ItemPointerGetBlockNumber(tid),
|
||||
ItemPointerGetOffsetNumber(tid));
|
||||
|
||||
LockRelease(LockTableId, &tag, GetTopTransactionId(), lockmode);
|
||||
}
|
||||
|
||||
/*
|
||||
* XactLockTableInsert
|
||||
*
|
||||
@ -417,3 +457,87 @@ XactLockTableWait(TransactionId xid)
|
||||
if (!TransactionIdDidCommit(xid) && !TransactionIdDidAbort(xid))
|
||||
TransactionIdAbort(xid);
|
||||
}
|
||||
|
||||
|
||||
/*
|
||||
* LockDatabaseObject
|
||||
*
|
||||
* Obtain a lock on a general object of the current database. Don't use
|
||||
* this for shared objects (such as tablespaces). It's usually unwise to
|
||||
* apply it to entire relations, also, since a lock taken this way will
|
||||
* NOT conflict with LockRelation.
|
||||
*/
|
||||
void
|
||||
LockDatabaseObject(Oid classid, Oid objid, uint16 objsubid,
|
||||
LOCKMODE lockmode)
|
||||
{
|
||||
LOCKTAG tag;
|
||||
|
||||
SET_LOCKTAG_OBJECT(tag,
|
||||
MyDatabaseId,
|
||||
classid,
|
||||
objid,
|
||||
objsubid);
|
||||
|
||||
if (!LockAcquire(LockTableId, &tag, GetTopTransactionId(),
|
||||
lockmode, false))
|
||||
elog(ERROR, "LockAcquire failed");
|
||||
}
|
||||
|
||||
/*
|
||||
* UnlockDatabaseObject
|
||||
*/
|
||||
void
|
||||
UnlockDatabaseObject(Oid classid, Oid objid, uint16 objsubid,
|
||||
LOCKMODE lockmode)
|
||||
{
|
||||
LOCKTAG tag;
|
||||
|
||||
SET_LOCKTAG_OBJECT(tag,
|
||||
MyDatabaseId,
|
||||
classid,
|
||||
objid,
|
||||
objsubid);
|
||||
|
||||
LockRelease(LockTableId, &tag, GetTopTransactionId(), lockmode);
|
||||
}
|
||||
|
||||
/*
|
||||
* LockSharedObject
|
||||
*
|
||||
* Obtain a lock on a shared-across-databases object.
|
||||
*/
|
||||
void
|
||||
LockSharedObject(Oid classid, Oid objid, uint16 objsubid,
|
||||
LOCKMODE lockmode)
|
||||
{
|
||||
LOCKTAG tag;
|
||||
|
||||
SET_LOCKTAG_OBJECT(tag,
|
||||
InvalidOid,
|
||||
classid,
|
||||
objid,
|
||||
objsubid);
|
||||
|
||||
if (!LockAcquire(LockTableId, &tag, GetTopTransactionId(),
|
||||
lockmode, false))
|
||||
elog(ERROR, "LockAcquire failed");
|
||||
}
|
||||
|
||||
/*
|
||||
* UnlockSharedObject
|
||||
*/
|
||||
void
|
||||
UnlockSharedObject(Oid classid, Oid objid, uint16 objsubid,
|
||||
LOCKMODE lockmode)
|
||||
{
|
||||
LOCKTAG tag;
|
||||
|
||||
SET_LOCKTAG_OBJECT(tag,
|
||||
InvalidOid,
|
||||
classid,
|
||||
objid,
|
||||
objsubid);
|
||||
|
||||
LockRelease(LockTableId, &tag, GetTopTransactionId(), lockmode);
|
||||
}
|
||||
|
||||
@ -7,7 +7,7 @@
|
||||
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
|
||||
* Portions Copyright (c) 1994, Regents of the University of California
|
||||
*
|
||||
* $PostgreSQL: pgsql/src/include/storage/lmgr.h,v 1.47 2005/04/29 22:28:24 tgl Exp $
|
||||
* $PostgreSQL: pgsql/src/include/storage/lmgr.h,v 1.48 2005/04/30 19:03:33 tgl Exp $
|
||||
*
|
||||
*-------------------------------------------------------------------------
|
||||
*/
|
||||
@ -17,6 +17,7 @@
|
||||
#include "storage/lock.h"
|
||||
#include "utils/rel.h"
|
||||
|
||||
|
||||
/* These are the valid values of type LOCKMODE: */
|
||||
|
||||
/* NoLock is not a lock mode, but a flag value meaning "don't get a lock" */
|
||||
@ -60,9 +61,25 @@ extern void LockPage(Relation relation, BlockNumber blkno, LOCKMODE lockmode);
|
||||
extern bool ConditionalLockPage(Relation relation, BlockNumber blkno, LOCKMODE lockmode);
|
||||
extern void UnlockPage(Relation relation, BlockNumber blkno, LOCKMODE lockmode);
|
||||
|
||||
/* Lock a tuple (see heap_lock_tuple before assuming you understand this) */
|
||||
extern void LockTuple(Relation relation, ItemPointer tid, LOCKMODE lockmode);
|
||||
extern void UnlockTuple(Relation relation, ItemPointer tid, LOCKMODE lockmode);
|
||||
|
||||
/* Lock an XID (used to wait for a transaction to finish) */
|
||||
extern void XactLockTableInsert(TransactionId xid);
|
||||
extern void XactLockTableDelete(TransactionId xid);
|
||||
extern void XactLockTableWait(TransactionId xid);
|
||||
|
||||
/* Lock a general object (other than a relation) of the current database */
|
||||
extern void LockDatabaseObject(Oid classid, Oid objid, uint16 objsubid,
|
||||
LOCKMODE lockmode);
|
||||
extern void UnlockDatabaseObject(Oid classid, Oid objid, uint16 objsubid,
|
||||
LOCKMODE lockmode);
|
||||
|
||||
/* Lock a shared-across-databases object (other than a relation) */
|
||||
extern void LockSharedObject(Oid classid, Oid objid, uint16 objsubid,
|
||||
LOCKMODE lockmode);
|
||||
extern void UnlockSharedObject(Oid classid, Oid objid, uint16 objsubid,
|
||||
LOCKMODE lockmode);
|
||||
|
||||
#endif /* LMGR_H */
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user