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Implement sharable row-level locks, and use them for foreign key references

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to eliminate unnecessary deadlocks.  This commit adds SELECT ... FOR SHARE
paralleling SELECT ... FOR UPDATE.  The implementation uses a new SLRU
data structure (managed much like pg_subtrans) to represent multiple-
transaction-ID sets.  When more than one transaction is holding a shared
lock on a particular row, we create a MultiXactId representing that set
of transactions and store its ID in the row's XMAX.  This scheme allows
an effectively unlimited number of row locks, just as we did before,
while not costing any extra overhead except when a shared lock actually
has to be shared.   Still TODO: use the regular lock manager to control
the grant order when multiple backends are waiting for a row lock.

Alvaro Herrera and Tom Lane.
This commit is contained in:
Tom Lane
2005-04-28 21:47:18 +00:00
parent d902e7d63b
commit bedb78d386
55 changed files with 2802 additions and 439 deletions
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28
src/backend/executor/execMain.c
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@ -26,7 +26,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.246 2005/04/14 01:38:17 tgl Exp $
* $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.247 2005/04/28 21:47:12 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -560,9 +560,10 @@ InitPlan(QueryDesc *queryDesc, bool explainOnly)
}
/*
* Have to lock relations selected for update
* Have to lock relations selected FOR UPDATE/FOR SHARE
*/
estate->es_rowMark = NIL;
estate->es_forUpdate = parseTree->forUpdate;
if (parseTree->rowMarks != NIL)
{
ListCell *l;
@ -986,7 +987,7 @@ ExecEndPlan(PlanState *planstate, EState *estate)
heap_close(estate->es_into_relation_descriptor, NoLock);
/*
* close any relations selected FOR UPDATE, again keeping locks
* close any relations selected FOR UPDATE/FOR SHARE, again keeping locks
*/
foreach(l, estate->es_rowMark)
{
@ -1126,6 +1127,9 @@ lnext: ;
* ctid!! */
tupleid = &tuple_ctid;
}
/*
* Process any FOR UPDATE or FOR SHARE locking requested.
*/
else if (estate->es_rowMark != NIL)
{
ListCell *l;
@ -1137,6 +1141,7 @@ lnext: ;
Buffer buffer;
HeapTupleData tuple;
TupleTableSlot *newSlot;
LockTupleMode lockmode;
HTSU_Result test;
if (!ExecGetJunkAttribute(junkfilter,
@ -1151,9 +1156,15 @@ lnext: ;
if (isNull)
elog(ERROR, "\"%s\" is NULL", erm->resname);
if (estate->es_forUpdate)
lockmode = LockTupleExclusive;
else
lockmode = LockTupleShared;
tuple.t_self = *((ItemPointer) DatumGetPointer(datum));
test = heap_mark4update(erm->relation, &tuple, &buffer,
estate->es_snapshot->curcid);
test = heap_lock_tuple(erm->relation, &tuple, &buffer,
estate->es_snapshot->curcid,
lockmode);
ReleaseBuffer(buffer);
switch (test)
{
@ -1189,7 +1200,7 @@ lnext: ;
goto lnext;
default:
elog(ERROR, "unrecognized heap_mark4update status: %u",
elog(ERROR, "unrecognized heap_lock_tuple status: %u",
test);
return (NULL);
}
@ -1574,8 +1585,8 @@ ExecUpdate(TupleTableSlot *slot,
* If we generate a new candidate tuple after EvalPlanQual testing, we
* must loop back here and recheck constraints. (We don't need to
* redo triggers, however. If there are any BEFORE triggers then
* trigger.c will have done mark4update to lock the correct tuple, so
* there's no need to do them again.)
* trigger.c will have done heap_lock_tuple to lock the correct tuple,
* so there's no need to do them again.)
*/
lreplace:;
if (resultRelationDesc->rd_att->constr)
@ -2088,6 +2099,7 @@ EvalPlanQualStart(evalPlanQual *epq, EState *estate, evalPlanQual *priorepq)
epqstate->es_param_exec_vals = (ParamExecData *)
palloc0(estate->es_topPlan->nParamExec * sizeof(ParamExecData));
epqstate->es_rowMark = estate->es_rowMark;
epqstate->es_forUpdate = estate->es_forUpdate;
epqstate->es_instrument = estate->es_instrument;
epqstate->es_select_into = estate->es_select_into;
epqstate->es_into_oids = estate->es_into_oids;