Re-implement EvalPlanQual processing to improve its performance and eliminate

a lot of strange behaviors that occurred in join cases.  We now identify the
"current" row for every joined relation in UPDATE, DELETE, and SELECT FOR
UPDATE/SHARE queries.  If an EvalPlanQual recheck is necessary, we jam the
appropriate row into each scan node in the rechecking plan, forcing it to emit
only that one row.  The former behavior could rescan the whole of each joined
relation for each recheck, which was terrible for performance, and what's much
worse could result in duplicated output tuples.

Also, the original implementation of EvalPlanQual could not re-use the recheck
execution tree --- it had to go through a full executor init and shutdown for
every row to be tested.  To avoid this overhead, I've associated a special
runtime Param with each LockRows or ModifyTable plan node, and arranged to
make every scan node below such a node depend on that Param.  Thus, by
signaling a change in that Param, the EPQ machinery can just rescan the
already-built test plan.

This patch also adds a prohibition on set-returning functions in the
targetlist of SELECT FOR UPDATE/SHARE.  This is needed to avoid the
duplicate-output-tuple problem.  It seems fairly reasonable since the
other restrictions on SELECT FOR UPDATE are meant to ensure that there
is a unique correspondence between source tuples and result tuples,
which an output SRF destroys as much as anything else does.

1 files changed, 27 insertions, 50 deletions

diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index 0520b726cfa..b136825dc8f 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.135 2009/09/27 21:10:53 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.136 2009/10/26 02:26:31 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -52,7 +52,6 @@ IndexNext(IndexScanState *node)
 	ExprContext *econtext;
 	ScanDirection direction;
 	IndexScanDesc scandesc;
-	Index		scanrelid;
 	HeapTuple	tuple;
 	TupleTableSlot *slot;
 
@@ -72,36 +71,6 @@ IndexNext(IndexScanState *node)
 	scandesc = node->iss_ScanDesc;
 	econtext = node->ss.ps.ps_ExprContext;
 	slot = node->ss.ss_ScanTupleSlot;
-	scanrelid = ((IndexScan *) node->ss.ps.plan)->scan.scanrelid;
-
-	/*
-	 * Check if we are evaluating PlanQual for tuple of this relation.
-	 * Additional checking is not good, but no other way for now. We could
-	 * introduce new nodes for this case and handle IndexScan --> NewNode
-	 * switching in Init/ReScan plan...
-	 */
-	if (estate->es_evTuple != NULL &&
-		estate->es_evTuple[scanrelid - 1] != NULL)
-	{
-		if (estate->es_evTupleNull[scanrelid - 1])
-			return ExecClearTuple(slot);
-
-		ExecStoreTuple(estate->es_evTuple[scanrelid - 1],
-					   slot, InvalidBuffer, false);
-
-		/* Does the tuple meet the indexqual condition? */
-		econtext->ecxt_scantuple = slot;
-
-		ResetExprContext(econtext);
-
-		if (!ExecQual(node->indexqualorig, econtext, false))
-			ExecClearTuple(slot);		/* would not be returned by scan */
-
-		/* Flag for the next call that no more tuples */
-		estate->es_evTupleNull[scanrelid - 1] = true;
-
-		return slot;
-	}
 
 	/*
 	 * ok, now that we have what we need, fetch the next tuple.
@@ -140,6 +109,27 @@ IndexNext(IndexScanState *node)
 	return ExecClearTuple(slot);
 }
 
+/*
+ * IndexRecheck -- access method routine to recheck a tuple in EvalPlanQual
+ */
+static bool
+IndexRecheck(IndexScanState *node, TupleTableSlot *slot)
+{
+	ExprContext *econtext;
+
+	/*
+	 * extract necessary information from index scan node
+	 */
+	econtext = node->ss.ps.ps_ExprContext;
+
+	/* Does the tuple meet the indexqual condition? */
+	econtext->ecxt_scantuple = slot;
+
+	ResetExprContext(econtext);
+
+	return ExecQual(node->indexqualorig, econtext, false);
+}
+
 /* ----------------------------------------------------------------
  *		ExecIndexScan(node)
  * ----------------------------------------------------------------
@@ -153,10 +143,9 @@ ExecIndexScan(IndexScanState *node)
 	if (node->iss_NumRuntimeKeys != 0 && !node->iss_RuntimeKeysReady)
 		ExecReScan((PlanState *) node, NULL);
 
-	/*
-	 * use IndexNext as access method
-	 */
-	return ExecScan(&node->ss, (ExecScanAccessMtd) IndexNext);
+	return ExecScan(&node->ss,
+					(ExecScanAccessMtd) IndexNext,
+					(ExecScanRecheckMtd) IndexRecheck);
 }
 
 /* ----------------------------------------------------------------
@@ -172,15 +161,9 @@ ExecIndexScan(IndexScanState *node)
 void
 ExecIndexReScan(IndexScanState *node, ExprContext *exprCtxt)
 {
-	EState	   *estate;
 	ExprContext *econtext;
-	Index		scanrelid;
 
-	estate = node->ss.ps.state;
 	econtext = node->iss_RuntimeContext;		/* context for runtime keys */
-	scanrelid = ((IndexScan *) node->ss.ps.plan)->scan.scanrelid;
-
-	node->ss.ps.ps_TupFromTlist = false;
 
 	if (econtext)
 	{
@@ -216,16 +199,10 @@ ExecIndexReScan(IndexScanState *node, ExprContext *exprCtxt)
 								 node->iss_NumRuntimeKeys);
 	node->iss_RuntimeKeysReady = true;
 
-	/* If this is re-scanning of PlanQual ... */
-	if (estate->es_evTuple != NULL &&
-		estate->es_evTuple[scanrelid - 1] != NULL)
-	{
-		estate->es_evTupleNull[scanrelid - 1] = false;
-		return;
-	}
-
 	/* reset index scan */
 	index_rescan(node->iss_ScanDesc, node->iss_ScanKeys);
+
+	ExecScanReScan(&node->ss);
 }