1 files changed, 351 insertions, 0 deletions
diff --git a/src/backend/executor/nodeCtescan.c b/src/backend/executor/nodeCtescan.c
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+++ b/src/backend/executor/nodeCtescan.c
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+/*-------------------------------------------------------------------------
+ *
+ * nodeCtescan.c
+ *	  routines to handle CteScan nodes.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/executor/nodeCtescan.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "executor/execdebug.h"
+#include "executor/nodeCtescan.h"
+#include "miscadmin.h"
+
+static TupleTableSlot *CteScanNext(CteScanState *node);
+
+/* ----------------------------------------------------------------
+ *		CteScanNext
+ *
+ *		This is a workhorse for ExecCteScan
+ * ----------------------------------------------------------------
+ */
+static TupleTableSlot *
+CteScanNext(CteScanState *node)
+{
+	EState	   *estate;
+	ScanDirection dir;
+	bool		forward;
+	Tuplestorestate *tuplestorestate;
+	bool		eof_tuplestore;
+	TupleTableSlot *slot;
+
+	/*
+	 * get state info from node
+	 */
+	estate = node->ss.ps.state;
+	dir = estate->es_direction;
+	forward = ScanDirectionIsForward(dir);
+	tuplestorestate = node->leader->cte_table;
+	tuplestore_select_read_pointer(tuplestorestate, node->readptr);
+	slot = node->ss.ss_ScanTupleSlot;
+
+	/*
+	 * If we are not at the end of the tuplestore, or are going backwards, try
+	 * to fetch a tuple from tuplestore.
+	 */
+	eof_tuplestore = tuplestore_ateof(tuplestorestate);
+
+	if (!forward && eof_tuplestore)
+	{
+		if (!node->leader->eof_cte)
+		{
+			/*
+			 * When reversing direction at tuplestore EOF, the first
+			 * gettupleslot call will fetch the last-added tuple; but we want
+			 * to return the one before that, if possible. So do an extra
+			 * fetch.
+			 */
+			if (!tuplestore_advance(tuplestorestate, forward))
+				return NULL;	/* the tuplestore must be empty */
+		}
+		eof_tuplestore = false;
+	}
+
+	/*
+	 * If we can fetch another tuple from the tuplestore, return it.
+	 *
+	 * Note: we have to use copy=true in the tuplestore_gettupleslot call,
+	 * because we are sharing the tuplestore with other nodes that might write
+	 * into the tuplestore before we get called again.
+	 */
+	if (!eof_tuplestore)
+	{
+		if (tuplestore_gettupleslot(tuplestorestate, forward, true, slot))
+			return slot;
+		if (forward)
+			eof_tuplestore = true;
+	}
+
+	/*
+	 * If necessary, try to fetch another row from the CTE query.
+	 *
+	 * Note: the eof_cte state variable exists to short-circuit further calls
+	 * of the CTE plan.  It's not optional, unfortunately, because some plan
+	 * node types are not robust about being called again when they've already
+	 * returned NULL.
+	 */
+	if (eof_tuplestore && !node->leader->eof_cte)
+	{
+		TupleTableSlot *cteslot;
+
+		/*
+		 * We can only get here with forward==true, so no need to worry about
+		 * which direction the subplan will go.
+		 */
+		cteslot = ExecProcNode(node->cteplanstate);
+		if (TupIsNull(cteslot))
+		{
+			node->leader->eof_cte = true;
+			return NULL;
+		}
+
+		/*
+		 * There are corner cases where the subplan could change which
+		 * tuplestore read pointer is active, so be sure to reselect ours
+		 * before storing the tuple we got.
+		 */
+		tuplestore_select_read_pointer(tuplestorestate, node->readptr);
+
+		/*
+		 * Append a copy of the returned tuple to tuplestore.  NOTE: because
+		 * our read pointer is certainly in EOF state, its read position will
+		 * move forward over the added tuple.  This is what we want.  Also,
+		 * any other readers will *not* move past the new tuple, which is what
+		 * they want.
+		 */
+		tuplestore_puttupleslot(tuplestorestate, cteslot);
+
+		/*
+		 * We MUST copy the CTE query's output tuple into our own slot. This
+		 * is because other CteScan nodes might advance the CTE query before
+		 * we are called again, and our output tuple must stay stable over
+		 * that.
+		 */
+		return ExecCopySlot(slot, cteslot);
+	}
+
+	/*
+	 * Nothing left ...
+	 */
+	return ExecClearTuple(slot);
+}
+
+/*
+ * CteScanRecheck -- access method routine to recheck a tuple in EvalPlanQual
+ */
+static bool
+CteScanRecheck(CteScanState *node, TupleTableSlot *slot)
+{
+	/* nothing to check */
+	return true;
+}
+
+/* ----------------------------------------------------------------
+ *		ExecCteScan(node)
+ *
+ *		Scans the CTE sequentially and returns the next qualifying tuple.
+ *		We call the ExecScan() routine and pass it the appropriate
+ *		access method functions.
+ * ----------------------------------------------------------------
+ */
+static TupleTableSlot *
+ExecCteScan(PlanState *pstate)
+{
+	CteScanState *node = castNode(CteScanState, pstate);
+
+	return ExecScan(&node->ss,
+					(ExecScanAccessMtd) CteScanNext,
+					(ExecScanRecheckMtd) CteScanRecheck);
+}
+
+
+/* ----------------------------------------------------------------
+ *		ExecInitCteScan
+ * ----------------------------------------------------------------
+ */
+CteScanState *
+ExecInitCteScan(CteScan *node, EState *estate, int eflags)
+{
+	CteScanState *scanstate;
+	ParamExecData *prmdata;
+
+	/* check for unsupported flags */
+	Assert(!(eflags & EXEC_FLAG_MARK));
+
+	/*
+	 * For the moment we have to force the tuplestore to allow REWIND, because
+	 * we might be asked to rescan the CTE even though upper levels didn't
+	 * tell us to be prepared to do it efficiently.  Annoying, since this
+	 * prevents truncation of the tuplestore.  XXX FIXME
+	 *
+	 * Note: if we are in an EPQ recheck plan tree, it's likely that no access
+	 * to the tuplestore is needed at all, making this even more annoying.
+	 * It's not worth improving that as long as all the read pointers would
+	 * have REWIND anyway, but if we ever improve this logic then that aspect
+	 * should be considered too.
+	 */
+	eflags |= EXEC_FLAG_REWIND;
+
+	/*
+	 * CteScan should not have any children.
+	 */
+	Assert(outerPlan(node) == NULL);
+	Assert(innerPlan(node) == NULL);
+
+	/*
+	 * create new CteScanState for node
+	 */
+	scanstate = makeNode(CteScanState);
+	scanstate->ss.ps.plan = (Plan *) node;
+	scanstate->ss.ps.state = estate;
+	scanstate->ss.ps.ExecProcNode = ExecCteScan;
+	scanstate->eflags = eflags;
+	scanstate->cte_table = NULL;
+	scanstate->eof_cte = false;
+
+	/*
+	 * Find the already-initialized plan for the CTE query.
+	 */
+	scanstate->cteplanstate = (PlanState *) list_nth(estate->es_subplanstates,
+													 node->ctePlanId - 1);
+
+	/*
+	 * The Param slot associated with the CTE query is used to hold a pointer
+	 * to the CteState of the first CteScan node that initializes for this
+	 * CTE.  This node will be the one that holds the shared state for all the
+	 * CTEs, particularly the shared tuplestore.
+	 */
+	prmdata = &(estate->es_param_exec_vals[node->cteParam]);
+	Assert(prmdata->execPlan == NULL);
+	Assert(!prmdata->isnull);
+	scanstate->leader = castNode(CteScanState, DatumGetPointer(prmdata->value));
+	if (scanstate->leader == NULL)
+	{
+		/* I am the leader */
+		prmdata->value = PointerGetDatum(scanstate);
+		scanstate->leader = scanstate;
+		scanstate->cte_table = tuplestore_begin_heap(true, false, work_mem);
+		tuplestore_set_eflags(scanstate->cte_table, scanstate->eflags);
+		scanstate->readptr = 0;
+	}
+	else
+	{
+		/* Not the leader */
+		/* Create my own read pointer, and ensure it is at start */
+		scanstate->readptr =
+			tuplestore_alloc_read_pointer(scanstate->leader->cte_table,
+										  scanstate->eflags);
+		tuplestore_select_read_pointer(scanstate->leader->cte_table,
+									   scanstate->readptr);
+		tuplestore_rescan(scanstate->leader->cte_table);
+	}
+
+	/*
+	 * Miscellaneous initialization
+	 *
+	 * create expression context for node
+	 */
+	ExecAssignExprContext(estate, &scanstate->ss.ps);
+
+	/*
+	 * The scan tuple type (ie, the rowtype we expect to find in the work
+	 * table) is the same as the result rowtype of the CTE query.
+	 */
+	ExecInitScanTupleSlot(estate, &scanstate->ss,
+						  ExecGetResultType(scanstate->cteplanstate),
+						  &TTSOpsMinimalTuple);
+
+	/*
+	 * Initialize result type and projection.
+	 */
+	ExecInitResultTypeTL(&scanstate->ss.ps);
+	ExecAssignScanProjectionInfo(&scanstate->ss);
+
+	/*
+	 * initialize child expressions
+	 */
+	scanstate->ss.ps.qual =
+		ExecInitQual(node->scan.plan.qual, (PlanState *) scanstate);
+
+	return scanstate;
+}
+
+/* ----------------------------------------------------------------
+ *		ExecEndCteScan
+ *
+ *		frees any storage allocated through C routines.
+ * ----------------------------------------------------------------
+ */
+void
+ExecEndCteScan(CteScanState *node)
+{
+	/*
+	 * Free exprcontext
+	 */
+	ExecFreeExprContext(&node->ss.ps);
+
+	/*
+	 * clean out the tuple table
+	 */
+	if (node->ss.ps.ps_ResultTupleSlot)
+		ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);
+	ExecClearTuple(node->ss.ss_ScanTupleSlot);
+
+	/*
+	 * If I am the leader, free the tuplestore.
+	 */
+	if (node->leader == node)
+	{
+		tuplestore_end(node->cte_table);
+		node->cte_table = NULL;
+	}
+}
+
+/* ----------------------------------------------------------------
+ *		ExecReScanCteScan
+ *
+ *		Rescans the relation.
+ * ----------------------------------------------------------------
+ */
+void
+ExecReScanCteScan(CteScanState *node)
+{
+	Tuplestorestate *tuplestorestate = node->leader->cte_table;
+
+	if (node->ss.ps.ps_ResultTupleSlot)
+		ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);
+
+	ExecScanReScan(&node->ss);
+
+	/*
+	 * Clear the tuplestore if a new scan of the underlying CTE is required.
+	 * This implicitly resets all the tuplestore's read pointers.  Note that
+	 * multiple CTE nodes might redundantly clear the tuplestore; that's OK,
+	 * and not unduly expensive.  We'll stop taking this path as soon as
+	 * somebody has attempted to read something from the underlying CTE
+	 * (thereby causing its chgParam to be cleared).
+	 */
+	if (node->leader->cteplanstate->chgParam != NULL)
+	{
+		tuplestore_clear(tuplestorestate);
+		node->leader->eof_cte = false;
+	}
+	else
+	{
+		/*
+		 * Else, just rewind my own pointer.  Either the underlying CTE
+		 * doesn't need a rescan (and we can re-read what's in the tuplestore
+		 * now), or somebody else already took care of it.
+		 */
+		tuplestore_select_read_pointer(tuplestorestate, node->readptr);
+		tuplestore_rescan(tuplestorestate);
+	}
+}