Assorted cosmetic cleanup of run-time-partition-pruning code.

Use "subplan" rather than "subnode" to refer to the child plans of
a partitioning Append; this seems a bit more specific and hence
clearer.  Improve assorted comments.  No non-cosmetic changes.

David Rowley and Tom Lane

Discussion: https://postgr.es/m/CAFj8pRBjrufA3ocDm8o4LPGNye9Y+pm1b9kCwode4X04CULG3g@mail.gmail.com

Author: tglsfdc

src/backend/executor/execPartition.c

@@ -1334,9 +1334,9 @@ adjust_partition_tlist(List *tlist, TupleConversionMap *map)
  * Run-Time Partition Pruning Support.
  *
  * The following series of functions exist to support the removal of unneeded
- * subnodes for queries against partitioned tables.  The supporting functions
- * here are designed to work with any node type which supports an arbitrary
- * number of subnodes, e.g. Append, MergeAppend.
+ * subplans for queries against partitioned tables.  The supporting functions
+ * here are designed to work with any plan type which supports an arbitrary
+ * number of subplans, e.g. Append, MergeAppend.
  *
  * When pruning involves comparison of a partition key to a constant, it's
  * done by the planner.  However, if we have a comparison to a non-constant
@@ -1346,85 +1346,83 @@ adjust_partition_tlist(List *tlist, TupleConversionMap *map)
  *
  * We must distinguish expressions containing PARAM_EXEC Params from
  * expressions that don't contain those.  Even though a PARAM_EXEC Param is
- * considered to be a stable expression, it can change value from one node
- * scan to the next during query execution.  Stable comparison expressions
- * that don't involve such Params allow partition pruning to be done once
- * during executor startup.  Expressions that do involve such Params require
- * us to prune separately for each scan of the parent plan node.
+ * considered to be a stable expression, it can change value from one plan
+ * node scan to the next during query execution.  Stable comparison
+ * expressions that don't involve such Params allow partition pruning to be
+ * done once during executor startup.  Expressions that do involve such Params
+ * require us to prune separately for each scan of the parent plan node.
  *
- * Note that pruning away unneeded subnodes during executor startup has the
- * added benefit of not having to initialize the unneeded subnodes at all.
+ * Note that pruning away unneeded subplans during executor startup has the
+ * added benefit of not having to initialize the unneeded subplans at all.
  *
  *
  * Functions:
  *
  * ExecSetupPartitionPruneState:
- *		This must be called by nodes before any partition pruning is
- *		attempted.  Normally executor startup is a good time. This function
- *		creates the PartitionPruneState details which are required by each
- *		of the two pruning functions, details include information about
- *		how to map the partition index details which are returned by the
- *		planner's partition prune function into subnode indexes.
+ *		Creates the PartitionPruneState required by each of the two pruning
+ *		functions.  Details stored include how to map the partition index
+ *		returned by the partition pruning code into subplan indexes.
  *
  * ExecFindInitialMatchingSubPlans:
- *		Returns indexes of matching subnodes.  Partition pruning is attempted
+ *		Returns indexes of matching subplans.  Partition pruning is attempted
  *		without any evaluation of expressions containing PARAM_EXEC Params.
- *		This function must be called during executor startup for the given
- *		node before the subnodes themselves are initialized.  Subnodes which
- *		are found not to match by this function must not be included in the
- *		node's list of subnodes as this function performs a remap of the
- *		partition index to subplan index map and the newly created map
- *		provides indexes only for subnodes which remain after calling this
- *		function.
+ *		This function must be called during executor startup for the parent
+ *		plan before the subplans themselves are initialized.  Subplans which
+ *		are found not to match by this function must be removed from the
+ *		plan's list of subplans during execution, as this function performs a
+ *		remap of the partition index to subplan index map and the newly
+ *		created map provides indexes only for subplans which remain after
+ *		calling this function.
  *
  * ExecFindMatchingSubPlans:
- *		Returns indexes of matching subnodes after evaluating all available
- *		expressions.  This function can only be called while the executor is
- *		running.
+ *		Returns indexes of matching subplans after evaluating all available
+ *		expressions.  This function can only be called during execution and
+ *		must be called again each time the value of a Param listed in
+ *		PartitionPruneState's 'execparamids' changes.
  *-------------------------------------------------------------------------
  */
 
 /*
  * ExecSetupPartitionPruneState
- *		Setup the required data structure which is required for calling
+ *		Set up the data structure required for calling
  *		ExecFindInitialMatchingSubPlans and ExecFindMatchingSubPlans.
  *
+ * 'planstate' is the parent plan node's execution state.
+ *
  * 'partitionpruneinfo' is a List of PartitionPruneInfos as generated by
- * make_partition_pruneinfo.  Here we build a PartitionPruneContext for each
- * item in the List.  These contexts can be re-used each time we re-evaulate
- * which partitions match the pruning steps provided in each
- * PartitionPruneInfo.
+ * make_partition_pruneinfo.  Here we build a PartitionPruneState containing a
+ * PartitionPruningData for each item in that List.  This data can be re-used
+ * each time we re-evaluate which partitions match the pruning steps provided
+ * in each PartitionPruneInfo.
  */
 PartitionPruneState *
 ExecSetupPartitionPruneState(PlanState *planstate, List *partitionpruneinfo)
 {
-	PartitionPruningData *prunedata;
 	PartitionPruneState *prunestate;
+	PartitionPruningData *prunedata;
 	ListCell   *lc;
 	int			i;
 
 	Assert(partitionpruneinfo != NIL);
 
+	/*
+	 * Allocate the data structure
+	 */
 	prunestate = (PartitionPruneState *) palloc(sizeof(PartitionPruneState));
 	prunedata = (PartitionPruningData *)
 		palloc(sizeof(PartitionPruningData) * list_length(partitionpruneinfo));
 
-	/*
-	 * The first item in the array contains the details for the query's target
-	 * partition, so record that as the root of the partition hierarchy.
-	 */
 	prunestate->partprunedata = prunedata;
 	prunestate->num_partprunedata = list_length(partitionpruneinfo);
 	prunestate->do_initial_prune = false;	/* may be set below */
 	prunestate->do_exec_prune = false;	/* may be set below */
 	prunestate->execparamids = NULL;
 
 	/*
-	 * Create a sub memory context which we'll use when making calls to the
-	 * query planner's function to determine which partitions will match.  The
-	 * planner is not too careful about freeing memory, so we'll ensure we
-	 * call the function in this context to avoid any memory leaking in the
-	 * executor's memory context.
+	 * Create a short-term memory context which we'll use when making calls to
+	 * the partition pruning functions.  This avoids possible memory leaks,
+	 * since the pruning functions call comparison functions that aren't under
+	 * our control.
 	 */
 	prunestate->prune_context =
 		AllocSetContextCreate(CurrentMemoryContext,
@@ -1448,8 +1446,8 @@ ExecSetupPartitionPruneState(PlanState *planstate, List *partitionpruneinfo)
 		 * We must make a copy of this rather than pointing directly to the
 		 * plan's version as we may end up making modifications to it later.
 		 */
-		pprune->subnode_map = palloc(sizeof(int) * pinfo->nparts);
-		memcpy(pprune->subnode_map, pinfo->subnode_map,
+		pprune->subplan_map = palloc(sizeof(int) * pinfo->nparts);
+		memcpy(pprune->subplan_map, pinfo->subplan_map,
 			   sizeof(int) * pinfo->nparts);
 
 		/* We can use the subpart_map verbatim, since we never modify it */
@@ -1525,7 +1523,7 @@ ExecSetupPartitionPruneState(PlanState *planstate, List *partitionpruneinfo)
 
 		/*
 		 * Accumulate the IDs of all PARAM_EXEC Params affecting the
-		 * partitioning decisions at this node.
+		 * partitioning decisions at this plan node.
 		 */
 		prunestate->execparamids = bms_add_members(prunestate->execparamids,
 												   pinfo->execparamids);
@@ -1540,22 +1538,19 @@ ExecSetupPartitionPruneState(PlanState *planstate, List *partitionpruneinfo)
 
 /*
  * ExecFindInitialMatchingSubPlans
- *		Determine which subset of subplan nodes we need to initialize based
- *		on the details stored in 'prunestate'.  Here we only determine the
- *		matching partitions using values known during plan startup, which
- *		excludes any expressions containing PARAM_EXEC Params.
+ *		Identify the set of subplans that cannot be eliminated by initial
+ *		pruning (disregarding any pruning constraints involving PARAM_EXEC
+ *		Params).  Also re-map the translation matrix which allows conversion
+ *		of partition indexes into subplan indexes to account for the unneeded
+ *		subplans having been removed.
  *
- * It is expected that callers of this function do so only once during their
- * init plan.  The caller must only initialize the subnodes which are returned
- * by this function. The remaining subnodes should be discarded.  Once this
- * function has been called, future calls to ExecFindMatchingSubPlans will
- * return its matching subnode indexes assuming that the caller discarded
- * the original non-matching subnodes.
+ * Must only be called once per 'prunestate', and only if initial pruning
+ * is required.
  *
- * 'nsubnodes' must be passed as the total number of unpruned subnodes.
+ * 'nsubplans' must be passed as the total number of unpruned subplans.
  */
 Bitmapset *
-ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate, int nsubnodes)
+ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate, int nsubplans)
 {
 	PartitionPruningData *pprune;
 	MemoryContext oldcontext;
@@ -1584,33 +1579,33 @@ ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate, int nsubnodes)
 	ResetExprContext(pprune->context.planstate->ps_ExprContext);
 
 	/*
-	 * If any subnodes were pruned, we must re-sequence the subnode indexes so
+	 * If any subplans were pruned, we must re-sequence the subplan indexes so
 	 * that ExecFindMatchingSubPlans properly returns the indexes from the
-	 * subnodes which will remain after execution of this function.
+	 * subplans which will remain after execution of this function.
 	 */
-	if (bms_num_members(result) < nsubnodes)
+	if (bms_num_members(result) < nsubplans)
 	{
-		int		   *new_subnode_indexes;
+		int		   *new_subplan_indexes;
 		int			i;
 		int			newidx;
 
 		/*
 		 * First we must build an array which we can use to adjust the
-		 * existing subnode_map so that it contains the new subnode indexes.
+		 * existing subplan_map so that it contains the new subplan indexes.
 		 */
-		new_subnode_indexes = (int *) palloc(sizeof(int) * nsubnodes);
+		new_subplan_indexes = (int *) palloc(sizeof(int) * nsubplans);
 		newidx = 0;
-		for (i = 0; i < nsubnodes; i++)
+		for (i = 0; i < nsubplans; i++)
 		{
 			if (bms_is_member(i, result))
-				new_subnode_indexes[i] = newidx++;
+				new_subplan_indexes[i] = newidx++;
 			else
-				new_subnode_indexes[i] = -1;	/* Newly pruned */
+				new_subplan_indexes[i] = -1;	/* Newly pruned */
 		}
 
 		/*
-		 * Now we can re-sequence each PartitionPruneInfo's subnode_map so
-		 * that they point to the new index of the subnode.
+		 * Now we can re-sequence each PartitionPruneInfo's subplan_map so
+		 * that they point to the new index of the subplan.
 		 */
 		for (i = 0; i < prunestate->num_partprunedata; i++)
 		{
@@ -1622,7 +1617,7 @@ ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate, int nsubnodes)
 
 			/*
 			 * We also need to reset the present_parts field so that it only
-			 * contains partition indexes that we actually still have subnodes
+			 * contains partition indexes that we actually still have subplans
 			 * for.  It seems easier to build a fresh one, rather than trying
 			 * to update the existing one.
 			 */
@@ -1631,20 +1626,20 @@ ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate, int nsubnodes)
 
 			for (j = 0; j < nparts; j++)
 			{
-				int			oldidx = pprune->subnode_map[j];
+				int			oldidx = pprune->subplan_map[j];
 
 				/*
-				 * If this partition existed as a subnode then change the old
-				 * subnode index to the new subnode index.  The new index may
+				 * If this partition existed as a subplan then change the old
+				 * subplan index to the new subplan index.  The new index may
 				 * become -1 if the partition was pruned above, or it may just
-				 * come earlier in the subnode list due to some subnodes being
+				 * come earlier in the subplan list due to some subplans being
 				 * removed earlier in the list.
 				 */
 				if (oldidx >= 0)
 				{
-					pprune->subnode_map[j] = new_subnode_indexes[oldidx];
+					pprune->subplan_map[j] = new_subplan_indexes[oldidx];
 
-					if (new_subnode_indexes[oldidx] >= 0)
+					if (new_subplan_indexes[oldidx] >= 0)
 						pprune->present_parts =
 							bms_add_member(pprune->present_parts, j);
 				}
@@ -1686,7 +1681,7 @@ ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate, int nsubnodes)
 			}
 		}
 
-		pfree(new_subnode_indexes);
+		pfree(new_subplan_indexes);
 	}
 
 	return result;
@@ -1695,7 +1690,7 @@ ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate, int nsubnodes)
 /*
  * ExecFindMatchingSubPlans
  *		Determine which subplans match the pruning steps detailed in
- *		'pprune' for the current comparison expression values.
+ *		'prunestate' for the current comparison expression values.
  *
  * Here we assume we may evaluate PARAM_EXEC Params.
  */
@@ -1767,28 +1762,24 @@ find_matching_subplans_recurse(PartitionPruneState *prunestate,
 		partset = pprune->present_parts;
 	}
 
-	/* Translate partset into subnode indexes */
+	/* Translate partset into subplan indexes */
 	i = -1;
 	while ((i = bms_next_member(partset, i)) >= 0)
 	{
-		if (pprune->subnode_map[i] >= 0)
+		if (pprune->subplan_map[i] >= 0)
 			*validsubplans = bms_add_member(*validsubplans,
-											pprune->subnode_map[i]);
+											pprune->subplan_map[i]);
 		else
 		{
 			int			partidx = pprune->subpart_map[i];
 
-			if (partidx != -1)
+			if (partidx >= 0)
 				find_matching_subplans_recurse(prunestate,
 											   &prunestate->partprunedata[partidx],
 											   initial_prune, validsubplans);
 			else
 			{
-				/*
-				 * This could only happen if clauses used in planning where
-				 * more restrictive than those used here, or if the maps are
-				 * somehow corrupt.
-				 */
+				/* Shouldn't happen */
 				elog(ERROR, "partition missing from subplans");
 			}
 		}

src/backend/nodes/copyfuncs.c

@@ -1186,7 +1186,7 @@ _copyPartitionPruneInfo(const PartitionPruneInfo *from)
 	COPY_BITMAPSET_FIELD(present_parts);
 	COPY_SCALAR_FIELD(nparts);
 	COPY_SCALAR_FIELD(nexprs);
-	COPY_POINTER_FIELD(subnode_map, from->nparts * sizeof(int));
+	COPY_POINTER_FIELD(subplan_map, from->nparts * sizeof(int));
 	COPY_POINTER_FIELD(subpart_map, from->nparts * sizeof(int));
 	COPY_POINTER_FIELD(hasexecparam, from->nexprs * sizeof(bool));
 	COPY_SCALAR_FIELD(do_initial_prune);

src/backend/nodes/outfuncs.c

@@ -1023,9 +1023,9 @@ _outPartitionPruneInfo(StringInfo str, const PartitionPruneInfo *node)
 	WRITE_INT_FIELD(nparts);
 	WRITE_INT_FIELD(nexprs);
 
-	appendStringInfoString(str, " :subnode_map");
+	appendStringInfoString(str, " :subplan_map");
 	for (i = 0; i < node->nparts; i++)
-		appendStringInfo(str, " %d", node->subnode_map[i]);
+		appendStringInfo(str, " %d", node->subplan_map[i]);
 
 	appendStringInfoString(str, " :subpart_map");
 	for (i = 0; i < node->nparts; i++)

src/backend/nodes/readfuncs.c

@@ -2333,7 +2333,7 @@ _readPartitionPruneInfo(void)
 	READ_BITMAPSET_FIELD(present_parts);
 	READ_INT_FIELD(nparts);
 	READ_INT_FIELD(nexprs);
-	READ_INT_ARRAY(subnode_map, local_node->nparts);
+	READ_INT_ARRAY(subplan_map, local_node->nparts);
 	READ_INT_ARRAY(subpart_map, local_node->nparts);
 	READ_BOOL_ARRAY(hasexecparam, local_node->nexprs);
 	READ_BOOL_FIELD(do_initial_prune);