Support partition pruning at execution time

Existing partition pruning is only able to work at plan time, for query
quals that appear in the parsed query.  This is good but limiting, as
there can be parameters that appear later that can be usefully used to
further prune partitions.

This commit adds support for pruning subnodes of Append which cannot
possibly contain any matching tuples, during execution, by evaluating
Params to determine the minimum set of subnodes that can possibly match.
We support more than just simple Params in WHERE clauses. Support
additionally includes:

1. Parameterized Nested Loop Joins: The parameter from the outer side of the
   join can be used to determine the minimum set of inner side partitions to
   scan.

2. Initplans: Once an initplan has been executed we can then determine which
   partitions match the value from the initplan.

Partition pruning is performed in two ways.  When Params external to the plan
are found to match the partition key we attempt to prune away unneeded Append
subplans during the initialization of the executor.  This allows us to bypass
the initialization of non-matching subplans meaning they won't appear in the
EXPLAIN or EXPLAIN ANALYZE output.

For parameters whose value is only known during the actual execution
then the pruning of these subplans must wait.  Subplans which are
eliminated during this stage of pruning are still visible in the EXPLAIN
output.  In order to determine if pruning has actually taken place, the
EXPLAIN ANALYZE must be viewed.  If a certain Append subplan was never
executed due to the elimination of the partition then the execution
timing area will state "(never executed)".  Whereas, if, for example in
the case of parameterized nested loops, the number of loops stated in
the EXPLAIN ANALYZE output for certain subplans may appear lower than
others due to the subplan having been scanned fewer times.  This is due
to the list of matching subnodes having to be evaluated whenever a
parameter which was found to match the partition key changes.

This commit required some additional infrastructure that permits the
building of a data structure which is able to perform the translation of
the matching partition IDs, as returned by get_matching_partitions, into
the list index of a subpaths list, as exist in node types such as
Append, MergeAppend and ModifyTable.  This allows us to translate a list
of clauses into a Bitmapset of all the subpath indexes which must be
included to satisfy the clause list.

Author: David Rowley, based on an earlier effort by Beena Emerson
Reviewers: Amit Langote, Robert Haas, Amul Sul, Rajkumar Raghuwanshi,
Jesper Pedersen
Discussion: https://postgr.es/m/CAOG9ApE16ac-_VVZVvv0gePSgkg_BwYEV1NBqZFqDR2bBE0X0A@mail.gmail.com

src/include/executor/execPartition.h

@@ -17,6 +17,7 @@
 #include "nodes/execnodes.h"
 #include "nodes/parsenodes.h"
 #include "nodes/plannodes.h"
+#include "partitioning/partprune.h"
 
 /*-----------------------
  * PartitionDispatch - information about one partitioned table in a partition
@@ -108,6 +109,77 @@ typedef struct PartitionTupleRouting
 	TupleTableSlot *root_tuple_slot;
 } PartitionTupleRouting;
 
+/*-----------------------
+ * PartitionPruningData - Encapsulates all information required to support
+ * elimination of partitions in node types which support arbitrary Lists of
+ * subplans.  Information stored here allows the planner's partition pruning
+ * functions to be called and the return value of partition indexes translated
+ * into the subpath indexes of node types such as Append, thus allowing us to
+ * bypass certain subnodes when we have proofs that indicate that no tuple
+ * matching the 'pruning_steps' will be found within.
+ *
+ * subnode_map					An array containing the subnode index which
+ *								matches this partition index, or -1 if the
+ *								subnode has been pruned already.
+ * subpart_map					An array containing the offset into the
+ *								'partprunedata' array in PartitionPruning, or
+ *								-1 if there is no such element in that array.
+ * present_parts				A Bitmapset of the partition index that we have
+ *								subnodes mapped for.
+ * context						Contains the context details required to call
+ *								the partition pruning code.
+ * pruning_steps				Contains a list of PartitionPruneStep used to
+ *								perform the actual pruning.
+ * extparams					Contains paramids of external params found
+ *								matching partition keys in 'pruning_steps'.
+ * allparams					As 'extparams' but also including exec params.
+ *-----------------------
+ */
+typedef struct PartitionPruningData
+{
+	int		   *subnode_map;
+	int		   *subpart_map;
+	Bitmapset  *present_parts;
+	PartitionPruneContext context;
+	List	   *pruning_steps;
+	Bitmapset  *extparams;
+	Bitmapset  *allparams;
+} PartitionPruningData;
+
+/*-----------------------
+ * PartitionPruneState - State object required for executor nodes to perform
+ * partition pruning elimination of their subnodes.  This encapsulates a
+ * flattened hierarchy of PartitionPruningData structs and also stores all
+ * paramids which were found to match the partition keys of each partition.
+ * This struct can be attached to node types which support arbitrary Lists of
+ * subnodes containing partitions to allow subnodes to be eliminated due to
+ * the clauses being unable to match to any tuple that the subnode could
+ * possibly produce.
+ *
+ * partprunedata		Array of PartitionPruningData for the node's target
+ *						partitioned relation. First element contains the
+ *						details for the target partitioned table.
+ * num_partprunedata	Number of items in 'partprunedata' array.
+ * prune_context		A memory context which can be used to call the query
+ *						planner's partition prune functions.
+ * extparams			All PARAM_EXTERN paramids which were found to match a
+ *						partition key in each of the contained
+ *						PartitionPruningData structs.
+ * execparams			As above but for PARAM_EXEC.
+ * allparams			Union of 'extparams' and 'execparams', saved to avoid
+ *						recalculation.
+ *-----------------------
+ */
+typedef struct PartitionPruneState
+{
+	PartitionPruningData *partprunedata;
+	int			num_partprunedata;
+	MemoryContext prune_context;
+	Bitmapset  *extparams;
+	Bitmapset  *execparams;
+	Bitmapset  *allparams;
+} PartitionPruneState;
+
 extern PartitionTupleRouting *ExecSetupPartitionTupleRouting(ModifyTableState *mtstate,
 							   Relation rel);
 extern int ExecFindPartition(ResultRelInfo *resultRelInfo,
@@ -133,5 +205,10 @@ extern HeapTuple ConvertPartitionTupleSlot(TupleConversionMap *map,
 						  TupleTableSlot **p_my_slot);
 extern void ExecCleanupTupleRouting(ModifyTableState *mtstate,
 						PartitionTupleRouting *proute);
+extern PartitionPruneState *ExecSetupPartitionPruneState(PlanState *planstate,
+						  List *partitionpruneinfo);
+extern Bitmapset *ExecFindMatchingSubPlans(PartitionPruneState *prunestate);
+extern Bitmapset *ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate,
+								int nsubnodes);
 
 #endif							/* EXECPARTITION_H */

src/include/nodes/execnodes.h

@@ -1123,8 +1123,13 @@ typedef struct ModifyTableState
 /* ----------------
  *	 AppendState information
  *
- *		nplans			how many plans are in the array
- *		whichplan		which plan is being executed (0 .. n-1)
+ *		nplans				how many plans are in the array
+ *		whichplan			which plan is being executed (0 .. n-1), or a
+ *							special negative value. See nodeAppend.c.
+ *		pruningstate		details required to allow partitions to be
+ *							eliminated from the scan, or NULL if not possible.
+ *		valid_subplans		for runtime pruning, valid appendplans indexes to
+ *							scan.
  * ----------------
  */
 
@@ -1132,6 +1137,7 @@ struct AppendState;
 typedef struct AppendState AppendState;
 struct ParallelAppendState;
 typedef struct ParallelAppendState ParallelAppendState;
+struct PartitionPruneState;
 
 struct AppendState
 {
@@ -1141,6 +1147,8 @@ struct AppendState
 	int			as_whichplan;
 	ParallelAppendState *as_pstate; /* parallel coordination info */
 	Size		pstate_len;		/* size of parallel coordination info */
+	struct PartitionPruneState *as_prune_state;
+	Bitmapset  *as_valid_subplans;
 	bool		(*choose_next_subplan) (AppendState *);
 };
 

src/include/nodes/nodes.h

@@ -196,6 +196,7 @@ typedef enum NodeTag
 	T_PartitionPruneStep,
 	T_PartitionPruneStepOp,
 	T_PartitionPruneStepCombine,
+	T_PartitionPruneInfo,
 
 	/*
 	 * TAGS FOR EXPRESSION STATE NODES (execnodes.h)

src/include/nodes/plannodes.h

@@ -256,6 +256,11 @@ typedef struct Append
 	List	   *partitioned_rels;
 	List	   *appendplans;
 	int			first_partial_plan;
+
+	/*
+	 * Mapping details for run-time subplan pruning, one per partitioned_rels
+	 */
+	List	   *part_prune_infos;
 } Append;
 
 /* ----------------

src/include/nodes/primnodes.h

@@ -1581,4 +1581,27 @@ typedef struct PartitionPruneStepCombine
 	List	   *source_stepids;
 } PartitionPruneStepCombine;
 
+/*----------
+ * PartitionPruneInfo - Details required to allow the executor to prune
+ * partitions.
+ *
+ * Here we store mapping details to allow translation of a partitioned table's
+ * index into subnode indexes for node types which support arbitrary numbers
+ * of sub nodes, such as Append.
+ *----------
+ */
+typedef struct PartitionPruneInfo
+{
+	NodeTag		type;
+	Oid			reloid;			/* Oid of partition rel */
+	List	   *pruning_steps;	/* List of PartitionPruneStep */
+	Bitmapset  *present_parts;	/* Indexes of all partitions which subnodes
+								 * are present for. */
+	int			nparts;			/* The length of the following two arrays */
+	int		   *subnode_map;	/* subnode index by partition id, or -1 */
+	int		   *subpart_map;	/* subpart index by partition id, or -1 */
+	Bitmapset  *extparams;		/* All external paramids seen in prunesteps */
+	Bitmapset  *execparams;		/* All exec paramids seen in prunesteps */
+} PartitionPruneInfo;
+
 #endif							/* PRIMNODES_H */

src/include/optimizer/pathnode.h

@@ -64,7 +64,7 @@ extern BitmapOrPath *create_bitmap_or_path(PlannerInfo *root,
 					  List *bitmapquals);
 extern TidPath *create_tidscan_path(PlannerInfo *root, RelOptInfo *rel,
 					List *tidquals, Relids required_outer);
-extern AppendPath *create_append_path(RelOptInfo *rel,
+extern AppendPath *create_append_path(PlannerInfo *root, RelOptInfo *rel,
 				   List *subpaths, List *partial_subpaths,
 				   Relids required_outer,
 				   int parallel_workers, bool parallel_aware,

src/include/partitioning/partprune.h

@@ -37,9 +37,23 @@ typedef struct PartitionPruneContext
 
 	/* Partition boundary info */
 	PartitionBoundInfo boundinfo;
+
+	/*
+	 * Can be set when the context is used from the executor to allow params
+	 * found matching the partition key to be evaulated.
+	 */
+	PlanState  *planstate;
+
+	/*
+	 * Parameters that are safe to be used for partition pruning. execparams
+	 * are not safe to use until the executor is running.
+	 */
+	Bitmapset  *safeparams;
 } PartitionPruneContext;
 
 
+extern List *make_partition_pruneinfo(PlannerInfo *root, List *partition_rels,
+						 List *subpaths, List *prunequal);
 extern Relids prune_append_rel_partitions(RelOptInfo *rel);
 extern Bitmapset *get_matching_partitions(PartitionPruneContext *context,
 						List *pruning_steps);