Faster partition pruning

Add a new module backend/partitioning/partprune.c, implementing a more
sophisticated algorithm for partition pruning.  The new module uses each
partition's "boundinfo" for pruning instead of constraint exclusion,
based on an idea proposed by Robert Haas of a "pruning program": a list
of steps generated from the query quals which are run iteratively to
obtain a list of partitions that must be scanned in order to satisfy
those quals.

At present, this targets planner-time partition pruning, but there exist
further patches to apply partition pruning at execution time as well.

This commit also moves some definitions from include/catalog/partition.h
to a new file include/partitioning/partbounds.h, in an attempt to
rationalize partitioning related code.

Authors: Amit Langote, David Rowley, Dilip Kumar
Reviewers: Robert Haas, Kyotaro Horiguchi, Ashutosh Bapat, Jesper Pedersen.
Discussion: https://postgr.es/m/098b9c71-1915-1a2a-8d52-1a7a50ce79e8@lab.ntt.co.jp

src/include/nodes/primnodes.h

@@ -18,6 +18,7 @@
 #define PRIMNODES_H
 
 #include "access/attnum.h"
+#include "access/stratnum.h"
 #include "nodes/bitmapset.h"
 #include "nodes/pg_list.h"
 
@@ -1506,4 +1507,78 @@ typedef struct OnConflictExpr
 	List	   *exclRelTlist;	/* tlist of the EXCLUDED pseudo relation */
 } OnConflictExpr;
 
+
+/*
+ * Node types to represent a partition pruning step.
+ */
+
+/*
+ * The base Node type.  step_id is the global identifier of a given step
+ * within a given pruning context.
+ */
+typedef struct PartitionPruneStep
+{
+	NodeTag		type;
+	int			step_id;
+} PartitionPruneStep;
+
+/*----------
+ * PartitionPruneStepOp - Information to prune using a set of mutually AND'd
+ *							OpExpr clauses
+ *
+ * This contains information extracted from up to partnatts OpExpr clauses,
+ * where partnatts is the number of partition key columns.  'opstrategy' is the
+ * strategy of the operator in the clause matched to the last partition key.
+ * 'exprs' contains expressions which comprise the lookup key to be passed to
+ * the partition bound search function.  'cmpfns' contains the OIDs of
+ * comparison function used to compare aforementioned expressions with
+ * partition bounds.  Both 'exprs' and 'cmpfns' contain the same number of
+ * items up to partnatts items.
+ *
+ * Once we find the offset of a partition bound using the lookup key, we
+ * determine which partitions to include in the result based on the value of
+ * 'opstrategy'.  For example, if it were equality, we'd return just the
+ * partition that would contain that key or a set of partitions if the key
+ * didn't consist of all partitioning columns.  For non-equality strategies,
+ * we'd need to include other partitions as appropriate.
+ *
+ * 'nullkeys' is the set containing the offset of the partition keys (0 to
+ * partnatts - 1) that were matched to an IS NULL clause.  This is only
+ * considered for hash partitioning as we need to pass which keys are null
+ * to the hash partition bound search function.  It is never possible to
+ * have an expression be present in 'exprs' for a given partition key and
+ * the corresponding bit set in 'nullkeys'.
+ *----------
+ */
+typedef struct PartitionPruneStepOp
+{
+	PartitionPruneStep step;
+
+	StrategyNumber opstrategy;
+	List	   *exprs;
+	List	   *cmpfns;
+	Bitmapset  *nullkeys;
+} PartitionPruneStepOp;
+
+/*----------
+ * PartitionPruneStepCombine - Information to prune using a BoolExpr clause
+ *
+ * For BoolExpr clauses, we combine the set of partitions determined for each
+ * of its argument clauses.
+ *----------
+ */
+typedef enum PartitionPruneCombineOp
+{
+	PARTPRUNE_COMBINE_UNION,
+	PARTPRUNE_COMBINE_INTERSECT
+} PartitionPruneCombineOp;
+
+typedef struct PartitionPruneStepCombine
+{
+	PartitionPruneStep step;
+
+	PartitionPruneCombineOp combineOp;
+	List	   *source_stepids;
+} PartitionPruneStepCombine;
+
 #endif							/* PRIMNODES_H */