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

1 files changed, 77 insertions, 0 deletions

diff --git a/src/include/executor/execPartition.h b/src/include/executor/execPartition.h
index 63c883093ea..b2daf24c41d 100644
--- a/src/include/executor/execPartition.h
+++ b/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 */