Restructure creation of run-time pruning steps.

Previously, gen_partprune_steps() always built executor pruning steps
using all suitable clauses, including those containing PARAM_EXEC
Params.  This meant that the pruning steps were only completely safe
for executor run-time (scan start) pruning.  To prune at executor
startup, we had to ignore the steps involving exec Params.  But this
doesn't really work in general, since there may be logic changes
needed as well --- for example, pruning according to the last operator's
btree strategy is the wrong thing if we're not applying that operator.
The rules embodied in gen_partprune_steps() and its minions are
sufficiently complicated that tracking their incremental effects in
other logic seems quite impractical.

Short of a complete redesign, the only safe fix seems to be to run
gen_partprune_steps() twice, once to create executor startup pruning
steps and then again for run-time pruning steps.  We can save a few
cycles however by noting during the first scan whether we rejected
any clauses because they involved exec Params --- if not, we don't
need to do the second scan.

In support of this, refactor the internal APIs in partprune.c to make
more use of passing information in the GeneratePruningStepsContext
struct, rather than as separate arguments.

This is, I hope, the last piece of our response to a bug report from
Alan Jackson.  Back-patch to v11 where this code came in.

Discussion: https://postgr.es/m/FAD28A83-AC73-489E-A058-2681FA31D648@tvsquared.com

1 files changed, 13 insertions, 11 deletions

diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 1cce7621c2..1241245566 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -1109,21 +1109,23 @@ typedef struct PartitionedRelPruneInfo
 {
 	NodeTag		type;
 	Index		rtindex;		/* RT index of partition rel for this level */
-	List	   *pruning_steps;	/* List of PartitionPruneStep, see below */
 	Bitmapset  *present_parts;	/* Indexes of all partitions which subplans or
-								 * subparts are present for. */
-	int			nparts;			/* Length of subplan_map[] and subpart_map[] */
-	int			nexprs;			/* Length of hasexecparam[] */
+								 * subparts are present for */
+	int			nparts;			/* Length of the following arrays: */
 	int		   *subplan_map;	/* subplan index by partition index, or -1 */
 	int		   *subpart_map;	/* subpart index by partition index, or -1 */
 	Oid		   *relid_map;		/* relation OID by partition index, or 0 */
-	bool	   *hasexecparam;	/* true if corresponding pruning_step contains
-								 * any PARAM_EXEC Params. */
-	bool		do_initial_prune;	/* true if pruning should be performed
-									 * during executor startup. */
-	bool		do_exec_prune;	/* true if pruning should be performed during
-								 * executor run. */
-	Bitmapset  *execparamids;	/* All PARAM_EXEC Param IDs in pruning_steps */
+
+	/*
+	 * initial_pruning_steps shows how to prune during executor startup (i.e.,
+	 * without use of any PARAM_EXEC Params); it is NIL if no startup pruning
+	 * is required.  exec_pruning_steps shows how to prune with PARAM_EXEC
+	 * Params; it is NIL if no per-scan pruning is required.
+	 */
+	List	   *initial_pruning_steps;	/* List of PartitionPruneStep */
+	List	   *exec_pruning_steps; /* List of PartitionPruneStep */
+	Bitmapset  *execparamids;	/* All PARAM_EXEC Param IDs in
+								 * exec_pruning_steps */
 } PartitionedRelPruneInfo;
 
 /*