Refactor and cleanup runtime partition prune code a little

* Move the execution pruning initialization steps that are common
between both ExecInitAppend() and ExecInitMergeAppend() into a new
function ExecInitPartitionPruning() defined in execPartition.c.
Those steps include creation of a PartitionPruneState to be used for
all instances of pruning and determining the minimal set of child
subplans that need to be initialized by performing initial pruning if
needed, and finally adjusting the subplan_map arrays in the
PartitionPruneState to reflect the new set of subplans remaining
after initial pruning if it was indeed performed.
ExecCreatePartitionPruneState() is no longer exported out of
execPartition.c and has been renamed to CreatePartitionPruneState()
as a local sub-routine of ExecInitPartitionPruning().

* Likewise, ExecFindInitialMatchingSubPlans() that was in charge of
performing initial pruning no longer needs to be exported.  In fact,
since it would now have the same body as the more generally named
ExecFindMatchingSubPlans(), except differing in the value of
initial_prune passed to the common subroutine
find_matching_subplans_recurse(), it seems better to remove it and add
an initial_prune argument to ExecFindMatchingSubPlans().

* Add an ExprContext field to PartitionPruneContext to remove the
implicit assumption in the runtime pruning code that the ExprContext to
use to compute pruning expressions that need one can always rely on the
PlanState providing it.  A future patch will allow runtime pruning (at
least the initial pruning steps) to be performed without the
corresponding PlanState yet having been created, so this will help.

Author: Amit Langote <[email protected]>
Discussion: https://postgr.es/m/CA+HiwqEYCpEqh2LMDOp9mT+4-QoVe8HgFMKBjntEMCTZLpcCCA@mail.gmail.com

1 files changed, 15 insertions, 9 deletions

diff --git a/src/backend/partitioning/partprune.c b/src/backend/partitioning/partprune.c
index 1bc00826c10..9d3c05aed3b 100644
--- a/src/backend/partitioning/partprune.c
+++ b/src/backend/partitioning/partprune.c
@@ -798,6 +798,7 @@ prune_append_rel_partitions(RelOptInfo *rel)
 
 	/* These are not valid when being called from the planner */
 	context.planstate = NULL;
+	context.exprcontext = NULL;
 	context.exprstates = NULL;
 
 	/* Actual pruning happens here. */
@@ -808,8 +809,8 @@ prune_append_rel_partitions(RelOptInfo *rel)
  * get_matching_partitions
  *		Determine partitions that survive partition pruning
  *
- * Note: context->planstate must be set to a valid PlanState when the
- * pruning_steps were generated with a target other than PARTTARGET_PLANNER.
+ * Note: context->exprcontext must be valid when the pruning_steps were
+ * generated with a target other than PARTTARGET_PLANNER.
  *
  * Returns a Bitmapset of the RelOptInfo->part_rels indexes of the surviving
  * partitions.
@@ -3654,9 +3655,9 @@ match_boolean_partition_clause(Oid partopfamily, Expr *clause, Expr *partkey,
  * exprstate array.
  *
  * Note that the evaluated result may be in the per-tuple memory context of
- * context->planstate->ps_ExprContext, and we may have leaked other memory
- * there too.  This memory must be recovered by resetting that ExprContext
- * after we're done with the pruning operation (see execPartition.c).
+ * context->exprcontext, and we may have leaked other memory there too.
+ * This memory must be recovered by resetting that ExprContext after
+ * we're done with the pruning operation (see execPartition.c).
  */
 static void
 partkey_datum_from_expr(PartitionPruneContext *context,
@@ -3677,13 +3678,18 @@ partkey_datum_from_expr(PartitionPruneContext *context,
 		ExprContext *ectx;
 
 		/*
-		 * We should never see a non-Const in a step unless we're running in
-		 * the executor.
+		 * We should never see a non-Const in a step unless the caller has
+		 * passed a valid ExprContext.
+		 *
+		 * When context->planstate is valid, context->exprcontext is same as
+		 * context->planstate->ps_ExprContext.
 		 */
-		Assert(context->planstate != NULL);
+		Assert(context->planstate != NULL || context->exprcontext != NULL);
+		Assert(context->planstate == NULL ||
+			   (context->exprcontext == context->planstate->ps_ExprContext));
 
 		exprstate = context->exprstates[stateidx];
-		ectx = context->planstate->ps_ExprContext;
+		ectx = context->exprcontext;
 		*value = ExecEvalExprSwitchContext(exprstate, ectx, isnull);
 	}
 }