Improve run-time partition pruning to handle any stable expression.

The initial coding of the run-time-pruning feature only coped with cases
where the partition key(s) are compared to Params.  That is a bit silly;
we can allow it to work with any non-Var-containing stable expression, as
long as we take special care with expressions containing PARAM_EXEC Params.
The code is hardly any longer this way, and it's considerably clearer
(IMO at least).  Per gripe from Pavel Stehule.

David Rowley, whacked around a bit by me

Discussion: https://postgr.es/m/CAFj8pRBjrufA3ocDm8o4LPGNye9Y+pm1b9kCwode4X04CULG3g@mail.gmail.com

1 files changed, 12 insertions, 8 deletions

diff --git a/src/include/partitioning/partprune.h b/src/include/partitioning/partprune.h
index 3d114b4c71f..e3b3bfb7c11 100644
--- a/src/include/partitioning/partprune.h
+++ b/src/include/partitioning/partprune.h
@@ -40,23 +40,27 @@ typedef struct PartitionPruneContext
 	PartitionBoundInfo boundinfo;
 
 	/*
-	 * Can be set when the context is used from the executor to allow params
-	 * found matching the partition key to be evaluated.
+	 * This will be set when the context is used from the executor, to allow
+	 * Params to be evaluated.
 	 */
 	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;
-
-	/*
 	 * Array of ExprStates, indexed as per PruneCtxStateIdx; one for each
 	 * partkey in each pruning step.  Allocated if planstate is non-NULL,
 	 * otherwise NULL.
 	 */
 	ExprState **exprstates;
+
+	/*
+	 * Similar array of flags, each true if corresponding 'exprstate'
+	 * expression contains any PARAM_EXEC Params.  (Can be NULL if planstate
+	 * is NULL.)
+	 */
+	bool	   *exprhasexecparam;
+
+	/* true if it's safe to evaluate PARAM_EXEC Params */
+	bool		evalexecparams;
 } PartitionPruneContext;
 
 #define PruneCxtStateIdx(partnatts, step_id, keyno) \