Revise child-to-root tuple conversion map management.

Store the tuple conversion map to convert a tuple from a child table's
format to the root format in a new ri_ChildToRootMap field in
ResultRelInfo. It is initialized if transition tuple capture for FOR
STATEMENT triggers or INSERT tuple routing on a partitioned table is
needed. Previously, ModifyTable kept the maps in the per-subplan
ModifyTableState->mt_per_subplan_tupconv_maps array, or when tuple
routing was used, in
ResultRelInfo->ri_Partitioninfo->pi_PartitionToRootMap. The new field
replaces both of those.

Now that the child-to-root tuple conversion map is always available in
ResultRelInfo (when needed), remove the TransitionCaptureState.tcs_map
field. The callers of Exec*Trigger() functions no longer need to set or
save it, which is much less confusing and bug-prone. Also, as a future
optimization, this will allow us to delay creating the map for a given
result relation until the relation is actually processed during
execution.

Author: Amit Langote
Discussion: https://www.postgresql.org/message-id/CA%2BHiwqHtCWLdK-LO%3DNEsvOdHx%2B7yv4mE_zYK0i3BH7dXb-wxog%40mail.gmail.com

1 files changed, 6 insertions, 23 deletions

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 531bd7c73a5..b4ccd35ec18 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -3106,31 +3106,14 @@ CopyFrom(CopyState cstate)
 
 			/*
 			 * If we're capturing transition tuples, we might need to convert
-			 * from the partition rowtype to root rowtype.
+			 * from the partition rowtype to root rowtype. But if there are no
+			 * BEFORE triggers on the partition that could change the tuple,
+			 * we can just remember the original unconverted tuple to avoid a
+			 * needless round trip conversion.
 			 */
 			if (cstate->transition_capture != NULL)
-			{
-				if (has_before_insert_row_trig)
-				{
-					/*
-					 * If there are any BEFORE triggers on the partition,
-					 * we'll have to be ready to convert their result back to
-					 * tuplestore format.
-					 */
-					cstate->transition_capture->tcs_original_insert_tuple = NULL;
-					cstate->transition_capture->tcs_map =
-						resultRelInfo->ri_PartitionInfo->pi_PartitionToRootMap;
-				}
-				else
-				{
-					/*
-					 * Otherwise, just remember the original unconverted
-					 * tuple, to avoid a needless round trip conversion.
-					 */
-					cstate->transition_capture->tcs_original_insert_tuple = myslot;
-					cstate->transition_capture->tcs_map = NULL;
-				}
-			}
+				cstate->transition_capture->tcs_original_insert_tuple =
+					!has_before_insert_row_trig ? myslot : NULL;
 
 			/*
 			 * We might need to convert from the root rowtype to the partition