Allow UPDATE to move rows between partitions.

When an UPDATE causes a row to no longer match the partition
constraint, try to move it to a different partition where it does
match the partition constraint.  In essence, the UPDATE is split into
a DELETE from the old partition and an INSERT into the new one.  This
can lead to surprising behavior in concurrency scenarios because
EvalPlanQual rechecks won't work as they normally did; the known
problems are documented.  (There is a pending patch to improve the
situation further, but it needs more review.)

Amit Khandekar, reviewed and tested by Amit Langote, David Rowley,
Rajkumar Raghuwanshi, Dilip Kumar, Amul Sul, Thomas Munro, Álvaro
Herrera, Amit Kapila, and me.  A few final revisions by me.

Discussion: http://postgr.es/m/CAJ3gD9do9o2ccQ7j7+tSgiE1REY65XRiMb=yJO3u3QhyP8EEPQ@mail.gmail.com

1 files changed, 7 insertions, 33 deletions

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 6bfca2a4af2..04a24c60824 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -170,7 +170,6 @@ typedef struct CopyStateData
 	PartitionTupleRouting *partition_tuple_routing;
 
 	TransitionCaptureState *transition_capture;
-	TupleConversionMap **transition_tupconv_maps;
 
 	/*
 	 * These variables are used to reduce overhead in textual COPY FROM.
@@ -2481,19 +2480,7 @@ CopyFrom(CopyState cstate)
 		 * tuple).
 		 */
 		if (cstate->transition_capture != NULL)
-		{
-			int			i;
-
-			cstate->transition_tupconv_maps = (TupleConversionMap **)
-				palloc0(sizeof(TupleConversionMap *) * proute->num_partitions);
-			for (i = 0; i < proute->num_partitions; ++i)
-			{
-				cstate->transition_tupconv_maps[i] =
-					convert_tuples_by_name(RelationGetDescr(proute->partitions[i]->ri_RelationDesc),
-										   RelationGetDescr(cstate->rel),
-										   gettext_noop("could not convert row type"));
-			}
-		}
+			ExecSetupChildParentMapForLeaf(proute);
 	}
 
 	/*
@@ -2587,7 +2574,6 @@ CopyFrom(CopyState cstate)
 		if (cstate->partition_tuple_routing)
 		{
 			int			leaf_part_index;
-			TupleConversionMap *map;
 			PartitionTupleRouting *proute = cstate->partition_tuple_routing;
 
 			/*
@@ -2651,7 +2637,8 @@ CopyFrom(CopyState cstate)
 					 */
 					cstate->transition_capture->tcs_original_insert_tuple = NULL;
 					cstate->transition_capture->tcs_map =
-						cstate->transition_tupconv_maps[leaf_part_index];
+						TupConvMapForLeaf(proute, saved_resultRelInfo,
+										  leaf_part_index);
 				}
 				else
 				{
@@ -2668,23 +2655,10 @@ CopyFrom(CopyState cstate)
 			 * We might need to convert from the parent rowtype to the
 			 * partition rowtype.
 			 */
-			map = proute->partition_tupconv_maps[leaf_part_index];
-			if (map)
-			{
-				Relation	partrel = resultRelInfo->ri_RelationDesc;
-
-				tuple = do_convert_tuple(tuple, map);
-
-				/*
-				 * We must use the partition's tuple descriptor from this
-				 * point on.  Use a dedicated slot from this point on until
-				 * we're finished dealing with the partition.
-				 */
-				slot = proute->partition_tuple_slot;
-				Assert(slot != NULL);
-				ExecSetSlotDescriptor(slot, RelationGetDescr(partrel));
-				ExecStoreTuple(tuple, slot, InvalidBuffer, true);
-			}
+			tuple = ConvertPartitionTupleSlot(proute->parent_child_tupconv_maps[leaf_part_index],
+											  tuple,
+											  proute->partition_tuple_slot,
+											  &slot);
 
 			tuple->t_tableOid = RelationGetRelid(resultRelInfo->ri_RelationDesc);
 		}