MERGE SQL Command following SQL:2016

MERGE performs actions that modify rows in the target table
using a source table or query. MERGE provides a single SQL
statement that can conditionally INSERT/UPDATE/DELETE rows
a task that would other require multiple PL statements.
e.g.

MERGE INTO target AS t
USING source AS s
ON t.tid = s.sid
WHEN MATCHED AND t.balance > s.delta THEN
  UPDATE SET balance = t.balance - s.delta
WHEN MATCHED THEN
  DELETE
WHEN NOT MATCHED AND s.delta > 0 THEN
  INSERT VALUES (s.sid, s.delta)
WHEN NOT MATCHED THEN
  DO NOTHING;

MERGE works with regular and partitioned tables, including
column and row security enforcement, as well as support for
row, statement and transition triggers.

MERGE is optimized for OLTP and is parameterizable, though
also useful for large scale ETL/ELT. MERGE is not intended
to be used in preference to existing single SQL commands
for INSERT, UPDATE or DELETE since there is some overhead.
MERGE can be used statically from PL/pgSQL.

MERGE does not yet support inheritance, write rules,
RETURNING clauses, updatable views or foreign tables.
MERGE follows SQL Standard per the most recent SQL:2016.

Includes full tests and documentation, including full
isolation tests to demonstrate the concurrent behavior.

This version written from scratch in 2017 by Simon Riggs,
using docs and tests originally written in 2009. Later work
from Pavan Deolasee has been both complex and deep, leaving
the lead author credit now in his hands.
Extensive discussion of concurrency from Peter Geoghegan,
with thanks for the time and effort contributed.

Various issues reported via sqlsmith by Andreas Seltenreich

Authors: Pavan Deolasee, Simon Riggs
Reviewer: Peter Geoghegan, Amit Langote, Tomas Vondra, Simon Riggs

Discussion:
https://postgr.es/m/CANP8+jKitBSrB7oTgT9CY2i1ObfOt36z0XMraQc+Xrz8QB0nXA@mail.gmail.com
https://postgr.es/m/CAH2-WzkJdBuxj9PO=2QaO9-3h3xGbQPZ34kJH=HukRekwM-GZg@mail.gmail.com

1 files changed, 116 insertions, 0 deletions

diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
index 9a131886491..a6a7885abd1 100644
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -67,6 +67,8 @@ ExecSetupPartitionTupleRouting(ModifyTableState *mtstate, Relation rel)
 	ResultRelInfo *update_rri = NULL;
 	int			num_update_rri = 0,
 				update_rri_index = 0;
+	bool		is_update = false;
+	bool		is_merge = false;
 	PartitionTupleRouting *proute;
 	int			nparts;
 	ModifyTable *node = mtstate ? (ModifyTable *) mtstate->ps.plan : NULL;
@@ -89,13 +91,22 @@ ExecSetupPartitionTupleRouting(ModifyTableState *mtstate, Relation rel)
 
 	/* Set up details specific to the type of tuple routing we are doing. */
 	if (node && node->operation == CMD_UPDATE)
+		is_update = true;
+	else if (node && node->operation == CMD_MERGE)
+		is_merge = true;
+
+	if (is_update)
 	{
 		update_rri = mtstate->resultRelInfo;
 		num_update_rri = list_length(node->plans);
 		proute->subplan_partition_offsets =
 			palloc(num_update_rri * sizeof(int));
 		proute->num_subplan_partition_offsets = num_update_rri;
+	}
+
 
+	if (is_update || is_merge)
+	{
 		/*
 		 * We need an additional tuple slot for storing transient tuples that
 		 * are converted to the root table descriptor.
@@ -300,6 +311,25 @@ ExecFindPartition(ResultRelInfo *resultRelInfo, PartitionDispatch *pd,
 }
 
 /*
+ * Given OID of the partition leaf, return the index of the leaf in the
+ * partition hierarchy.
+ */
+int
+ExecFindPartitionByOid(PartitionTupleRouting *proute, Oid partoid)
+{
+	int	i;
+
+	for (i = 0; i < proute->num_partitions; i++)
+	{
+		if (proute->partition_oids[i] == partoid)
+			break;
+	}
+
+	Assert(i < proute->num_partitions);
+	return i;
+}
+
+/*
  * ExecInitPartitionInfo
  *		Initialize ResultRelInfo and other information for a partition if not
  *		already done
@@ -337,6 +367,8 @@ ExecInitPartitionInfo(ModifyTableState *mtstate,
 					  rootrel,
 					  estate->es_instrument);
 
+	leaf_part_rri->ri_PartitionLeafIndex = partidx;
+
 	/*
 	 * Verify result relation is a valid target for an INSERT.  An UPDATE of a
 	 * partition-key becomes a DELETE+INSERT operation, so this check is still
@@ -625,6 +657,90 @@ ExecInitPartitionInfo(ModifyTableState *mtstate,
 	Assert(proute->partitions[partidx] == NULL);
 	proute->partitions[partidx] = leaf_part_rri;
 
+	/*
+	 * Initialize information about this partition that's needed to handle
+	 * MERGE.
+	 */
+	if (node && node->operation == CMD_MERGE)
+	{
+		TupleDesc	partrelDesc = RelationGetDescr(partrel);
+		TupleConversionMap *map = proute->parent_child_tupconv_maps[partidx];
+		int			firstVarno = mtstate->resultRelInfo[0].ri_RangeTableIndex;
+		Relation	firstResultRel = mtstate->resultRelInfo[0].ri_RelationDesc;
+
+		/*
+		 * If the root parent and partition have the same tuple
+		 * descriptor, just reuse the original MERGE state for partition.
+		 */
+		if (map == NULL)
+		{
+			leaf_part_rri->ri_mergeState = resultRelInfo->ri_mergeState;
+		}
+		else
+		{
+			/* Convert expressions contain partition's attnos. */
+			List	   *conv_tl, *conv_qual;
+			ListCell   *l;
+			List	   *matchedActionStates = NIL;
+			List	   *notMatchedActionStates = NIL;
+
+			foreach (l, node->mergeActionList)
+			{
+				MergeAction *action = lfirst_node(MergeAction, l);
+				MergeActionState *action_state = makeNode(MergeActionState);
+				TupleDesc	tupDesc;
+				ExprContext *econtext;
+
+				action_state->matched = action->matched;
+				action_state->commandType = action->commandType;
+
+				conv_qual = (List *) action->qual;
+				conv_qual = map_partition_varattnos(conv_qual,
+							firstVarno, partrel,
+							firstResultRel, NULL);
+
+				action_state->whenqual = ExecInitQual(conv_qual, &mtstate->ps);
+
+				conv_tl = (List *) action->targetList;
+				conv_tl = map_partition_varattnos(conv_tl,
+							firstVarno, partrel,
+							firstResultRel, NULL);
+
+				conv_tl = adjust_partition_tlist( conv_tl, map);
+
+				tupDesc = ExecTypeFromTL(conv_tl, partrelDesc->tdhasoid);
+				action_state->tupDesc = tupDesc;
+
+				/* build action projection state */
+				econtext = mtstate->ps.ps_ExprContext;
+				action_state->proj =
+					ExecBuildProjectionInfo(conv_tl, econtext,
+							mtstate->mt_mergeproj,
+							&mtstate->ps,
+							partrelDesc);
+
+				if (action_state->matched)
+					matchedActionStates =
+						lappend(matchedActionStates, action_state);
+				else
+					notMatchedActionStates =
+						lappend(notMatchedActionStates, action_state);
+			}
+			leaf_part_rri->ri_mergeState->matchedActionStates =
+				matchedActionStates;
+			leaf_part_rri->ri_mergeState->notMatchedActionStates =
+				notMatchedActionStates;
+		}
+
+		/*
+		 * get_partition_dispatch_recurse() and expand_partitioned_rtentry()
+		 * fetch the leaf OIDs in the same order. So we can safely derive the
+		 * index of the merge target relation corresponding to this partition
+		 * by simply adding partidx + 1 to the root's merge target relation.
+		 */
+		leaf_part_rri->ri_mergeTargetRTI = node->mergeTargetRelation +
+			partidx + 1;
+	}
 	MemoryContextSwitchTo(oldContext);
 
 	return leaf_part_rri;