Implement ALTER TABLE ... SPLIT PARTITION ... command

This new DDL command splits a single partition into several parititions.
Just like ALTER TABLE ... MERGE PARTITIONS ... command, new patitions are
created using createPartitionTable() function with parent partition as the
template.

This commit comprises quite naive implementation which works in single process
and holds the ACCESS EXCLUSIVE LOCK on the parent table during all the
operations including the tuple routing.  This is why this new DDL command
can't be recommended for large partitioned tables under a high load.  However,
this implementation come in handy in certain cases even as is.
Also, it could be used as a foundation for future implementations with lesser
locking and possibly parallel.

Discussion: https://postgr.es/m/c73a1746-0cd0-6bdd-6b23-3ae0b7c0c582%40postgrespro.ru
Author: Dmitry Koval
Reviewed-by: Matthias van de Meent, Laurenz Albe, Zhihong Yu, Justin Pryzby
Reviewed-by: Alvaro Herrera, Robert Haas, Stephane Tachoires

1 files changed, 52 insertions, 10 deletions

diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index 48a23c7ca42..88a4a41186a 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -136,7 +136,7 @@ static void transformConstraintAttrs(CreateStmtContext *cxt,
 									 List *constraintList);
 static void transformColumnType(CreateStmtContext *cxt, ColumnDef *column);
 static void setSchemaName(const char *context_schema, char **stmt_schema_name);
-static void transformPartitionCmd(CreateStmtContext *cxt, PartitionCmd *cmd);
+static void transformPartitionCmd(CreateStmtContext *cxt, PartitionBoundSpec *bound);
 static List *transformPartitionRangeBounds(ParseState *pstate, List *blist,
 										   Relation parent);
 static void validateInfiniteBounds(ParseState *pstate, List *blist);
@@ -3416,6 +3416,43 @@ transformRuleStmt(RuleStmt *stmt, const char *queryString,
 
 
 /*
+ * transformPartitionCmdForSplit
+ *		Analyze the ALTER TABLLE ... SPLIT PARTITION command
+ *
+ * For each new partition sps->bound is set to the transformed value of bound.
+ * Does checks for bounds of new partitions.
+ */
+static void
+transformPartitionCmdForSplit(CreateStmtContext *cxt, PartitionCmd *partcmd)
+{
+	Relation	parent = cxt->rel;
+	Oid			splitPartOid;
+	ListCell   *listptr;
+
+	if (parent->rd_rel->relkind != RELKIND_PARTITIONED_TABLE)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("\"%s\" is not a partitioned table", RelationGetRelationName(parent))));
+
+	/* Transform partition bounds for all partitions in the list: */
+	foreach(listptr, partcmd->partlist)
+	{
+		SinglePartitionSpec *sps = (SinglePartitionSpec *) lfirst(listptr);
+
+		cxt->partbound = NULL;
+		transformPartitionCmd(cxt, sps->bound);
+		/* Assign transformed value of the partition bound. */
+		sps->bound = cxt->partbound;
+	}
+
+	splitPartOid = RangeVarGetRelid(partcmd->name, NoLock, false);
+
+	/* Then we should check partitions with transformed bounds. */
+	check_partitions_for_split(parent, splitPartOid, partcmd->name, partcmd->partlist, cxt->pstate);
+}
+
+
+/*
  * transformPartitionCmdForMerge
  *		Analyze the ALTER TABLLE ... MERGE PARTITIONS command
  *
@@ -3751,7 +3788,7 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 				{
 					PartitionCmd *partcmd = (PartitionCmd *) cmd->def;
 
-					transformPartitionCmd(&cxt, partcmd);
+					transformPartitionCmd(&cxt, partcmd->bound);
 					/* assign transformed value of the partition bound */
 					partcmd->bound = cxt.partbound;
 				}
@@ -3759,6 +3796,7 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 				newcmds = lappend(newcmds, cmd);
 				break;
 
+			case AT_SplitPartition:
 			case AT_MergePartitions:
 				{
 					PartitionCmd *partcmd = (PartitionCmd *) cmd->def;
@@ -3767,7 +3805,11 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 						ereport(ERROR,
 								(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 								 errmsg("list of new partitions should contains at least two items")));
-					transformPartitionCmdForMerge(&cxt, partcmd);
+
+					if (cmd->subtype == AT_SplitPartition)
+						transformPartitionCmdForSplit(&cxt, partcmd);
+					else
+						transformPartitionCmdForMerge(&cxt, partcmd);
 					newcmds = lappend(newcmds, cmd);
 					break;
 				}
@@ -4172,13 +4214,13 @@ setSchemaName(const char *context_schema, char **stmt_schema_name)
 
 /*
  * transformPartitionCmd
- *		Analyze the ATTACH/DETACH PARTITION command
+ *		Analyze the ATTACH/DETACH/SPLIT PARTITION command
  *
- * In case of the ATTACH PARTITION command, cxt->partbound is set to the
- * transformed value of cmd->bound.
+ * In case of the ATTACH/SPLIT PARTITION command, cxt->partbound is set to the
+ * transformed value of bound.
  */
 static void
-transformPartitionCmd(CreateStmtContext *cxt, PartitionCmd *cmd)
+transformPartitionCmd(CreateStmtContext *cxt, PartitionBoundSpec *bound)
 {
 	Relation	parentRel = cxt->rel;
 
@@ -4187,9 +4229,9 @@ transformPartitionCmd(CreateStmtContext *cxt, PartitionCmd *cmd)
 		case RELKIND_PARTITIONED_TABLE:
 			/* transform the partition bound, if any */
 			Assert(RelationGetPartitionKey(parentRel) != NULL);
-			if (cmd->bound != NULL)
+			if (bound != NULL)
 				cxt->partbound = transformPartitionBound(cxt->pstate, parentRel,
-														 cmd->bound);
+														 bound);
 			break;
 		case RELKIND_PARTITIONED_INDEX:
 
@@ -4197,7 +4239,7 @@ transformPartitionCmd(CreateStmtContext *cxt, PartitionCmd *cmd)
 			 * A partitioned index cannot have a partition bound set.  ALTER
 			 * INDEX prevents that with its grammar, but not ALTER TABLE.
 			 */
-			if (cmd->bound != NULL)
+			if (bound != NULL)
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 						 errmsg("\"%s\" is not a partitioned table",