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, 37 insertions, 1 deletions

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 1fcdb25142f..ee7a89045c3 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -269,6 +269,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	PartitionElem *partelem;
 	PartitionSpec *partspec;
 	PartitionBoundSpec *partboundspec;
+	SinglePartitionSpec *singlepartspec;
 	RoleSpec   *rolespec;
 	PublicationObjSpec *publicationobjectspec;
 	struct SelectLimit *selectlimit;
@@ -646,6 +647,8 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <partelem>	part_elem
 %type <list>		part_params
 %type <partboundspec> PartitionBoundSpec
+%type <singlepartspec>	SinglePartitionSpec
+%type <list>		partitions_list
 %type <list>		hash_partbound
 %type <defelt>		hash_partbound_elem
 
@@ -777,7 +780,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	SAVEPOINT SCALAR SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT
 	SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SPLIT SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRING_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
@@ -2307,6 +2310,23 @@ alter_table_cmds:
 			| alter_table_cmds ',' alter_table_cmd	{ $$ = lappend($1, $3); }
 		;
 
+partitions_list:
+			SinglePartitionSpec							{ $$ = list_make1($1); }
+			| partitions_list ',' SinglePartitionSpec	{ $$ = lappend($1, $3); }
+		;
+
+SinglePartitionSpec:
+			PARTITION qualified_name PartitionBoundSpec
+				{
+					SinglePartitionSpec *n = makeNode(SinglePartitionSpec);
+
+					n->name = $2;
+					n->bound = $3;
+
+					$$ = n;
+				}
+		;
+
 partition_cmd:
 			/* ALTER TABLE <name> ATTACH PARTITION <table_name> FOR VALUES */
 			ATTACH PARTITION qualified_name PartitionBoundSpec
@@ -2351,6 +2371,20 @@ partition_cmd:
 					n->def = (Node *) cmd;
 					$$ = (Node *) n;
 				}
+			/* ALTER TABLE <name> SPLIT PARTITION <partition_name> INTO () */
+			| SPLIT PARTITION qualified_name INTO '(' partitions_list ')'
+				{
+					AlterTableCmd *n = makeNode(AlterTableCmd);
+					PartitionCmd *cmd = makeNode(PartitionCmd);
+
+					n->subtype = AT_SplitPartition;
+					cmd->name = $3;
+					cmd->bound = NULL;
+					cmd->partlist = $6;
+					cmd->concurrent = false;
+					n->def = (Node *) cmd;
+					$$ = (Node *) n;
+				}
 			/* ALTER TABLE <name> MERGE PARTITIONS () INTO <partition_name> */
 			| MERGE PARTITIONS '(' qualified_name_list ')' INTO qualified_name
 				{
@@ -17756,6 +17790,7 @@ unreserved_keyword:
 			| SKIP
 			| SNAPSHOT
 			| SOURCE
+			| SPLIT
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -18393,6 +18428,7 @@ bare_label_keyword:
 			| SNAPSHOT
 			| SOME
 			| SOURCE
+			| SPLIT
 			| SQL_P
 			| STABLE
 			| STANDALONE_P