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

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

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

Discussion: https://postgr.es/m/c73a1746-0cd0-6bdd-6b23-3ae0b7c0c582%40postgrespro.ru
Author: Dmitry Koval <d.koval@postgrespro.ru>
Co-authored-by: Alexander Korotkov <aekorotkov@gmail.com>
Co-authored-by: Tender Wang <tndrwang@gmail.com>
Co-authored-by: Richard Guo <guofenglinux@gmail.com>
Co-authored-by: Dagfinn Ilmari Mannsaker <ilmari@ilmari.org>
Co-authored-by: Fujii Masao <masao.fujii@gmail.com>
Co-authored-by: Jian He <jian.universality@gmail.com>
Reviewed-by: Matthias van de Meent <boekewurm+postgres@gmail.com>
Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Reviewed-by: Zhihong Yu <zyu@yugabyte.com>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Robert Haas <rhaas@postgresql.org>
Reviewed-by: Stephane Tachoires <stephane.tachoires@gmail.com>
Reviewed-by: Jian He <jian.universality@gmail.com>
Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>
Reviewed-by: Pavel Borisov <pashkin.elfe@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Alexander Lakhin <exclusion@gmail.com>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Daniel Gustafsson <dgustafsson@postgresql.org>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Noah Misch <noah@leadboat.com>

1 files changed, 29 insertions, 5 deletions

diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index e43a1f946a9..bc7adba4a0f 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -966,16 +966,39 @@ typedef struct PartitionRangeDatum
 } PartitionRangeDatum;
 
 /*
+ * PartitionDesc - info about a single partition for the ALTER TABLE SPLIT
+ *	  PARTITION command
+ */
+typedef struct SinglePartitionSpec
+{
+	NodeTag		type;
+
+	RangeVar   *name;			/* name of partition */
+	PartitionBoundSpec *bound;	/* FOR VALUES, if attaching */
+} SinglePartitionSpec;
+
+/*
  * PartitionCmd - info for ALTER TABLE/INDEX ATTACH/DETACH PARTITION and for
- *	  ALTER TABLE MERGE PARTITIONS commands
+ *	  ALTER TABLE SPLIT/MERGE PARTITION(S) commands
  */
 typedef struct PartitionCmd
 {
 	NodeTag		type;
-	RangeVar   *name;			/* name of partition to attach/detach/merge */
-	PartitionBoundSpec *bound;	/* FOR VALUES, if attaching */
-	List	   *partlist;		/* list of partitions to be merged, used in
-								 * ALTER TABLE MERGE PARTITIONS */
+
+	/* name of partition to attach/detach/merge/split */
+	RangeVar   *name;
+
+	/* FOR VALUES, if attaching */
+	PartitionBoundSpec *bound;
+
+	/*
+	 * list of partitions to be split/merged, used in ALTER TABLE MERGE
+	 * PARTITIONS and ALTER TABLE SPLIT PARTITIONS. For merge partitions,
+	 * partlist is a list of RangeVar; For split partition, it is a list of
+	 * SinglePartitionSpec.
+	 */
+	List	   *partlist;
+
 	bool		concurrent;
 } PartitionCmd;
 
@@ -2479,6 +2502,7 @@ typedef enum AlterTableType
 	AT_AttachPartition,			/* ATTACH PARTITION */
 	AT_DetachPartition,			/* DETACH PARTITION */
 	AT_DetachPartitionFinalize, /* DETACH PARTITION FINALIZE */
+	AT_SplitPartition,			/* SPLIT PARTITION */
 	AT_MergePartitions,			/* MERGE PARTITIONS */
 	AT_AddIdentity,				/* ADD IDENTITY */
 	AT_SetIdentity,				/* SET identity column options */