Add hash partitioning.

Hash partitioning is useful when you want to partition a growing data
set evenly.  This can be useful to keep table sizes reasonable, which
makes maintenance operations such as VACUUM faster, or to enable
partition-wise join.

At present, we still depend on constraint exclusion for partitioning
pruning, and the shape of the partition constraints for hash
partitioning is such that that doesn't work.  Work is underway to fix
that, which should both improve performance and make partitioning
pruning work with hash partitioning.

Amul Sul, reviewed and tested by Dilip Kumar, Ashutosh Bapat, Yugo
Nagata, Rajkumar Raghuwanshi, Jesper Pedersen, and by me.  A few
final tweaks also by me.

Discussion: http://postgr.es/m/CAAJ_b96fhpJAP=ALbETmeLk1Uni_GFZD938zgenhF49qgDTjaQ@mail.gmail.com

1 files changed, 34 insertions, 14 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index b7ddb335d2d..165b165d558 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -471,7 +471,7 @@ static void RangeVarCallbackForAlterRelation(const RangeVar *rv, Oid relid,
 static bool is_partition_attr(Relation rel, AttrNumber attnum, bool *used_in_expr);
 static PartitionSpec *transformPartitionSpec(Relation rel, PartitionSpec *partspec, char *strategy);
 static void ComputePartitionAttrs(Relation rel, List *partParams, AttrNumber *partattrs,
-					  List **partexprs, Oid *partopclass, Oid *partcollation);
+					  List **partexprs, Oid *partopclass, Oid *partcollation, char strategy);
 static void CreateInheritance(Relation child_rel, Relation parent_rel);
 static void RemoveInheritance(Relation child_rel, Relation parent_rel);
 static ObjectAddress ATExecAttachPartition(List **wqueue, Relation rel,
@@ -894,7 +894,7 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 
 		ComputePartitionAttrs(rel, stmt->partspec->partParams,
 							  partattrs, &partexprs, partopclass,
-							  partcollation);
+							  partcollation, strategy);
 
 		StorePartitionKey(rel, strategy, partnatts, partattrs, partexprs,
 						  partopclass, partcollation);
@@ -13337,7 +13337,9 @@ transformPartitionSpec(Relation rel, PartitionSpec *partspec, char *strategy)
 	newspec->location = partspec->location;
 
 	/* Parse partitioning strategy name */
-	if (pg_strcasecmp(partspec->strategy, "list") == 0)
+	if (pg_strcasecmp(partspec->strategy, "hash") == 0)
+		*strategy = PARTITION_STRATEGY_HASH;
+	else if (pg_strcasecmp(partspec->strategy, "list") == 0)
 		*strategy = PARTITION_STRATEGY_LIST;
 	else if (pg_strcasecmp(partspec->strategy, "range") == 0)
 		*strategy = PARTITION_STRATEGY_RANGE;
@@ -13407,10 +13409,12 @@ transformPartitionSpec(Relation rel, PartitionSpec *partspec, char *strategy)
  */
 static void
 ComputePartitionAttrs(Relation rel, List *partParams, AttrNumber *partattrs,
-					  List **partexprs, Oid *partopclass, Oid *partcollation)
+					  List **partexprs, Oid *partopclass, Oid *partcollation,
+					  char strategy)
 {
 	int			attn;
 	ListCell   *lc;
+	Oid			am_oid;
 
 	attn = 0;
 	foreach(lc, partParams)
@@ -13570,25 +13574,41 @@ ComputePartitionAttrs(Relation rel, List *partParams, AttrNumber *partattrs,
 		partcollation[attn] = attcollation;
 
 		/*
-		 * Identify a btree opclass to use. Currently, we use only btree
-		 * operators, which seems enough for list and range partitioning.
+		 * Identify the appropriate operator class.  For list and range
+		 * partitioning, we use a btree operator class; hash partitioning uses
+		 * a hash operator class.
 		 */
+		if (strategy == PARTITION_STRATEGY_HASH)
+			am_oid = HASH_AM_OID;
+		else
+			am_oid = BTREE_AM_OID;
+
 		if (!pelem->opclass)
 		{
-			partopclass[attn] = GetDefaultOpClass(atttype, BTREE_AM_OID);
+			partopclass[attn] = GetDefaultOpClass(atttype, am_oid);
 
 			if (!OidIsValid(partopclass[attn]))
-				ereport(ERROR,
-						(errcode(ERRCODE_UNDEFINED_OBJECT),
-						 errmsg("data type %s has no default btree operator class",
-								format_type_be(atttype)),
-						 errhint("You must specify a btree operator class or define a default btree operator class for the data type.")));
+			{
+				if (strategy == PARTITION_STRATEGY_HASH)
+					ereport(ERROR,
+							(errcode(ERRCODE_UNDEFINED_OBJECT),
+							 errmsg("data type %s has no default hash operator class",
+									format_type_be(atttype)),
+							 errhint("You must specify a hash operator class or define a default hash operator class for the data type.")));
+				else
+					ereport(ERROR,
+							(errcode(ERRCODE_UNDEFINED_OBJECT),
+							 errmsg("data type %s has no default btree operator class",
+									format_type_be(atttype)),
+							 errhint("You must specify a btree operator class or define a default btree operator class for the data type.")));
+
+			}
 		}
 		else
 			partopclass[attn] = ResolveOpClass(pelem->opclass,
 											   atttype,
-											   "btree",
-											   BTREE_AM_OID);
+											   am_oid == HASH_AM_OID ? "hash" : "btree",
+											   am_oid);
 
 		attn++;
 	}