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

2 files changed, 101 insertions, 4 deletions

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 09b9a899e49..c301ca465d4 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -579,7 +579,8 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <list>		part_params
 %type <partboundspec> PartitionBoundSpec
 %type <node>		partbound_datum PartitionRangeDatum
-%type <list>		partbound_datum_list range_datum_list
+%type <list>		hash_partbound partbound_datum_list range_datum_list
+%type <defelt>		hash_partbound_elem
 
 /*
  * Non-keyword token types.  These are hard-wired into the "flex" lexer.
@@ -2638,8 +2639,61 @@ alter_identity_column_option:
 		;
 
 PartitionBoundSpec:
+			/* a HASH partition*/
+			FOR VALUES WITH '(' hash_partbound ')'
+				{
+					ListCell   *lc;
+					PartitionBoundSpec *n = makeNode(PartitionBoundSpec);
+
+					n->strategy = PARTITION_STRATEGY_HASH;
+					n->modulus = n->remainder = -1;
+
+					foreach (lc, $5)
+					{
+						DefElem    *opt = lfirst_node(DefElem, lc);
+
+						if (strcmp(opt->defname, "modulus") == 0)
+						{
+							if (n->modulus != -1)
+								ereport(ERROR,
+										(errcode(ERRCODE_DUPLICATE_OBJECT),
+										 errmsg("modulus for hash partition provided more than once"),
+										 parser_errposition(opt->location)));
+							n->modulus = defGetInt32(opt);
+						}
+						else if (strcmp(opt->defname, "remainder") == 0)
+						{
+							if (n->remainder != -1)
+								ereport(ERROR,
+										(errcode(ERRCODE_DUPLICATE_OBJECT),
+										 errmsg("remainder for hash partition provided more than once"),
+										 parser_errposition(opt->location)));
+							n->remainder = defGetInt32(opt);
+						}
+						else
+							ereport(ERROR,
+									(errcode(ERRCODE_SYNTAX_ERROR),
+									 errmsg("unrecognized hash partition bound specification \"%s\"",
+											opt->defname),
+									 parser_errposition(opt->location)));
+					}
+
+					if (n->modulus == -1)
+						ereport(ERROR,
+								(errcode(ERRCODE_SYNTAX_ERROR),
+								 errmsg("modulus for hash partition must be specified")));
+					if (n->remainder == -1)
+						ereport(ERROR,
+								(errcode(ERRCODE_SYNTAX_ERROR),
+								 errmsg("remainder for hash partition must be specified")));
+
+					n->location = @3;
+
+					$$ = n;
+				}
+
 			/* a LIST partition */
-			FOR VALUES IN_P '(' partbound_datum_list ')'
+			| FOR VALUES IN_P '(' partbound_datum_list ')'
 				{
 					PartitionBoundSpec *n = makeNode(PartitionBoundSpec);
 
@@ -2677,6 +2731,24 @@ PartitionBoundSpec:
 				}
 		;
 
+hash_partbound_elem:
+		NonReservedWord Iconst
+			{
+				$$ = makeDefElem($1, (Node *)makeInteger($2), @1);
+			}
+		;
+
+hash_partbound:
+		hash_partbound_elem
+			{
+				$$ = list_make1($1);
+			}
+		| hash_partbound ',' hash_partbound_elem
+			{
+				$$ = lappend($1, $3);
+			}
+		;
+
 partbound_datum:
 			Sconst			{ $$ = makeStringConst($1, @1); }
 			| NumericOnly	{ $$ = makeAConst($1, @1); }
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index 30fc2d9ff84..8461da490ac 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -3310,6 +3310,11 @@ transformPartitionBound(ParseState *pstate, Relation parent,
 
 	if (spec->is_default)
 	{
+		if (strategy == PARTITION_STRATEGY_HASH)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("a hash-partitioned table may not have a default partition")));
+
 		/*
 		 * In case of the default partition, parser had no way to identify the
 		 * partition strategy. Assign the parent's strategy to the default
@@ -3320,7 +3325,27 @@ transformPartitionBound(ParseState *pstate, Relation parent,
 		return result_spec;
 	}
 
-	if (strategy == PARTITION_STRATEGY_LIST)
+	if (strategy == PARTITION_STRATEGY_HASH)
+	{
+		if (spec->strategy != PARTITION_STRATEGY_HASH)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("invalid bound specification for a hash partition"),
+					 parser_errposition(pstate, exprLocation((Node *) spec))));
+
+		if (spec->modulus <= 0)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("modulus for hash partition must be a positive integer")));
+
+		Assert(spec->remainder >= 0);
+
+		if (spec->remainder >= spec->modulus)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("remainder for hash partition must be less than modulus")));
+	}
+	else if (strategy == PARTITION_STRATEGY_LIST)
 	{
 		ListCell   *cell;
 		char	   *colname;
@@ -3485,7 +3510,7 @@ transformPartitionBound(ParseState *pstate, Relation parent,
 static void
 validateInfiniteBounds(ParseState *pstate, List *blist)
 {
-	ListCell *lc;
+	ListCell   *lc;
 	PartitionRangeDatumKind kind = PARTITION_RANGE_DATUM_VALUE;
 
 	foreach(lc, blist)