Add hash support functions and hash opclass for contrib/ltree.

This also enables hash join and hash aggregation on ltree columns.

Tommy Pavlicek, reviewed by jian he

Discussion: https://postgr.es/m/CAEhP-W9ZEoHeaP_nKnPCVd_o1c3BAUvq1gWHrq8EbkNRiS9CvQ@mail.gmail.com

contrib/ltree/Makefile

@@ -14,7 +14,8 @@ OBJS = \
 	ltxtquery_op.o
 
 EXTENSION = ltree
-DATA = ltree--1.1--1.2.sql ltree--1.1.sql ltree--1.0--1.1.sql
+DATA = ltree--1.2--1.3.sql ltree--1.1--1.2.sql ltree--1.1.sql \
+	ltree--1.0--1.1.sql
 PGFILEDESC = "ltree - hierarchical label data type"
 
 HEADERS = ltree.h

contrib/ltree/expected/ltree.out

@@ -1433,8 +1433,27 @@ SELECT '{j.k.l.m, g.b.c.d.e}'::ltree[] ?~ 'A*@|g.b.c.d.e';
  g.b.c.d.e
 (1 row)
 
+-- Check that the hash_ltree() and hash_ltree_extended() function's lower
+-- 32 bits match when the seed is 0 and do not match when the seed != 0
+SELECT v as value, hash_ltree(v)::bit(32) as standard,
+       hash_ltree_extended(v, 0)::bit(32) as extended0,
+       hash_ltree_extended(v, 1)::bit(32) as extended1
+FROM   (VALUES (NULL::ltree), (''::ltree), ('0'::ltree), ('0.1'::ltree),
+       ('0.1.2'::ltree), ('0'::ltree), ('0_asd.1_ASD'::ltree)) x(v)
+WHERE  hash_ltree(v)::bit(32) != hash_ltree_extended(v, 0)::bit(32)
+       OR hash_ltree(v)::bit(32) = hash_ltree_extended(v, 1)::bit(32);
+ value | standard | extended0 | extended1 
+-------+----------+-----------+-----------
+(0 rows)
+
 CREATE TABLE ltreetest (t ltree);
 \copy ltreetest FROM 'data/ltree.data'
+SELECT count(*) from ltreetest;
+ count 
+-------
+  1006
+(1 row)
+
 SELECT * FROM ltreetest WHERE t <  '12.3' order by t asc;
                 t                 
 ----------------------------------
@@ -7833,6 +7852,55 @@ SELECT * FROM ltreetest WHERE t ? '{23.*.1,23.*.2}' order by t asc;
 (4 rows)
 
 drop index tstidx;
+--- test hash index
+create index tstidx on ltreetest using hash (t);
+set enable_seqscan=off;
+set enable_bitmapscan=off;
+EXPLAIN (COSTS OFF)
+SELECT * FROM ltreetest WHERE t =  '12.3' order by t asc;
+              QUERY PLAN              
+--------------------------------------
+ Index Scan using tstidx on ltreetest
+   Index Cond: (t = '12.3'::ltree)
+(2 rows)
+
+SELECT * FROM ltreetest WHERE t =  '12.3' order by t asc;
+  t   
+------
+ 12.3
+(1 row)
+
+reset enable_seqscan;
+reset enable_bitmapscan;
+-- test hash aggregate
+set enable_hashagg=on;
+set enable_sort=off;
+EXPLAIN (COSTS OFF)
+SELECT count(*) FROM (
+SELECT t FROM (SELECT * FROM ltreetest UNION ALL SELECT * FROM ltreetest) t1 GROUP BY t
+) t2;
+                     QUERY PLAN                      
+-----------------------------------------------------
+ Aggregate
+   ->  HashAggregate
+         Group Key: ltreetest.t
+         ->  Append
+               ->  Seq Scan on ltreetest
+               ->  Seq Scan on ltreetest ltreetest_1
+(6 rows)
+
+SELECT count(*) FROM (
+SELECT t FROM (SELECT * FROM ltreetest UNION ALL SELECT * FROM ltreetest) t1 GROUP BY t
+) t2;
+ count 
+-------
+  1006
+(1 row)
+
+reset enable_hashagg;
+reset enable_sort;
+drop index tstidx;
+-- test gist index
 create index tstidx on ltreetest using gist (t gist_ltree_ops(siglen=0));
 ERROR:  value 0 out of bounds for option "siglen"
 DETAIL:  Valid values are between "4" and "2024".

contrib/ltree/ltree--1.2--1.3.sql

@@ -0,0 +1,23 @@
+/* contrib/ltree/ltree--1.2--1.3.sql */
+
+-- complain if script is sourced in psql, rather than via ALTER EXTENSION
+\echo Use "ALTER EXTENSION ltree UPDATE TO '1.3'" to load this file. \quit
+
+CREATE FUNCTION hash_ltree(ltree)
+RETURNS integer
+AS 'MODULE_PATHNAME'
+LANGUAGE C STRICT IMMUTABLE PARALLEL SAFE;
+
+CREATE FUNCTION hash_ltree_extended(ltree, bigint)
+RETURNS bigint
+AS 'MODULE_PATHNAME'
+LANGUAGE C STRICT IMMUTABLE PARALLEL SAFE;
+
+CREATE OPERATOR CLASS hash_ltree_ops
+DEFAULT FOR TYPE ltree USING hash
+AS
+	OPERATOR	1	= ,
+	FUNCTION	1	hash_ltree(ltree),
+	FUNCTION	2	hash_ltree_extended(ltree, bigint);
+
+ALTER OPERATOR =(ltree, ltree) SET (HASHES);

contrib/ltree/ltree.control

@@ -1,6 +1,6 @@
 # ltree extension
 comment = 'data type for hierarchical tree-like structures'
-default_version = '1.2'
+default_version = '1.3'
 module_pathname = '$libdir/ltree'
 relocatable = true
 trusted = true

contrib/ltree/ltree_op.c

@@ -9,6 +9,7 @@
 
 #include "access/htup_details.h"
 #include "catalog/pg_statistic.h"
+#include "common/hashfn.h"
 #include "ltree.h"
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
@@ -24,6 +25,8 @@ PG_FUNCTION_INFO_V1(ltree_eq);
 PG_FUNCTION_INFO_V1(ltree_ne);
 PG_FUNCTION_INFO_V1(ltree_ge);
 PG_FUNCTION_INFO_V1(ltree_gt);
+PG_FUNCTION_INFO_V1(hash_ltree);
+PG_FUNCTION_INFO_V1(hash_ltree_extended);
 PG_FUNCTION_INFO_V1(nlevel);
 PG_FUNCTION_INFO_V1(ltree_isparent);
 PG_FUNCTION_INFO_V1(ltree_risparent);
@@ -129,6 +132,72 @@ ltree_ne(PG_FUNCTION_ARGS)
 	PG_RETURN_BOOL(res != 0);
 }
 
+/* Compute a hash for the ltree */
+Datum
+hash_ltree(PG_FUNCTION_ARGS)
+{
+	ltree	   *a = PG_GETARG_LTREE_P(0);
+	uint32		result = 1;
+	int			an = a->numlevel;
+	ltree_level *al = LTREE_FIRST(a);
+
+	while (an > 0)
+	{
+		uint32		levelHash = DatumGetUInt32(hash_any((unsigned char *) al->name, al->len));
+
+		/*
+		 * Combine hash values of successive elements by multiplying the
+		 * current value by 31 and adding on the new element's hash value.
+		 *
+		 * This method is borrowed from hash_array(), which see for further
+		 * commentary.
+		 */
+		result = (result << 5) - result + levelHash;
+
+		an--;
+		al = LEVEL_NEXT(al);
+	}
+
+	PG_FREE_IF_COPY(a, 0);
+	PG_RETURN_UINT32(result);
+}
+
+/* Compute an extended hash for the ltree */
+Datum
+hash_ltree_extended(PG_FUNCTION_ARGS)
+{
+	ltree	   *a = PG_GETARG_LTREE_P(0);
+	const uint64 seed = PG_GETARG_INT64(1);
+	uint64		result = 1;
+	int			an = a->numlevel;
+	ltree_level *al = LTREE_FIRST(a);
+
+	/*
+	 * If the path has length zero, return 1 + seed to ensure that the low 32
+	 * bits of the result match hash_ltree when the seed is 0, as required by
+	 * the hash index support functions, but to also return a different value
+	 * when there is a seed.
+	 */
+	if (an == 0)
+	{
+		PG_FREE_IF_COPY(a, 0);
+		PG_RETURN_UINT64(result + seed);
+	}
+
+	while (an > 0)
+	{
+		uint64		levelHash = DatumGetUInt64(hash_any_extended((unsigned char *) al->name, al->len, seed));
+
+		result = (result << 5) - result + levelHash;
+
+		an--;
+		al = LEVEL_NEXT(al);
+	}
+
+	PG_FREE_IF_COPY(a, 0);
+	PG_RETURN_UINT64(result);
+}
+
 Datum
 nlevel(PG_FUNCTION_ARGS)
 {

contrib/ltree/ltreetest.sql

@@ -19,3 +19,4 @@ INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy.Galaxies');
 INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy.Astronauts');
 CREATE INDEX path_gist_idx ON test USING gist(path);
 CREATE INDEX path_idx ON test USING btree(path);
+CREATE INDEX path_hash_idx ON test USING hash(path);

contrib/ltree/meson.build

@@ -30,8 +30,9 @@ contrib_targets += ltree
 install_data(
   'ltree.control',
   'ltree--1.0--1.1.sql',
-  'ltree--1.1--1.2.sql',
   'ltree--1.1.sql',
+  'ltree--1.1--1.2.sql',
+  'ltree--1.2--1.3.sql',
   kwargs: contrib_data_args,
 )
 

contrib/ltree/sql/ltree.sql

@@ -282,9 +282,21 @@ SELECT ('{3456,1.2.3.4}'::ltree[] ?<@ '1.2.5') is null;
 SELECT '{ltree.asd, tree.awdfg}'::ltree[] ?@ 'tree & aWdfg@'::ltxtquery;
 SELECT '{j.k.l.m, g.b.c.d.e}'::ltree[] ?~ 'A*@|g.b.c.d.e';
 
+-- Check that the hash_ltree() and hash_ltree_extended() function's lower
+-- 32 bits match when the seed is 0 and do not match when the seed != 0
+SELECT v as value, hash_ltree(v)::bit(32) as standard,
+       hash_ltree_extended(v, 0)::bit(32) as extended0,
+       hash_ltree_extended(v, 1)::bit(32) as extended1
+FROM   (VALUES (NULL::ltree), (''::ltree), ('0'::ltree), ('0.1'::ltree),
+       ('0.1.2'::ltree), ('0'::ltree), ('0_asd.1_ASD'::ltree)) x(v)
+WHERE  hash_ltree(v)::bit(32) != hash_ltree_extended(v, 0)::bit(32)
+       OR hash_ltree(v)::bit(32) = hash_ltree_extended(v, 1)::bit(32);
+
 CREATE TABLE ltreetest (t ltree);
 \copy ltreetest FROM 'data/ltree.data'
 
+SELECT count(*) from ltreetest;
+
 SELECT * FROM ltreetest WHERE t <  '12.3' order by t asc;
 SELECT * FROM ltreetest WHERE t <= '12.3' order by t asc;
 SELECT * FROM ltreetest WHERE t =  '12.3' order by t asc;
@@ -329,6 +341,41 @@ SELECT * FROM ltreetest WHERE t ~ '23.*.2' order by t asc;
 SELECT * FROM ltreetest WHERE t ? '{23.*.1,23.*.2}' order by t asc;
 
 drop index tstidx;
+
+--- test hash index
+
+create index tstidx on ltreetest using hash (t);
+set enable_seqscan=off;
+set enable_bitmapscan=off;
+
+EXPLAIN (COSTS OFF)
+SELECT * FROM ltreetest WHERE t =  '12.3' order by t asc;
+SELECT * FROM ltreetest WHERE t =  '12.3' order by t asc;
+
+reset enable_seqscan;
+reset enable_bitmapscan;
+
+-- test hash aggregate
+
+set enable_hashagg=on;
+set enable_sort=off;
+
+EXPLAIN (COSTS OFF)
+SELECT count(*) FROM (
+SELECT t FROM (SELECT * FROM ltreetest UNION ALL SELECT * FROM ltreetest) t1 GROUP BY t
+) t2;
+
+SELECT count(*) FROM (
+SELECT t FROM (SELECT * FROM ltreetest UNION ALL SELECT * FROM ltreetest) t1 GROUP BY t
+) t2;
+
+reset enable_hashagg;
+reset enable_sort;
+
+drop index tstidx;
+
+-- test gist index
+
 create index tstidx on ltreetest using gist (t gist_ltree_ops(siglen=0));
 create index tstidx on ltreetest using gist (t gist_ltree_ops(siglen=2025));
 create index tstidx on ltreetest using gist (t gist_ltree_ops(siglen=2028));

doc/src/sgml/ltree.sgml

@@ -623,6 +623,13 @@ Europe & Russia*@ & !Transportation
      <literal>&gt;=</literal>, <literal>&gt;</literal>
     </para>
    </listitem>
+   <listitem>
+    <para>
+     Hash index over <type>ltree</type>:
+     <literal>=</literal>
+    </para>
+   </listitem>
+
    <listitem>
     <para>
      GiST index over <type>ltree</type> (<literal>gist_ltree_ops</literal>
@@ -712,6 +719,7 @@ INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy.Galaxies');
 INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy.Astronauts');
 CREATE INDEX path_gist_idx ON test USING GIST (path);
 CREATE INDEX path_idx ON test USING BTREE (path);
+CREATE INDEX path_hash_idx ON test USING HASH (path);
 </programlisting>
 
   <para>