Add prefix operator for TEXT type.

The prefix operator along with SP-GiST indexes can be used as an alternative
for LIKE 'word%' commands  and it doesn't have a limitation of string/prefix
length as B-Tree has.

Bump catalog version

Author: Ildus Kurbangaliev with some editorization by me
Review by: Arthur Zakirov, Alexander Korotkov, and me
Discussion: https://www.postgresql.org/message-id/flat/20180202180327.222b04b3@wp.localdomain

doc/src/sgml/func.sgml

@@ -2274,6 +2274,21 @@
        <entry><literal>ph</literal></entry>
       </row>
 
+      <row>
+       <entry>
+        <indexterm>
+         <primary>starts_with</primary>
+        </indexterm>
+        <literal><function>starts_with(<parameter>string</parameter>, <parameter>prefix</parameter>)</function></literal>
+       </entry>
+       <entry><type>bool</type></entry>
+       <entry>
+        Returns true if <parameter>string</parameter> starts with <parameter>prefix</parameter>.
+       </entry>
+       <entry><literal>starts_with('alphabet', 'alph')</literal></entry>
+       <entry><literal>t</literal></entry>
+      </row>
+
       <row>
        <entry>
         <indexterm>
@@ -4033,6 +4048,12 @@ cast(-44 as bit(12))           <lineannotation>111111010100</lineannotation>
     ILIKE</function>, respectively.  All of these operators are
     <productname>PostgreSQL</productname>-specific.
    </para>
+
+   <para>
+    There is also the prefix operator <literal>^@</literal> and corresponding
+    <function>starts_with</function> function which covers cases when only
+    searching by beginning of the string is needed.
+   </para>
   </sect2>
 
 

doc/src/sgml/spgist.sgml

@@ -161,6 +161,7 @@
        <literal>~&lt;~</literal>
        <literal>~&gt;=~</literal>
        <literal>~&gt;~</literal>
+       <literal>^@</literal>
       </entry>
      </row>
      <row>

src/backend/access/spgist/spgtextproc.c

@@ -67,6 +67,20 @@
  */
 #define SPGIST_MAX_PREFIX_LENGTH	Max((int) (BLCKSZ - 258 * 16 - 100), 32)
 
+/*
+ * Strategy for collation aware operator on text is equal to btree strategy
+ * plus value of 10.
+ *
+ * Current collation aware strategies and their corresponding btree strategies:
+ * 11 BTLessStrategyNumber
+ * 12 BTLessEqualStrategyNumber
+ * 14 BTGreaterEqualStrategyNumber
+ * 15 BTGreaterStrategyNumber
+ */
+#define SPG_STRATEGY_ADDITION	(10)
+#define SPG_IS_COLLATION_AWARE_STRATEGY(s) ((s) > SPG_STRATEGY_ADDITION \
+										 && (s) != RTPrefixStrategyNumber)
+
 /* Struct for sorting values in picksplit */
 typedef struct spgNodePtr
 {
@@ -496,10 +510,10 @@ spg_text_inner_consistent(PG_FUNCTION_ARGS)
 			 * well end with a partial multibyte character, so that applying
 			 * any encoding-sensitive test to it would be risky anyhow.)
 			 */
-			if (strategy > 10)
+			if (SPG_IS_COLLATION_AWARE_STRATEGY(strategy))
 			{
 				if (collate_is_c)
-					strategy -= 10;
+					strategy -= SPG_STRATEGY_ADDITION;
 				else
 					continue;
 			}
@@ -526,6 +540,10 @@ spg_text_inner_consistent(PG_FUNCTION_ARGS)
 					if (r < 0)
 						res = false;
 					break;
+				case RTPrefixStrategyNumber:
+					if (r != 0)
+						res = false;
+					break;
 				default:
 					elog(ERROR, "unrecognized strategy number: %d",
 						 in->scankeys[j].sk_strategy);
@@ -605,10 +623,27 @@ spg_text_leaf_consistent(PG_FUNCTION_ARGS)
 		int			queryLen = VARSIZE_ANY_EXHDR(query);
 		int			r;
 
-		if (strategy > 10)
+		if (strategy == RTPrefixStrategyNumber)
+		{
+			/*
+			 * if level >= length of query then reconstrValue is began with
+			 * query (prefix) string and we don't need to check it again.
+			 */
+
+			res = (level >= queryLen) ||
+					DatumGetBool(DirectFunctionCall2(text_starts_with,
+								 out->leafValue, PointerGetDatum(query)));
+
+			if (!res) /* no need to consider remaining conditions */
+				break;
+
+			continue;
+		}
+
+		if (SPG_IS_COLLATION_AWARE_STRATEGY(strategy))
 		{
 			/* Collation-aware comparison */
-			strategy -= 10;
+			strategy -= SPG_STRATEGY_ADDITION;
 
 			/* If asserts enabled, verify encoding of reconstructed string */
 			Assert(pg_verifymbstr(fullValue, fullLen, false));

src/backend/utils/adt/selfuncs.c

@@ -1488,6 +1488,16 @@ likesel(PG_FUNCTION_ARGS)
 }
 
 /*
+ *		prefixsel			- selectivity of prefix operator
+ */
+Datum
+prefixsel(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_FLOAT8(patternsel(fcinfo, Pattern_Type_Prefix, false));
+}
+
+/*
+ *
  *		iclikesel			- Selectivity of ILIKE pattern match.
  */
 Datum
@@ -2906,6 +2916,15 @@ likejoinsel(PG_FUNCTION_ARGS)
 	PG_RETURN_FLOAT8(patternjoinsel(fcinfo, Pattern_Type_Like, false));
 }
 
+/*
+ *		prefixjoinsel			- Join selectivity of prefix operator
+ */
+Datum
+prefixjoinsel(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_FLOAT8(patternjoinsel(fcinfo, Pattern_Type_Prefix, false));
+}
+
 /*
  *		iclikejoinsel			- Join selectivity of ILIKE pattern match.
  */
@@ -5947,6 +5966,20 @@ pattern_fixed_prefix(Const *patt, Pattern_Type ptype, Oid collation,
 			result = regex_fixed_prefix(patt, true, collation,
 										prefix, rest_selec);
 			break;
+		case Pattern_Type_Prefix:
+			/* Prefix type work is trivial.  */
+			result = Pattern_Prefix_Partial;
+			*rest_selec = 1.0;	/* all */
+			*prefix = makeConst(patt->consttype,
+								patt->consttypmod,
+								patt->constcollid,
+								patt->constlen,
+								datumCopy(patt->constvalue,
+										  patt->constbyval,
+										  patt->constlen),
+								patt->constisnull,
+								patt->constbyval);
+			break;
 		default:
 			elog(ERROR, "unrecognized ptype: %d", (int) ptype);
 			result = Pattern_Prefix_None;	/* keep compiler quiet */

src/backend/utils/adt/varlena.c

@@ -1761,6 +1761,34 @@ text_ge(PG_FUNCTION_ARGS)
 	PG_RETURN_BOOL(result);
 }
 
+Datum
+text_starts_with(PG_FUNCTION_ARGS)
+{
+	Datum		arg1 = PG_GETARG_DATUM(0);
+	Datum		arg2 = PG_GETARG_DATUM(1);
+	bool		result;
+	Size		len1,
+				len2;
+
+	len1 = toast_raw_datum_size(arg1);
+	len2 = toast_raw_datum_size(arg2);
+	if (len2 > len1)
+		result = false;
+	else
+	{
+		text	   *targ1 = DatumGetTextPP(arg1);
+		text	   *targ2 = DatumGetTextPP(arg2);
+
+		result = (memcmp(VARDATA_ANY(targ1), VARDATA_ANY(targ2),
+						 VARSIZE_ANY_EXHDR(targ2)) == 0);
+
+		PG_FREE_IF_COPY(targ1, 0);
+		PG_FREE_IF_COPY(targ2, 1);
+	}
+
+	PG_RETURN_BOOL(result);
+}
+
 Datum
 bttextcmp(PG_FUNCTION_ARGS)
 {

src/include/access/stratnum.h

@@ -68,8 +68,9 @@ typedef uint16 StrategyNumber;
 #define RTSubEqualStrategyNumber		25	/* for inet <<= */
 #define RTSuperStrategyNumber			26	/* for inet << */
 #define RTSuperEqualStrategyNumber		27	/* for inet >>= */
+#define RTPrefixStrategyNumber			28	/* for text ^@ */
 
-#define RTMaxStrategyNumber				27
+#define RTMaxStrategyNumber				28
 
 
 #endif							/* STRATNUM_H */

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201803311
+#define CATALOG_VERSION_NO	201804031
 
 #endif

src/include/catalog/pg_amop.h

@@ -799,6 +799,7 @@ DATA(insert (	4017   25 25 11 s	664 4000 0 ));
 DATA(insert (	4017   25 25 12 s	665 4000 0 ));
 DATA(insert (	4017   25 25 14 s	667 4000 0 ));
 DATA(insert (	4017   25 25 15 s	666 4000 0 ));
+DATA(insert (	4017   25 25 28 s	3877 4000 0 ));
 
 /*
  * btree jsonb_ops

src/include/catalog/pg_operator.h

@@ -134,6 +134,8 @@ DESCR("less than");
 DATA(insert OID =  98 ( "="		   PGNSP PGUID b t t	25	25	16	98 531 texteq eqsel eqjoinsel ));
 DESCR("equal");
 #define TextEqualOperator	98
+DATA(insert OID =  3877 ( "^@"	   PGNSP PGUID b f f	25	25	16	0 0 starts_with prefixsel prefixjoinsel ));
+DESCR("starts with");
 
 DATA(insert OID = 349 (  "||"	   PGNSP PGUID b f f 2277 2283 2277 0 0 array_append   -	   -	 ));
 DESCR("append element onto end of array");

src/include/catalog/pg_proc.h

@@ -209,6 +209,7 @@ DATA(insert OID =  64 (  int2lt			   PGNSP PGUID 12 1 0 0 0 f f t t f i s 2 0 16
 DATA(insert OID =  65 (  int4eq			   PGNSP PGUID 12 1 0 0 0 f f t t f i s 2 0 16 "23 23" _null_ _null_ _null_ _null_ _null_ int4eq _null_ _null_ _null_ ));
 DATA(insert OID =  66 (  int4lt			   PGNSP PGUID 12 1 0 0 0 f f t t f i s 2 0 16 "23 23" _null_ _null_ _null_ _null_ _null_ int4lt _null_ _null_ _null_ ));
 DATA(insert OID =  67 (  texteq			   PGNSP PGUID 12 1 0 0 0 f f t t f i s 2 0 16 "25 25" _null_ _null_ _null_ _null_ _null_ texteq _null_ _null_ _null_ ));
+DATA(insert OID =  3696 ( starts_with	   PGNSP PGUID 12 1 0 0 0 f f t t f i s 2 0 16 "25 25" _null_ _null_ _null_ _null_ _null_ text_starts_with _null_ _null_ _null_ ));
 DATA(insert OID =  68 (  xideq			   PGNSP PGUID 12 1 0 0 0 f f t t f i s 2 0 16 "28 28" _null_ _null_ _null_ _null_ _null_ xideq _null_ _null_ _null_ ));
 DATA(insert OID = 3308 (  xidneq		   PGNSP PGUID 12 1 0 0 0 f f t t f i s 2 0 16 "28 28" _null_ _null_ _null_ _null_ _null_ xidneq _null_ _null_ _null_ ));
 DATA(insert OID =  69 (  cideq			   PGNSP PGUID 12 1 0 0 0 f f t t f i s 2 0 16 "29 29" _null_ _null_ _null_ _null_ _null_ cideq _null_ _null_ _null_ ));
@@ -2584,6 +2585,10 @@ DATA(insert OID = 1828 ( nlikejoinsel		PGNSP PGUID 12 1 0 0 0 f f f t f s s 5 0
 DESCR("join selectivity of NOT LIKE");
 DATA(insert OID = 1829 ( icregexnejoinsel	PGNSP PGUID 12 1 0 0 0 f f f t f s s 5 0 701 "2281 26 2281 21 2281" _null_ _null_ _null_ _null_  _null_ icregexnejoinsel _null_ _null_ _null_ ));
 DESCR("join selectivity of case-insensitive regex non-match");
+DATA(insert OID = 3437 ( prefixsel			PGNSP PGUID 12 1 0 0 0 f f f t f s s 4 0 701 "2281 26 2281 23" _null_ _null_ _null_ _null_ _null_ prefixsel _null_ _null_ _null_ ));
+DESCR("restriction selectivity of exact prefix");
+DATA(insert OID = 3438 ( prefixjoinsel		PGNSP PGUID 12 1 0 0 0 f f f t f s s 5 0 701 "2281 26 2281 21 2281" _null_ _null_ _null_ _null_  _null_ prefixjoinsel _null_ _null_ _null_ ));
+DESCR("join selectivity of exact prefix");
 
 /* Aggregate-related functions */
 DATA(insert OID = 1830 (  float8_avg	   PGNSP PGUID 12 1 0 0 0 f f f t f i s 1 0 701 "1022" _null_ _null_ _null_ _null_ _null_ float8_avg _null_ _null_ _null_ ));

src/include/utils/selfuncs.h

@@ -87,8 +87,11 @@ typedef struct VariableStatData
 
 typedef enum
 {
-	Pattern_Type_Like, Pattern_Type_Like_IC,
-	Pattern_Type_Regex, Pattern_Type_Regex_IC
+	Pattern_Type_Like,
+	Pattern_Type_Like_IC,
+	Pattern_Type_Regex,
+	Pattern_Type_Regex_IC,
+	Pattern_Type_Prefix
 } Pattern_Type;
 
 typedef enum

src/test/regress/expected/create_index.out

@@ -372,6 +372,12 @@ SELECT count(*) FROM radix_text_tbl WHERE t ~>~  'Worth
     48
 (1 row)
 
+SELECT count(*) FROM radix_text_tbl WHERE t ^@  'Worth';
+ count 
+-------
+     2
+(1 row)
+
 SELECT * FROM gpolygon_tbl ORDER BY f1 <-> '(0,0)'::point LIMIT 10;
                        f1                        
 -------------------------------------------------
@@ -1182,6 +1188,21 @@ SELECT count(*) FROM radix_text_tbl WHERE t ~>~  'Worth
     48
 (1 row)
 
+EXPLAIN (COSTS OFF)
+SELECT count(*) FROM radix_text_tbl WHERE t ^@	 'Worth';
+                         QUERY PLAN                         
+------------------------------------------------------------
+ Aggregate
+   ->  Index Only Scan using sp_radix_ind on radix_text_tbl
+         Index Cond: (t ^@ 'Worth'::text)
+(3 rows)
+
+SELECT count(*) FROM radix_text_tbl WHERE t ^@	 'Worth';
+ count 
+-------
+     2
+(1 row)
+
 EXPLAIN (COSTS OFF)
 SELECT * FROM gpolygon_tbl ORDER BY f1 <-> '(0,0)'::point LIMIT 10;
                      QUERY PLAN                      
@@ -1763,6 +1784,23 @@ SELECT count(*) FROM radix_text_tbl WHERE t ~>~  'Worth
     48
 (1 row)
 
+EXPLAIN (COSTS OFF)
+SELECT count(*) FROM radix_text_tbl WHERE t ^@	 'Worth';
+                   QUERY PLAN                   
+------------------------------------------------
+ Aggregate
+   ->  Bitmap Heap Scan on radix_text_tbl
+         Recheck Cond: (t ^@ 'Worth'::text)
+         ->  Bitmap Index Scan on sp_radix_ind
+               Index Cond: (t ^@ 'Worth'::text)
+(5 rows)
+
+SELECT count(*) FROM radix_text_tbl WHERE t ^@	 'Worth';
+ count 
+-------
+     2
+(1 row)
+
 RESET enable_seqscan;
 RESET enable_indexscan;
 RESET enable_bitmapscan;

src/test/regress/expected/opr_sanity.out

@@ -718,6 +718,7 @@ sha224(bytea)
 sha256(bytea)
 sha384(bytea)
 sha512(bytea)
+starts_with(text,text)
 macaddr8_eq(macaddr8,macaddr8)
 macaddr8_lt(macaddr8,macaddr8)
 macaddr8_le(macaddr8,macaddr8)
@@ -1887,7 +1888,8 @@ ORDER BY 1, 2, 3;
        4000 |           25 | <<=
        4000 |           26 | >>
        4000 |           27 | >>=
-(121 rows)
+       4000 |           28 | ^@
+(122 rows)
 
 -- Check that all opclass search operators have selectivity estimators.
 -- This is not absolutely required, but it seems a reasonable thing

src/test/regress/sql/create_index.sql

@@ -224,6 +224,8 @@ SELECT count(*) FROM radix_text_tbl WHERE t >    'Worth
 
 SELECT count(*) FROM radix_text_tbl WHERE t ~>~  'Worth                         St  ';
 
+SELECT count(*) FROM radix_text_tbl WHERE t ^@  'Worth';
+
 SELECT * FROM gpolygon_tbl ORDER BY f1 <-> '(0,0)'::point LIMIT 10;
 
 SELECT circle_center(f1), round(radius(f1)) as radius FROM gcircle_tbl ORDER BY f1 <-> '(200,300)'::point LIMIT 10;
@@ -441,6 +443,10 @@ EXPLAIN (COSTS OFF)
 SELECT count(*) FROM radix_text_tbl WHERE t ~>~  'Worth                         St  ';
 SELECT count(*) FROM radix_text_tbl WHERE t ~>~  'Worth                         St  ';
 
+EXPLAIN (COSTS OFF)
+SELECT count(*) FROM radix_text_tbl WHERE t ^@	 'Worth';
+SELECT count(*) FROM radix_text_tbl WHERE t ^@	 'Worth';
+
 EXPLAIN (COSTS OFF)
 SELECT * FROM gpolygon_tbl ORDER BY f1 <-> '(0,0)'::point LIMIT 10;
 SELECT * FROM gpolygon_tbl ORDER BY f1 <-> '(0,0)'::point LIMIT 10;
@@ -578,6 +584,10 @@ EXPLAIN (COSTS OFF)
 SELECT count(*) FROM radix_text_tbl WHERE t ~>~  'Worth                         St  ';
 SELECT count(*) FROM radix_text_tbl WHERE t ~>~  'Worth                         St  ';
 
+EXPLAIN (COSTS OFF)
+SELECT count(*) FROM radix_text_tbl WHERE t ^@	 'Worth';
+SELECT count(*) FROM radix_text_tbl WHERE t ^@	 'Worth';
+
 RESET enable_seqscan;
 RESET enable_indexscan;
 RESET enable_bitmapscan;