Add min() and max() aggregates for pg_lsn

This is useful for monitoring, when it comes for example to calculations
of WAL retention with replication slots and delays with a set of
standbys.

Bump catalog version.

Author: Fabrízio de Royes Mello
Reviewed-by: Surafel Temesgen
Discussion: https://postgr.es/m/CAFcNs+oc8ZoHhowA4rR1GGCgG8QNgK_TOwPRVYQo5rYy8_PXzA@mail.gmail.com

doc/src/sgml/func.sgml

@@ -14804,7 +14804,7 @@ NULL baz</literallayout>(3 rows)</entry>
        </indexterm>
        <function>max(<replaceable class="parameter">expression</replaceable>)</function>
       </entry>
-      <entry>any numeric, string, date/time, network, or enum type,
+      <entry>any numeric, string, date/time, network, pg_lsn, or enum type,
              or arrays of these types</entry>
       <entry>same as argument type</entry>
       <entry>Yes</entry>
@@ -14822,7 +14822,7 @@ NULL baz</literallayout>(3 rows)</entry>
        </indexterm>
        <function>min(<replaceable class="parameter">expression</replaceable>)</function>
       </entry>
-      <entry>any numeric, string, date/time, network, or enum type,
+      <entry>any numeric, string, date/time, network, pg_lsn, or enum type,
              or arrays of these types</entry>
       <entry>same as argument type</entry>
       <entry>Yes</entry>

src/backend/utils/adt/pg_lsn.c

@@ -171,6 +171,24 @@ pg_lsn_ge(PG_FUNCTION_ARGS)
 	PG_RETURN_BOOL(lsn1 >= lsn2);
 }
 
+Datum
+pg_lsn_larger(PG_FUNCTION_ARGS)
+{
+	XLogRecPtr	lsn1 = PG_GETARG_LSN(0);
+	XLogRecPtr	lsn2 = PG_GETARG_LSN(1);
+
+	PG_RETURN_LSN((lsn1 > lsn2) ? lsn1 : lsn2);
+}
+
+Datum
+pg_lsn_smaller(PG_FUNCTION_ARGS)
+{
+	XLogRecPtr	lsn1 = PG_GETARG_LSN(0);
+	XLogRecPtr	lsn2 = PG_GETARG_LSN(1);
+
+	PG_RETURN_LSN((lsn1 < lsn2) ? lsn1 : lsn2);
+}
+
 /* btree index opclass support */
 Datum
 pg_lsn_cmp(PG_FUNCTION_ARGS)

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201907052
+#define CATALOG_VERSION_NO	201907053
 
 #endif

src/include/catalog/pg_aggregate.dat

@@ -146,6 +146,9 @@
 { aggfnoid => 'max(inet)', aggtransfn => 'network_larger',
   aggcombinefn => 'network_larger', aggsortop => '>(inet,inet)',
   aggtranstype => 'inet' },
+{ aggfnoid => 'max(pg_lsn)', aggtransfn => 'pg_lsn_larger',
+  aggcombinefn => 'pg_lsn_larger', aggsortop => '>(pg_lsn,pg_lsn)',
+  aggtranstype => 'pg_lsn' },
 
 # min
 { aggfnoid => 'min(int8)', aggtransfn => 'int8smaller',
@@ -208,6 +211,9 @@
 { aggfnoid => 'min(inet)', aggtransfn => 'network_smaller',
   aggcombinefn => 'network_smaller', aggsortop => '<(inet,inet)',
   aggtranstype => 'inet' },
+{ aggfnoid => 'min(pg_lsn)', aggtransfn => 'pg_lsn_smaller',
+  aggcombinefn => 'pg_lsn_smaller', aggsortop => '<(pg_lsn,pg_lsn)',
+  aggtranstype => 'pg_lsn' },
 
 # count
 { aggfnoid => 'count(any)', aggtransfn => 'int8inc_any',

src/include/catalog/pg_proc.dat

@@ -6219,6 +6219,9 @@
 { oid => '3564', descr => 'maximum value of all inet input values',
   proname => 'max', prokind => 'a', proisstrict => 'f', prorettype => 'inet',
   proargtypes => 'inet', prosrc => 'aggregate_dummy' },
+{ oid => '4189', descr => 'maximum value of all pg_lsn input values',
+  proname => 'max', prokind => 'a', proisstrict => 'f', prorettype => 'pg_lsn',
+  proargtypes => 'pg_lsn', prosrc => 'aggregate_dummy' },
 
 { oid => '2131', descr => 'minimum value of all bigint input values',
   proname => 'min', prokind => 'a', proisstrict => 'f', prorettype => 'int8',
@@ -6283,6 +6286,9 @@
 { oid => '3565', descr => 'minimum value of all inet input values',
   proname => 'min', prokind => 'a', proisstrict => 'f', prorettype => 'inet',
   proargtypes => 'inet', prosrc => 'aggregate_dummy' },
+{ oid => '4190', descr => 'minimum value of all pg_lsn input values',
+  proname => 'min', prokind => 'a', proisstrict => 'f', prorettype => 'pg_lsn',
+  proargtypes => 'pg_lsn', prosrc => 'aggregate_dummy' },
 
 # count has two forms: count(any) and count(*)
 { oid => '2147',
@@ -8385,6 +8391,12 @@
 { oid => '3413', descr => 'hash',
   proname => 'pg_lsn_hash_extended', prorettype => 'int8',
   proargtypes => 'pg_lsn int8', prosrc => 'pg_lsn_hash_extended' },
+{ oid => '4187', descr => 'larger of two',
+  proname => 'pg_lsn_larger', prorettype => 'pg_lsn',
+  proargtypes => 'pg_lsn pg_lsn', prosrc => 'pg_lsn_larger' },
+{ oid => '4188', descr => 'smaller of two',
+  proname => 'pg_lsn_smaller', prorettype => 'pg_lsn',
+  proargtypes => 'pg_lsn pg_lsn', prosrc => 'pg_lsn_smaller' },
 
 # enum related procs
 { oid => '3504', descr => 'I/O',

src/test/regress/expected/pg_lsn.out

@@ -26,6 +26,13 @@ INSERT INTO PG_LSN_TBL VALUES ('/ABCD');
 ERROR:  invalid input syntax for type pg_lsn: "/ABCD"
 LINE 1: INSERT INTO PG_LSN_TBL VALUES ('/ABCD');
                                        ^
+-- Min/Max aggregation
+SELECT MIN(f1), MAX(f1) FROM PG_LSN_TBL;
+ min |        max        
+-----+-------------------
+ 0/0 | FFFFFFFF/FFFFFFFF
+(1 row)
+
 DROP TABLE PG_LSN_TBL;
 -- Operators
 SELECT '0/16AE7F8' = '0/16AE7F8'::pg_lsn;

src/test/regress/sql/pg_lsn.sql

@@ -14,6 +14,10 @@ INSERT INTO PG_LSN_TBL VALUES ('-1/0');
 INSERT INTO PG_LSN_TBL VALUES (' 0/12345678');
 INSERT INTO PG_LSN_TBL VALUES ('ABCD/');
 INSERT INTO PG_LSN_TBL VALUES ('/ABCD');
+
+-- Min/Max aggregation
+SELECT MIN(f1), MAX(f1) FROM PG_LSN_TBL;
+
 DROP TABLE PG_LSN_TBL;
 
 -- Operators