Add max() and min() aggregate functions for pg_lsn data type.

Makefile

@@ -9,7 +9,7 @@ REGRESS = pg_cheat_funcs pg_eucjp
 MAJORVERSION_INT = $(shell echo $(MAJORVERSION).0 | cut -d . -f 1-2 | tr -d .)
 REGRESS += $(shell if [ $(MAJORVERSION_INT) -ge 96 ]; then echo pg_stat_get_memory_context; fi)
 REGRESS += $(shell if [ $(MAJORVERSION_INT) -ge 95 ]; then echo pglz_compress; fi)
-REGRESS += $(shell if [ $(MAJORVERSION_INT) -ge 94 ]; then echo pg_chr; else echo pg_chr_91_93; fi)
+REGRESS += $(shell if [ $(MAJORVERSION_INT) -ge 94 ]; then echo pg_chr pg_lsn; else echo pg_chr_91_93; fi)
 
 PGFILEDESC = "pg_cheat_funcs - provides cheat (but useful) functions"
 

README.md

@@ -93,6 +93,16 @@ That is, this function can return bogus WAL file name.
 For details of this conversion, please see [PostgreSQL document](http://www.postgresql.org/docs/devel/static/functions-admin.html#FUNCTIONS-ADMIN-BACKUP).
 This function is available only in PostgreSQL 9.4 or later.
 
+### pg_lsn max(SETOF pg_lsn)
+This is max() aggregate function for pg_lsn data type.
+This aggregate function computes and returns a maximum pg_lsn value
+from a set of pg_lsn input values.
+
+### pg_lsn min(SETOF pg_lsn)
+This is min() aggregate function for pg_lsn data type.
+This aggregate function computes and returns a minimum pg_lsn value
+from a set of pg_lsn input values.
+
 ### SETOF record pg_stat_get_syncrep_waiters()
 Return statistics about all server processes waiting for
 synchronous replication.

pg_cheat_funcs--1.0.sql

@@ -42,7 +42,7 @@ AS 'MODULE_PATHNAME'
 LANGUAGE C STRICT VOLATILE;
 REVOKE ALL ON FUNCTION pg_process_config_file() FROM PUBLIC;
 
-/* pg_xlogfile_name function is available only in 9.4 or later */
+/* Any functions using pg_lsn data type are available only in 9.4 or later */
 DO $$
 DECLARE
     pgversion INTEGER;
@@ -55,6 +55,31 @@ BEGIN
         RETURNS text
         AS 'MODULE_PATHNAME'
         LANGUAGE C STRICT VOLATILE;
+
+        -- Aggregate functions for pg_lsn data type.
+        CREATE FUNCTION pg_lsn_larger(pg_lsn, pg_lsn)
+        RETURNS pg_lsn
+        AS 'MODULE_PATHNAME'
+        LANGUAGE C STRICT IMMUTABLE;
+
+        CREATE FUNCTION pg_lsn_smaller(pg_lsn, pg_lsn)
+        RETURNS pg_lsn
+        AS 'MODULE_PATHNAME'
+        LANGUAGE C STRICT IMMUTABLE;
+
+        CREATE AGGREGATE max(pg_lsn)  (
+            SFUNC = pg_lsn_larger,
+            STYPE = pg_lsn,
+            SORTOP = >,
+            COMBINEFUNC = pg_lsn_larger
+        );
+
+        CREATE AGGREGATE min(pg_lsn)  (
+            SFUNC = pg_lsn_smaller,
+            STYPE = pg_lsn,
+            SORTOP = <,
+            COMBINEFUNC = pg_lsn_smaller
+        );
     END IF;
 END;
 $$;

pg_cheat_funcs.c

@@ -90,6 +90,8 @@ PG_FUNCTION_INFO_V1(pg_signal_process);
 PG_FUNCTION_INFO_V1(pg_process_config_file);
 #if PG_VERSION_NUM >= 90400
 PG_FUNCTION_INFO_V1(pg_xlogfile_name);
+PG_FUNCTION_INFO_V1(pg_lsn_larger);
+PG_FUNCTION_INFO_V1(pg_lsn_smaller);
 PG_FUNCTION_INFO_V1(pg_stat_get_syncrep_waiters);
 PG_FUNCTION_INFO_V1(pg_wait_syncrep);
 #endif
@@ -581,6 +583,36 @@ pg_xlogfile_name(PG_FUNCTION_ARGS)
 	PG_RETURN_TEXT_P(cstring_to_text(xlogfilename));
 }
 
+/*
+ * Return larger pg_lsn value.
+ */
+Datum
+pg_lsn_larger(PG_FUNCTION_ARGS)
+{
+	XLogRecPtr	lsn1 = PG_GETARG_LSN(0);
+	XLogRecPtr	lsn2 = PG_GETARG_LSN(1);
+	XLogRecPtr	result;
+
+	result = ((lsn1 > lsn2) ? lsn1 : lsn2);
+
+	PG_RETURN_LSN(result);
+}
+
+/*
+ * Return smaller pg_lsn value.
+ */
+Datum
+pg_lsn_smaller(PG_FUNCTION_ARGS)
+{
+	XLogRecPtr	lsn1 = PG_GETARG_LSN(0);
+	XLogRecPtr	lsn2 = PG_GETARG_LSN(1);
+	XLogRecPtr	result;
+
+	result = ((lsn1 < lsn2) ? lsn1 : lsn2);
+
+	PG_RETURN_LSN(result);
+}
+
 /*
  * Return statistics about all syncrep waiters.
  */