Add pg_dissect_walfile_name()

This function takes in input a WAL segment name and returns a tuple made
of the segment sequence number (dependent on the WAL segment size of the
cluster) and its timeline, as of a thin SQL wrapper around the existing
XLogFromFileName().

This function has multiple usages, like being able to compile a LSN from
a file name and an offset, or finding the timeline of a segment without
having to do to some maths based on the first eight characters of the
segment.

Bump catalog version.

Author: Bharath Rupireddy
Reviewed-by: Nathan Bossart, Kyotaro Horiguchi, Maxim Orlov, Michael
Paquier
Discussion: https://postgr.es/m/CALj2ACWV=FCddsxcGbVOA=cvPyMr75YCFbSQT6g4KDj=gcJK4g@mail.gmail.com

5 files changed, 92 insertions, 1 deletions

diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 487d5d9cac7..0a31837ef18 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -433,6 +433,59 @@ pg_walfile_name(PG_FUNCTION_ARGS)
 }
 
 /*
+ * Extract the sequence number and the timeline ID from given a WAL file
+ * name.
+ */
+Datum
+pg_dissect_walfile_name(PG_FUNCTION_ARGS)
+{
+#define PG_DISSECT_WALFILE_NAME_COLS 2
+	char	   *fname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+	char	   *fname_upper;
+	char	   *p;
+	TimeLineID	tli;
+	XLogSegNo	segno;
+	Datum		values[PG_DISSECT_WALFILE_NAME_COLS] = {0};
+	bool		isnull[PG_DISSECT_WALFILE_NAME_COLS] = {0};
+	TupleDesc	tupdesc;
+	HeapTuple	tuple;
+	char		buf[256];
+	Datum		result;
+
+	fname_upper = pstrdup(fname);
+
+	/* Capitalize WAL file name. */
+	for (p = fname_upper; *p; p++)
+		*p = pg_toupper((unsigned char) *p);
+
+	if (!IsXLogFileName(fname_upper))
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("invalid WAL file name \"%s\"", fname)));
+
+	XLogFromFileName(fname_upper, &tli, &segno, wal_segment_size);
+
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	/* Convert to numeric. */
+	snprintf(buf, sizeof buf, UINT64_FORMAT, segno);
+	values[0] = DirectFunctionCall3(numeric_in,
+									CStringGetDatum(buf),
+									ObjectIdGetDatum(0),
+									Int32GetDatum(-1));
+
+	values[1] = Int64GetDatum(tli);
+
+	tuple = heap_form_tuple(tupdesc, values, isnull);
+	result = HeapTupleGetDatum(tuple);
+
+	PG_RETURN_DATUM(result);
+
+#undef PG_DISSECT_WALFILE_NAME_COLS
+}
+
+/*
  * pg_wal_replay_pause - Request to pause recovery
  *
  * Permission checking for this function is managed through the normal
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 094f59f82db..091ad94c5eb 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202212191
+#define CATALOG_VERSION_NO	202212201
 
 #endif
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index d763419c0de..98d90d93389 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -6372,6 +6372,13 @@
 { oid => '2851', descr => 'wal filename, given a wal location',
   proname => 'pg_walfile_name', prorettype => 'text', proargtypes => 'pg_lsn',
   prosrc => 'pg_walfile_name' },
+{ oid => '8205',
+  descr => 'sequence number and timeline ID given a wal filename',
+  proname => 'pg_dissect_walfile_name', provolatile => 's',
+  prorettype => 'record', proargtypes => 'text',
+  proallargtypes => '{text,numeric,int8}', proargmodes => '{i,o,o}',
+  proargnames => '{file_name,segno,timeline_id}',
+  prosrc => 'pg_dissect_walfile_name' },
 
 { oid => '3165', descr => 'difference in bytes, given two wal locations',
   proname => 'pg_wal_lsn_diff', prorettype => 'numeric',
diff --git a/src/test/regress/expected/misc_functions.out b/src/test/regress/expected/misc_functions.out
index 88bb696ded8..2907f779a75 100644
--- a/src/test/regress/expected/misc_functions.out
+++ b/src/test/regress/expected/misc_functions.out
@@ -619,3 +619,26 @@ SELECT count(*) > 0 AS ok FROM pg_control_system();
  t
 (1 row)
 
+-- pg_dissect_walfile_name
+SELECT * FROM pg_dissect_walfile_name(NULL);
+ segno | timeline_id 
+-------+-------------
+       |            
+(1 row)
+
+SELECT * FROM pg_dissect_walfile_name('invalid');
+ERROR:  invalid WAL file name "invalid"
+SELECT segno > 0 AS ok_segno, timeline_id
+  FROM pg_dissect_walfile_name('000000010000000100000000');
+ ok_segno | timeline_id 
+----------+-------------
+ t        |           1
+(1 row)
+
+SELECT segno > 0 AS ok_segno, timeline_id
+  FROM pg_dissect_walfile_name('ffffffFF00000001000000af');
+ ok_segno | timeline_id 
+----------+-------------
+ t        |  4294967295
+(1 row)
+
diff --git a/src/test/regress/sql/misc_functions.sql b/src/test/regress/sql/misc_functions.sql
index b07e9e8dbb3..0c3d75fd1ac 100644
--- a/src/test/regress/sql/misc_functions.sql
+++ b/src/test/regress/sql/misc_functions.sql
@@ -229,3 +229,11 @@ SELECT count(*) > 0 AS ok FROM pg_control_checkpoint();
 SELECT count(*) > 0 AS ok FROM pg_control_init();
 SELECT count(*) > 0 AS ok FROM pg_control_recovery();
 SELECT count(*) > 0 AS ok FROM pg_control_system();
+
+-- pg_dissect_walfile_name
+SELECT * FROM pg_dissect_walfile_name(NULL);
+SELECT * FROM pg_dissect_walfile_name('invalid');
+SELECT segno > 0 AS ok_segno, timeline_id
+  FROM pg_dissect_walfile_name('000000010000000100000000');
+SELECT segno > 0 AS ok_segno, timeline_id
+  FROM pg_dissect_walfile_name('ffffffFF00000001000000af');