diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 48631cc..04bc24d 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -14378,6 +14378,9 @@ SELECT set_config('log_statement_stats', 'off', false);
pg_xlogfile_name_offset
+
+ pg_xlog_location_diff
+
The functions shown in text, integer
Convert transaction log location string to file name and decimal byte offset within file
+
+
+ pg_xlog_location_diff(location text, location text)
+
+ numeric
+ Calculate the difference between two transaction log locations
+
@@ -14543,6 +14553,13 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
+ pg_xlog_location_diff calculates the difference in bytes
+ between two transaction log locations. It can be used with
+ pg_stat_replication or some functions shown in
+ to get the replication lag.
+
+
+
For details about proper usage of these functions, see
.
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 2e10d4d..e03c5e8 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -26,6 +26,7 @@
#include "replication/walreceiver.h"
#include "storage/smgr.h"
#include "utils/builtins.h"
+#include "utils/numeric.h"
#include "utils/guc.h"
#include "utils/timestamp.h"
@@ -465,3 +466,84 @@ pg_is_in_recovery(PG_FUNCTION_ARGS)
{
PG_RETURN_BOOL(RecoveryInProgress());
}
+
+static void
+validate_xlog_location(char *str)
+{
+#define MAXLSNCOMPONENT 8
+
+ int len1, len2;
+
+ len1 = strspn(str, "0123456789abcdefABCDEF");
+ if (len1 < 1 || len1 > MAXLSNCOMPONENT || str[len1] != '/')
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
+ errmsg("invalid input syntax for transaction log location: \"%s\"", str)));
+ len2 = strspn(str + len1 + 1, "0123456789abcdefABCDEF");
+ if (len2 < 1 || len2 > MAXLSNCOMPONENT || str[len1 + 1 + len2] != '\0')
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
+ errmsg("invalid input syntax for transaction log location: \"%s\"", str)));
+}
+
+/*
+ * Compute the difference in bytes between two WAL locations.
+ */
+Datum
+pg_xlog_location_diff(PG_FUNCTION_ARGS)
+{
+ text *location1 = PG_GETARG_TEXT_P(0);
+ text *location2 = PG_GETARG_TEXT_P(1);
+ char *str1, *str2;
+ uint64 xlogid1, xrecoff1;
+ uint64 xlogid2, xrecoff2;
+ Numeric result;
+
+ /*
+ * Read and parse input
+ */
+ str1 = text_to_cstring(location1);
+ str2 = text_to_cstring(location2);
+
+ validate_xlog_location(str1);
+ validate_xlog_location(str2);
+
+ if (sscanf(str1, "%8lX/%8lX", &xlogid1, &xrecoff1) != 2)
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("could not parse transaction log location \"%s\"", str1)));
+ if (sscanf(str2, "%8lX/%8lX", &xlogid2, &xrecoff2) != 2)
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("could not parse transaction log location \"%s\"", str2)));
+
+ /*
+ * Sanity check
+ */
+ if (xrecoff1 > XLogFileSize)
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("xrecoff \"%lX\" is out of valid range, 0..%X", xrecoff1, XLogFileSize)));
+ if (xrecoff2 > XLogFileSize)
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("xrecoff \"%lX\" is out of valid range, 0..%X", xrecoff2, XLogFileSize)));
+
+ /*
+ * result = XLogFileSize * (xlogid1 - xlogid2) + xrecoff1 - xrecoff2
+ */
+ result = DatumGetNumeric(DirectFunctionCall2(numeric_sub,
+ DirectFunctionCall1(int8_numeric, Int64GetDatum(xlogid1)),
+ DirectFunctionCall1(int8_numeric, Int64GetDatum(xlogid2))));
+ result = DatumGetNumeric(DirectFunctionCall2(numeric_mul,
+ DirectFunctionCall1(int8_numeric, Int64GetDatum(XLogFileSize)),
+ NumericGetDatum(result)));
+ result = DatumGetNumeric(DirectFunctionCall2(numeric_add,
+ NumericGetDatum(result),
+ DirectFunctionCall1(int8_numeric, Int64GetDatum(xrecoff1))));
+ result = DatumGetNumeric(DirectFunctionCall2(numeric_sub,
+ NumericGetDatum(result),
+ DirectFunctionCall1(int8_numeric, Int64GetDatum(xrecoff2))));
+
+ PG_RETURN_NUMERIC(result);
+}
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index db6380f..fa45aa1 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -281,5 +281,6 @@ extern Datum pg_is_in_recovery(PG_FUNCTION_ARGS);
extern Datum pg_xlog_replay_pause(PG_FUNCTION_ARGS);
extern Datum pg_xlog_replay_resume(PG_FUNCTION_ARGS);
extern Datum pg_is_xlog_replay_paused(PG_FUNCTION_ARGS);
+extern Datum pg_xlog_location_diff(PG_FUNCTION_ARGS);
#endif /* XLOG_INTERNAL_H */
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index b6ac195..9940658 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -2902,6 +2902,8 @@ DATA(insert OID = 2850 ( pg_xlogfile_name_offset PGNSP PGUID 12 1 0 0 0 f f f t
DESCR("xlog filename and byte offset, given an xlog location");
DATA(insert OID = 2851 ( pg_xlogfile_name PGNSP PGUID 12 1 0 0 0 f f f t f i 1 0 25 "25" _null_ _null_ _null_ _null_ pg_xlogfile_name _null_ _null_ _null_ ));
DESCR("xlog filename, given an xlog location");
+DATA(insert OID = 3150 ( pg_xlog_location_diff PGNSP PGUID 12 1 0 0 0 f f f t f i 2 0 1700 "25 25" _null_ _null_ _null_ _null_ pg_xlog_location_diff _null_ _null_ _null_ ));
+DESCR("difference in bytes, given two xlog locations");
DATA(insert OID = 3809 ( pg_export_snapshot PGNSP PGUID 12 1 0 0 0 f f f t f v 0 0 25 "" _null_ _null_ _null_ _null_ pg_export_snapshot _null_ _null_ _null_ ));
DESCR("export a snapshot");