0001-Make-it-easy-to-print-LSN.patch

From 698e481f5f55b967b5c60dba4bc577f8baa20ff4 Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.bapat@2ndquadrant.com>
Date: Fri, 16 Oct 2020 17:09:29 +0530
Subject: [PATCH] Make it easy to print LSN

The commit introduces following macros and functions to make it easy to
use LSNs in printf variants, elog, ereport and appendStringInfo
variants.

LSN_FORMAT - macro representing the format in which LSN is printed

LSN_FORMAT_ARG - macro to pass LSN as an argument to the above format

pg_lsn_out_internal - a function which returns palloc'ed char array
containing string representation of given LSN.

pg_lsn_out_buffer - similar to above but accepts and returns a char
array of size (MAXPG_LSNLEN + 1)

The commit also has some example usages of these.

Ashutosh Bapat
---
 contrib/pageinspect/rawpage.c                |  3 +-
 src/backend/access/rmgrdesc/replorigindesc.c |  5 +-
 src/backend/access/rmgrdesc/xlogdesc.c       |  3 +-
 src/backend/access/transam/xlog.c            |  8 ++--
 src/backend/utils/adt/pg_lsn.c               | 49 ++++++++++++++------
 src/include/access/xlogdefs.h                |  7 +++
 src/include/utils/pg_lsn.h                   |  3 ++
 7 files changed, 55 insertions(+), 23 deletions(-)

diff --git a/contrib/pageinspect/rawpage.c b/contrib/pageinspect/rawpage.c
index c0181506a5..2cd055a5f0 100644
--- a/contrib/pageinspect/rawpage.c
+++ b/contrib/pageinspect/rawpage.c
@@ -261,8 +261,7 @@ page_header(PG_FUNCTION_ARGS)
 	{
 		char		lsnchar[64];
 
-		snprintf(lsnchar, sizeof(lsnchar), "%X/%X",
-				 (uint32) (lsn >> 32), (uint32) lsn);
+		snprintf(lsnchar, sizeof(lsnchar), LSN_FORMAT, LSN_FORMAT_ARG(lsn));
 		values[0] = CStringGetTextDatum(lsnchar);
 	}
 	else
diff --git a/src/backend/access/rmgrdesc/replorigindesc.c b/src/backend/access/rmgrdesc/replorigindesc.c
index 19e14f910b..a3f49b5750 100644
--- a/src/backend/access/rmgrdesc/replorigindesc.c
+++ b/src/backend/access/rmgrdesc/replorigindesc.c
@@ -29,10 +29,9 @@ replorigin_desc(StringInfo buf, XLogReaderState *record)
 
 				xlrec = (xl_replorigin_set *) rec;
 
-				appendStringInfo(buf, "set %u; lsn %X/%X; force: %d",
+				appendStringInfo(buf, "set %u; lsn " LSN_FORMAT "; force: %d",
 								 xlrec->node_id,
-								 (uint32) (xlrec->remote_lsn >> 32),
-								 (uint32) xlrec->remote_lsn,
+								 LSN_FORMAT_ARG(xlrec->remote_lsn),
 								 xlrec->force);
 				break;
 			}
diff --git a/src/backend/access/rmgrdesc/xlogdesc.c b/src/backend/access/rmgrdesc/xlogdesc.c
index 3200f777f5..22bdae5d9a 100644
--- a/src/backend/access/rmgrdesc/xlogdesc.c
+++ b/src/backend/access/rmgrdesc/xlogdesc.c
@@ -89,8 +89,7 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
 		XLogRecPtr	startpoint;
 
 		memcpy(&startpoint, rec, sizeof(XLogRecPtr));
-		appendStringInfo(buf, "%X/%X",
-						 (uint32) (startpoint >> 32), (uint32) startpoint);
+		appendStringInfo(buf, LSN_FORMAT, LSN_FORMAT_ARG(startpoint));
 	}
 	else if (info == XLOG_PARAMETER_CHANGE)
 	{
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 13f1d8c3dc..2436af5244 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -79,6 +79,7 @@
 #include "utils/pg_rusage.h"
 #include "utils/snapmgr.h"
 #include "utils/timestamp.h"
+#include "utils/pg_lsn.h"
 
 extern uint32 bootstrap_data_checksum_version;
 
@@ -5886,15 +5887,16 @@ recoveryStopsAfter(XLogReaderState *record)
 		recoveryTargetInclusive &&
 		record->ReadRecPtr >= recoveryTargetLSN)
 	{
+		char		buf[MAXPG_LSNLEN + 1];
+
 		recoveryStopAfter = true;
 		recoveryStopXid = InvalidTransactionId;
 		recoveryStopLSN = record->ReadRecPtr;
 		recoveryStopTime = 0;
 		recoveryStopName[0] = '\0';
 		ereport(LOG,
-				(errmsg("recovery stopping after WAL location (LSN) \"%X/%X\"",
-						(uint32) (recoveryStopLSN >> 32),
-						(uint32) recoveryStopLSN)));
+				(errmsg("recovery stopping after WAL location (LSN) \"%s\"",
+						pg_lsn_out_buffer(recoveryStopLSN, buf))));
 		return true;
 	}
 
diff --git a/src/backend/utils/adt/pg_lsn.c b/src/backend/utils/adt/pg_lsn.c
index ad0a7bd869..403a20c568 100644
--- a/src/backend/utils/adt/pg_lsn.c
+++ b/src/backend/utils/adt/pg_lsn.c
@@ -19,7 +19,6 @@
 #include "utils/numeric.h"
 #include "utils/pg_lsn.h"
 
-#define MAXPG_LSNLEN			17
 #define MAXPG_LSNCOMPONENT	8
 
 /*----------------------------------------------------------
@@ -81,18 +80,7 @@ Datum
 pg_lsn_out(PG_FUNCTION_ARGS)
 {
 	XLogRecPtr	lsn = PG_GETARG_LSN(0);
-	char		buf[MAXPG_LSNLEN + 1];
-	char	   *result;
-	uint32		id,
-				off;
-
-	/* Decode ID and offset */
-	id = (uint32) (lsn >> 32);
-	off = (uint32) lsn;
-
-	snprintf(buf, sizeof buf, "%X/%X", id, off);
-	result = pstrdup(buf);
-	PG_RETURN_CSTRING(result);
+	PG_RETURN_CSTRING(pg_lsn_out_internal(lsn));
 }
 
 Datum
@@ -317,3 +305,38 @@ pg_lsn_mii(PG_FUNCTION_ARGS)
 	/* Convert to pg_lsn */
 	return DirectFunctionCall1(numeric_pg_lsn, res);
 }
+
+/*
+ * pg_lsn_out_internal
+ *
+ * Returns palloc'ed string representation of an LSN. Used by pg_lsn_out() but
+ * is useful to print LSN in non-performance critical paths. The caller may
+ * pfree the returned memory chunk.
+ */
+char *
+pg_lsn_out_internal(XLogRecPtr lsn)
+{
+	char		buf[MAXPG_LSNLEN + 1];
+
+	snprintf(buf, sizeof(buf), LSN_FORMAT, LSN_FORMAT_ARG(lsn));
+
+	return pstrdup(buf);
+}
+
+/*
+ * pg_lsn_out_buffer
+ *
+ * Similar to the above function but saves the string representation of LSN in
+ * the given buffer which is expected to be at least MAXPG_LSNLEN long. It can
+ * be used in performance critical paths to avoid expensive memory allocation.
+ *
+ * The function returns pointer to the input buffer so that it can be used in
+ * printf variants.
+ */
+char *
+pg_lsn_out_buffer(XLogRecPtr lsn, char *buf)
+{
+	snprintf(buf, sizeof(buf), LSN_FORMAT, LSN_FORMAT_ARG(lsn));
+
+	return buf;
+}
diff --git a/src/include/access/xlogdefs.h b/src/include/access/xlogdefs.h
index e1f5812213..c704ca2454 100644
--- a/src/include/access/xlogdefs.h
+++ b/src/include/access/xlogdefs.h
@@ -35,6 +35,13 @@ typedef uint64 XLogRecPtr;
  */
 #define FirstNormalUnloggedLSN	((XLogRecPtr) 1000)
 
+/* Handy macros to print LSN */
+#define LSN_FORMAT "%X/%X"
+#define LSN_FORMAT_ARG(lsn) (uint32) ((lsn) >> 32), (uint32) (lsn)
+
+/* Maximum length of string representation of an LSN */
+#define MAXPG_LSNLEN			17
+
 /*
  * XLogSegNo - physical log file sequence number.
  */
diff --git a/src/include/utils/pg_lsn.h b/src/include/utils/pg_lsn.h
index 25d6c5b38e..7a8637d2bd 100644
--- a/src/include/utils/pg_lsn.h
+++ b/src/include/utils/pg_lsn.h
@@ -26,4 +26,7 @@
 
 extern XLogRecPtr pg_lsn_in_internal(const char *str, bool *have_error);
 
+extern char *pg_lsn_out_internal(XLogRecPtr lsn);
+extern char *pg_lsn_out_buffer(XLogRecPtr lsn, char *buf);
+
 #endif							/* PG_LSN_H */
-- 
2.17.1