Change the display of WAL usage statistics in Explain.

In commit 33e05f89c5, we have added the option to display WAL usage
statistics in Explain and auto_explain.  The display format used two spaces
between each field which is inconsistent with Buffer usage statistics which
is using one space between each field.  Change the format to make WAL usage
statistics consistent with Buffer usage statistics.

This commit also changed the usage of "full page writes" to
"full page images" for WAL usage statistics to make it consistent with
other parts of code and docs.

Author: Julien Rouhaud, Amit Kapila
Reviewed-by: Justin Pryzby, Kyotaro Horiguchi and Amit Kapila
Discussion: https://postgr.es/m/CAB-hujrP8ZfUkvL5OYETipQwA=e3n7oqHFU=4ZLxWS_Cza3kQQ@mail.gmail.com

contrib/pg_stat_statements/pg_stat_statements--1.7--1.8.sql

@@ -43,7 +43,7 @@ CREATE FUNCTION pg_stat_statements(IN showtext boolean,
     OUT blk_read_time float8,
     OUT blk_write_time float8,
     OUT wal_records int8,
-    OUT wal_fpw int8,
+    OUT wal_fpi int8,
     OUT wal_bytes numeric
 )
 RETURNS SETOF record

contrib/pg_stat_statements/pg_stat_statements.c

@@ -189,7 +189,7 @@ typedef struct Counters
 	double		blk_write_time; /* time spent writing, in msec */
 	double		usage;			/* usage factor */
 	int64		wal_records;	/* # of WAL records generated */
-	int64		wal_fpw;	/* # of WAL full page writes generated */
+	int64		wal_fpi;		/* # of WAL full page images generated */
 	uint64		wal_bytes;		/* total amount of WAL bytes generated */
 } Counters;
 
@@ -1432,7 +1432,7 @@ pgss_store(const char *query, uint64 queryId,
 		e->counters.blk_write_time += INSTR_TIME_GET_MILLISEC(bufusage->blk_write_time);
 		e->counters.usage += USAGE_EXEC(total_time);
 		e->counters.wal_records += walusage->wal_records;
-		e->counters.wal_fpw += walusage->wal_fpw;
+		e->counters.wal_fpi += walusage->wal_fpi;
 		e->counters.wal_bytes += walusage->wal_bytes;
 
 		SpinLockRelease(&e->mutex);
@@ -1824,7 +1824,7 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
 			Datum		wal_bytes;
 
 			values[i++] = Int64GetDatumFast(tmp.wal_records);
-			values[i++] = Int64GetDatumFast(tmp.wal_fpw);
+			values[i++] = Int64GetDatumFast(tmp.wal_fpi);
 
 			snprintf(buf, sizeof buf, UINT64_FORMAT, tmp.wal_bytes);
 

doc/src/sgml/pgstatstatements.sgml

@@ -283,11 +283,11 @@
      </row>
 
      <row>
-      <entry><structfield>wal_fpw</structfield></entry>
+      <entry><structfield>wal_fpi</structfield></entry>
       <entry><type>bigint</type></entry>
       <entry></entry>
       <entry>
-        Total number of WAL full page writes generated by the statement
+        Total number of WAL full page images generated by the statement
       </entry>
      </row>
 

doc/src/sgml/ref/explain.sgml

@@ -198,8 +198,8 @@ ROLLBACK;
     <listitem>
      <para>
       Include information on WAL record generation. Specifically, include the
-      number of records, number of full page writes and amount of WAL bytes
+      number of records, number of full page images (fpi) and amount of WAL
-      generated.  In text format, only non-zero values are printed.  This
+      bytes generated.  In text format, only non-zero values are printed.  This
       parameter may only be used when <literal>ANALYZE</literal> is also
       enabled.  It defaults to <literal>FALSE</literal>.
      </para>

src/backend/access/heap/vacuumlazy.c

@@ -673,10 +673,10 @@ heap_vacuum_rel(Relation onerel, VacuumParams *params,
 							 read_rate, write_rate);
 			appendStringInfo(&buf, _("system usage: %s\n"), pg_rusage_show(&ru0));
 			appendStringInfo(&buf,
-							 _("WAL usage: %ld records, %ld full page writes, "
+							 _("WAL usage: %ld records, %ld full page images, "
 							   UINT64_FORMAT " bytes"),
 							 walusage.wal_records,
-							 walusage.wal_fpw,
+							 walusage.wal_fpi,
 							 walusage.wal_bytes);
 
 			ereport(LOG,

src/backend/access/transam/xlog.c

@@ -998,7 +998,7 @@ XLogRecPtr
 XLogInsertRecord(XLogRecData *rdata,
 				 XLogRecPtr fpw_lsn,
 				 uint8 flags,
-				 int num_fpw)
+				 int num_fpi)
 {
 	XLogCtlInsert *Insert = &XLogCtl->Insert;
 	pg_crc32c	rdata_crc;
@@ -1259,7 +1259,7 @@ XLogInsertRecord(XLogRecData *rdata,
 	{
 		pgWalUsage.wal_bytes += rechdr->xl_tot_len;
 		pgWalUsage.wal_records++;
-		pgWalUsage.wal_fpw += num_fpw;
+		pgWalUsage.wal_fpi += num_fpi;
 	}
 
 	return EndPos;

src/backend/access/transam/xloginsert.c

@@ -109,7 +109,7 @@ static MemoryContext xloginsert_cxt;
 
 static XLogRecData *XLogRecordAssemble(RmgrId rmid, uint8 info,
 									   XLogRecPtr RedoRecPtr, bool doPageWrites,
-									   XLogRecPtr *fpw_lsn, int *num_fpw);
+									   XLogRecPtr *fpw_lsn, int *num_fpi);
 static bool XLogCompressBackupBlock(char *page, uint16 hole_offset,
 									uint16 hole_length, char *dest, uint16 *dlen);
 
@@ -449,7 +449,7 @@ XLogInsert(RmgrId rmid, uint8 info)
 		bool		doPageWrites;
 		XLogRecPtr	fpw_lsn;
 		XLogRecData *rdt;
-		int			num_fpw = 0;
+		int			num_fpi = 0;
 
 		/*
 		 * Get values needed to decide whether to do full-page writes. Since
@@ -459,9 +459,9 @@ XLogInsert(RmgrId rmid, uint8 info)
 		GetFullPageWriteInfo(&RedoRecPtr, &doPageWrites);
 
 		rdt = XLogRecordAssemble(rmid, info, RedoRecPtr, doPageWrites,
-								 &fpw_lsn, &num_fpw);
+								 &fpw_lsn, &num_fpi);
 
-		EndPos = XLogInsertRecord(rdt, fpw_lsn, curinsert_flags, num_fpw);
+		EndPos = XLogInsertRecord(rdt, fpw_lsn, curinsert_flags, num_fpi);
 	} while (EndPos == InvalidXLogRecPtr);
 
 	XLogResetInsertion();
@@ -484,7 +484,7 @@ XLogInsert(RmgrId rmid, uint8 info)
 static XLogRecData *
 XLogRecordAssemble(RmgrId rmid, uint8 info,
 				   XLogRecPtr RedoRecPtr, bool doPageWrites,
-				   XLogRecPtr *fpw_lsn, int *num_fpw)
+				   XLogRecPtr *fpw_lsn, int *num_fpi)
 {
 	XLogRecData *rdt;
 	uint32		total_len = 0;
@@ -638,7 +638,7 @@ XLogRecordAssemble(RmgrId rmid, uint8 info,
 			bkpb.fork_flags |= BKPBLOCK_HAS_IMAGE;
 
 			/* Report a full page image constructed for the WAL record */
-			*num_fpw += 1;
+			*num_fpi += 1;
 
 			/*
 			 * Construct XLogRecData entries for the page content.

src/backend/commands/explain.c

@@ -3343,31 +3343,31 @@ show_wal_usage(ExplainState *es, const WalUsage *usage)
 	if (es->format == EXPLAIN_FORMAT_TEXT)
 	{
 		/* Show only positive counter values. */
-		if ((usage->wal_records > 0) || (usage->wal_fpw > 0) ||
+		if ((usage->wal_records > 0) || (usage->wal_fpi > 0) ||
 			(usage->wal_bytes > 0))
 		{
 			ExplainIndentText(es);
 			appendStringInfoString(es->str, "WAL:");
 
 			if (usage->wal_records > 0)
-				appendStringInfo(es->str, "  records=%ld",
+				appendStringInfo(es->str, " records=%ld",
 								 usage->wal_records);
-			if (usage->wal_fpw > 0)
+			if (usage->wal_fpi > 0)
-				appendStringInfo(es->str, "  full page writes=%ld",
+				appendStringInfo(es->str, " fpi=%ld",
-								 usage->wal_fpw);
+								 usage->wal_fpi);
 			if (usage->wal_bytes > 0)
-				appendStringInfo(es->str, "  bytes=" UINT64_FORMAT,
+				appendStringInfo(es->str, " bytes=" UINT64_FORMAT,
 								 usage->wal_bytes);
 			appendStringInfoChar(es->str, '\n');
 		}
 	}
 	else
 	{
-		ExplainPropertyInteger("WAL records", NULL,
+		ExplainPropertyInteger("WAL Records", NULL,
 							   usage->wal_records, es);
-		ExplainPropertyInteger("WAL full page writes", NULL,
+		ExplainPropertyInteger("WAL FPI", NULL,
-							   usage->wal_fpw, es);
+							   usage->wal_fpi, es);
-		ExplainPropertyUInteger("WAL bytes", NULL,
+		ExplainPropertyUInteger("WAL Bytes", NULL,
 								usage->wal_bytes, es);
 	}
 }

src/backend/executor/instrument.c

@@ -248,7 +248,7 @@ WalUsageAdd(WalUsage *dst, WalUsage *add)
 {
 	dst->wal_bytes += add->wal_bytes;
 	dst->wal_records += add->wal_records;
-	dst->wal_fpw += add->wal_fpw;
+	dst->wal_fpi += add->wal_fpi;
 }
 
 void
@@ -256,5 +256,5 @@ WalUsageAccumDiff(WalUsage *dst, const WalUsage *add, const WalUsage *sub)
 {
 	dst->wal_bytes += add->wal_bytes - sub->wal_bytes;
 	dst->wal_records += add->wal_records - sub->wal_records;
-	dst->wal_fpw += add->wal_fpw - sub->wal_fpw;
+	dst->wal_fpi += add->wal_fpi - sub->wal_fpi;
 }

src/include/access/xlog.h

@@ -280,7 +280,7 @@ struct XLogRecData;
 extern XLogRecPtr XLogInsertRecord(struct XLogRecData *rdata,
 								   XLogRecPtr fpw_lsn,
 								   uint8 flags,
-								   int num_fpw);
+								   int num_fpi);
 extern void XLogFlush(XLogRecPtr RecPtr);
 extern bool XLogBackgroundFlush(void);
 extern bool XLogNeedsFlush(XLogRecPtr RecPtr);

src/include/executor/instrument.h

@@ -35,7 +35,7 @@ typedef struct BufferUsage
 typedef struct WalUsage
 {
 	long		wal_records;	/* # of WAL records produced */
-	long		wal_fpw;	/* # of WAL full page writes produced */
+	long		wal_fpi;		/* # of WAL full page images produced */
 	uint64		wal_bytes;		/* size of WAL records produced */
 } WalUsage;