Re: Add information to rm_redo_error_callback()

[Michael Paquier]

On Thu, Sep 24, 2020 at 03:03:46PM +0900, Michael Paquier wrote:
> Hmm.  I still think that knowing at least about a FPW could be an
> interesting piece of information even here.  Anyway, instead of
> copying a logic that exists already in xlog_outrec(), why not moving
> the block information print into a separate routine out of the
> WAL_DEBUG section, and just reuse the same format for the context of
> the redo error callback?  That would also be more consistent with what
> we do in pg_waldump where we don't show the fork name of a block when
> it is on a MAIN_FORKNUM.  And this would avoid a third copy of the
> same logic.  If we add the XID, previous LSN and the record length
> on the stack of what is printed, we could just reuse the existing
> routine, still that's perhaps too much information displayed.

Seeing nothing, I took a swing at that, and finished with the
attached that refactors the logic and prints the block information as
wanted.  Any objections to that?
--
Michael

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 79a77ebbfe..e96075158a 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -940,6 +940,7 @@ static bool CheckForStandbyTrigger(void);
 #ifdef WAL_DEBUG
 static void xlog_outrec(StringInfo buf, XLogReaderState *record);
 #endif
+static void xlog_block_info(StringInfo buf, XLogReaderState *record);
 static void xlog_outdesc(StringInfo buf, XLogReaderState *record);
 static void pg_start_backup_callback(int code, Datum arg);
 static void pg_stop_backup_callback(int code, Datum arg);
@@ -10258,6 +10259,19 @@ xlog_outrec(StringInfo buf, XLogReaderState *record)
 	appendStringInfo(buf, "; len %u",
 					 XLogRecGetDataLen(record));
 
+	xlog_block_info(buf, record);
+}
+#endif							/* WAL_DEBUG */
+
+/*
+ * Returns a string giving information about all the blocks in an
+ * XLogRecord.
+ */
+static void
+xlog_block_info(StringInfo buf, XLogReaderState *record)
+{
+	int block_id;
+
 	/* decode block references */
 	for (block_id = 0; block_id <= record->max_block_id; block_id++)
 	{
@@ -10284,7 +10298,6 @@ xlog_outrec(StringInfo buf, XLogReaderState *record)
 			appendStringInfoString(buf, " FPW");
 	}
 }
-#endif							/* WAL_DEBUG */
 
 /*
  * Returns a string describing an XLogRecord, consisting of its identity
@@ -11765,6 +11778,7 @@ rm_redo_error_callback(void *arg)
 
 	initStringInfo(&buf);
 	xlog_outdesc(&buf, record);
+	xlog_block_info(&buf, record);
 
 	/* translator: %s is a WAL record description */
 	errcontext("WAL redo at %X/%X for %s",

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