pgsql: Add block information in error context of WAL REDO apply loop

Hi,

On 2020-10-02 00:41:12 +0000, Michael Paquier wrote:

Add block information in error context of WAL REDO apply loop

Providing this information can be useful for example when diagnosing
problems related to recovery conflicts or for recovery issues without
having to go through the output generated by pg_waldump to get some
information about the blocks a WAL record works on.

The block information is printed in the same format as pg_waldump. This
already existed in xlog.c for debugging purposes with -DWAL_DEBUG, so
adding the block information in the callback has required just a small
refactoring.

Author: Bertrand Drouvot
Reviewed-by: Michael Paquier, Masahiko Sawada
Discussion: /messages/by-id/c31e2cba-efda-762c-f4ad-5c25e5dac3d0@amazon.com

My compiler quite justifiably complains about:

+#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 */

because as far as I can see there's no remaining use of block_id in
xlog_outrec() after this change.

Greetings,

Andres Freund

On Mon, Oct 05, 2020 at 07:38:02PM -0700, Andres Freund wrote:

My compiler quite justifiably complains about:

Thanks, fixed.
--
Michael