MDEV-23711 make mariabackup innodb redo log read error message more clear

log_group_read_log_seg() returns error when:

1) Calculated log block number does not correspond to read log block
number. This can be caused by:
  a) Garbage or an incompletely written log block. We can exclude this
  case by checking log block checksum if it's enabled(see innodb-log-checksums,
  encrypted log block contains checksum always).
  b) The log block is overwritten. In this case checksum will be correct and
  read log block number will be greater then requested one.

2) When log block length is wrong. In this case recv_sys->found_corrupt_log
is set.

3) When redo log block checksum is wrong. In this case innodb code
writes messages to error log with the following prefix: "Invalid log
block checksum."

The fix processes all the cases above.

1 files changed, 16 insertions, 3 deletions

diff --git a/extra/mariabackup/xtrabackup.cc b/extra/mariabackup/xtrabackup.cc
index 4845f51e6b2..231e3c04f16 100644
--- a/extra/mariabackup/xtrabackup.cc
+++ b/extra/mariabackup/xtrabackup.cc
@@ -2773,6 +2773,7 @@ static bool xtrabackup_copy_logfile(bool last = false)
 	ut_a(dst_log_file != NULL);
 	ut_ad(recv_sys != NULL);
 
+	bool overwritten_block;
 	lsn_t	start_lsn;
 	lsn_t	end_lsn;
 
@@ -2799,6 +2800,12 @@ static bool xtrabackup_copy_logfile(bool last = false)
 		}
 
 		if (lsn == start_lsn) {
+			overwritten_block= !recv_sys->found_corrupt_log
+				&& (innodb_log_checksums || log_sys->log.is_encrypted())
+				&& log_block_calc_checksum_crc32(log_sys->buf) ==
+					log_block_get_checksum(log_sys->buf)
+				&& log_block_get_hdr_no(log_sys->buf) >
+					log_block_convert_lsn_to_no(start_lsn);
 			start_lsn = 0;
 		} else {
 			mutex_enter(&recv_sys->mutex);
@@ -2809,9 +2816,15 @@ static bool xtrabackup_copy_logfile(bool last = false)
 		log_mutex_exit();
 
 		if (!start_lsn) {
-			die(recv_sys->found_corrupt_log
-			    ? "xtrabackup_copy_logfile() failed: corrupt log."
-			    : "xtrabackup_copy_logfile() failed.");
+			const char *reason = recv_sys->found_corrupt_log
+				? "corrupt log."
+				: (overwritten_block
+					? "redo log block is overwritten, please increase redo log size with innodb_log_file_size parameter."
+					: ((innodb_log_checksums || log_sys->log.is_encrypted())
+						? "redo log block checksum does not match."
+						: "unknown reason as innodb_log_checksums is switched off and redo"
+							" log is not encrypted."));
+			die("xtrabackup_copy_logfile() failed: %s", reason);
 			return true;
 		}
 	} while (start_lsn == end_lsn);