PXB-3606 Backup may succeed with incomplete redo log

storage/innobase/xtrabackup/src/redo_log.cc

@@ -273,6 +273,8 @@ lsn_t Redo_Log_Reader::read_log_seg_8030(log_t &log, byte *buf, lsn_t start_lsn,
 
   ut_ad(file != log.m_files.end());
 
+  debug_sync_point("pause_before_open_redo");
+
   auto file_handle = file->open(Log_file_access_mode::READ_ONLY);
 
   if (!file_handle.is_open()) {
@@ -1498,10 +1500,20 @@ bool Redo_Log_Data_Manager::stop_at(lsn_t lsn, lsn_t checkpoint_lsn) {
              << SQUOTE(last_checkpoint_lsn);
   xb::info() << "Stopping log copying thread at LSN " << lsn;
 
+  DBUG_EXECUTE_IF("xtrabackup_pause_before_stop_copy_redo",
+    const char *key = "pause_before_open_redo";
+    *const_cast<const char **>(&xtrabackup_debug_sync) = key;);
+
   stop_lsn = lsn;
   os_event_set(event);
   thread.join();
 
+  /* Check for errors during copying to last_lsn */
+  if (error) {
+    xb::error() << "Error occured when copying to last_lsn.";
+    return false;
+  }
+
   archived_log_monitor.stop();
 
   /* to ensure redo logs are not disabled during the backup, reopen the log

storage/innobase/xtrabackup/test/t/pxb-3606.sh

@@ -0,0 +1,65 @@
+##########################################################################
+# pxb-3003-redo-log-purge-race.sh script has tested two possible scenarios 
+# where redo log purges can cause backup failures. We also discovered that, 
+# once a redo log purge occurs between the completion of the non-InnoDB file 
+# backup and the end of the redo log copy, it can result in incomplete redo 
+# log copying, while the backup still completes successfully.
+#
+# This test should make sure that, in this scenario, backup will fail due to
+# incomplete redo log copying.
+# ########################################################################
+
+. inc/common.sh
+
+MYSQLD_EXTRA_MY_CNF_OPTS="
+innodb_redo_log_capacity=8M
+"
+
+require_debug_pxb_version
+start_server
+
+function run_inserts()
+{
+  for i in $(seq 1000);
+  do
+    $MYSQL $MYSQL_ARGS -Ns -e "INSERT INTO test.t1 VALUES (NULL, REPEAT('a', 63 * 1024))";
+  done
+}
+$MYSQL $MYSQL_ARGS -Ns -e "CREATE TABLE t1 (
+  id INT PRIMARY KEY AUTO_INCREMENT,
+  str BLOB
+);" test
+
+
+$MYSQL $MYSQL_ARGS -Ns -e "INSERT INTO test.t1 VALUES (NULL, REPEAT('a', 63 * 1024))"
+$MYSQL $MYSQL_ARGS -Ns -e "INSERT INTO test.t1 VALUES (NULL, REPEAT('a', 63 * 1024))"
+
+mkdir -p $topdir/backup/
+
+run_cmd_expect_failure xtrabackup --backup --target-dir=$topdir/backup --debug=d,xtrabackup_pause_before_stop_copy_redo \
+  2> >( tee $topdir/xtrabackup_pause_before_stop_copy_redo.log) &
+job_pid=$!
+pid_file=$topdir/backup/xtrabackup_debug_sync
+wait_for_xb_to_suspend $pid_file
+xb_pid=`cat $pid_file`
+
+vlog "backup pid is $job_pid"
+
+INITIAL_MIN_FILEID=`$MYSQL $MYSQL_ARGS -Ns -e "SELECT MIN(file_id) FROM performance_schema.innodb_redo_log_files"`
+
+run_inserts &
+insert_pid=$!
+CURRENT_MIN_FILEID=`$MYSQL $MYSQL_ARGS -Ns -e "SELECT MIN(file_id) FROM performance_schema.innodb_redo_log_files"`
+while [ "${INITIAL_MIN_FILEID}" -eq "${CURRENT_MIN_FILEID}" ]
+do
+  sleep 1;
+  vlog "Waiting for redo log files to be created. Current MIN_FILEID: $CURRENT_MIN_FILEID Initial MIN_FILEID: $INITIAL_MIN_FILEID"
+  CURRENT_MIN_FILEID=`$MYSQL $MYSQL_ARGS -Ns -e "SELECT MIN(file_id) FROM performance_schema.innodb_redo_log_files"`
+done
+# Resume the xtrabackup process
+vlog "Resuming xtrabackup"
+kill -SIGCONT $xb_pid
+
+run_cmd wait $insert_pid
+
+rm -rf $topdir/backup/*