Problem:
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mariadb-backup creates one background thread to copy innodb redo log.
It does copy all the data file (in main thread and other concurrent threads),
till it explicitly mentions the redo log thread to exit. This redo log copier
thread run keep printing the current states of redo log copied lsn for
every 15 seconds. If BACKUP STAGE command takes time to finish or any stall
during data copy then redo log background continuously emitting the same log
copy status gives the impression that redo log is being stuck
Solution:
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backup_log_report(): Reports the log progress report information
for backup only when InnoDB does have any redo log to copy
xtrabackup_copy_logfile(): Print the redo log progress information
after coping the new redo log.
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