PURGE BINARY LOGS does not always purge

Purging binary logs does not always purge and delete it. This typically happens when only one binary log is there (little traffic or short purge interval). This is reproducible and does NOT happen with a competitive product.

Good case:

ll ~/database/mariadb-103/binlog/ ~/bck/mariadb-103/binlog/ ; cat ~/database/mariadb-103/binlog/binlog.index

/home/mysql/bck/mariadb-103/binlog/:
total 1560
rw-rr- 1 mysql mysql 779746 Jul 30 18:02 bck_binlog.000390.gz
rw-rr- 1 mysql mysql 424587 Jul 30 18:03 bck_binlog.000391.gz
rw-rr- 1 mysql mysql 388928 Jul 30 18:04 bck_binlog.000392.gz

/home/mysql/database/mariadb-103/binlog/:
total 30912
rw-rw--- 1 mysql mysql 13367733 Jul 30 18:07 binlog.000393
rw-rw--- 1 mysql mysql 18268189 Jul 30 18:12 binlog.000394
rw-rw--- 1 mysql mysql 108 Jul 30 18:07 binlog.index
rw-rw--- 1 mysql mysql 12 Jul 25 09:56 binlog.state

/home/mysql/database/mariadb-103/binlog/binlog.000393
/home/mysql/database/mariadb-103/binlog/binlog.000394

bman --target=brman:secret@127.0.0.1:3318 --type=binlog --policy=binlog --mode=logical --backupdir=/home/mysql/bck/mariadb-103

Start backup at 2019-07-30_18:12:39
Binlog Index file is: /home/mysql/database/mariadb-103/binlog/binlog.index
Getting lock: /home/oli/fromdual_devel/brman/lck/binlog-logical-binlog.lock
Releasing lock: /home/oli/fromdual_devel/brman/lck/binlog-logical-binlog.lock
FLUSH /*!50503 BINARY */ LOGS

Copy /home/mysql/database/mariadb-103/binlog/binlog.000393 to /home/mysql/bck/mariadb-103/binlog/bck_binlog.000393
Binary log binlog.000393 begin datetime is: 2019-07-30 18:04:10 and end datetime is: 2019-07-30 18:07:34
Do MD5 checksum of /home/mysql/bck/mariadb-103/binlog/bck_binlog.000393
md5sum --binary /home/mysql/bck/mariadb-103/binlog/bck_binlog.000393
md5 = 54c59d6ec5f14d04176065f50634c7dd
/usr/bin/pigz -6 /home/mysql/bck/mariadb-103/binlog/bck_binlog.000393
PURGE BINARY LOGS TO 'binlog.000394'

Copy /home/mysql/database/mariadb-103/binlog/binlog.000394 to /home/mysql/bck/mariadb-103/binlog/bck_binlog.000394
Binary log binlog.000394 begin datetime is: 2019-07-30 18:07:34 and end datetime is: 2019-07-30 18:12:39
Do MD5 checksum of /home/mysql/bck/mariadb-103/binlog/bck_binlog.000394
md5sum --binary /home/mysql/bck/mariadb-103/binlog/bck_binlog.000394
md5 = 01538bee0e2de03eaa42b385d369387a
/usr/bin/pigz -6 /home/mysql/bck/mariadb-103/binlog/bck_binlog.000394
PURGE BINARY LOGS TO 'binlog.000395'
End backup at 2019-07-30 18:12:40 (rc=0)

ll ~/database/mariadb-103/binlog/ ~/bck/mariadb-103/binlog/ ; cat ~/database/mariadb-103/binlog/binlog.index

/home/mysql/bck/mariadb-103/binlog/:
total 7152
rw-rr- 1 mysql mysql 779746 Jul 30 18:02 bck_binlog.000390.gz
rw-rr- 1 mysql mysql 424587 Jul 30 18:03 bck_binlog.000391.gz
rw-rr- 1 mysql mysql 388928 Jul 30 18:04 bck_binlog.000392.gz
rw-rr- 1 mysql mysql 2330609 Jul 30 18:07 bck_binlog.000393.gz
rw-rr- 1 mysql mysql 3390627 Jul 30 18:12 bck_binlog.000394.gz

/home/mysql/database/mariadb-103/binlog/:
total 540
rw-rw--- 1 mysql mysql 542899 Jul 30 18:12 binlog.000395
rw-rw--- 1 mysql mysql 54 Jul 30 18:12 binlog.index
rw-rw--- 1 mysql mysql 12 Jul 25 09:56 binlog.state

/home/mysql/database/mariadb-103/binlog/binlog.000395

Bad case:

bman --target=brman:secret@127.0.0.1:3318 --type=binlog --policy=binlog --mode=logical --backupdir=/home/mysql/bck/mariadb-103

Start backup at 2019-07-30_18:12:56
Binlog Index file is: /home/mysql/database/mariadb-103/binlog/binlog.index
Getting lock: /home/oli/fromdual_devel/brman/lck/binlog-logical-binlog.lock
Releasing lock: /home/oli/fromdual_devel/brman/lck/binlog-logical-binlog.lock
FLUSH /*!50503 BINARY */ LOGS

Copy /home/mysql/database/mariadb-103/binlog/binlog.000395 to /home/mysql/bck/mariadb-103/binlog/bck_binlog.000395
Binary log binlog.000395 begin datetime is: 2019-07-30 18:12:39 and end datetime is: 2019-07-30 18:12:56
Do MD5 checksum of /home/mysql/bck/mariadb-103/binlog/bck_binlog.000395
md5sum --binary /home/mysql/bck/mariadb-103/binlog/bck_binlog.000395
md5 = 6b83ea44eb4a86cff21aa0e68d78e7d0
/usr/bin/pigz -6 /home/mysql/bck/mariadb-103/binlog/bck_binlog.000395
PURGE BINARY LOGS TO 'binlog.000396'
End backup at 2019-07-30 18:12:56 (rc=0)

ll ~/database/mariadb-103/binlog/ ~/bck/mariadb-103/binlog/ ; cat ~/database/mariadb-103/binlog/binlog.index

/home/mysql/bck/mariadb-103/binlog/:
total 7344
rw-rr- 1 mysql mysql 779746 Jul 30 18:02 bck_binlog.000390.gz
rw-rr- 1 mysql mysql 424587 Jul 30 18:03 bck_binlog.000391.gz
rw-rr- 1 mysql mysql 388928 Jul 30 18:04 bck_binlog.000392.gz
rw-rr- 1 mysql mysql 2330609 Jul 30 18:07 bck_binlog.000393.gz
rw-rr- 1 mysql mysql 3390627 Jul 30 18:12 bck_binlog.000394.gz
rw-rr- 1 mysql mysql 195160 Jul 30 18:12 bck_binlog.000395.gz

/home/mysql/database/mariadb-103/binlog/:
total 1260
rw-rw--- 1 mysql mysql 1116483 Jul 30 18:12 binlog.000395
rw-rw--- 1 mysql mysql 161749 Jul 30 18:12 binlog.000396
rw-rw--- 1 mysql mysql 108 Jul 30 18:12 binlog.index
rw-rw--- 1 mysql mysql 12 Jul 25 09:56 binlog.state

/home/mysql/database/mariadb-103/binlog/binlog.000395
/home/mysql/database/mariadb-103/binlog/binlog.000396

This makes behaviour completely unpredictable for more sophisticated backup software and follow-up backup jobs will fail.