Empty xtrabackup_slave_info file is created if --slave info passed with master server

[Shahriyar Rzayev]

Testing latest 2.4 and 2.4 branch.
Taking backup with 2.4 + PS 5.6 master server:

/home/shahriyar.rzaev/XB_TEST/server_dir/target/percona-xtrabackup-2.4.x-debug/bin/xtrabackup --defaults-file=/home/shahriyar.rzaev/sandboxes/rsandbox_Percona-Server-5_6_36/master/my.sandbox.cnf --user=root --password=msandbox --target-dir=/home/shahriyar.rzaev/XB_TEST/backup_dir/ps_5_7_x_2_4/full/2017-11-27_11-35-36 --backup --socket=/tmp/mysql_sandbox23901.sock --slave-info --no-version-check --core-file --parallel=10 --throttle=40 --keyring-file-data=/home/shahriyar.rzaev/XB_TEST/server_dir/PS231117-5.7.20-18-linux-x86_64-debug/mysql-keyring/keyring

The result:

xtrabackup: The latest check point (for incremental): '1632376'
xtrabackup: Stopping log copying thread.
.171127 12:58:32 >> log scanned up to (1632376)

171127 12:58:32 Executing UNLOCK BINLOG
171127 12:58:32 Executing UNLOCK TABLES
171127 12:58:32 All tables unlocked
171127 12:58:32 Backup created in directory '/home/shahriyar.rzaev/XB_TEST/backup_dir/ps_5_7_x_2_4/full/2017-11-27_11-35-36/'
MySQL binlog position: filename 'mysql-bin.000002', position '151', GTID of the last change ''
171127 12:58:32 [00] Writing /home/shahriyar.rzaev/XB_TEST/backup_dir/ps_5_7_x_2_4/full/2017-11-27_11-35-36/backup-my.cnf
171127 12:58:32 [00] ...done
171127 12:58:32 [00] Writing /home/shahriyar.rzaev/XB_TEST/backup_dir/ps_5_7_x_2_4/full/2017-11-27_11-35-36/xtrabackup_info
171127 12:58:32 [00] ...done
xtrabackup: Transaction log of lsn (1632369) to (1632376) was copied.
171127 12:58:33 completed OK!

In backup directory:

$ ls
backup-my.cnf ibdata1 mysql performance_schema test xtrabackup_binlog_info xtrabackup_checkpoints xtrabackup_info xtrabackup_logfile xtrabackup_slave_info
$ cat xtrabackup_slave_info
$ ls -ltr xtrabackup_slave_info
-rw-r----- 1 shahriyar.rzaev shahriyar.rzaev 0 Noy 27 12:58 xtrabackup_slave_info

Doing same thing with PXB 2.3 + PS 5.6:

/home/shahriyar.rzaev/XB_TEST/server_dir/target/percona-xtrabackup-2.3.x-debug/bin/xtrabackup --defaults-file=/home/shahriyar.rzaev/sandboxes/rsandbox_Percona-Server-5_6_36/master/my.sandbox.cnf --user=root --password=msandbox --target-dir=/home/shahriyar.rzaev/XB_TEST/backup_dir/ps_5_7_x_2_4/full/2017-11-27_11-35-36 --backup --socket=/tmp/mysql_sandbox23901.sock --slave-info --no-version-check --core-file --parallel=10 --throttle=40 --keyring-file-data=/home/shahriyar.rzaev/XB_TEST/server_dir/PS231117-5.7.20-18-linux-x86_64-debug/mysql-keyring/keyring

171127 13:03:01 Executing LOCK BINLOG FOR BACKUP...
Failed to get master binlog coordinates from SHOW SLAVE STATUS
This means that the server is not a replication slave. Ignoring the --slave-info option
171127 13:03:01 [00] Writing xtrabackup_binlog_info
171127 13:03:01 [00] ...done
171127 13:03:01 Executing FLUSH NO_WRITE_TO_BINLOG ENGINE LOGS...
xtrabackup: The latest check point (for incremental): '1632383'
xtrabackup: Stopping log copying thread.
.171127 13:03:01 >> log scanned up to (1632383)

171127 13:03:02 Executing UNLOCK BINLOG
171127 13:03:02 Executing UNLOCK TABLES
171127 13:03:02 All tables unlocked
171127 13:03:02 Backup created in directory '/home/shahriyar.rzaev/XB_TEST/backup_dir/ps_5_7_x_2_4/full/2017-11-27_11-35-36/'
MySQL binlog position: filename 'mysql-bin.000002', position '151', GTID of the last change ''
171127 13:03:02 [00] Writing backup-my.cnf
171127 13:03:02 [00] ...done
171127 13:03:02 [00] Writing xtrabackup_info
171127 13:03:02 [00] ...done
xtrabackup: Transaction log of lsn (1632376) to (1632383) was copied.
171127 13:03:02 completed OK!

There is no xtrabackup_slave_info file inside backup dir:

$ ls
backup-my.cnf ibdata1 mysql performance_schema test xtrabackup_binlog_info xtrabackup_checkpoints xtrabackup_info xtrabackup_logfile

Also please note the difference between outputs:
With 2.3 there is a note about ignoring --slave-info:

171127 13:03:01 Executing LOCK BINLOG FOR BACKUP...
Failed to get master binlog coordinates from SHOW SLAVE STATUS
This means that the server is not a replication slave. Ignoring the --slave-info option
171127 13:03:01 [00] Writing xtrabackup_binlog_info

With 2.4 there is no such thing.

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PXB-517