Lock-free Backups
Lock-free backups are enabled when the lockfree_backup engine variable is set to ON and the disable_update-delete_distributed_transactions engine variable is set to OFF. The default values of lockfree_backup and disable_update-delete_distributed_transactions are ON and OFF, respectively.
Lock-free backups do not block INSERT, UPDATE, and DELETE operations at any point during a backup. They do not need to lock and wait for write queries.
However ALTER and SNAPSHOT commands will not run while there is a backup job active on the relevant database. There is no difference between lock-free backup and the original locking backup with respect to the cluster operations lock. The backup takes the cluster operations lock for the entirety of the backup.
Note
Lock-free backups cannot be made using BACKUP DATABASE ... WITH SPLIT PARTITIONS ....
Locking that Occurs if Lock-free Backups are Disabled
If lock-free backups are disabled and BACKUP DATABASE is run, the following applies before the backup starts: