> (you don't have to strictly follow this form)

**Use case**

Sometimes, for really sophisticated scenarios it can be hard to control the amount of in-progress backups run externally. For the purpose of simpler control we can introduce server-level setting which disallows running concurrent backups of any type. 

Something like this in `config.xml` (enabled by default):
`<allow_concurrent_backups>true</allow_concurrent_backups>`

**Describe the solution you'd like**

It's important that backups can be executed in distributed way on multiple servers. Need to take it into account.

**Describe alternatives you've considered**
External check of `system.backups` table, but it can be complex.

};
}
#define LIST_OF_BACKUP_SETTINGS(M) \
    M(String, id) \
    M(String, compression_method) \
    M(String, password) \
    M(Bool, structure_only) \
    M(Bool, async) \
    M(Bool, deduplicate_files) \
    M(UInt64, shard_num) \
    M(UInt64, replica_num) \
    M(Bool, internal) \
    M(String, host_id) \
    M(String, coordination_zk_path) \
    M(OptionalUUID, backup_uuid)
    
BackupSettings BackupSettings::fromBackupQuery(const ASTBackupQuery & query)