> (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.

enum class RestoreTableCreationMode
{
    
    kCreate,
    
    kMustExist,
    
    kCreateIfNotExists,
};
using RestoreDatabaseCreationMode = RestoreTableCreationMode;
enum class RestoreAccessCreationMode
{
    
    kCreate,
    
    kCreateIfNotExists,
    
    kReplace,
};
using RestoreUDFCreationMode = RestoreAccessCreationMode;
struct RestoreSettings
{
    
    String id;
    
    
    std::optional<BackupInfo> base_backup_info;