Did some investigation around

rocksdb_create_checkpoint variable

It's a global variable.

set global rocksdb_create_checkpoint='/path/to/checkpoint'

will cause a checkpoint to be created at the specified path. The value of the variable will not change.

Checkpoints inside RocksDB

RocksDB provides a function to create checkpoints but then it doesn't remember that they were created.
There is no function to remove the created checkpoint.

Issues with the suggested approach:

Server crashes/shutdowns.

Suppose the server is shut down after the snapshot creation has started but before mariabackup issues a command to release it. The new server will not remember that it created the snapshot and there will be no way to delete it.

Multiple concurrent backups

What happens in this scenario:

• Client1 creates a snapshot S1 and starts backing it up
• client2 creates a snapshot S2 ...
• Client1 finishes work and instructs the server to delete the snapshot.

Here, the server needs to know that S1 must be deleted while S2 must still be kept.

we can prevent multiple concurrent backups, with user level locks. So far, mariabackups uses hardcoded name for the temp-checkpoint directory, so second attempt to create checkpoint will fail anyway. Server (or backup) crashes /kills are not handled very well in this scenario, would require manual cleanup.

One possible way out:

• Let the rocksdb_create_checkpoint remember paths to the checkpoints it has created (possibly even permanently, store them inside MyRocks).
• Provide a command to remove the directories that were created with set rocksdb_create_checkpoint

Takeaways from Slack discussion:

• Mariabackup always creates the snapshot at `$datadir/#rocksdb/mariabackup`.This is to make sure the volume is the same and hardlinking is possible.
• There can be only one backup running at the same time.
• If the server is restarted, the snapshot can be deleted

We can meet mariabackup's requirements with this:

• At server start, $datadir/#rocksdb/mariabackup is removed. It is a directory that only has regular files (i.e. hard links). If we find a soft link there, it's an error.

• There is a global variable rocksdb_delete_mariabackup_checkpoint. Setting it to any value will cause $datadir/#rocksdb/mariabackup to be deleted.

Setting a global variable requires a "super" privelege; one can only use this to delete a specific directory - this will not open any vulnerabilities.