Summary:
We have a request for RocksDB to essentially support
disconnected incremental backup. In other words, if there is limited
or no connectivity to the primary backup dir, we should still be able to
take an incremental backup relative to that primary backup dir,
assuming some metadata about that primary dir is available (and
obviously anticipating primary backup dir will be fully available if
restore is needed).
To support that, this feature allows the API user to "exclude" DB
files from backup. This only applies to files that can be shared
between backups (sst and blob files), and excluded files are
tracked in the backup metadata sufficiently to ensure they are
restored at restore time. At restore time, the user provides
a set of alternate backup directories (as open BackupEngines, which
can be read-only), and excluded files must be found in one of the
backup directories ("included" in some backup).
This feature depends on backup schema version 2 features, though
schema version 2.0 support is not sufficient to read / restore a
backup with exclusions. This change updates the schema version to
2.1 because of this feature, so that it's easy to recognize whether
a RocksDB release supports this feature, while backups not using the
feature are fully compatible with 2.0.
Also in this PR:
* Stacked on https://github.com/facebook/rocksdb/pull/11029
* Allow progress_callback to be empty, not just no-op function, and
recover from exceptions thrown by BackupEngine callbacks.
* The internal-only `AsBackupEngine()` function is working around the
diamond hierarchy of `BackupEngineImplThreadSafe` to get to the
internals, without using confusing features like virtual inheritance.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/11030
Test Plan: unit tests added / updated
Reviewed By: ajkr
Differential Revision: D42004388
Pulled By: pdillinger
fbshipit-source-id: 31b6e533d308a5462e528d9012d650482d974077
Peter Dillinger