Add BackupEngine feature to exclude files (#11030)
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
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