v2.0:

Breaking changes:

• When creating a new repo, the first commit is now always empty. Repo.create_from_commit has been removed; all repos should now be created with Repo.create.
• Removed Repo.apply_writes, format_commit, apply_commit, and writes_to_commit_ops. Use the new Storage.commit method instead.
• If no sequence number has ever been allocated for a given NSID, Storage.last_seq now returns None, and does not initialize the sequence.

Non-breaking changes:

Add new feature to allocate sequence numbers from memcache, atomically, backed by the datastore in batches. Reduces datastore contention when writing commits at 5-10qps and higher. Enable by passing a MemcacheSequences to the DatastoreStorage constructor; configure with the MEMCACHE_SEQUENCE_BUFFER and MEMCACHE_SEQUENCE_BATCH environment variables.

• Add new SUBSCRIBE_REPOS_SKIPPED_SEQ_WINDOW and SUBSCRIBE_REPOS_SKIPPED_SEQ_DELAY environment variables for subscribeRepos (firehose) serving.
• AtpRemoteBlob:
  • Add repos property to track which repos have which blobs.
  • Switch image handling to pymediainfo, drop Pillow dependency.
• did:
  • Add new rollback_plc function.
  • resolve_handle: raise ValueError if the handle has an _ (underscore), since Bluesky handles don't allow them.
• firehose:
  • Omit prevData in initial commits instead of setting it to null. (It's not a nullable field in subscribeRepos#commit.)
• repo:
  • Add lost_seq kwarg to repo callback for marking sequence numbers lost.
• storage:
  • Add new abstract Sequences class and concrete subclasses MemorySequences, DatastoreSequences, and MemcacheSequences.
  • Add new optional sequences kwarg to Storage and subclasses' constructors.
• xrpc_repo:
  • describe_repo: add app.bsky.graph.listblock.
• xrpc_sync:
  • get_blob: periodically check remote blobs with HTTP GET requests to see if they're still serving.
  • get_record: include MST covering proof blocks for record.
  • Implement listBlobs.
  • subscribeRepos/firehose: handle uncaught exceptions and continue serving (snarfed/bridgy-fed#2150).