The only version so far.

MVCCMetadata holds MVCC metadata for a key.

MVCCPersistentStats is convertible to MVCCStats, but uses signed variable width encodings for most fields that make it efficient to store positive values but inefficient to store negative values.

MVCCStats tracks byte and instance counts for various groups of keys, values, or key-value pairs; see the field comments for details.

MVCCStatsDelta is convertible to MVCCStats, but uses signed variable width encodings for most fields that make it more efficient to store negative values.

RangeAppliedState combines the raft and lease applied indices with mvcc stats.

Registry describes how a files are handled.

SSTUserProperties contains the user-added properties of a single sstable.

SSTUserPropertiesCollection contains the user-added properties of every sstable in a RocksDB instance.

TxnMeta is the metadata of a Transaction record.

TODO(tschottdorf): Should not live in enginepb (but can't live in roachpb either).