Slide 7 : Log Structured Store
This slide summarises the features of the Log Structured Store (LSS), which is used to persist all the objects in the OODB as binary blobs.
The LSS has all the features required for an industrial strength storage system. In particular it fully supports transactions and guarantees their atomicity in the face of power failures.
Multiplexing of the output allows for hotstandby and backup consistent with 24 x 7 operation.
The LSS has excellent performance. Typically write performance is at least twice as fast as other systems such as BTrieve or ObjectStore.
Most DB systems employ data that is read or written in pages, and atomicity of transactions is achieved by the technique of Write Ahead Logging (WAL) of changes to the data pages to a separate log file, which can be scanned during recovery as required to undo/redo partially completed transactions.
The LSS achieves excellent write performance by treating the log itself as the data! Therefore all writing occurs at the end of the log, allowing for continuous writing with minimal movements of the disk head.