This is the 13th release of Apache BookKeeper!
The 4.8.0 release incorporates hundreds of bug fixes, improvements, and features since previous major release, 4.7.0. It is a new big milestone in Apache BookKeeper community, this release include great new features, like Relaxed Durability, Stream Storage service and Multiple active Entrylogs.
Apache BookKeeper/DistributedLog users are encouraged to upgrade to 4.8.0. The technical details of this release are summarized below.
The main features in 4.8.0 are around following areas:
The writer may ask for temporary relaxed durability writes, that is to receive early acknowledge from Bookies, before an fsync() on Journal. Together with this new flag we introduced the new WriteHandle#force() API, this this API the writer is able to request an explicit guarantee of durability to the Bookies it is mostly like and explicit fsync() on a file system.
See DEFERRED_SYNC and force() for reference
All the client side APIs which take ByteBufs now will have the net effect of decrementing by 1 the refcount. This is consistent with general contract of Netty. It is expected that the client passes the ownership of the ByteBuf to BookKeeper client.
It is now possible on the Bookie to have multiple active entry loggers, this new feature will help with compaction performance and some specific workloads.
From this version we are providing the a table (key/value) service embedded in Bookies.
See BP-30: BookKeeper Table Service
ExplicitLAC was contributed from Salesforce in 4.5.0 release, but in the first release it was a beft-effort in-memory mechanism. Now you can configure Bookies to store durably ExplicitLAC.
See Make ExplicitLAC persistent
We are handling more gracefully the case of a failure of a Bookie in spite of a succeeded write. If you are writing with Ack Quorum = 2 and Write Quorum = 3, writes will succeeed even if 1 of 3 Bookies fail, now BookKeeper will trigger an ensemble change and replace the failed bookie earlier.
See Ensemble change on Delayed Write Failure