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:

  • Durability
  • ExplicitLAC feature
  • New Table Storage Service
  • Bug Fixes


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

New behaviour for Netty ByteBuf reference count management

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.

Multiple Active Entrylogs

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.

See Multiple active entrylogs

Table Storage Service

From this version we are providing the a table (key/value) service embedded in Bookies.

See BP-30: BookKeeper Table Service

Make ExplicitLAC persistent

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

Ensemble change on Delayed Write Failure

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

Full list of changes

An entry is a sequence of bytes (plus some metadata) written to a BookKeeper ledger. Entries are also known as records.

A ledger is a sequence of entries written to BookKeeper. Entries are written sequentially to ledgers and at most once, giving ledgers append-only semantics.

A bookie is an individual BookKeeper storage server.

Bookies store the content of ledgers and act as a distributed ensemble.

A subsystem that runs in the background on bookies to ensure that ledgers are fully replicated even if one bookie from the ensemble is down.

Striping is the process of distributing BookKeeper ledgers to sub-groups of bookies rather than to all bookies in a BookKeeper ensemble.

Striping is essential to ensuring fast performance.

A journal file stores BookKeeper transaction logs.

When a reader forces a ledger to close, preventing any further entries from being written to the ledger.

A record is a sequence of bytes (plus some metadata) written to a BookKeeper ledger. Records are also known as entries.