BookKeeper offers a few APIs that applications can use to interact with it:

  • The ledger API is a lower-level API that enables you to interact with ledgers directly
  • The [Ledger Advanced API)(../ledger-adv-api) is an advanced extension to Ledger API to provide more flexibilities to applications.
  • The DistributedLog API is a higher-level API that provides convenient abstractions.


The Ledger API provides direct access to ledgers and thus enables you to use BookKeeper however you’d like.

However, in most of use cases, if you want a log stream-like abstraction, it requires you to manage things like tracking list of ledgers, managing rolling ledgers and data retention on your own. In such cases, you are recommended to use DistributedLog API, with semantics resembling continous log streams from the standpoint of applications.

BookKeeper API

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.