Bookies are individual BookKeeper servers. You can run an ensemble of bookies locally on a single machine using the localbookie command of the bookkeeper CLI tool and specifying the number of bookies you’d like to include in the ensemble.

This would start up an ensemble with 10 bookies:

$ bookeeper-server/bin/bookeeper localbookie 10

When you start up an ensemble using localbookie, all bookies run in a single JVM process.

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.