Zab: High-performance broadcast for primary-backup systems

Zab: High-performance broadcast for primary-backup systems Flavio P. Junqueira, Benjamin C. Reed, and Marco Serafini Yahoo! Research ffpj,breed,serafinig@yahoo-inc.com Abstract—Zab is a crash-recovery atomic broadcast algorithm scheme [5], [6], [7] to maintain the state of replica processes we designed for the ZooKeeper coordination service. ZooKeeper consistent. With ZooKeeper, a primary process receives all implements a primary-backup scheme in which a primary incoming client requests, executes them, and propagates the process executes clients operations and uses Zab to propagate the 1 resulting non-commutative, incremental state changes in thecorresponding incremental state changes to backup processes . form of transactions to the backup replicas using Zab, theDue the dependence of an incremental state change on the sequence of changes previously generated, Zab must guarantee ZooKeeper atomic broadcast protocol. Upon primary crashes, that if it delivers a given state change, then all other changes it processes execute a recovery protocol both to agree upon a depends upon must be delivered first. Since primaries may crash, common consistent state before resuming regular operation Zab must satisfy this requirement despite crashes of primaries. and to establish a new primary to broadcast state changes.