huiwenhan / incubator-pegasus

Apache Pegasus - A horizontally scalable, strongly consistent and high-performance key-value store

Note: The master branch may be in an unstable or even in a broken state during development. Please use GitHub Releases instead of the master branch in order to get stable binaries.

Apache Pegasus is a distributed key-value storage system which is designed to be:

• horizontally scalable: distributed using hash-based partitioning
• strongly consistent: ensured by PacificA consensus protocol
• high-performance: using RocksDB as underlying storage engine
• simple: well-defined, easy-to-use APIs

Background

Pegasus targets to fill the gap between Redis and HBase. As the former is in-memory, low latency, but does not provide a strong-consistency guarantee. And unlike the latter, Pegasus is entirely written in C++ and its write-path relies merely on the local filesystem.

Apart from the performance requirements, we also need a storage system to ensure multiple-level data safety and support fast data migration between data centers, automatic load balancing, and online partition split.

Features

• Persistence of data: Each write is replicated three-way to different ReplicaServers before responding to the client. Using PacificA protocol, Pegasus has the ability for strong consistent replication and membership changes.

• Automatic load balancing over ReplicaServers: Load balancing is a builtin function of MetaServer, which manages the distribution of replicas. When the cluster is in an inbalance state, the administrator can invoke a simple rebalance command that automatically schedules the replica migration.

• Cold Backup: Pegasus supports an extensible backup and restore mechanism to ensure data safety. The location of snapshot could be a distributed filesystem like HDFS or local filesystem. The snapshot storing in the filesystem can be further used for analysis based on pegasus-spark.

• Eventually-consistent intra-datacenter replication: This is a feature we called duplication. It allows a change made in the local cluster accesible after a short time period by the remote cluster. It help achieving higher availability of your service and gaining better performance by accessing only local cluster.

To start using Pegasus

See our documentation on the Pegasus Website.

Client drivers

Pegasus has support for several languages:

• Java

• C++
• Go
• Python
• Node.js
• Scala

Contact us

• Send emails to the Apache Pegasus developer mailing list: [email protected]. This is the place where topics around development, community, and problems are officially discussed. Please remember to subscribe to the mailing list via [email protected].

• GitHub Issues: submit an issue when you have any idea to improve Pegasus, and when you encountered some bugs or problems.

Related Projects

Test tools:

• Java YCSB

Data import/export tools:

• DataX

License

Copyright 2020 The Apache Software Foundation. Licensed under the Apache License, Version 2.0: http://www.apache.org/licenses/LICENSE-2.0