[ZOOKEEPER-704] GSoC 2010: Read-Only Mode

• Type: Wish
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Labels: gsoc mentor
• Assignee: Sergey Doroshenko
• Reporter: Henry Robinson
• Created: 13/Mar/10 00:59
• Updated: 27/Jan/11 17:45

Description

Read-only mode
Possible Mentor
Henry Robinson (henry at apache dot org)

Requirements
Java and TCP/IP networking

Description
When a ZooKeeper server loses contact with over half of the other servers in an ensemble ('loses a quorum'), it stops responding to client requests because it cannot guarantee that writes will get processed correctly. For some applications, it would be beneficial if a server still responded to read requests when the quorum is lost, but caused an error condition when a write request was attempted.

This project would implement a 'read-only' mode for ZooKeeper servers (maybe only for Observers) that allowed read requests to be served as long as the client can contact a server.

This is a great project for getting really hands-on with the internals of ZooKeeper - you must be comfortable with Java and networking otherwise you'll have a hard time coming up to speed.

Issue Links

• is related to: ZOOKEEPER-769 Leader can treat observers as quorum members

Sub-Tasks

• server-side functionality for read-only mode: Closed
• enable r/o mode in C client library: Resolved
• forrest docs for read-only mode: Open