[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: 14/Apr/21 05:57

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

• Dependent: REEF-1291 Driver gets FailedEvaluator message even if evaluator shuts down properly
• Dependent: SPARK-2876 RDD.partitionBy loads entire partition into memory
• Dependent: HBASE-2531 32-bit encoding of regionnames waaaaaaayyyyy too susceptible to hash clashes
• Dependent: DRILL-4387 Improve execution side when it handles skipAll query
• Dependent: QPID-6275 reduce default timeout for durable subscription queues
• Dependent: DRILL-4530 Improve metadata cache performance for queries with single partition
• Dependent: HADOOP-10561 Copy command with preserve option should handle Xattrs
• Dependent: HDFS-3259 NameNode#initializeSharedEdits should populate shared edits dir with edit log segments
• 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