[CASSANDRA-4705] Speculative execution for reads / eager retries

• Type: Improvement
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 2.0 beta 1
• Assignee: Vijay
• Reporter: Vijay

Authors

Vijay

Reviewers

Jonathan Ellis

• Created: 22/Sep/12 18:25
• Updated: 16/Apr/19 09:32
• Resolved: 29/Jan/13 06:00

Description

When read_repair is not 1.0, we send the request to one node for some of the requests. When a node goes down or when a node is too busy the client has to wait for the timeout before it can retry.

It would be nice to watch for latency and execute an additional request to a different node, if the response is not received within average/99% of the response times recorded in the past.

CASSANDRA-2540 might be able to solve the variance when read_repair is set to 1.0

1) May be we need to use metrics-core to record various Percentiles
2) Modify ReadCallback.get to execute additional request speculatively.

Issue Links

• relates to: CASSANDRA-5932 Speculative read performance data show unexpected results
• relates to: CASSANDRA-5014 Convert timeout from milli second to micro second.