[GIRAPH-306] Netty requests should be reliable and implement exactly once semantics

• Type: Improvement
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Assignee: Avery Ching
• Reporter: Avery Ching
• Created: 18/Aug/12 07:50
• Updated: 03/Sep/12 05:07
• Resolved: 21/Aug/12 22:23

Description

One of the biggest scalability challenges is getting Giraph to run reliably on a large number of tasks (i.e. > 200). Several problems exist:

1) If the connection fails after the initial connection was made, the job will die.
2) Requests must be completed exactly once. This is difficult to implement, but required since we cannot have multiple retried requests succeed (i.e. a vertex gets more messages than expected).
3) Sometimes there are unresolved addresses, causing failure.

This patch addresses these issues by re-establishing failed connections and keep tracking of every request sent to every worker. If the request fails or passes a timeout, it will be resent. The server will keep track of requests that succeeded to insure that the same request won't be processed more than once. The structure for keeping track of the succeeded requests on the server is efficient for handling increasing request ids (IncreasingBitSet). For handling unresolved addresses, I added retry logic to keep trying to resolve the problem.

This patch also adds several unit tests that use fault injection to simulate a lost response or a closed channel exception on the server. It also has unittests for IncreasingBitSet to insure it is working correctly and efficiently.

This passes all unittests (including the new ones). Additionally, I have some experience results as well.

Previously, I was unable to run reliably with more than 200 workers. With this change I can reliably run 500+ workers. I also ran with 600 workers successfully. This is a really big reliability win for us.

I can see the code working to do reconnections and re-issue requests when necessary. It's very cool.

I.e.

2012-08-18 00:16:52,109 INFO org.apache.giraph.comm.NettyClient: checkAndFixChannel: Fixing disconnected channel to xxx.xxx.xxx.xxx/xx.xx.xx.xx:30455, open = false, bound = false
2012-08-18 00:16:52,111 INFO org.apache.giraph.comm.NettyClient: checkAndFixChannel: Connected to xxx.xxx.xxx.xxx/xxx.xxx.xxx.xxx:30455!
2012-08-18 00:16:52,123 INFO org.apache.giraph.comm.NettyClient: checkAndFixChannel: Fixing disconnected channel to xxx.xxx.xxx.xxx/xxx.xxx.xxx.xxx, open = false, bound = false
2012-08-18 00:16:52,124 INFO org.apache.giraph.comm.NettyClient: checkAndFixChannel: Connected to xxx.xxx.xxx.xxx/xxx.xxx.xxx.xxx:30117!

Issue Links

• contains: GIRAPH-304 Closed channels between workers
• is related to: GIRAPH-319 Receiving two responses for a request causes an exception