Registration also involves statistics and diagnostics upload, for the
purposes of remote management. This means there will be long-running
goroutines in effect. Therefore move the code to a service model.
Everytime the purge check was running, a new segment was being added.
This meant the list of almost-empty files in the HH directories would
grow continually.
I believe this change address the issues with hinted-handoff not fully replicating all data to nodes that come back online after an outage.. A detailed explanation follows.
During testing of of hinted-handoff (HH) under various scenarios, HH stats showed that the HH Processor was occasionally encountering errors while unmarshalling hinted data. This error was not handled completely correctly, and in clusters with more than 3 nodes, this could cause the HH service to stall until the node was restarted. This was the high-level reason why HH data was not being replicated.
Furthermore by watching, at the byte-level, the hinted-handoff data it could be seen that HH segment block lengths were getting randomly set to 0, but the block data itself was fine (Block data contains hinted writes). This was the root cause of the unmarshalling errors outlined above. This, in turn, was tracked down to the HH system opening each segment file multiple times concurrently, which was not file-level thread-safe, so these mutiple open calls were corrupting the file.
Finally, the reason a segment file was being opened multiple times in parallel was because WriteShard on the HH Processor was checking for node queues in an unsafe manner. Since WriteShard can be called concurrently this was adding queues for the same node more than once, and each queue-addition results in opening segment files.
This change fixes the locking in WriteShard such the check for an existing HH queue for a given node is performed in a synchronized manner.
Nathaniel Cook
Philip O'Toole
Philip O'Toole
David Norton
Nathaniel Cook
Sean Beckett
Daniel Morsing
Cameron Sparr
Nick Dawbarn
Rob Wilson
Paul Dix
Jason Wilder
Cory LaNou