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From "Brandon Williams (Commented) (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-3722) Send Hints to Dynamic Snitch when Compaction or repair is going on for a node.
Date Wed, 11 Jan 2012 19:05:39 GMT


Brandon Williams commented on CASSANDRA-3722:

bq. Hi Brandon, Will it make sense for the remote node to avoid traffic for a given the start
and end?

Sure, but my point is that's going to happen already:

* node X begins a repair, adversely affecting its read latency
* node Y tries to read data from X, and scores it badly due to the extra latency

At this point, node Y will not try to read from X again until either:

* all other members of X's replica set perform *worse* than X
* the RESET_INTERVAL_IN_MS elapses, and the entire process starts over again

Eventually, node X finishes the validation compaction and when the reset interval elapses,
its reads are more equal to the rest of the replica set and everything is back to normal.

Telling the dsnitch when a remote node starts and stop compacting doesn't seem like it's going
to improve on this a whole lot.

> Send Hints to Dynamic Snitch when Compaction or repair is going on for a node.
> ------------------------------------------------------------------------------
>                 Key: CASSANDRA-3722
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 1.1
>            Reporter: Vijay
>            Assignee: Vijay
>            Priority: Minor
> Currently Dynamic snitch looks at the latency for figuring out which node will be better
serving the requests, this works great but there is a part of the traffic sent to collect
this data... There is also a window when Snitch doesn't know about some major event which
are going to happen on the node (Node which is going to receive the data request).
> It would be great if we can send some sort hints to the Snitch so they can score based
on known events causing higher latencies.

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