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From James Estes <james.es...@gmail.com>
Subject Optional Channels
Date Mon, 02 Dec 2013 17:21:19 GMT
Hoping someone can point me in the right direction.  We're indexing our logs into elastic search
just for added real time convenience and want to make that step optional.  Essentially, if
we fall behind writing to ES, we would prefer to just skip ES (since we have a more durable
channel for higher latency querying of the same data).  Optional Channels seemed to fit, but
we haven't had much success. 

First, we set our config to have a Memory Channel and made it optional.  If the ES sink fell
behind, the channel would fill and reject new events.  However, the channel throws an exception
and the Channel Processor rolls back the transaction, causing the events to be put back on
the queue to be attempted again.  The doc for getOptionalChannels says "A failure in writing
the event to these channels must be ignored."  Should the transaction just always commit when
optional channels fail (basically a best-effort commit-what-you-could since it was optional

Second, we tried the PseudoTxMemoryChannel, but found it to also continue to bottleneck on
ES.  Turns out that it uses queue.put instead of queue.offer, which means it will block until
there is room in the queue to add the event.  MemoryChannel uses offer.  Should PseudoTxMemoryChannel
switch to using offer always, or at least have an optional 'failFast' to enable that behavior?

Is there another way I can accomplish truly optional channels?  I do find it encouraging it
takes this much effort to make Flume drop events :)



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