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From Arvind Prabhakar <arv...@apache.org>
Subject Re: Flume NG reliability and failover mechanisms
Date Fri, 13 Jan 2012 17:26:13 GMT
Hi Connolly,

Thanks for taking time to evaluate Flume NG. Please see my comments inline
below:

On Thu, Jan 12, 2012 at 5:17 PM, Connolly Juhani <
juhani_connolly@cyberagent.co.jp> wrote:

> Hi,
>
> Coming into the new year we've been trying out flume NG, and run into
> some questions. Tried to pick up what was possible from the javadoc and
> source but pardon me if some of these are obvious.
>
> 1) Reading
> http://www.cloudera.com/blog/2011/12/apache-flume-architecture-of-flume-ng-2/
> describes the reliability, but what happens if we lose a node?
> 1.1)Presumably the data stored in its channel is gone?
>

It depends upon the kind of channel you have. If you use a memory channel,
the data will be gone. If you use file channel the data will be available.
If you use JDBC channel, it is guaranteed to be available.


> 1.2) If we restart the node and the channel is a persisting one(file or
> jdbc based),  will it then happily start feeding data into the sink?
>

Correct.


>
> 2) Is there some way to deliver data along multiple paths but make sure
> it only gets persisted to a sink once? To avoid  loss of data to a dying
> node.
>

We have talked about fail-over sink implementations. Although we don't have
it implemented yet, we do intend to provide these faciliteis.


> 2.1) Will there be stuff equivalent to the E2E mode of OG?
>

If you mean end-to-end reliable delivery guarantee, Flume NG already
provides that. You can get this by configuring your flow with reliable
channels (JDBC).


> 2.2) Anything else planned but further down along the horizon? Didn't
> see much at
> https://cwiki.apache.org/confluence/display/FLUME/Features+and+Use+Cases
> but that doesn't look very up to date.
>

Most of the discussion is now moved to JIRA and dev-list. Features such as
channel multiplexing from same source, compatible source implementation for
hybrid installation of previous version of Flume and NG together, event
prioritization have been discussed among many others. As and when resources
permit, we will be addressing these going forward.


>
> 3) Using the hdfs sink, we're getting tons of really small files. I
> suspect this is related to append, and having a poke around the source,
> it turns out that append is only used(by  if hdfs.append.support is set
> to true. The hdfs-default.xml name for this variable is
> dfs.support.append . Is this intentional? Should we be adding
> hdfs.append.support manually to our config, or is there something else
> going on here(regarding all the tiny files)?
>

(Leaving this for Prasad who did the implementation of HDFS sink)


>
> Any help with these issues would be greatly appreciated.
>

Thanks,
Arvind

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