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Flume >> mail # user >> Problem Events

Jeremy Karlson 2013-07-24, 21:52
Roshan Naik 2013-07-24, 22:36
Hari Shreedharan 2013-07-24, 22:45
Jeremy Karlson 2013-07-24, 22:56
Arvind Prabhakar 2013-07-25, 02:51
Jeremy Karlson 2013-07-25, 16:50
Arvind Prabhakar 2013-07-26, 00:35
Anat Rozenzon 2013-08-01, 07:59
Ashish 2013-08-01, 08:13
Anat Rozenzon 2013-08-01, 09:42
Jeremy Karlson 2013-08-01, 16:26
Roshan Naik 2013-08-01, 17:26
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RE: Problem Events
There's no way to deal with a bad event once it's in the channel, but you can mitigate future issues by having a timestamp interceptor bound to the source feeding the channel. There is a parameter 'preserve existing' that will only add the header if it doesn't exist. If you don't want to have 'bad' time data in there you could try a static interceptor with a specific past date so that corrupt events fall into a deterministic path in HDFS.

I use this technique to prevent stuck events for both timestamp headers as well as some of our own custom headers we use for tokenized paths. The static interceptor will insert an arbitrary header if it doesn't exist so I have a couple that put in the value 'Unknown' so that I can still send the events through the HDFS sink but I can also find them later if need be.

hope that helps,
Paul Chavez

From: Roshan Naik [mailto:[EMAIL PROTECTED]]
Sent: Thursday, August 01, 2013 10:27 AM
Subject: Re: Problem Events

some questions:
- why is the sink unable to consume the event ?
- how would you like to identify such an event ? by examining its content ? or by the fact that its ping-pong-ing between channel and sink ?
- what would you prefer to do with such an event ? merely drop it ?
On Thu, Aug 1, 2013 at 9:26 AM, Jeremy Karlson <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:
To my knowledge (which is admittedly limited), there is no way to deal with these in a way that will make your day.  I'm happy if someone can say otherwise.

This is very similar to a problem I had a week or two ago.  I fixed it by restarting Flume with debugging on, connecting to it with the debugger, and finding the message in the sink.  Discover a bug in the sink.  Downloaded Flume, fixed bug, recompiled, installed custom version, etc.

I agree that this is not a practical solution, and I still believe that Flume needs some sort of "sink of last resort" option or something, like JMS implementations.

-- Jeremy

On Thu, Aug 1, 2013 at 2:42 AM, Anat Rozenzon <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:
The message is already in the channel.
Is there a way to write an interceptor to work after the channel? or before the sink?

The only thing I found is to stop everything and delete the channel files, but I won't be able to use this approach in production :-(
On Thu, Aug 1, 2013 at 11:13 AM, Ashish <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:

On Thu, Aug 1, 2013 at 1:29 PM, Anat Rozenzon <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:

I'm having the same problem with HDFS sink.

A 'poison' message which doesn't have timestamp header in it as the sink expects.
This causes a NPE which ends in returning the message to the channel , over and over again.

Is my only option to re-write the HDFS sink?
Isn't there any way to intercept in the sink work?

You can write a custom interceptor and remove/modify the poison message.

Interceptors are called before message makes it way into the channel.


I wrote a blog about it a while back http://www.ashishpaliwal.com/blog/2013/06/flume-cookbook-implementing-custom-interceptors/

On Fri, Jul 26, 2013 at 3:35 AM, Arvind Prabhakar <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:
Sounds like a bug in ElasticSearch sink to me. Do you mind filing a Jira to track this? Sample data to cause this would be even better.

Arvind Prabhakar
On Thu, Jul 25, 2013 at 9:50 AM, Jeremy Karlson <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:
This was using the provided ElasticSearch sink.  The logs were not helpful.  I ran it through with the debugger and found the source of the problem.

ContentBuilderUtil uses a very "aggressive" method to determine if the content is JSON; if it contains a "{" anywhere in it, it's considered JSON.  My body contained that but wasn't JSON, causing the JSON parser to throw a CharConversionException from addComplexField(...) (but not the expected JSONException).  We've changed addComplexField(...) to catch different types of exceptions and fall back to treating it as a simple field.  We'll probably submit a patch for this soon.

I'm reasonably happy with this, but I still think that in the bigger picture there should be some sort of mechanism to automatically detect and toss / skip / flag problematic events without them plugging up the flow.

On Wed, Jul 24, 2013 at 7:51 PM, Arvind Prabhakar <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:
Jeremy, would it be possible for you to show us logs for the part where the sink fails to remove an event from the channel? I am assuming this is a standard sink that Flume provides and not a custom one.

The reason I ask is because sinks do not introspect the event, and hence there is no reason why it will fail during the event's removal. It is more likely that there is a problem within the channel in that it cannot dereference the event correctly. Looking at the logs will help us identify the root cause for what you are experiencing.

Arvind Prabhakar
On Wed, Jul 24, 2013 at 3:56 PM, Jeremy Karlson <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:
Both reasonable suggestions.  What would a custom sink look like in this case, and how would I only eliminate the problem events since I don't know what they are until they are attempted by the "real" sink?

My philosophical concern (in general) is that we're taking the approach of exhaustively finding and eliminating possible failure cases.  It's not possible to eliminate every single failure case, so shouldn't there be a method of last resort to eliminate problem events from the channel?
On Wed, Jul 24, 2013 at 3:45 PM, Hari Shreedharan <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:
Or you could write a custom sink that removes this event (more work of course)
Arvind Prabhakar 2013-08-01, 22:25
Connor Woodson 2013-08-03, 01:27
Connor Woodson 2013-08-03, 06:56
Anat Rozenzon 2013-08-04, 05:45
Anat Rozenzon 2013-08-07, 05:40
Jonathan Cooper-Ellis 2013-08-07, 14:14
Anat Rozenzon 2013-08-08, 05:26
Connor Woodson 2013-08-10, 01:08
Hari Shreedharan 2013-08-07, 16:50