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From Aljoscha Krettek <aljos...@apache.org>
Subject Re: Reload DistributedCache file?
Date Fri, 25 Aug 2017 15:35:49 GMT
Hi,

You are right in your analysis that updating the entry in the DistributedCache will not in
fact update the file on already running operators. The DistributedCache is only read when
initially setting up operations. You might be able to use a file source (with CONTINUOUS processing
mode) and a connected stream where the first input is your normal input and the second input
are the (periodically updated) contents of your file in HDFS.

Would this work for you?

Best,
Aljoscha

> On 17. Aug 2017, at 10:00, Conrad Crampton <conrad.crampton@SecData.com> wrote:
> 
> Whilst this looks great and thanks for pointing this out, the problem isn’t so much
as with identifying changes in the HDFS file as the overhead in re-loading it isn’t significant
(10s of lines long) but the problem is more to do with using the Flink mechanisms i.e. DistributedCache
and refreshing this on a local level (to the taskmanager node).
>  
> I may have to read HDFS directly in the FilterFunction to keep it up to date.
>  
> Thanks
> Conrad
>  
> From: Ted Yu <yuzhihong@gmail.com>
> Date: Wednesday, 16 August 2017 at 18:11
> To: Conrad Crampton <conrad.crampton@SecData.com>
> Cc: "user@flink.apache.org" <user@flink.apache.org>
> Subject: Re: Reload DistributedCache file?
>  
> For hdfs, there is iNotify mechanism.
>  
> https://issues.apache.org/jira/browse/HDFS-6634 <https://issues.apache.org/jira/browse/HDFS-6634>
>  
> https://www.slideshare.net/Hadoop_Summit/keep-me-in-the-loop-inotify-in-hdfs <https://www.slideshare.net/Hadoop_Summit/keep-me-in-the-loop-inotify-in-hdfs>
>  
> FYI
>  
> On Wed, Aug 16, 2017 at 9:41 AM, Conrad Crampton <conrad.crampton@secdata.com <mailto:conrad.crampton@secdata.com>>
wrote:
> Hi,
> I have a simple text file that is stored in HDFS which I use in a RichFilterFunction
by way of DistributedCache file. The file is externally edited periodically to have other
lines added to it. My FilterFunction also implements Runnable whose run method is run as a
scheduleAtFixedRate method of ScheduledExectutorService which reloads the file and stores
the results in a List in the Filter class.
>  
> I have realized the errors of my ways as the file that is reloaded is the cached file
that is copied to temporary file location on the node which this instance of Filter class
is loaded and not the file from HDFS directly (as this has been copied when the Flink job
started.
>  
> Can anyone suggest a solution to this? It is I think a similar problem that Add Side
Inputs in Flink [1] proposal is trying to address but not finalized yet.
> Can anyone see a problem if I have a thread that reloads the HDFS file being in the main
body of my Flink program and registers the cache file within that reload process e.g.
>  
> env.registerCachedFile(properties.getProperty("whitelist.location"), WHITELIST);
>  
> i.e. does this actually copy the file again from HDFS to temporary files on each node?
I think I’d have to have the same schedule I have currently that reload within my Filter
function too though as all the previous process would do is to push the HDFS file to temp
location and not actually refresh my List.
>  
> Any suggestions would be welcome.
>  
> Thanks
> Conrad
>  
> [1] https://docs.google.com/document/d/1hIgxi2Zchww_5fWUHLoYiXwSBXjv-M5eOv-MKQYN3m4/edit#heading=h.pqg5z6g0mjm7
<https://docs.google.com/document/d/1hIgxi2Zchww_5fWUHLoYiXwSBXjv-M5eOv-MKQYN3m4/edit#heading=h.pqg5z6g0mjm7>
>  
> 
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