-Re: HDFS Sink Config Help
Jeremy Karlson 2013-11-01, 16:50
Thanks for your suggestions. My only Flume experience so far is with the
Elasticsearch sink, which serializes (headers and body) to JSON
automatically. I was expecting something similar from the HDFS sink and
when it didn't do that I started questioning the file format when I should
have been looking at the serializer. A misunderstanding on my part.
I just finished serializing to JSON when I saw you suggested Avro. I'll
look into that. Is that what you would use if you were going to query with
Hive external tables?
On Thu, Oct 31, 2013 at 4:42 PM, Jeff Lord <[EMAIL PROTECTED]> wrote:
> Datastream fileType will let you write text files.
> CompressedStream will do just that.
> SequenceFile will create sequence files as you have guessed and you can
> use either Text or Writeable (bytes) for your data here.
> So flume is configureable out of the box with regards to the size of your
> files. Yes you are correct that it is better to create files that are at
> least the size of a full block.
> You can roll your files based on time, size, or number of events. Rolling
> on an hourly basis makes perfect sense.
> With all that said we recommend writing to avro container files as that
> format is most well suited for being used in the Hadoop ecosystem.
> Avro has many benefits which include support for compression, code
> generation, versioning and schema evolution.
> You can do this with flume by specifying the avro_event type for the
> serializer property in your hdfs sink.
> Hope this helps.
> On Wed, Oct 30, 2013 at 4:15 PM, Jeremy Karlson <[EMAIL PROTECTED]>wrote:
>> Hi everyone.
>> I'm trying to set up Flume to log into HDFS. Along the way, Flume
>> attaches a number of headers (environment, hostname, etc) that I would also
>> like to store with my log messages. Ideally, I'd like to be able to use
>> Hive to query all of this later. I must also admit to knowing next to
>> nothing about HDFS. That probably doesn't help. :-P
>> I'm confused about the HDFS sink configuration. Specifically, I'm trying
>> to understand what these two options do (and how they interact):
>> File Type:
>> DataStream - This appears to write the event body, and loses all headers.
>> CompressedStream - I assume just a compressed data stream.
>> SequenceFile - I think this is what I want, since it seems to be a
>> key/value based thing, which I assume means it will include headers.
>> Write Format: This seems to only apply for SequenceFile above, but lots
>> of Internet examples seem to state otherwise. I'm also unclear on the
>> difference here. Isn't "Text" just a specific type of "Writable" in HDFS?
>> Also, I'm unclear on why Flume, by default, seems to be set up to make
>> such small HDFS files. Isn't HDFS designed (and more efficient) when
>> storing larger files that are closer to the size of a full block? I was
>> thinking it made more sense to write all log data to a single file, and
>> roll that file hourly (or whatever, depending on volume). Thoughts here?
>> Thanks a lot.
>> -- Jeremy