Okay, so the display of there being 0 bytes in the file is a misnomer in all likelihood.  This is a bit unfortunate as for our use case we then need to wait an hour to find out how much data is actually in each file. 

My understanding is that by default, hdfs appends are NOT active.  I guess the remaining question is what, if anything will having append turned on affect?

On Tue, May 14, 2013 at 2:26 PM, Gary Malouf <malouf.gary@gmail.com> wrote:
I've previously posted something similar to this on StackOverflow:  http://stackoverflow.com/questions/16548358/how-come-flume-ng-hdfs-sink-does-not-write-to-file-when-the-number-of-events-equ

My understanding of batch size from looking at the code in flume-ng 1.3.x is that batch size determines at what point data is written to hdfs.  With my configuration below, I am not seeing any data written to file until the rollInterval has passed.

imp-agent.channels.imp-ch1.type = memory
imp-agent.channels.imp-ch1.capacity = 40000
imp-agent.channels.imp-ch1.transactionCapacity = 1000

imp-agent.sources.avro-imp-source1.channels = imp-ch1
imp-agent.sources.avro-imp-source1.type = avro
imp-agent.sources.avro-imp-source1.bind =
imp-agent.sources.avro-imp-source1.port = 41414

imp-agent.sources.avro-imp-source1.interceptors = host1 timestamp1
imp-agent.sources.avro-imp-source1.interceptors.host1.type = host
imp-agent.sources.avro-imp-source1.interceptors.host1.useIP = false
imp-agent.sources.avro-imp-source1.interceptors.timestamp1.type = timestamp

imp-agent.sinks.hdfs-imp-sink1.channel = imp-ch1
imp-agent.sinks.hdfs-imp-sink1.type = hdfs
imp-agent.sinks.hdfs-imp-sink1.hdfs.path = hdfs://mynamenode:8020/flume/impressions/yr=%Y/mo=%m/d=%d/logger=%{host}s1/
imp-agent.sinks.hdfs-imp-sink1.hdfs.filePrefix = Impr
imp-agent.sinks.hdfs-imp-sink1.hdfs.batchSize = 10
imp-agent.sinks.hdfs-imp-sink1.hdfs.rollInterval = 3600
imp-agent.sinks.hdfs-imp-sink1.hdfs.rollCount = 0
imp-agent.sinks.hdfs-imp-sink1.hdfs.rollSize = 66584576

imp-agent.channels = imp-ch1
imp-agent.sources = avro-imp-source1
imp-agent.sinks = hdfs-imp-sink1
I bring this up as I want to know that after the 'batchSize' number of messages are sent to flume that they have been put into HDFS rather than waiting for the log roll time to do all of the writing.  My strong preference if possible is to make sure that data is being written to '.tmp' file throughout the hour and then rolled after the 'rollInterval' amount of time has passed.