How come Flume-NG HDFS sink does not write to file when the number of events equals or exceeds the batchSize?

Question

I am trying to configure Flume such that logs roll hourly or when they reach the default block size of HDFS (64 MB). Below is my current configuration:

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 = 0.0.0.0
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

My intention with the configuration above is to write to HDFS in batches of 10 and then roll the file being written to hourly. What I am seeing is that all of the data appears to be held in memory until since I am under 64MB until the files rolls after 1 hour. Are there any settings I should be tweaking in order to get my desired behavior?

Answer 1

To answer myself, Flume is writing the data to HDFS in batches. The file length is reported as open because a block is in process of being written to.