最近接触了一下kafka， 想要从kafka每半小时获取数据用于更新学习， 找了相关的朋友推荐，是用flume来实现半小时日志回滚，具体代码如下

# Name the components on this agent

a1.sources = r1

a1.sinks = k1

a1.channels = c1

# Describe/configure the source

a1.sources.r1.type = org.apache.flume.source.kafka.KafkaSource

a1.sources.r1.batchSize = 5000

a1.sources.r1.batchDurationMillis = 2000

a1.sources.r1.kafka.zookeeperConnect = host

a1.sources.r1.kafka.topics = topic

# Use a channel which buffers events in memory

a1.channels.c1.type = file

# Bind the source and sink to the channel

a1.sources.r1.channels = c1

a1.sinks.k1.channel = c1

a1.sinks.k1.type = file_roll

a1.sinks.k1.sink.directory = /home/flume_log

a1.sinks.k1.sink.rollInterval=1800

a1.sinks.k1.channel = c1

日志是成功的每1800s生成了，但是不知道为什么有请求的情况下，日志仍旧是空的？是否在哪个地方有写得不对？

另外是否可以直接从kafka实现每半小时读取一次数据，或者半小时内的数据线写到缓存区， 半小时一到就写到文件里？