关于Flume中Chanel.Selector.header解释

flume内置的ChannelSelector有两种，分别是Replicating和Multiplexing。

Replicating类型的ChannelSelector会针对每一个Event，拷贝到所有的Channel中，这是默认的ChannelSelector。

replicating类型的ChannelSelector例子如下

 a1.sources = r1
 a1.channels = c1 c2 # 如果有100个Event，那么c1和c2中都会有这100个事件
 
 a1.channels.c1.type = memory
 a1.channels.c1.capacity =
 a1.channels.c1.transactionCapacity = 
 
 a1.channels.c2.type = memory
 a1.channels.c2.capacity =
 a1.channels.c2.transactionCapacity = 

Multiplexing类型的ChannelSelector会根据Event中Header中的某个属性决定分发到哪个Channel。

multiplexing类型的ChannelSelector例子如下：

 a1.sources = r1
 
 a1.sources.source1.selector.type = multiplexing
 a1.sources.source1.selector.header = validation # 以header中的validation对应的值作为条件
 a1.sources.source1.selector.mapping.SUCCESS = c2 # 如果header中validation的值为SUCCESS，使用c2这个channel
 a1.sources.source1.selector.mapping.FAIL = c1 # 如果header中validation的值为FAIL，使用c1这个channel
 a1.sources.source1.selector.default = c1 # 默认使用c1这个channel

a1.sources.source1.selector.header = validation # 以header中的validation对应的值作为条件
 
同理，如下conf文件：

 a1.sources = r1
 a1.sinks = k1 k2
 a1.channels = c1 c2
 
 # Describe/configure the source
 a1.sources.r1.type = exec
 a1.sources.r1.command = tail -F /usr/lib/flume-ng/test.log
 a1.sources.r1.interceptors = i1
 a1.sources.r1.interceptors.i1.type = regex_extractor
 a1.sources.r1.interceptors.i1.regex = (\\w+):(\\w+):(\\w+)
 a1.sources.r1.interceptors.i1.serializers = s1 s2 s3
 a1.sources.r1.interceptors.i1.serializers.s1.name = ip
 a1.sources.r1.interceptors.i1.serializers.s2.name = domain
 a1.sources.r1.interceptors.i1.serializers.s3.name = course
 
 a1.sources.r1.selector.type = multiplexing
 a1.sources.r1.selector.header = course
 a1.sources.r1.selector.mapping.hadoop = c1
 a1.sources.r1.selector.default = c2
 
 # Describe the sink
 a1.sinks.k1.type = file_roll
 a1.sinks.k1.channel = c1
 a1.sinks.k1.sink.directory = /tmp/multiplexing/flume_sink1
 
 a1.sinks.k2.type = file_roll
 a1.sinks.k2.channel = c2
 a1.sinks.k2.sink.directory = /tmp/multiplexing/flume_sink2
 
 # Use a channel which buffers events in memory
 a1.channels.c1.type = memory
 a1.channels.c1.capacity =
 a1.channels.c1.transactionCapacity = 
 
 a1.channels.c2.type = memory
 a1.channels.c2.capacity =
 a1.channels.c2.transactionCapacity = 
 
 # Bind the source and sink to the channel
 a1.sources.r1.channels = c1 c2
 a1.sinks.k1.channel = c1
 a1.sinks.k2.channel = c2

interceptor只对头部进行改变。

source r1中的头部有IP、Domain和cource三种信息，而r1的selector.header = course，表示selector只对IP，Domain和Cource中的Cource进行判断选择，然后再划分channel。