Samza 写入HDFS
samza-hdfs 模块实现了一个 Samza Producer 来写入 HDFS。当前的实现包括一个现成的 HdfsSystemProducer，和三个 HdfsWriterS：一个写入原始字节的消息到SequenceFile 的 BytesWritable 键和值；另一个写入 UTF-8 Strings 到一个 SequenceFile 与 LongWritable 键和 Text 值；最后一个写出 Avro 数据文件，包括自动反映的 POJO 对象的模式。
配置 HdfsSystemProducer
您可以像任何其他 Samza 系统一样配置 HdfsSystemProducer：使用 job.properties 文件中设置的配置键和值。您可以配置系统生产者以供您使用，StreamTasks 如下所示：
# set the SystemFactory implementation to instantiate HdfsSystemProducer aliased to 'hdfs-clickstream'
systems.hdfs-clickstream.samza.factory=org.apache.samza.system.hdfs.HdfsSystemFactory
# define a serializer/deserializer for the hdfs-clickstream system
# DO NOT define (i.e. comment out) a SerDe when using the AvroDataFileHdfsWriter so it can reflect the schema
systems.hdfs-clickstream.samza.msg.serde=some-serde-impl
# consumer configs not needed for HDFS system, reader is not implemented yet
# Assign a Metrics implementation via a label we defined earlier in the props file
systems.hdfs-clickstream.streams.metrics.samza.msg.serde=some-metrics-impl
# Assign the implementation class for this system's HdfsWriter
systems.hdfs-clickstream.producer.hdfs.writer.class=org.apache.samza.system.hdfs.writer.TextSequenceFileHdfsWriter
#systems.hdfs-clickstream.producer.hdfs.writer.class=org.apache.samza.system.hdfs.writer.AvroDataFileHdfsWriter
# Set compression type supported by chosen Writer. Only BLOCK compression is supported currently
# AvroDataFileHdfsWriter supports snappy, bzip2, deflate or none (null, anything other than the first three)
systems.hdfs-clickstream.producer.hdfs.compression.type=snappy
# The base dir for HDFS output. The default Bucketer for SequenceFile HdfsWriters
# is currently /BASE/JOB_NAME/DATE_PATH/FILES, where BASE is set below
systems.hdfs-clickstream.producer.hdfs.base.output.dir=/user/me/analytics/clickstream_data
# Assign the implementation class for the HdfsWriter's Bucketer
systems.hdfs-clickstream.producer.hdfs.bucketer.class=org.apache.samza.system.hdfs.writer.JobNameDateTimeBucketer
# Configure the DATE_PATH the Bucketer will set to bucket output files by day for this job run.
systems.hdfs-clickstream.producer.hdfs.bucketer.date.path.format=yyyy_MM_dd
# Optionally set the max output bytes (records for AvroDataFileHdfsWriter) per file.
# A new file will be cut and output continued on the next write call each time this many bytes
# (records for AvroDataFileHdfsWriter) are written.
systems.hdfs-clickstream.producer.hdfs.write.batch.size.bytes=134217728
#systems.hdfs-clickstream.producer.hdfs.write.batch.size.records=10000 假设上述配置已经针对同一文件中的其他位置的标签 some-serde-impl 和 some-metrics-impl 标签正确配置了度量标准和序列实现 job.properties。这些属性中的每一个都具有合理的默认值，因此您可以省略不需要为您的工作运行定制的属性。
