spark streaming write orc suddenly slow?

[446463...@qq.com]

Hi All：
when I use sparking streaming to consume kafka data to stroe in HDFS with orc 
files format.
it's fast in the beginning,but it's slow in several hours later.
environment:
spark version: 2.1.0
kafka version 0.10.1.1
spark-streaming-kafka jar's version: spark-streaming-kafka-0-8-2.11



446463...@qq.com