ElasticSearch workers thread number?

[Marina]

One more question on Flume ElasticSearchSink. I see that for HDFS sink, you can 
control the number of worker threads using this parameter: 
hdfs.threadsPoolSize. However, I do not see any such parameter for 
ElasticSearchSink.... Does it mean that ElasticSsearchSink will span only one 
thread to push events form Flume to ES? If I have rates of a few hundred events 
per second (say, up to 3K) - this will become a performance bottleneck.
thanks!Marina