We upgraded to 1.5.3 and I see what I think is a new Logstash thread. This thread is not named, it just shows as "java" in top with threads turned on.
This process takes a lot of CPU time... usually worker threads take the most, now this "new" java thread is.
At the same time, we are not able to index data as fast as before so this is the motivation for asking about this.
In the mean time, I may revert to an old version of LS to compare.