Support Questions

Find answers, ask questions, and share your expertise
Celebrating as our community reaches 100,000 members! Thank you!

namenode handler count


I do see the value of namenode handler count set in out cluster as below.

<property> <name>dfs.namenode.handler.count</name> <value>800</value> </property>

This value is set up by ambari during installation. We have the namenode machine with 128 GB of RAM. Is this value of 800 correct or it is too high




It's very high

The Hadoop RPC server consists of a single RPC queue per port and multiple handler (worker) threads that dequeue and process requests. If the number of handlers is insufficient, then the RPC queue starts building up and eventually overflows. You may start seeing task failures and eventually job failures and unhappy users.

It is recommended that the RPC handler count is set to 20 * log2(Cluster Size) with an upper limit of 200.

e.g. for a 64 node cluster you should initialize this to 20 * log2(64) = 120. The RPC handler count can be configured with the following setting in hdfs-site.xml


This heuristic is from the excellent Hadoop Operations book. If you are using Ambari to manage your cluster this setting can be changed via a slider in the Ambari Server Web UI.

Link. Hope this helps your.