Tuning Guide

In order to tune the cluster infrastructure, we first need to enumerate the resources that are available. For example, with d2.2xlarge instances we have

  • 8 CPU cores
  • 1 EBS mounted root partition (50G)
  • 6 x 2T spinning disks
  • 60GB of memory

Focusing on our workers, we need to split these resources among the following

  • Linux OS
  • Accumulo Tablet Server
  • HDFS DataNode
  • YARN NodeManager
  • YARN applications (MR and Spark jobs)

A good rule of thumb would be, for an 8 CPU node, to give 3 CPUs for the OS, Accumulo Tablet Server, DataNode, and NodeManager (Accumulo Tablet Server being the only process that is going to demand significant CPU resources). Then we have 5 CPUs left for YARN apps.

Memory-wise, 1G should work well for both the DataNode and NodeManager. Accumulo should have more than the defaults, 4-8GB is a good start. Leaving a few GB for the OS and the rest we can allocate to YARN apps, in this case 40G which gives us approximately 8GB per CPU core for YARN apps.

Based on this example, the following configurations would apply.

Accumulo

  • master_max_heapsize: 4G //this is actually running on the koverse node
  • tserver_max_heapsize: 8G
  • tserver.memory.maps.max: 2G

YARN

  • yarn.nodemanager.resource.memory-mb: 40G       // total memory for YARN apps per node
  • yarn.nodemanager.resource.cpu-vcores: 5        // total CPUs for YARN apps per node
  • yarn.scheduler.minimum-allocation-mb: 2G       // min container memory
  • yarn.scheduler.maximum-allocation-mb: 8G       // max container memory

Spark

These would go in /etc/spark/conf/spark-defaults.conf:

  • spark.dynamicAllocation.enabled: true // dynamically add/remove executors as needed by the job
  • spark.shuffle.service.enabled: true // required by dynamicAllocation
  • spark.executor.cores: 2                        // each executor can use 2 CPU cores
  • spark.executor.memory: 7g                     // leave room for overhead between this and container
  • spark.driver.memory: 2g // increase from the default 512m

MapReduce

These would go in koverse-server settings.xml:

  • mapreduce.map.memory.mb: 8G
  • mapreduce.map.java.opts.max.heap: 8/1.2 = 6.66G
  • mapreduce.map.cpu.vcores: 1
  • mapreduce.reduce.memory.mb: 8G
  • mapreduce.reduce.java.opts.max.heap: 8/1.2 = 6.66G
  • mapreduce.reduce.cpu.vcores: 1

HDFS

It has come up on some smaller clusters that having HDFS Trash enabled, coupled with decent amounts of ingest, can cause disk space to quickly fill up due to Accumulo’s Write-Ahead-Log (WAL) filling up HDFS Trash as files are removed during compaction. In these low disk space environments, you can disable HDFS Trash (fs.trash.interval = 0) or set it to something far lower than a day which is ofter the default value from a Hadoop distribution. Alternatively you can set gc.trash.ignore to true in Accumulo http://accumulo.apache.org/1.6/accumulo_user_manual.html#_gc_trash_ignore.

Max Files, Processes

Another key set of configurations, which must be cluster wide, are the max number of processes and files a user can have open. These two configs: “open files” and “max user processes” - can be seen by running:

ulimit -a

It seems Cloudera often takes care of these, per user, in /etc/security/limit.d/<koverse-user>.conf. However if checking as the koverse user shows defaults of 1024 for each, create a /etc/security/limit.d/<koverse-user>.conf (in this case koverse-user is koverse) with:

  • koverse hard memlock unlimited
  • koverse soft memlock unlimited
  • koverse hard nofile 1048576
  • koverse soft nofile 32768
  • koverse soft nproc 65536
  • koverse hard nproc unlimited

Install this file on all nodes in the cluster. No reboots needed to take effect.

Additional information on cluster tuning can be found here: