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Automating HBase Major Compactions with Cron and Kerberos

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Major compactions in HBase can be scheduled during low-traffic hours to reduce load on RegionServers. This guide shows how to trigger a compaction from the HBase shell using a simple Ruby script and how to wrap it in a Kerberos-aware cron job. It reflects common operational practice in legacy Hadoop clusters where maintenance windows still matter.

Why Schedule Major Compactions?

Major compactions rewrite all store files of an HBase table, improving read performance but putting additional pressure on the cluster. Many administrators run them during off-peak windows. HBase itself does not provide built-in scheduling, so automation is typically handled with cron or at.

Ruby Script for HBase Shell

HBase shell executes commands through JRuby, so a simple script triggers the compaction: 

# m_compact.rb
major_compact 't1'
exit

Cron-Compatible Shell Wrapper

Below is an example daily_compact script that refreshes a Kerberos ticket and runs the compaction via the HBase shell. Adapt table names, realms and keytabs to your environment. 

#!/bin/bash

USER=hbase
PWD=$(echo ~$USER)
TABLE=t1

# Kerberos settings
KEYTAB=/etc/hbase/conf/hbase.keytab
HOST=$(hostname)
REALM=ALO.ALT

LOG=/var/log/daily_compact

# Acquire Kerberos ticket
sudo -u $USER kinit -k -t $KEYTAB $USER/$HOST@$REALM

# Trigger major compaction
sudo -u $USER hbase shell $PWD/m_compact.rb 2>&1 | tee -a $LOG

Log Output

All messages are appended to /var/log/daily_compact. Example output may look like: 

WARN conf.Configuration: hadoop.native.lib is deprecated
12 row(s) in 0.7800 seconds

Operational Notes (Modern Context)

  • Major compactions increase disk and network load; avoid running on overloaded RegionServers.
  • Consider minor compactions and compaction policies before scheduling forced majors.
  • In cloud migrations or HBase-on-EMR clusters, perform compactions during autoscaling-stable hours.
  • Always verify ticket renewal for Kerberos environments as shared keytabs often expire silently.
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