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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="schedule_random_replica" rev="2.5.0">
<title>SCHEDULE_RANDOM_REPLICA Query Option (<keyword keyref="impala25"/> or higher only)</title>
<titlealts audience="PDF">
<data name="Category" value="Impala"/>
<data name="Category" value="Impala Query Options"/>
<data name="Category" value="Performance"/>
<data name="Category" value="Developers"/>
<data name="Category" value="Data Analysts"/>
The <codeph>SCHEDULE_RANDOM_REPLICA</codeph> query option fine-tunes the scheduling
algorithm for deciding which host processes each HDFS data block or Kudu tablet to reduce
the chance of CPU hotspots.
By default, Impala estimates how much work each host has done for the query, and selects
the host that has the lowest workload. This algorithm is intended to reduce CPU hotspots
arising when the same host is selected to process multiple data blocks / tablets. Use the
<codeph>SCHEDULE_RANDOM_REPLICA</codeph> query option if hotspots still arise for some
combinations of queries and data layout.
The <codeph>SCHEDULE_RANDOM_REPLICA</codeph> query option only applies to tables and
partitions that are not enabled for the HDFS caching.
<p conref="../shared/impala_common.xml#common/type_boolean"/>
<p conref="../shared/impala_common.xml#common/default_false"/>
<p conref="../shared/impala_common.xml#common/added_in_250"/>
<p conref="../shared/impala_common.xml#common/related_info"/>
<xref href="impala_perf_hdfs_caching.xml#hdfs_caching"/>,
href="impala_scalability.xml#scalability_hotspots"/> ,