docs/topics/impala_max_num_runtime_filters.xml

<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="max_num_runtime_filters" rev="2.5.0">

  <title>MAX_NUM_RUNTIME_FILTERS Query Option (<keyword keyref="impala25"/> or higher only)</title>
  <titlealts audience="PDF"><navtitle>MAX_NUM_RUNTIME_FILTERS</navtitle></titlealts>
  <prolog>
    <metadata>
      <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"/>
    </metadata>
  </prolog>

  <conbody>

    <p rev="2.5.0">
      <indexterm audience="hidden">MAX_NUM_RUNTIME_FILTERS query option</indexterm>
      The <codeph>MAX_NUM_RUNTIME_FILTERS</codeph> query option
      sets an upper limit on the number of runtime filters that can be produced for each query.
    </p>

    <p conref="../shared/impala_common.xml#common/type_integer"/>

    <p>
      <b>Default:</b> 10
    </p>

    <p conref="../shared/impala_common.xml#common/added_in_250"/>

    <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

    <p>
      Each runtime filter imposes some memory overhead on the query.
      Depending on the setting of the <codeph>RUNTIME_BLOOM_FILTER_SIZE</codeph>
      query option, each filter might consume between 1 and 16 megabytes
      per plan fragment. There are typically 5 or fewer filters per plan fragment.
    </p>

    <p>
      Impala evaluates the effectiveness of each filter, and keeps the
      ones that eliminate the largest number of partitions or rows.
      Therefore, this setting can protect against
      potential problems due to excessive memory overhead for filter production,
      while still allowing a high level of optimization for suitable queries.
    </p>

    <p conref="../shared/impala_common.xml#common/runtime_filtering_option_caveat"/>

    <p conref="../shared/impala_common.xml#common/kudu_blurb"/>

    <p rev="2.11.0 IMPALA-4252" conref="../shared/impala_common.xml#common/filter_option_bloom_only"/>

    <p conref="../shared/impala_common.xml#common/related_info"/>
    <p>
      <xref href="impala_runtime_filtering.xml"/>,
      <!-- <xref href="impala_partitioning.xml#dynamic_partition_pruning"/>, -->
      <xref href="impala_runtime_bloom_filter_size.xml#runtime_bloom_filter_size"/>,
      <xref href="impala_runtime_filter_mode.xml#runtime_filter_mode"/>
    </p>

  </conbody>
</concept>