<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>Logging · Apache Druid</title><meta name="viewport" content="width=device-width"/><link rel="canonical" href="https://druid.apache.org/docs/0.23.0/configuration/logging.html"/><meta name="generator" content="Docusaurus"/><meta name="description" content="&lt;!--"/><meta name="docsearch:language" content="en"/><meta name="docsearch:version" content="0.23.0" /><meta property="og:title" content="Logging · Apache Druid"/><meta property="og:type" content="website"/><meta property="og:url" content="https://druid.apache.org/index.html"/><meta property="og:description" content="&lt;!--"/><meta property="og:image" content="https://druid.apache.org/img/druid_nav.png"/><meta name="twitter:card" content="summary"/><meta name="twitter:image" content="https://druid.apache.org/img/druid_nav.png"/><link rel="shortcut icon" href="/img/favicon.png"/><link rel="stylesheet" href="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.css"/><link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/default.min.css"/><script async="" src="https://www.googletagmanager.com/gtag/js?id=UA-131010415-1"></script><script>
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6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/index.html">Ingestion</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/data-formats.html">Data formats</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/data-model.html">Data model</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/rollup.html">Data rollup</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/partitioning.html">Partitioning</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/ingestion-spec.html">Ingestion spec</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/schema-design.html">Schema design tips</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/data-management.html">Data management</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/compaction.html">Compaction</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Stream ingestion</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/extensions-core/kafka-ingestion.html">Apache Kafka ingestion</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/extensions-core/kafka-supervisor-reference.html">Apache Kafka supervisor</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/extensions-core/kafka-supervisor-operations.html">Apache Kafka operations</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/extensions-core/kinesis-ingestion.html">Amazon Kinesis</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Batch ingestion</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/native-batch.html">Native batch</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/native-batch-simple-task.html">Simple task indexing</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/native-batch-input-sources.html">Input sources</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/native-batch-firehose.html">Firehose</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/hadoop.html">Hadoop-based</a></li></ul></div><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/tasks.html">Task reference</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/faq.html">Troubleshooting FAQ</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Querying<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Druid SQL</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/sql.html">Overview and syntax</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/sql-data-types.html">SQL data types</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/sql-operators.html">Operators</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/sql-scalar.html">Scalar functions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/sql-aggregations.html">Aggregation functions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/sql-multivalue-string-functions.html">Multi-value string functions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/sql-api.html">Druid SQL API</a></li><li class="navListItem"><a 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href="/docs/0.23.0/querying/datasource.html">Datasources</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/joins.html">Joins</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/lookups.html">Lookups</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/multi-value-dimensions.html">Multi-value dimensions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/multitenancy.html">Multitenancy</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/caching.html">Query caching</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/using-caching.html">Using query caching</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/query-context.html">Query context</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Native query types</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/timeseriesquery.html">Timeseries</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/topnquery.html">TopN</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/groupbyquery.html">GroupBy</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/scan-query.html">Scan</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/searchquery.html">Search</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/timeboundaryquery.html">TimeBoundary</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/segmentmetadataquery.html">SegmentMetadata</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/datasourcemetadataquery.html">DatasourceMetadata</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Native query components</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/filters.html">Filters</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/granularities.html">Granularities</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/dimensionspecs.html">Dimensions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/aggregations.html">Aggregations</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/post-aggregations.html">Post-aggregations</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/misc/math-expr.html">Expressions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/having.html">Having filters (groupBy)</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/limitspec.html">Sorting and limiting (groupBy)</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/topnmetricspec.html">Sorting (topN)</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/sorting-orders.html">String comparators</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/virtual-columns.html">Virtual columns</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/geo.html">Spatial filters</a></li></ul></div></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Configuration<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/0.23.0/configuration/index.html">Configuration reference</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/extensions.html">Extensions</a></li><li class="navListItem navListItemActive"><a class="navItem" href="/docs/0.23.0/configuration/logging.html">Logging</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Operations<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/druid-console.html">Web console</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/getting-started.html">Getting started with Apache Druid</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Security</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/security-overview.html">Security overview</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/security-user-auth.html">User authentication and authorization</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/auth-ldap.html">LDAP auth</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/password-provider.html">Password providers</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/dynamic-config-provider.html">Dynamic Config Providers</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/tls-support.html">TLS support</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Performance tuning</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/basic-cluster-tuning.html">Basic cluster tuning</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/segment-optimization.html">Segment Size Optimization</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/mixed-workloads.html">Mixed workloads</a></li><li class="navListItem"><a 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href="/docs/0.23.0/operations/rolling-updates.html">Rolling updates</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/rule-configuration.html">Retaining or automatically dropping data</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/other-hadoop.html">Working with different versions of Apache Hadoop</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Misc</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/management-uis.html">Legacy Management UIs</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/dump-segment.html">dump-segment tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/reset-cluster.html">reset-cluster tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/insert-segment-to-db.html">insert-segment-to-db tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/pull-deps.html">pull-deps tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/deep-storage-migration.html">Deep storage migration</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/export-metadata.html">Export Metadata Tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/metadata-migration.html">Metadata Migration</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/use_sbt_to_build_fat_jar.html">Content for build.sbt</a></li></ul></div></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Development<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/overview.html">Developing on Druid</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/modules.html">Creating extensions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/javascript.html">JavaScript functionality</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/build.html">Build from source</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/versioning.html">Versioning</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/experimental.html">Experimental features</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Misc<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a 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<p>Apache Druid processes will emit logs that are useful for debugging to log files.
These processes also emit periodic <a href="/docs/0.23.0/configuration/index.html#enabling-metrics">metrics</a> about their state.
Metric info logs can be disabled with <code>-Ddruid.emitter.logging.logLevel=debug</code>.</p>
<p>Druid uses <a href="http://logging.apache.org/log4j/2.x/">log4j2</a> for logging.
The default configuration file log4j2.xml ships with Druid under conf/druid/{config}/_common/log4j2.xml .</p>
<p>By default, Druid uses <code>RollingRandomAccessFile</code> for rollover daily, and keeps log files up to 7 days.
If that's not suitable in your case, you could modify the log4j2.xml to meet your need.</p>
<p>An example log4j2.xml file is shown below:</p>
<pre><code class="hljs"><span class="xml"><span class="hljs-meta">&lt;?xml version="1.0" encoding="UTF-8" ?&gt;</span>
<span class="hljs-tag">&lt;<span class="hljs-name">Configuration</span> <span class="hljs-attr">status</span>=<span class="hljs-string">"WARN"</span>&gt;</span>
  <span class="hljs-tag">&lt;<span class="hljs-name">Console</span> <span class="hljs-attr">name</span>=<span class="hljs-string">"Console"</span> <span class="hljs-attr">target</span>=<span class="hljs-string">"SYSTEM_OUT"</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">PatternLayout</span> <span class="hljs-attr">pattern</span>=<span class="hljs-string">"%d</span></span></span><span class="hljs-template-variable">{ISO8601}</span><span class="xml"><span class="hljs-tag"><span class="hljs-string"> %p [%t] %c - %m%n"</span>/&gt;</span>
  <span class="hljs-tag">&lt;/<span class="hljs-name">Console</span>&gt;</span>
    
  <span class="hljs-tag">&lt;<span class="hljs-name">RollingRandomAccessFile</span> <span class="hljs-attr">name</span>=<span class="hljs-string">"FileAppender"</span>
                           <span class="hljs-attr">fileName</span>=<span class="hljs-string">"$</span></span></span><span class="hljs-template-variable">{sys:druid.log.path}</span><span class="xml"><span class="hljs-tag"><span class="hljs-string">/$</span></span></span><span class="hljs-template-variable">{sys:druid.node.type}</span><span class="xml"><span class="hljs-tag"><span class="hljs-string">.log"</span>
                           <span class="hljs-attr">filePattern</span>=<span class="hljs-string">"$</span></span></span><span class="hljs-template-variable">{sys:druid.log.path}</span><span class="xml"><span class="hljs-tag"><span class="hljs-string">/$</span></span></span><span class="hljs-template-variable">{sys:druid.node.type}</span><span class="xml"><span class="hljs-tag"><span class="hljs-string">.%d</span></span></span><span class="hljs-template-variable">{yyyyMMdd}</span><span class="xml"><span class="hljs-tag"><span class="hljs-string">.log"</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">PatternLayout</span> <span class="hljs-attr">pattern</span>=<span class="hljs-string">"%d</span></span></span><span class="hljs-template-variable">{ISO8601}</span><span class="xml"><span class="hljs-tag"><span class="hljs-string"> %p [%t] %c - %m%n"</span>/&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">Policies</span>&gt;</span>
        <span class="hljs-tag">&lt;<span class="hljs-name">TimeBasedTriggeringPolicy</span> <span class="hljs-attr">interval</span>=<span class="hljs-string">"1"</span> <span class="hljs-attr">modulate</span>=<span class="hljs-string">"true"</span>/&gt;</span>
    <span class="hljs-tag">&lt;/<span class="hljs-name">Policies</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">DefaultRolloverStrategy</span>&gt;</span>
      <span class="hljs-tag">&lt;<span class="hljs-name">Delete</span> <span class="hljs-attr">basePath</span>=<span class="hljs-string">"$</span></span></span><span class="hljs-template-variable">{sys:druid.log.path}</span><span class="xml"><span class="hljs-tag"><span class="hljs-string">/"</span> <span class="hljs-attr">maxDepth</span>=<span class="hljs-string">"1"</span>&gt;</span>
        <span class="hljs-tag">&lt;<span class="hljs-name">IfFileName</span> <span class="hljs-attr">glob</span>=<span class="hljs-string">"*.log"</span> /&gt;</span>
        <span class="hljs-tag">&lt;<span class="hljs-name">IfLastModified</span> <span class="hljs-attr">age</span>=<span class="hljs-string">"7d"</span> /&gt;</span>
      <span class="hljs-tag">&lt;/<span class="hljs-name">Delete</span>&gt;</span>
    <span class="hljs-tag">&lt;/<span class="hljs-name">DefaultRolloverStrategy</span>&gt;</span>
  <span class="hljs-tag">&lt;/<span class="hljs-name">RollingRandomAccessFile</span>&gt;</span>
  <span class="hljs-tag">&lt;<span class="hljs-name">Loggers</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">Root</span> <span class="hljs-attr">level</span>=<span class="hljs-string">"info"</span>&gt;</span>
      <span class="hljs-tag">&lt;<span class="hljs-name">AppenderRef</span> <span class="hljs-attr">ref</span>=<span class="hljs-string">"FileAppender"</span>/&gt;</span>
    <span class="hljs-tag">&lt;/<span class="hljs-name">Root</span>&gt;</span>

    <span class="hljs-comment">&lt;!-- Uncomment to enable logging of all HTTP requests
    &lt;Logger name="org.apache.druid.jetty.RequestLog" additivity="false" level="DEBUG"&gt;
        &lt;AppenderRef ref="FileAppender"/&gt;
    &lt;/Logger&gt;
    --&gt;</span>
  <span class="hljs-tag">&lt;/<span class="hljs-name">Loggers</span>&gt;</span>
<span class="hljs-tag">&lt;/<span class="hljs-name">Configuration</span>&gt;</span>
</span></code></pre>
<blockquote>
<p>NOTE:
Although the log4j configuration file is shared with Druid's task peon processes,
the appenders in this file DO NOT take effect for peon processes, which always output logs to standard output.
Middle Managers redirect task logs from standard output to <a href="/docs/0.23.0/configuration/index.html#log-long-term-storage">long-term storage</a>.</p>
<p>However, log level settings do take effect for these task peon processes,
which means you can still configure loggers at different logging level for task logs using <code>log4j2.xml</code>.</p>
</blockquote>
<h2><a class="anchor" aria-hidden="true" id="log-directory"></a><a href="#log-directory" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Log directory</h2>
<p>The included log4j2.xml configuration for Druid and ZooKeeper will output logs to the <code>log</code> directory at the root of the distribution.</p>
<p>If you want to change the log directory, set the environment variable <code>DRUID_LOG_DIR</code> to the right directory before you start Druid.</p>
<h2><a class="anchor" aria-hidden="true" id="all-in-one-start-commands"></a><a href="#all-in-one-start-commands" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>All-in-one start commands</h2>
<p>If you use one of the all-in-one start commands, such as <code>bin/start-micro-quickstart</code>, then in the default configuration
each service has two kind of log files. The main log file (for example, <code>log/historical.log</code>) is written by log4j2 and
is rotated periodically.</p>
<p>The secondary log file (for example, <code>log/historical.stdout.log</code>) contains anything that is written by the component
directly to standard output or standard error without going through log4j2. This consists mainly of messages from the
Java runtime itself. This file is not rotated, but it is generally small due to the low volume of messages. If
necessary, you can truncate it using the Linux command <code>truncate --size 0 log/historical.stdout.log</code>.</p>
<h2><a class="anchor" aria-hidden="true" id="avoid-reflective-access-warnings-in-logs"></a><a href="#avoid-reflective-access-warnings-in-logs" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Avoid reflective access warnings in logs</h2>
<p>On Java 11, you may see warnings like this in log files:</p>
<pre><code class="hljs"><span class="hljs-symbol">WARNING: </span>An illegal reflective access operation has occurred
<span class="hljs-symbol">WARNING: </span>Use --illegal-access=warn to enable warnings of further illegal reflective access operations
<span class="hljs-symbol">WARNING: </span>All illegal access operations will be denied in a future release
</code></pre>
<p>These messages do not cause harm, but you can avoid them by adding the following lines to your <code>jvm.config</code> files. These
lines are not part of the default JVM configs that ship with Druid, because Java 8 will not recognize these options and
will fail to start up.</p>
<pre><code class="hljs">--<span class="hljs-keyword">add</span>-exports=java.<span class="hljs-keyword">base</span>/jdk.<span class="hljs-keyword">internal</span>.<span class="hljs-keyword">ref</span>=ALL-UNNAMED
--<span class="hljs-keyword">add</span>-exports=java.<span class="hljs-keyword">base</span>/jdk.<span class="hljs-keyword">internal</span>.perf=ALL-UNNAMED
--<span class="hljs-keyword">add</span>-opens=java.<span class="hljs-keyword">base</span>/java.lang=ALL-UNNAMED
--<span class="hljs-keyword">add</span>-opens=jdk.management/com.sun.management.<span class="hljs-keyword">internal</span>=ALL-UNNAMED
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="my-logs-are-really-chatty-can-i-set-them-to-asynchronously-write"></a><a href="#my-logs-are-really-chatty-can-i-set-them-to-asynchronously-write" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>My logs are really chatty, can I set them to asynchronously write?</h2>
<p>Yes, using a <code>log4j2.xml</code> similar to the following causes some of the more chatty classes to write asynchronously:</p>
<pre><code class="hljs"><span class="xml"><span class="hljs-meta">&lt;?xml version="1.0" encoding="UTF-8" ?&gt;</span>
<span class="hljs-tag">&lt;<span class="hljs-name">Configuration</span> <span class="hljs-attr">status</span>=<span class="hljs-string">"WARN"</span>&gt;</span>
  <span class="hljs-tag">&lt;<span class="hljs-name">Appenders</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">Console</span> <span class="hljs-attr">name</span>=<span class="hljs-string">"Console"</span> <span class="hljs-attr">target</span>=<span class="hljs-string">"SYSTEM_OUT"</span>&gt;</span>
      <span class="hljs-tag">&lt;<span class="hljs-name">PatternLayout</span> <span class="hljs-attr">pattern</span>=<span class="hljs-string">"%d</span></span></span><span class="hljs-template-variable">{ISO8601}</span><span class="xml"><span class="hljs-tag"><span class="hljs-string"> %p [%t] %c - %m%n"</span>/&gt;</span>
    <span class="hljs-tag">&lt;/<span class="hljs-name">Console</span>&gt;</span>
  <span class="hljs-tag">&lt;/<span class="hljs-name">Appenders</span>&gt;</span>
  
<span class="hljs-tag">&lt;<span class="hljs-name">Loggers</span>&gt;</span>
    <span class="hljs-comment">&lt;!-- AsyncLogger instead of Logger --&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">AsyncLogger</span> <span class="hljs-attr">name</span>=<span class="hljs-string">"org.apache.druid.curator.inventory.CuratorInventoryManager"</span> <span class="hljs-attr">level</span>=<span class="hljs-string">"debug"</span> <span class="hljs-attr">additivity</span>=<span class="hljs-string">"false"</span>&gt;</span>
      <span class="hljs-tag">&lt;<span class="hljs-name">AppenderRef</span> <span class="hljs-attr">ref</span>=<span class="hljs-string">"Console"</span>/&gt;</span>
    <span class="hljs-tag">&lt;/<span class="hljs-name">AsyncLogger</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">AsyncLogger</span> <span class="hljs-attr">name</span>=<span class="hljs-string">"org.apache.druid.client.BatchServerInventoryView"</span> <span class="hljs-attr">level</span>=<span class="hljs-string">"debug"</span> <span class="hljs-attr">additivity</span>=<span class="hljs-string">"false"</span>&gt;</span>
      <span class="hljs-tag">&lt;<span class="hljs-name">AppenderRef</span> <span class="hljs-attr">ref</span>=<span class="hljs-string">"Console"</span>/&gt;</span>
    <span class="hljs-tag">&lt;/<span class="hljs-name">AsyncLogger</span>&gt;</span>
    <span class="hljs-comment">&lt;!-- Make extra sure nobody adds logs in a bad way that can hurt performance --&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">AsyncLogger</span> <span class="hljs-attr">name</span>=<span class="hljs-string">"org.apache.druid.client.ServerInventoryView"</span> <span class="hljs-attr">level</span>=<span class="hljs-string">"debug"</span> <span class="hljs-attr">additivity</span>=<span class="hljs-string">"false"</span>&gt;</span>
      <span class="hljs-tag">&lt;<span class="hljs-name">AppenderRef</span> <span class="hljs-attr">ref</span>=<span class="hljs-string">"Console"</span>/&gt;</span>
    <span class="hljs-tag">&lt;/<span class="hljs-name">AsyncLogger</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">AsyncLogger</span> <span class="hljs-attr">name</span> =<span class="hljs-string">"org.apache.druid.java.util.http.client.pool.ChannelResourceFactory"</span> <span class="hljs-attr">level</span>=<span class="hljs-string">"info"</span> <span class="hljs-attr">additivity</span>=<span class="hljs-string">"false"</span>&gt;</span>
      <span class="hljs-tag">&lt;<span class="hljs-name">AppenderRef</span> <span class="hljs-attr">ref</span>=<span class="hljs-string">"Console"</span>/&gt;</span>
    <span class="hljs-tag">&lt;/<span class="hljs-name">AsyncLogger</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">Root</span> <span class="hljs-attr">level</span>=<span class="hljs-string">"info"</span>&gt;</span>
      <span class="hljs-tag">&lt;<span class="hljs-name">AppenderRef</span> <span class="hljs-attr">ref</span>=<span class="hljs-string">"Console"</span>/&gt;</span>
    <span class="hljs-tag">&lt;/<span class="hljs-name">Root</span>&gt;</span>
  <span class="hljs-tag">&lt;/<span class="hljs-name">Loggers</span>&gt;</span>
<span class="hljs-tag">&lt;/<span class="hljs-name">Configuration</span>&gt;</span>
</span></code></pre>
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