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new cfd05265d7 Add website content generated from
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cfd05265d7 is described below
commit cfd05265d7d326152925a9a32ac04a82d895fba8
Author: ASF Logging Services RM <priv...@logging.apache.org>
AuthorDate: Tue May 21 11:19:15 2024 +0000
Add website content generated from
`f4cf44e988a31bb1deb2bb5b9f74105b02a7c14d`
---
manual/appenders.html | 102 ++++-
manual/async.html | 850 +++++++++++++++++++++++++++------------
manual/json-template-layout.html | 2 +-
manual/layouts.html | 88 ++++
manual/performance.html | 38 +-
manual/systemproperties.html | 17 +-
plugin-reference.html | 2 +-
release-notes.html | 3 +
sitemap.xml | 140 +++----
9 files changed, 899 insertions(+), 343 deletions(-)
diff --git a/manual/appenders.html b/manual/appenders.html
index ebc7152c0a..6c75bc2cf1 100644
--- a/manual/appenders.html
+++ b/manual/appenders.html
@@ -377,7 +377,67 @@ For non-JDK classes, these should usually be in
</div>
</div>
<div class="sect1">
-<h2 id="AsyncAppender"><a class="anchor"
href="#AsyncAppender"></a>AsyncAppender</h2>
+<h2 id="common-properties"><a class="anchor"
href="#common-properties"></a>Common properties</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>These configuration attributes are shared by multiple appenders:</p>
+</div>
+<div class="sect2">
+<h3 id="immediateFlush"><a class="anchor"
href="#immediateFlush"></a><code>immediateFlush</code></h3>
+<table class="tableblock frame-all grid-all stretch">
+<colgroup>
+<col style="width: 16.6666%;">
+<col style="width: 83.3334%;">
+</colgroup>
+<tbody>
+<tr>
+<th class="tableblock halign-left valign-top"><p
class="tableblock">Type</p></th>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>boolean</code></p></td>
+</tr>
+<tr>
+<th class="tableblock halign-left valign-top"><p class="tableblock">Default
value</p></th>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>true</code></p></td>
+</tr>
+</tbody>
+</table>
+<div class="paragraph">
+<p>If set to <code>true</code>, Log4j will flush all Java buffers at the end
of each event:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p>for appenders based on Java’s
+<a
href="https://docs.oracle.com/javase/8/docs/api/java/io/OutputStream.html";>OutputStream</a>
+a call to the <code>OutputStream.flush()</code> method is performed.</p>
+</li>
+<li>
+<p>if <a href="systemproperties.html#log4j2.enableDirectEncoders" class="xref
page">log4j2.enableDirectEncoders</a> is set to <code>true</code>, many Log4j
appenders use a
+<a
href="https://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html";>ByteBuffer</a>
+to format log events before sending them to the underlying resource.
+Setting <code>immediateFlush</code> to <code>true</code> flushes these buffers
at each event.</p>
+</li>
+</ul>
+</div>
+<div class="admonitionblock important">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-important" title="Important"></i>
+</td>
+<td class="content">
+<div class="paragraph">
+<p>This setting only guarantees that a byte representation of the log event is
passed to the operating system.
+It does not ensure that the operating system writes the event to the
underlying storage.</p>
+</div>
+</td>
+</tr>
+</table>
+</div>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="AsyncAppender"><a class="anchor" href="#AsyncAppender"></a><a
id="asyncappender"></a> AsyncAppender</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The AsyncAppender accepts references to other Appenders and causes
LogEvents to be written to them on a separate Thread.
@@ -393,6 +453,46 @@ Note that multi-threaded applications should exercise care
when using this appen
Consider using
<a href="async.html" class="xref page">lock-free Async Loggers</a> for optimal
performance.</p>
</div>
+<div class="admonitionblock note">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-note" title="Note"></i>
+</td>
+<td class="content">
+<div class="paragraph">
+<p>Log4j 2 brought the following enhancements to the Log4j 1 async
appender:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p>all appenders referenced by <code>AsyncAppender</code> flush their buffers
to the OS at the end of a batch, when the queue becomes empty.
+This guarantees that the batch of log events is passed to the OS and is a more
performant version of the <a
href="#immediateFlush"><code>immediateFlush</code></a> attribute.</p>
+<div class="admonitionblock warning">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-warning" title="Warning"></i>
+</td>
+<td class="content">
+Similarly to what happens with the <code>immediateFlush</code> attribute, this
does not guarantee that the OS stores the data on the underlying device.
+</td>
+</tr>
+</table>
+</div>
+</li>
+<li>
+<p>the type of queue is configurable to allow users to use faster and more
performant queues, such as those from the
+<a
href="https://github.com/JCTools/JCTools?tab=readme-ov-file#jctools";>JCTools</a>
+or
+<a href="https://github.com/conversant/disruptor";>Conversant Disruptor</a>
projects.</p>
+</li>
+</ul>
+</div>
+</td>
+</tr>
+</table>
+</div>
<table class="tableblock frame-all grid-all stretch">
<caption class="title">Table 1. AsyncAppender Parameters</caption>
<colgroup>
diff --git a/manual/async.html b/manual/async.html
index eecdde4726..cfb3de52d2 100644
--- a/manual/async.html
+++ b/manual/async.html
@@ -348,42 +348,52 @@
<div id="preamble">
<div class="sectionbody">
<div class="paragraph">
-<p>Asynchronous logging can improve your application’s performance by
-executing the I/O operations in a separate thread.
-Log4j 2 makes several improvements in this area.</p>
+<p>Asynchronous logging is a technique to improve application logging
performance by executing all I/O operations in a separate thread.</p>
</div>
-<div class="ulist">
-<ul>
-<li>
-<p><strong>Asynchronous Loggers</strong> are a new addition in Log4j 2. They
aim to
-return the call to Logger.log to the application as soon as
-possible. You can choose between making all Loggers asynchronous or
-using a mixture of synchronous and asynchronous Loggers. Making all
-Loggers asynchronous will give the best performance, while mixing gives
-you more flexibility.</p>
-</li>
-<li>
-<p><strong>LMAX Disruptor technology</strong>. Asynchronous Loggers internally
use the
-<a href="#UnderTheHood">Disruptor</a>, a lock-free inter-thread communication
-library, instead of queues, resulting in higher throughput and lower
-latency.</p>
-</li>
-<li>
-<p>As part of the work for Async Loggers, <strong>Asynchronous
Appenders</strong> have
-been enhanced to flush to disk at the end of a batch (when the queue is
-empty). This produces the same result as configuring
-"immediateFlush=true", that is, all received log events are always
-available on disk but are more efficient because it does not need to
-touch the disk on every log event. (Async Appenders use
-ArrayBlockingQueue internally and do not need the disruptor jar on the
-classpath.)</p>
-</li>
-</ul>
+<div class="paragraph">
+<p>Log4j offers out-of-the-box two different asynchronous logging
solutions:</p>
+</div>
+<div class="dlist">
+<dl>
+<dt class="hdlist1">Asynchronous appender</dt>
+<dd>
+<p>A classical queue-based asynchronous appender, which is available since
Log4j 1.</p>
+<div class="paragraph">
+<p>See <a href="appenders.html#AsyncAppender" class="xref page">Asynchronous
appender</a> for more details.</p>
+</div>
+</dd>
+<dt class="hdlist1">Asynchronous loggers</dt>
+<dd>
+<p>Asynchronous loggers are a new feature available since Log4j 2.
+They are based on
+<a href="https://lmax-exchange.github.io/disruptor";>LMAX Disruptor</a>,
+a lock-free inter-thread communication library, instead of queues, resulting
in higher throughput and lower latency.</p>
+<div class="paragraph">
+<p>The rest of this chapter is dedicated to this new component.</p>
+</div>
+</dd>
+</dl>
+</div>
+<div class="admonitionblock caution">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-caution" title="Caution"></i>
+</td>
+<td class="content">
+<div class="paragraph">
+<p>Logging performance depends greatly on the architecture of your application
and the way you use logging.
+The solutions offered by this chapter should be evaluated using benchmarks
against your own application.
+If benchmarks and profiling don’t show a statistically significant
difference between asynchronous and synchronous logging solutions, the latter
one is recommended, since it is the simplest one.</p>
+</div>
+</td>
+</tr>
+</table>
</div>
</div>
</div>
<div class="sect1">
-<h2 id="async-trade-offs"><a class="anchor"
href="#async-trade-offs"></a>Trade-offs</h2>
+<h2 id="trade-offs"><a class="anchor" href="#trade-offs"></a><a
id="Trade-offs"></a>Trade-offs</h2>
<div class="sectionbody">
<div class="paragraph">
<p>There are certain trade-offs associated with asynchronous logging:</p>
@@ -420,17 +430,39 @@ If neither of these is an option, you may get better
throughput and fewer latenc
<dd>
<p>If a problem happens during the logging process and an exception is thrown,
it is less easy for an asynchronous setting to signal this problem to the
application.
This can partly be alleviated by configuring an exception handler, but this
may still not cover all cases.</p>
+<div class="admonitionblock caution">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-caution" title="Caution"></i>
+</td>
+<td class="content">
+<div class="paragraph">
+<p>If logging is part of your business logic, e.g. you are using Log4j as an
audit logging framework, we would recommend to synchronously log those audit
messages.</p>
+</div>
+<div class="paragraph">
+<p>See
+<a href="#MixedSync-Async">mixed synchronous/asynchronous loggers</a> on how
to log some messages synchronously.</p>
+</div>
+</td>
+</tr>
+</table>
+</div>
</dd>
<dt class="hdlist1">Stateful messages</dt>
<dd>
-<p>In some rare cases, care must be taken with mutable messages.
-Most of the time you don’t need to worry about this.
-Log4 will ensure that log messages like <code>logger.debug("My object is {}",
myObject)</code> will use the state of the <code>myObject</code> parameter at
the time of the call to <code>logger.debug()</code>.
-The log message will not change even if <code>myObject</code> is modified
later.
-It is safe to asynchronously log mutable objects because most <a
href="messages.html" class="xref page">built-in <code>Message</code>
implementations</a> take a snapshot of the parameters on the calling thread
(see <a href="systemproperties.html#log4j2.formatMsgAsync" class="xref
page"><code>log4j2.formatMsgAsync</code></a>).</p>
+<p>Most
+<a
href="../javadoc/log4j-api/org/apache/logging/log4j/message/Message.html"><code>Message</code></a>
+implementations take a snapshot of the formatted message on the calling thread
(cf.
+<a href="systemproperties.html#log4j2.formatMsgAsync" class="xref
page"><code>log4j2.formatMsgAsync</code></a>).
+The log message will not change even if the arguments of the logging call are
modified later.</p>
<div class="paragraph">
-<p>There are some exceptions however: <a href="messages.html#MapMessage"
class="xref page"><code>MapMessage</code></a> and <a
href="messages.html#StructuredDataMessage" class="xref
page"><code>StructuredDataMessage</code></a> are mutable by design, fields can
be added to these messages after the message object was created.
-These messages should not be modified after they are logged with asynchronous
loggers or asynchronous appenders; you may or may not see the modifications in
the resulting log output.</p>
+<p>There are some exceptions to this rule.
+<a
href="../javadoc/log4j-api/org/apache/logging/log4j/message/MapMessage.html"><code>MapMessage</code></a>
+and
+<a
href="../javadoc/log4j-api/org/apache/logging/log4j/message/StructuredDataMessage.html"><code>StructuredDataMessage</code></a>
+for example are mutable by design: fields can be added to these messages after
the message object was created.
+These messages should not be modified after they are logged with asynchronous
loggers or asynchronous appenders.</p>
</div>
<div class="paragraph">
<p>Similarly, custom
@@ -449,88 +481,113 @@ implementations should be designed with asynchronous use
in mind, and either tak
</div>
</div>
<div class="sect1">
-<h2 id="AllAsync"><a class="anchor" href="#AllAsync"></a>Making All Loggers
Asynchronous</h2>
+<h2 id="installation"><a class="anchor"
href="#installation"></a>Installation</h2>
<div class="sectionbody">
-<div class="admonitionblock note">
-<table>
-<tr>
-<td class="icon">
-<i class="fa icon-note" title="Note"></i>
-</td>
-<td class="content">
-<em>Log4j-2.9 and higher require disruptor-3.3.4.jar or higher on the
-classpath. Prior to Log4j-2.9, disruptor-3.0.0.jar or higher was
-required.</em>
-</td>
-</tr>
-</table>
-</div>
<div class="paragraph">
-<p>This is the simplest to configure and gives the best performance.
-To make all loggers asynchronous, add the disruptor jar to the classpath and
set the system property <a href="systemproperties.html#log4j2.contextSelector"
class="xref page">log4j2.contextSelector</a> to
<code>org.apache.logging.log4j.core.async.AsyncLoggerContextSelector</code> or
<code>org.apache.logging.log4j.core.async.BasicAsyncLoggerContextSelector</code>.</p>
+<p>In order to use async loggers, you need to add LMAX Disruptor to you
application’s dependencies, by adding the following dependency to your
build tool:</p>
</div>
-<div class="paragraph">
-<p>By default, <a href="#Location">location</a> is not passed to the I/O
thread by
-asynchronous loggers. If one of your layouts or custom filters needs
-location information, you need to set "includeLocation=true" in the
-configuration of all relevant loggers, including the root logger.</p>
+<div id="_tabs_1" class="openblock tabs is-loading">
+<div class="content">
+<div class="ulist tablist">
+<ul>
+<li id="_tabs_1_maven" class="tab">
+<p>Maven</p>
+</li>
+<li id="_tabs_1_gradle" class="tab">
+<p>Gradle</p>
+</li>
+</ul>
+</div>
+<div id="_tabs_1_maven--panel" class="tabpanel"
aria-labelledby="_tabs_1_maven">
+<div class="listingblock">
+<div class="content">
+<pre class="highlightjs highlight"><code class="language-xml hljs"
data-lang="xml"><dependency>
+ <groupId>com.lmax</groupId>
+ <artifactId>disruptor</artifactId>
+ <version>4.0.0</version>
+ <scope>runtime</scope>
+</dependency></code></pre>
</div>
-<div class="paragraph">
-<p>A configuration that does not require location might look like:</p>
</div>
+</div>
+<div id="_tabs_1_gradle--panel" class="tabpanel"
aria-labelledby="_tabs_1_gradle">
<div class="listingblock">
<div class="content">
-<pre class="highlightjs highlight"><code class="language-xml hljs"
data-lang="xml"><?xml version="1.0" encoding="UTF-8"?>
-
-<!-- Don't forget to set system property
--Dlog4j2.contextSelector=org.apache.logging.log4j.core.async.AsyncLoggerContextSelector
-or
--Dlog4j2.contextSelector=org.apache.logging.log4j.core.async.BasicAsyncLoggerContextSelector
- to make all loggers asynchronous. -->
-
-<Configuration status="WARN">
- <Appenders>
- <!-- Async Loggers will auto-flush in batches, so switch off
immediateFlush. -->
- <RandomAccessFile name="RandomAccessFile" fileName="async.log"
immediateFlush="false" append="false">
- <PatternLayout>
- <Pattern>%d %p %c{1.} [%t] %m %ex%n</Pattern>
- </PatternLayout>
- </RandomAccessFile>
- </Appenders>
- <Loggers>
- <Root level="info" includeLocation="false">
- <AppenderRef ref="RandomAccessFile"/>
- </Root>
- </Loggers>
-</Configuration></code></pre>
+<pre class="highlightjs highlight"><code class="language-groovy hljs"
data-lang="groovy">runtimeOnly 'com.lmax:disruptor:4.0.0'</code></pre>
+</div>
+</div>
+</div>
+</div>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="configuration"><a class="anchor"
href="#configuration"></a>Configuration</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>There are two ways asynchronous loggers can be used in Log4j.
+You can:</p>
</div>
+<div class="ulist">
+<ul>
+<li>
+<p><a href="#AllAsync">Making all loggers asynchronous</a>, which gives a
better performance,</p>
+</li>
+<li>
+<p><a href="#MixedSync-Async">Mixing synchronous and asynchronous loggers</a>,
which gives more flexibility.</p>
+</li>
+</ul>
</div>
<div class="paragraph">
-<p>When <code>AsyncLoggerContextSelector</code> or
-<code>BasicAsyncLoggerContextSelector</code> is used to make all loggers
-asynchronous, make sure to use normal <code><root></code> and
<code><logger></code> elements
-in the configuration. The context selector will ensure that
-all loggers are asynchronous, using a mechanism that is different from
-what happens when you configure <code><asyncRoot></code> or
<code><asyncLogger></code>. The
-latter elements are intended for mixing async with sync loggers. If you
-use both mechanisms together you will end up with two background
-threads, where your application passes the log message to thread A,
-which passes the message to thread B, which then finally logs the
-message to disk. This works, but there will be an unnecessary step in
-the middle.</p>
+<p>Under the hood these methods use different Log4j plugins, but also share a
+<a href="#common-configuration-properties">set of common configuration
properties</a>.</p>
</div>
+<div class="sect2">
+<h3 id="AllAsync"><a class="anchor" href="#AllAsync"></a>Making all loggers
asynchronous</h3>
<div class="paragraph">
-<p>There are a few system properties you can use to control aspects of the
-asynchronous logging subsystem. Some of these can be used to tune
-logging performance.</p>
+<p>This is the simplest to configure and gives the best performance: to make
all logger asynchronous, <strong>all</strong> you need to set the
+<a href="systemproperties.html#log4j2.contextSelector" class="xref
page">log4j2.contextSelector</a>
+property to one of the asynchronous logger context selectors:</p>
+</div>
+<div class="dlist">
+<dl>
+<dt class="hdlist1"><a
href="../javadoc/log4j-core/org/apache/logging/log4j/core/async/BasicAsyncLoggerContextSelector">org.apache.logging.log4j.core.async.BasicAsyncLoggerContextSelector</a></dt>
+<dd>
+<p>This will create a single logger context and disruptor for all the classes
in the JVM,</p>
+</dd>
+<dt class="hdlist1"><a
href="../javadoc/log4j-core/org/apache/logging/log4j/core/async/AsyncLoggerContextSelector">org.apache.logging.log4j.core.async.AsyncLoggerContextSelector</a></dt>
+<dd>
+<p>This will create a different logger context and disruptor for each
classloader in the JVM.</p>
+</dd>
+</dl>
+</div>
+<div class="admonitionblock important">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-important" title="Important"></i>
+</td>
+<td class="content">
+<div class="paragraph">
+<p>When using an asynchronous logger context you should use only
<code>Root</code> and <code>Logger</code> elements (cf.
+<a href="configuration.html#configuring-loggers" class="xref page">Logger
configuration</a>).</p>
</div>
<div class="paragraph">
-<p>The below properties can also be specified by creating a file named
-<code>log4j2.component.properties</code> and including this file in the
classpath
-of the application.</p>
+<p>If you use <code>AsyncRoot</code> and <code>AsyncLogger</code>
configuration elements, two asynchronous barriers will be created instead of
one, which will impair performance.</p>
+</div>
+</td>
+</tr>
+</table>
+</div>
</div>
<div class="sect2">
-<h3 id="SysPropsAllAsync"><a class="anchor"
href="#SysPropsAllAsync"></a>Configuration Properties</h3>
+<h3 id="SysPropsAllAsync"><a class="anchor"
href="#SysPropsAllAsync"></a>Tuning a fully asynchronous configuration</h3>
+<div class="paragraph">
+<p>Since Disruptor is initialized at the same time as the logger context and
before any Log4j configuration file is loaded, tuning async loggers is only
possible through configuration properties.</p>
+</div>
+<div class="paragraph">
+<p>Beyond the <a href="#common-configuration-properties">common configuration
properties</a>, the following additional elements are configurable:</p>
+</div>
<div class="sect3">
<h4 id="log4j2.asyncLoggerExceptionHandler"><a class="anchor"
href="#log4j2.asyncLoggerExceptionHandler"></a><code>log4j2.asyncLoggerExceptionHandler</code></h4>
<table class="tableblock frame-all grid-all stretch">
@@ -608,7 +665,7 @@ The RingBuffer will be pre-allocated at first use and will
never grow or shrink
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p
class="tableblock">Type</p></th>
-<td class="tableblock halign-left valign-top"><p class="tableblock"><a
href="https://lmax-exchange.github.io/disruptor/javadoc/com.lmax.disruptor/com/lmax/disruptor/WaitStrategy.html";>Class<?
extends WaitStrategy></a> or predefined constant</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">predefined
constant</p></td>
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p class="tableblock">Default
value</p></th>
@@ -620,7 +677,7 @@ The RingBuffer will be pre-allocated at first use and will
never grow or shrink
<p>Specifies the <a
href="https://lmax-exchange.github.io/disruptor/javadoc/com.lmax.disruptor/com/lmax/disruptor/WaitStrategy.html";>WaitStrategy</a>
used by the LMAX Disruptor.</p>
</div>
<div class="paragraph">
-<p>The value needs to be a fully qualified class name of a custom
<code>WaitStrategy</code> implementation (cf. <a
href="#custom-waitstrategy">Custom WaitStrategy</a>) or one of the predefined
constants:</p>
+<p>The value needs to be one of the predefined constants:</p>
</div>
<div class="dlist">
<dl>
@@ -646,8 +703,7 @@ This wait strategy is <a href="garbagefree.html"
class="xref page">garbage free<
</dd>
<dt class="hdlist1">Yield</dt>
<dd>
-<p>is a strategy that uses a <code>Thread.yield()</code> for waiting for log
events after an initially spinning.
-Yield is a good compromise between performance and CPU resource, but may use
more CPU than <code>Sleep</code> in order to get the message logged to disk
sooner.
+<p>is a strategy that will use <code>100%</code> CPU, but will give up the CPU
if other threads require CPU resources.
This wait strategy is <a href="garbagefree.html" class="xref page">garbage
free</a>.</p>
</dd>
</dl>
@@ -813,97 +869,231 @@ Since JRE 8u102 the <code>Thread.getName()</code> method
does <strong>not</stron
</tr>
</table>
</div>
+<div class="ulist">
+<ul>
+<li>
+<p>the generic behavior of asynchronous components, such as the queue full
policy and message formatting.</p>
<div class="paragraph">
-<p>There are also a few system properties that can be used to maintain
-application throughput even when the underlying appender cannot keep up
-with the logging rate and the queue is filling up. See the details for
-system properties
-<a href="systemproperties.html#log4j2.asyncQueueFullPolicy" class="xref
page"><code>log4j2.asyncQueueFullPolicy</code>
-and <code>log4j2.discardThreshold</code></a>.</p>
-</div>
-</div>
+<p>See <a href="systemproperties.html#properties-async" class="xref
page">common asynchronous logging configurations</a> for more details.</p>
</div>
+</li>
+<li>
+<p>the parameters of the disruptor, such as the size of the ring buffer and
the wait strategy to use.</p>
+<div class="paragraph">
+<p>See <a href="systemproperties.html#properties-async-logger" class="xref
page">asynchronous logger configuration</a> for more details.</p>
</div>
+</li>
+</ul>
</div>
-<div class="sect1">
-<h2 id="MixedSync-Async"><a class="anchor" href="#MixedSync-Async"></a>Mixing
Synchronous and Asynchronous Loggers</h2>
-<div class="sectionbody">
-<div class="admonitionblock note">
+<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
-<i class="fa icon-note" title="Note"></i>
+<i class="fa icon-tip" title="Tip"></i>
</td>
<td class="content">
-<em>Log4j-2.9 and higher require disruptor-3.3.4.jar or higher on the
-classpath. Before Log4j-2.9, disruptor-3.0.0.jar or higher was
-required. There is no need to set the system property "Log4jContextSelector"
-to any value.</em>
+<div class="paragraph">
+<p>You can place the selected value of the
+<a href="systemproperties.html#log4j2.contextSelector" class="xref
page">log4j2.contextSelector</a> and other configuration properties in a
<code>log4j2.component.properties</code> file at the root of your
application’s classpath.</p>
+</div>
+<div class="paragraph">
+<p>See <a href="systemproperties.html#property-sources" class="xref
page">Property Sources</a> for more details.</p>
+</div>
</td>
</tr>
</table>
</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="MixedSync-Async"><a class="anchor" href="#MixedSync-Async"></a>Mixing
synchronous and asynchronous loggers</h3>
<div class="paragraph">
-<p>Synchronous and asynchronous loggers can be combined in configuration.
-This gives you more flexibility at the cost of a slight loss in
-performance (compared to making all loggers asynchronous). Use the
-<code><asyncRoot></code> or <code><asyncLogger></code>
configuration elements specify the
-loggers that need to be asynchronous. A configuration can contain only
-one root logger (either a <code><root></code> or an
<code><asyncRoot></code> element), but
-otherwise, async and non-async loggers may be combined. For example, a
-configuration file containing <code><asyncLogger></code> elements can
also contain
-<code><root></code> and <code><logger></code> elements for the
synchronous loggers.</p>
+<p>Synchronous and asynchronous loggers can be combined in a single
configuration.
+This gives you more flexibility at the cost of a slight loss in performance
(compared to making all loggers asynchronous).</p>
</div>
<div class="paragraph">
-<p>By default, <a href="#Location">location</a> is not passed to the I/O
thread by
-asynchronous loggers. If one of your layouts or custom filters needs
-location information, you need to set "includeLocation=true" in the
-configuration of all relevant loggers, including the root logger.</p>
+<p>In order to use this configuration, you need to keep the
+<a href="systemproperties.html#log4j2.contextSelector" class="xref
page">log4j2.contextSelector</a> at its default value and use one of the
+<code>AsyncRoot</code> and <code>AsyncLogger</code> configuration elements to
designate the loggers that you want to be asynchronous.</p>
</div>
<div class="paragraph">
<p>A configuration that mixes asynchronous loggers might look like:</p>
</div>
+<div id="_tabs_2" class="openblock tabs is-loading">
+<div class="content">
+<div class="ulist tablist">
+<ul>
+<li id="_tabs_2_xml" class="tab">
+<p>XML</p>
+</li>
+<li id="_tabs_2_json" class="tab">
+<p>JSON</p>
+</li>
+<li id="_tabs_2_yaml" class="tab">
+<p>YAML</p>
+</li>
+<li id="_tabs_2_java_properties" class="tab">
+<p>Java properties</p>
+</li>
+</ul>
+</div>
+<div id="_tabs_2_xml--panel" class="tabpanel" aria-labelledby="_tabs_2_xml">
<div class="listingblock">
<div class="content">
<pre class="highlightjs highlight"><code class="language-xml hljs"
data-lang="xml"><?xml version="1.0" encoding="UTF-8"?>
-
-<!-- No need to set system property "log4j2.contextSelector" to any value
- when using <asyncLogger> or <asyncRoot>. -->
-
-<Configuration status="WARN">
+<Configuration xmlns="https://logging.apache.org/xml/ns";
+ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
+ xsi:schemaLocation="
+ https://logging.apache.org/xml/ns
+ https://logging.apache.org/xml/ns/log4j-config-2.xsd">
<Appenders>
- <!-- Async Loggers will auto-flush in batches, so switch off
immediateFlush. -->
- <RandomAccessFile name="RandomAccessFile"
fileName="asyncWithLocation.log"
- immediateFlush="false" append="false">
- <PatternLayout>
- <Pattern>%d %p %class{1.} [%t] %location %m %ex%n</Pattern>
- </PatternLayout>
- </RandomAccessFile>
+ <File name="AUDIT" fileName="logs/audit.log"
ignoreExceptions="false">
+ <JsonTemplateLayout/>
+ </File>
+ <File name="DEBUG_LOG" fileName="logs/debug.log">
+ <PatternLayout/>
+ </File>
</Appenders>
<Loggers>
- <!-- pattern layout actually uses location, so we need to include it
-->
- <AsyncLogger name="com.foo.Bar" level="trace" includeLocation="true">
- <AppenderRef ref="RandomAccessFile"/>
- </AsyncLogger>
- <Root level="info" includeLocation="true">
- <AppenderRef ref="RandomAccessFile"/>
+ <Root level="INFO">
+ <AppenderRef ref="AUDIT"> <i class="conum"
data-value="1"></i><b>(1)</b>
+ <MarkerFilter marker="AUDIT" onMatch="ACCEPT" onMimatch="DENY"/>
+ </AppenderRef>
</Root>
+ <AsyncLogger name="com.example" level="TRACE">
+ <AppenderRef ref="DEBUG_LOG"/> <i class="conum"
data-value="2"></i><b>(2)</b>
+ </AsyncLogger>
</Loggers>
</Configuration></code></pre>
</div>
</div>
+</div>
+<div id="_tabs_2_json--panel" class="tabpanel" aria-labelledby="_tabs_2_json">
+<div class="listingblock">
+<div class="content">
+<pre class="highlightjs highlight"><code class="language-json hljs"
data-lang="json">{
+ "Configuration": {
+ "Appenders": [
+ {
+ "name": "AUDIT",
+ "fileName": "logs/audit.log",
+ "ignoreExceptions": false,
+ "JsonTemplateLayout": {}
+ },
+ {
+ "name": "DEBUG_LOG",
+ "fileName": "logs/debug.log",
+ "PatternLayout": {}
+ }
+ ]
+ },
+ "Loggers": {
+ "Root": {
+ "level": "INFO",
+ "AppenderRef": { <i class="conum" data-value="1"></i><b>(1)</b>
+ "ref": "AUDIT",
+ "MarkerFilter": {
+ "marker": "AUDIT",
+ "onMatch": "ACCEPT",
+ "onMismatch": "DENY"
+ }
+ }
+ },
+ "AsyncLogger": { <i class="conum" data-value="2"></i><b>(2)</b>
+ "name": "com.example",
+ "level": "TRACE",
+ "AppenderRef": {
+ "ref": "DEBUG_LOG"
+ }
+ }
+ }
+}</code></pre>
+</div>
+</div>
+</div>
+<div id="_tabs_2_yaml--panel" class="tabpanel" aria-labelledby="_tabs_2_yaml">
+<div class="listingblock">
+<div class="content">
+<pre class="highlightjs highlight"><code class="language-yaml hljs"
data-lang="yaml">Configuration:
+ Appenders:
+ File:
+ - name: "AUDIT"
+ fileName: "logs/audit.log"
+ ignoreExceptions: false
+ JsonTemplateLayout: {}
+ - name: "DEBUG_LOG"
+ fileName: "logs/debug.log"
+ PatternLayout: {}
+ Loggers:
+ Root:
+ level: "INFO"
+ AppenderRef: <i class="conum" data-value="1"></i><b>(1)</b>
+ ref: "AUDIT"
+ MarkerFilter:
+ marker: "AUDIT"
+ onMatch: "ACCEPT"
+ onMismatch: "DENY"
+ AsyncLogger:
+ name: "com.example"
+ level: "TRACE"
+ AppenderRef: <i class="conum" data-value="2"></i><b>(2)</b>
+ ref: "DEBUG_LOG"</code></pre>
+</div>
+</div>
+</div>
+<div id="_tabs_2_java_properties--panel" class="tabpanel"
aria-labelledby="_tabs_2_java_properties">
+<div class="listingblock">
+<div class="content">
+<pre class="highlightjs highlight"><code class="language-properties hljs"
data-lang="properties">appender.0.type = File
+appender.0.name = AUDIT
+appender.0.fileName = logs/audit.log
+appender.0.ignoreExceptions = false
+appender.0.layout.type = JsonTemplateLayout
+
+appender.1.type = File
+appender.1.name = DEBUG_LOG
+appender.1.fileName = logs/debug.log
+appender.1.layout.type = PatternLayout
+
+rootLogger.level = INFO
+rootLogger.appenderRef.0.ref = AUDIT <i class="conum"
data-value="1"></i><b>(1)</b>
+rootLogger.appenderRef.0.filter.0.type = MarkerFilter
+rootLogger.appenderRef.0.filter.0.marker = AUDIT
+rootLogger.appenderRef.0.filter.0.onMatch = ACCEPT
+rootLogger.appenderRef.0.filter.0.onMismatch = DENY
+
+logger.0.type = AsyncLogger
+logger.0.name = com.example
+logger.0.level = TRACE
+logger.0.appenderRef.0.ref = DEBUG_LOG <i class="conum"
data-value="2"></i><b>(2)</b></code></pre>
+</div>
+</div>
+</div>
+</div>
+</div>
+<div class="colist arabic">
+<table>
+<tr>
+<td><i class="conum" data-value="1"></i><b>1</b></td>
+<td>All the appenders referenced by <code>Root</code> and <code>Logger</code>
are called synchronously.
+This is especially important for audit logging, since exceptions can be
forwarded to the caller.</td>
+</tr>
+<tr>
+<td><i class="conum" data-value="2"></i><b>2</b></td>
+<td>All the appenders references by <code>AsyncRoot</code> and
<code>AsyncLogger</code> are called asynchronously.
+These log statements will cause a smaller latency for the caller.</td>
+</tr>
+</table>
+</div>
+</div>
+<div class="sect2">
+<h3 id="SysPropsMixedSync-Async"><a class="anchor"
href="#SysPropsMixedSync-Async"></a>Tuning a mixed synchronous/asynchronous
configuration</h3>
<div class="paragraph">
-<p>There are a few system properties you can use to control aspects of the
-asynchronous logging subsystem. Some of these can be used to tune
-logging performance.</p>
+<p>Since all <code>AsyncRoot</code> and <code>AsyncLogger</code> components
share the same Disruptor instance, its configuration is available through
configuration properties.</p>
</div>
<div class="paragraph">
-<p>The below properties can also be specified by creating a file named
-<code>log4j2.component.properties</code> and including this file in the
classpath
-of the application.</p>
+<p>Beyond the <a href="#common-configuration-properties">common configuration
properties</a>, the following additional elements are configurable:</p>
</div>
-<div class="sect2">
-<h3 id="SysPropsMixedSync-Async"><a class="anchor"
href="#SysPropsMixedSync-Async"></a>Configuration Properties</h3>
<div class="sect3">
<h4 id="log4j2.asyncLoggerConfigExceptionHandler"><a class="anchor"
href="#log4j2.asyncLoggerConfigExceptionHandler"></a><code>log4j2.asyncLoggerConfigExceptionHandler</code></h4>
<table class="tableblock frame-all grid-all stretch">
@@ -981,7 +1171,7 @@ The RingBuffer will be pre-allocated at first use and will
never grow or shrink
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p
class="tableblock">Type</p></th>
-<td class="tableblock halign-left valign-top"><p class="tableblock"><a
href="https://lmax-exchange.github.io/disruptor/javadoc/com.lmax.disruptor/com/lmax/disruptor/WaitStrategy.html";>Class<?
extends WaitStrategy></a> or predefined constant</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">predefined
constant</p></td>
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p class="tableblock">Default
value</p></th>
@@ -993,7 +1183,7 @@ The RingBuffer will be pre-allocated at first use and will
never grow or shrink
<p>Specifies the <a
href="https://lmax-exchange.github.io/disruptor/javadoc/com.lmax.disruptor/com/lmax/disruptor/WaitStrategy.html";>WaitStrategy</a>
used by the LMAX Disruptor.</p>
</div>
<div class="paragraph">
-<p>The value needs to be a fully qualified class name of a custom
<code>WaitStrategy</code> implementation (cf. <a
href="#custom-waitstrategy">Custom WaitStrategy</a>) or one of the predefined
constants:</p>
+<p>The value needs to be one of the predefined constants:</p>
</div>
<div class="dlist">
<dl>
@@ -1016,11 +1206,13 @@ This strategy has very low impact on the application
thread, in exchange for som
</dd>
<dt class="hdlist1">Yield</dt>
<dd>
-<p>is a strategy that uses a <code>Thread.yield()</code> for waiting for log
events after an initially spinning.
-Yield is a good compromise between performance and CPU resource, but may use
more CPU than <code>Sleep</code> in order to get the message logged to disk
sooner.</p>
+<p>is a strategy that will use <code>100%</code> CPU, but will give up the CPU
if other threads require CPU resources.</p>
</dd>
</dl>
</div>
+<div class="paragraph">
+<p>See also <a href="#custom-waitstrategy">Custom
<code>WaitStrategy</code></a> for an alternative way to configure the wait
strategy.</p>
+</div>
</div>
<div class="sect3">
<h4 id="log4j2.asyncLoggerConfigTimeout"><a class="anchor"
href="#log4j2.asyncLoggerConfigTimeout"></a><code>log4j2.asyncLoggerConfigTimeout</code></h4>
@@ -1128,135 +1320,285 @@ Users encountered excessive CPU utilization with
Disruptor v3.4.2 when the appli
CPU utilization is significantly reduced by restricting access to the enqueue
operation.
Setting this value to <code>false</code> may lead to very high CPU utilization
when the async logging queue is full.</p>
</div>
+<div class="admonitionblock tip">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-tip" title="Tip"></i>
+</td>
+<td class="content">
+<div class="paragraph">
+<p>You can place the values of configuration properties in a
<code>log4j2.component.properties</code> file at the root of your
application’s classpath.</p>
+</div>
+<div class="paragraph">
+<p>See <a href="systemproperties.html#property-sources" class="xref
page">Property Sources</a> for more details.</p>
+</div>
+</td>
+</tr>
+</table>
+</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="common-configuration-properties"><a class="anchor"
href="#common-configuration-properties"></a>Common configuration properties</h3>
+<div class="paragraph">
+<p>Regardless of the way you configure asynchronous loggers in Log4j, you can
use the following properties to further tune your installation:</p>
+</div>
+<div class="sect3">
+<h4 id="log4j2.formatMsgAsync"><a class="anchor"
href="#log4j2.formatMsgAsync"></a><code>log4j2.formatMsgAsync</code></h4>
+<table class="tableblock frame-all grid-all stretch">
+<colgroup>
+<col style="width: 16.6666%;">
+<col style="width: 83.3334%;">
+</colgroup>
+<tbody>
+<tr>
+<th class="tableblock halign-left valign-top"><p class="tableblock">Env.
variable</p></th>
+<td class="tableblock halign-left valign-top"><p
class="tableblock">LOG4J_FORMAT_MSG_ASYNC</p></td>
+</tr>
+<tr>
+<th class="tableblock halign-left valign-top"><p
class="tableblock">Type</p></th>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>boolean</code></p></td>
+</tr>
+<tr>
+<th class="tableblock halign-left valign-top"><p class="tableblock">Default
value</p></th>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>false</code></p></td>
+</tr>
+</tbody>
+</table>
+<div class="paragraph">
+<p>If <code>false</code>, Log4j will make sure the message is formatted in the
caller thread, otherwise the formatting will occur on the asynchronous
thread.</p>
+</div>
+<div class="paragraph">
+<p><strong>Remark</strong>: messages annotated with <a
href="../javadoc/log4j-api/org/apache/logging/log4j/message/AsynchronouslyFormattable">AsynchronouslyFormattable</a>
will be formatted on the async thread regardless of this setting.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="log4j2.asyncQueueFullPolicy"><a class="anchor"
href="#log4j2.asyncQueueFullPolicy"></a><code>log4j2.asyncQueueFullPolicy</code></h4>
+<table class="tableblock frame-all grid-all stretch">
+<colgroup>
+<col style="width: 16.6666%;">
+<col style="width: 83.3334%;">
+</colgroup>
+<tbody>
+<tr>
+<th class="tableblock halign-left valign-top"><p class="tableblock">Env.
variable</p></th>
+<td class="tableblock halign-left valign-top"><p
class="tableblock">LOG4J_ASYNC_QUEUE_FULL_POLICY</p></td>
+</tr>
+<tr>
+<th class="tableblock halign-left valign-top"><p
class="tableblock">Type</p></th>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><a
href="../javadoc/log4j-core/org/apache/logging/log4j/core/async/AsyncQueueFullPolicy">Class<?
extends AsyncQueueFullPolicy></a> or predefined constant</p></td>
+</tr>
+<tr>
+<th class="tableblock halign-left valign-top"><p class="tableblock">Default
value</p></th>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>Default</code></p></td>
+</tr>
+</tbody>
+</table>
+<div class="paragraph">
+<p>Determines the <a
href="../javadoc/log4j-core/org/apache/logging/log4j/core/async/AsyncQueueFullPolicy">AsyncQueueFullPolicy</a>
to use when the underlying async component cannot keep up with the logging
rate and the queue is filling up.</p>
+</div>
+<div class="paragraph">
+<p>Its value should be the fully qualified class name of an
<code>AsyncQueueFullPolicy</code> implementation or one of these
+predefined constants:</p>
+</div>
+<div class="dlist">
+<dl>
+<dt class="hdlist1">Default</dt>
+<dd>
+<p>blocks the calling thread until the event can be added to the queue.</p>
+</dd>
+<dt class="hdlist1">Discard</dt>
+<dd>
+<p>when the queue is full, it drops the events whose level is equal or less
than the threshold level (see
+<a
href="#log4j2.discardThreshold"><code>log4j2.discardThreshold</code></a>).</p>
+</dd>
+</dl>
+</div>
+</div>
+<div class="sect3">
+<h4 id="log4j2.discardThreshold"><a class="anchor"
href="#log4j2.discardThreshold"></a><code>log4j2.discardThreshold</code></h4>
+<table class="tableblock frame-all grid-all stretch">
+<colgroup>
+<col style="width: 16.6666%;">
+<col style="width: 83.3334%;">
+</colgroup>
+<tbody>
+<tr>
+<th class="tableblock halign-left valign-top"><p class="tableblock">Env.
variable</p></th>
+<td class="tableblock halign-left valign-top"><p
class="tableblock">LOG4J_DISCARD_THRESHOLD</p></td>
+</tr>
+<tr>
+<th class="tableblock halign-left valign-top"><p
class="tableblock">Type</p></th>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><a
href="../javadoc/log4j-api/org/apache/logging/log4j/Level">Level</a></p></td>
+</tr>
+<tr>
+<th class="tableblock halign-left valign-top"><p class="tableblock">Default
value</p></th>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>INFO</code></p></td>
+</tr>
+</tbody>
+</table>
<div class="paragraph">
-<p>There are also a few system properties that can be used to maintain
-application throughput even when the underlying appender cannot keep up
-with the logging rate and the queue is filling up. See the details for
-system properties
-<a href="systemproperties.html#log4j2.asyncQueueFullPolicy" class="xref
page"><code>log4j2.asyncQueueFullPolicy</code>
-and <code>log4j2.discardThreshold</code></a>.</p>
+<p>Determines the threshold level used by a <code>Discard</code> queue full
policy.
+Log events whose level is equal or less specific than the threshold level will
be discarded during a queue full event.
+See also <a
href="#log4j2.asyncQueueFullPolicy"><code>log4j2.asyncQueueFullPolicy</code></a>.</p>
</div>
</div>
</div>
</div>
</div>
<div class="sect1">
-<h2 id="custom-waitstrategy"><a class="anchor"
href="#custom-waitstrategy"></a>Custom WaitStrategy</h2>
+<h2 id="custom-waitstrategy"><a class="anchor"
href="#custom-waitstrategy"></a>Custom <code>WaitStrategy</code></h2>
<div class="sectionbody">
<div class="paragraph">
-<p>The system properties mentioned above allow only choice from among a fixed
set of predefined WaitStrategies.
-There may be cases where you want to configure a custom WaitStrategy that is
not in this list.
-This is possible by using a <code>AsyncWaitStrategyFactory</code> element in
the Log4j configuration.</p>
+<p>The system properties mentioned in the section above allow only to choose
from among a fixed set of wait strategies.</p>
</div>
<div class="paragraph">
-<p>A configuration that configures a custom WaitStrategy can look as
follows:</p>
+<p>In order to use a custom wait strategy you need to:</p>
</div>
+<div class="olist arabic">
+<ol class="arabic">
+<li>
+<p>Use the <a href="#MixedSync-Async">mixed sync/async configuration
method</a> above,</p>
+</li>
+<li>
+<p>Implement the interface
+<a
href="../javadoc/log4j-core/org/apache/logging/log4j/core/async/AsyncWaitStrategyFactory.html">AsyncWaitStrategyFactory</a>;
the implementation must have a public no-arg constructor,</p>
+</li>
+<li>
+<p>Add an <a
href="../plugin-reference.html#org-apache-logging-log4j_log4j-core_org-apache-logging-log4j-core-async-AsyncWaitStrategyFactoryConfig"
class="xref page">AsyncWaitStrategyFactory Log4j plugin</a>
+to your configuration.</p>
+</li>
+</ol>
+</div>
+<div id="_tabs_3" class="openblock tabs is-loading">
+<div class="content">
+<div class="ulist tablist">
+<ul>
+<li id="_tabs_3_xml" class="tab">
+<p>XML</p>
+</li>
+<li id="_tabs_3_json" class="tab">
+<p>JSON</p>
+</li>
+<li id="_tabs_3_yaml" class="tab">
+<p>YAML</p>
+</li>
+<li id="_tabs_3_java_properties" class="tab">
+<p>Java properties</p>
+</li>
+</ul>
+</div>
+<div id="_tabs_3_xml--panel" class="tabpanel" aria-labelledby="_tabs_3_xml">
<div class="listingblock">
<div class="content">
<pre class="highlightjs highlight"><code class="language-xml hljs"
data-lang="xml"><?xml version="1.0" encoding="UTF-8"?>
-<Configuration status="WARN">
-
- <AsyncWaitStrategyFactory
- class="my.custom.AsyncWaitStrategyFactory" />
-
- <Appenders>
- <File name="MyFile" fileName="logs/app.log">
- <PatternLayout pattern="%d %p %c{1.} [%t] %m%n" />
- </File>
- </Appenders>
- <Loggers>
- <AsyncRoot level="info">
- <AppenderRef ref="MyFile"/>
- </AsyncRoot>
- </Loggers>
+<Configuration xmlns="https://logging.apache.org/xml/ns";
+ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
+ xsi:schemaLocation="
+ https://logging.apache.org/xml/ns
+
https://logging.apache.org/xml/ns/log4j-config-2.xsd">
+ <AsyncWaitStrategyFactory
class="com.example.AsyncWaitStrategyFactory"/>
</Configuration></code></pre>
</div>
</div>
-<div class="paragraph">
-<p>The specified class must implement the
-<code>org.apache.logging.log4j.core.async.AsyncWaitStrategyFactory</code>
interface, which is defined as follows:</p>
</div>
+<div id="_tabs_3_json--panel" class="tabpanel" aria-labelledby="_tabs_3_json">
<div class="listingblock">
<div class="content">
-<pre class="highlightjs highlight"><code class="language-java hljs"
data-lang="java">public interface AsyncWaitStrategyFactory {
- /**
- * Returns a non-null implementation of the LMAX Disruptor's WaitStrategy
interface.
- * This WaitStrategy will be used by Log4j Async Loggers and Async
LoggerConfigs.
- *
- * @return the WaitStrategy instance to be used by Async Loggers and Async
LoggerConfigs
- */
- WaitStrategy createWaitStrategy();
+<pre class="highlightjs highlight"><code class="language-json hljs"
data-lang="json">{
+ "Configuration": {
+ "AsyncWaitStrategyFactor": {
+ "class": "com.example.AsyncWaitStrategyFactory"
+ }
+ }
}</code></pre>
</div>
</div>
-<div class="paragraph">
-<p>The specified class must also have a public no-argument constructor;
-Log4j will instantiate an instance of the specified factory class and use this
factory to create the WaitStrategy used by all Async Loggers.</p>
</div>
-<div class="paragraph">
-<p>WaitStrategy-related system properties are ignored if an
<code>AsyncWaitStrategyFactory</code> is configured.</p>
+<div id="_tabs_3_yaml--panel" class="tabpanel" aria-labelledby="_tabs_3_yaml">
+<div class="listingblock">
+<div class="content">
+<pre class="highlightjs highlight"><code class="language-yaml hljs"
data-lang="yaml">Configuration:
+ AsyncWaitStrategyFactory:
+ class: "com.example.AsyncWaitStrategyFactory"</code></pre>
</div>
</div>
</div>
-<div class="sect1">
-<h2 id="Location"><a class="anchor" href="#Location"></a>Location, location,
location…​</h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>If one of the layouts is configured with a location-related attribute
-like HTML <a href="layouts.html#HtmlLocationInfo" class="xref
page">locationInfo</a>, or one of
-the patterns <a href="layouts.html#PatternClass" class="xref page">%C or
$class</a>,
-<a href="layouts.html#PatternFile" class="xref page">%F or %file</a>,
-<a href="layouts.html#PatternLocation" class="xref page">%l or %location</a>,
-<a href="layouts.html#PatternLine" class="xref page">%L or %line</a>,
-<a href="layouts.html#PatternMethod" class="xref page">%M or %method</a>,
Log4j will take a
-snapshot of the stack, and walk the stack trace to find the location
-information.</p>
+<div id="_tabs_3_java_properties--panel" class="tabpanel"
aria-labelledby="_tabs_3_java_properties">
+<div class="listingblock">
+<div class="content">
+<pre class="highlightjs highlight"><code class="language-properties hljs"
data-lang="properties">strategy.type = AsyncWaitStrategyFactory
+strategy.class = com.exampleAsyncWaitStrategyFactory</code></pre>
+</div>
+</div>
</div>
-<div class="paragraph">
-<p>This is an expensive operation: 1.3 - 5 times slower for synchronous
-loggers. Synchronous loggers wait as long as possible before they take
-this stack snapshot. If no location is required, the snapshot will never
-be taken.</p>
</div>
-<div class="paragraph">
-<p>However, asynchronous loggers need to make this decision before passing
-the log message to another thread; the location information will be lost
-after that point. The performance impact of
-taking a stack trace snapshot is even higher for asynchronous loggers:
-logging with location is 30-100 times slower than without location. For
-this reason, asynchronous loggers and asynchronous appenders do not
-include location information by default.</p>
</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="Location"><a class="anchor" href="#Location"></a>Location
information</h2>
+<div class="sectionbody">
<div class="paragraph">
-<p>You can override the default behavior in your logger or asynchronous
-appender configuration by specifying <code>includeLocation="true"</code>.</p>
+<p><a href="layouts.html#location-information" class="xref page">Computing the
location information (i.e., the caller class, method, file, and line number) of
a log event is an expensive operation.</a>
+The impact on asynchronous loggers and appenders is even higher, since the
component must decide whether to compute it or not <strong>before</strong>
crossing the asynchronous barrier.
+Hence, the location information is disabled by default for asynchronous
loggers and appenders.
+In order to enable it for a certain logger, set its <a
href="configuration.html#logger-attributes-includeLocation" class="xref
page"><code>includeLocation</code></a> attribute to <code>true</code>.</p>
</div>
</div>
</div>
<div class="sect1">
-<h2 id="UnderTheHood"><a class="anchor" href="#UnderTheHood"></a>Under The
Hood</h2>
+<h2 id="exception-handler"><a class="anchor"
href="#exception-handler"></a>Exception handler</h2>
<div class="sectionbody">
<div class="paragraph">
-<p>Asynchronous Loggers are implemented using the
-<a href="https://lmax-exchange.github.io/disruptor/";>LMAX Disruptor</a>
inter-thread
-messaging library. From the LMAX website:</p>
+<p>In order to handle exceptions that occur on the asynchronous thread, you
can configure a custom
+<a
href="https://lmax-exchange.github.io/disruptor/javadoc/com.lmax.disruptor/com/lmax/disruptor/ExceptionHandler.html";>ExceptionHandler<T></a>.</p>
</div>
-<div class="quoteblock">
-<blockquote>
<div class="paragraph">
-<p>…​using queues to pass data between stages of the system was
-introducing latency, so we focused on optimizing this area. The
-Disruptor is the result of our research and testing. We found that cache
-misses at the CPU level, and locks requiring kernel arbitration are both
-extremely costly, so we created a framework that has "mechanical
-sympathy" for the hardware it’s running on, and that’s
lock-free.</p>
+<p>The exact type of handler depends on the configuration mode:</p>
</div>
-</blockquote>
+<div class="dlist">
+<dl>
+<dt class="hdlist1">Full asynchronous</dt>
+<dd>
+<div class="paragraph">
+<p>If all the loggers are asynchronous you need to:</p>
</div>
+<div class="ulist">
+<ul>
+<li>
+<p>implement an
+<a
href="../javadoc/log4j-core/org/apache/logging/log4j/core/async/RingBufferLogEvent.html">ExceptionHandler<?
super RingBufferLogEvent></a></p>
+</li>
+<li>
+<p>set its fully qualified class name as value of the
+<a href="systemproperties.html#log4j2.asyncLoggerExceptionHandler" class="xref
page">log4j2.asyncLoggerExceptionHandler</a>
+configuration property.</p>
+</li>
+</ul>
+</div>
+</dd>
+<dt class="hdlist1">Mixed synchronous/asynchronous</dt>
+<dd>
<div class="paragraph">
-<p>LMAX Disruptor internal performance comparisons with
-<code>java.util.concurrent.ArrayBlockingQueue</code> can be found
-<a
href="https://github.com/LMAX-Exchange/disruptor/wiki/Performance-Results";>here</a>.</p>
+<p>If you use a mix of synchronous and asynchronous loggers you need to:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p>implement a
+<a
href="../javadoc/log4j-core/org/apache/logging/log4j/core/async/AsyncLoggerConfigDisruptor.Log4jEventWrapper.html">ExceptionHandler<?
super AsyncLoggerConfigDisruptor.Log4jEventWrapper></a></p>
+</li>
+<li>
+<p>set its fully qualified class name as value of the
+<a href="systemproperties.html#log4j2.asyncLoggerConfigExceptionHandler"
class="xref page">log4j2.asyncLoggerConfigExceptionHandler</a>
+configuration property.</p>
+</li>
+</ul>
+</div>
+</dd>
+</dl>
</div>
</div>
</div>
diff --git a/manual/json-template-layout.html b/manual/json-template-layout.html
index e4594853f1..b70f4c2cbe 100644
--- a/manual/json-template-layout.html
+++ b/manual/json-template-layout.html
@@ -513,7 +513,7 @@ appender.console.layout.eventTemplateUri =
classpath:EcsLayout.json</code></pre>
<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>Charset</code> used for <code>String</code>
encoding</p></td>
</tr>
<tr>
-<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>locationInfoEnabled</code></p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a
id="locationInfoEnabled"></a>locationInfoEnabled</code></p></td>
<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>boolean</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">toggles
access to the <code>LogEvent</code> source; file name, line number, etc.
(defaults to <code>false</code> set by
<code>log4j.layout.jsonTemplate.locationInfoEnabled</code>
diff --git a/manual/layouts.html b/manual/layouts.html
index fee65383b2..617dd21098 100644
--- a/manual/layouts.html
+++ b/manual/layouts.html
@@ -367,6 +367,94 @@ See each layout below.</p>
</div>
</div>
<div class="sect1">
+<h2 id="common-concerns"><a class="anchor" href="#common-concerns"></a>Common
concerns</h2>
+<div class="sectionbody">
+<div class="sect2">
+<h3 id="location-information"><a class="anchor"
href="#location-information"></a>Location information</h3>
+<div class="paragraph">
+<p>Computing the location information of a logging statement is an expensive
operation.
+For this reason many Log4j components implement the
+<a
href="../javadoc/log4j-core/org/apache/logging/log4j/core/impl/LocationAware.html">LocationAware</a>
+interface to only compute location information when needed.</p>
+</div>
+<div class="paragraph">
+<p>Some layouts implement <code>LocationAware</code> and they determine if a
location information is required according to these rules:</p>
+</div>
+<div class="dlist">
+<dl>
+<dt class="hdlist1"><a href="#GELFLayout">GelfLayout</a></dt>
+<dd>
+<div class="paragraph">
+<p>The GELF layout requires location information only if the pattern of the
<code>messagePattern</code> requires location information.</p>
+</div>
+<div class="paragraph">
+<p>See <a href="#location-pattern-layout">PatternLayout case</a> below.</p>
+</div>
+</dd>
+<dt class="hdlist1"><a href="#HTMLLayout">HtmlLayout</a></dt>
+<dd>
+<div class="paragraph">
+<p>The HTML layout requires location information if the <a
href="#HtmlLocationInfo">locationInfo</a> configuration attribute is set to
<code>true</code>.</p>
+</div>
+</dd>
+<dt class="hdlist1"><a id="location-pattern-layout"></a><a
href="#PatternLayout">PatternLayout</a></dt>
+<dd>
+<div class="paragraph">
+<p>The pattern layout will require location information if at least one of
these patterns is used:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p><a href="#PatternClass"><code>%C</code> or <code>%class</code></a>,</p>
+</li>
+<li>
+<p><a href="#PatternFile"><code>%F</code> or <code>%file</code></a>,</p>
+</li>
+<li>
+<p><a href="#PatternLocation"><code>%l</code> or
<code>%location</code></a>,</p>
+</li>
+<li>
+<p><a href="#PatternLine"><code>%L</code> or <code>%line</code></a>,</p>
+</li>
+<li>
+<p><a href="#PatternMethod"><code>%M</code> or <code>%method</code></a>.</p>
+</li>
+</ul>
+</div>
+</dd>
+<dt class="hdlist1"><a href="json-template-layout.html" class="xref
page">JsonTemplateLayout</a></dt>
+<dd>
+<div class="paragraph">
+<p>The JSON template layout will require location information if the
+<a href="json-template-layout.html#locationInfoEnabled" class="xref
page">locationInfoEnabled</a>
+configuration attribute is set to <code>true</code>.</p>
+</div>
+</dd>
+</dl>
+</div>
+<div class="paragraph">
+<p>The remaining layouts do not require location information.</p>
+</div>
+<div class="admonitionblock note">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-note" title="Note"></i>
+</td>
+<td class="content">
+<div class="paragraph">
+<p>Even if a layout is configured not to <strong>request</strong> location
information, it might use it if the information is already available.
+This is always the case of information location computed at build time using
the
+<a href="/log4j/transform/latest/#log4j-transform-maven-plugin">Log4j
Transform Maven Plugin</a>.</p>
+</div>
+</td>
+</tr>
+</table>
+</div>
+</div>
+</div>
+</div>
+<div class="sect1">
<h2 id="CSVLayouts"><a class="anchor" href="#CSVLayouts"></a>CSV Layouts</h2>
<div class="sectionbody">
<div class="paragraph">
diff --git a/manual/performance.html b/manual/performance.html
index 5e79fb0717..b4d4be234d 100644
--- a/manual/performance.html
+++ b/manual/performance.html
@@ -612,7 +612,7 @@ How this works is that a minimum amount of work is done by
the application threa
As long as the queue is sized large enough, the application threads should be
able to spend very little time on the logging call and return to the business
logic very quickly.</p>
</div>
<div class="sect3">
-<h4 id="async-trade-offs"><a class="anchor"
href="#async-trade-offs"></a>Trade-offs</h4>
+<h4 id="trade-offs"><a class="anchor" href="#trade-offs"></a><a
id="Trade-offs"></a>Trade-offs</h4>
<div class="paragraph">
<p>There are certain trade-offs associated with asynchronous logging:</p>
</div>
@@ -648,17 +648,39 @@ If neither of these is an option, you may get better
throughput and fewer latenc
<dd>
<p>If a problem happens during the logging process and an exception is thrown,
it is less easy for an asynchronous setting to signal this problem to the
application.
This can partly be alleviated by configuring an exception handler, but this
may still not cover all cases.</p>
+<div class="admonitionblock caution">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-caution" title="Caution"></i>
+</td>
+<td class="content">
+<div class="paragraph">
+<p>If logging is part of your business logic, e.g. you are using Log4j as an
audit logging framework, we would recommend to synchronously log those audit
messages.</p>
+</div>
+<div class="paragraph">
+<p>See
+<a href="async.html#MixedSync-Async" class="xref page">mixed
synchronous/asynchronous loggers</a> on how to log some messages
synchronously.</p>
+</div>
+</td>
+</tr>
+</table>
+</div>
</dd>
<dt class="hdlist1">Stateful messages</dt>
<dd>
-<p>In some rare cases, care must be taken with mutable messages.
-Most of the time you don’t need to worry about this.
-Log4 will ensure that log messages like <code>logger.debug("My object is {}",
myObject)</code> will use the state of the <code>myObject</code> parameter at
the time of the call to <code>logger.debug()</code>.
-The log message will not change even if <code>myObject</code> is modified
later.
-It is safe to asynchronously log mutable objects because most <a
href="messages.html" class="xref page">built-in <code>Message</code>
implementations</a> take a snapshot of the parameters on the calling thread
(see <a href="systemproperties.html#log4j2.formatMsgAsync" class="xref
page"><code>log4j2.formatMsgAsync</code></a>).</p>
+<p>Most
+<a
href="../javadoc/log4j-api/org/apache/logging/log4j/message/Message.html"><code>Message</code></a>
+implementations take a snapshot of the formatted message on the calling thread
(cf.
+<a href="systemproperties.html#log4j2.formatMsgAsync" class="xref
page"><code>log4j2.formatMsgAsync</code></a>).
+The log message will not change even if the arguments of the logging call are
modified later.</p>
<div class="paragraph">
-<p>There are some exceptions however: <a href="messages.html#MapMessage"
class="xref page"><code>MapMessage</code></a> and <a
href="messages.html#StructuredDataMessage" class="xref
page"><code>StructuredDataMessage</code></a> are mutable by design, fields can
be added to these messages after the message object was created.
-These messages should not be modified after they are logged with asynchronous
loggers or asynchronous appenders; you may or may not see the modifications in
the resulting log output.</p>
+<p>There are some exceptions to this rule.
+<a
href="../javadoc/log4j-api/org/apache/logging/log4j/message/MapMessage.html"><code>MapMessage</code></a>
+and
+<a
href="../javadoc/log4j-api/org/apache/logging/log4j/message/StructuredDataMessage.html"><code>StructuredDataMessage</code></a>
+for example are mutable by design: fields can be added to these messages after
the message object was created.
+These messages should not be modified after they are logged with asynchronous
loggers or asynchronous appenders.</p>
</div>
<div class="paragraph">
<p>Similarly, custom
diff --git a/manual/systemproperties.html b/manual/systemproperties.html
index 3cdd601ee8..5b0213c211 100644
--- a/manual/systemproperties.html
+++ b/manual/systemproperties.html
@@ -1429,7 +1429,7 @@ The RingBuffer will be pre-allocated at first use and
will never grow or shrink
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p
class="tableblock">Type</p></th>
-<td class="tableblock halign-left valign-top"><p class="tableblock"><a
href="https://lmax-exchange.github.io/disruptor/javadoc/com.lmax.disruptor/com/lmax/disruptor/WaitStrategy.html";>Class<?
extends WaitStrategy></a> or predefined constant</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">predefined
constant</p></td>
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p class="tableblock">Default
value</p></th>
@@ -1441,7 +1441,7 @@ The RingBuffer will be pre-allocated at first use and
will never grow or shrink
<p>Specifies the <a
href="https://lmax-exchange.github.io/disruptor/javadoc/com.lmax.disruptor/com/lmax/disruptor/WaitStrategy.html";>WaitStrategy</a>
used by the LMAX Disruptor.</p>
</div>
<div class="paragraph">
-<p>The value needs to be a fully qualified class name of a custom
<code>WaitStrategy</code> implementation (cf. <a
href="async.html#custom-waitstrategy" class="xref page">Custom
WaitStrategy</a>) or one of the predefined constants:</p>
+<p>The value needs to be one of the predefined constants:</p>
</div>
<div class="dlist">
<dl>
@@ -1467,8 +1467,7 @@ This wait strategy is <a href="garbagefree.html"
class="xref page">garbage free<
</dd>
<dt class="hdlist1">Yield</dt>
<dd>
-<p>is a strategy that uses a <code>Thread.yield()</code> for waiting for log
events after an initially spinning.
-Yield is a good compromise between performance and CPU resource, but may use
more CPU than <code>Sleep</code> in order to get the message logged to disk
sooner.
+<p>is a strategy that will use <code>100%</code> CPU, but will give up the CPU
if other threads require CPU resources.
This wait strategy is <a href="garbagefree.html" class="xref page">garbage
free</a>.</p>
</dd>
</dl>
@@ -1718,7 +1717,7 @@ The RingBuffer will be pre-allocated at first use and
will never grow or shrink
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p
class="tableblock">Type</p></th>
-<td class="tableblock halign-left valign-top"><p class="tableblock"><a
href="https://lmax-exchange.github.io/disruptor/javadoc/com.lmax.disruptor/com/lmax/disruptor/WaitStrategy.html";>Class<?
extends WaitStrategy></a> or predefined constant</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">predefined
constant</p></td>
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p class="tableblock">Default
value</p></th>
@@ -1730,7 +1729,7 @@ The RingBuffer will be pre-allocated at first use and
will never grow or shrink
<p>Specifies the <a
href="https://lmax-exchange.github.io/disruptor/javadoc/com.lmax.disruptor/com/lmax/disruptor/WaitStrategy.html";>WaitStrategy</a>
used by the LMAX Disruptor.</p>
</div>
<div class="paragraph">
-<p>The value needs to be a fully qualified class name of a custom
<code>WaitStrategy</code> implementation (cf. <a
href="async.html#custom-waitstrategy" class="xref page">Custom
WaitStrategy</a>) or one of the predefined constants:</p>
+<p>The value needs to be one of the predefined constants:</p>
</div>
<div class="dlist">
<dl>
@@ -1753,11 +1752,13 @@ This strategy has very low impact on the application
thread, in exchange for som
</dd>
<dt class="hdlist1">Yield</dt>
<dd>
-<p>is a strategy that uses a <code>Thread.yield()</code> for waiting for log
events after an initially spinning.
-Yield is a good compromise between performance and CPU resource, but may use
more CPU than <code>Sleep</code> in order to get the message logged to disk
sooner.</p>
+<p>is a strategy that will use <code>100%</code> CPU, but will give up the CPU
if other threads require CPU resources.</p>
</dd>
</dl>
</div>
+<div class="paragraph">
+<p>See also <a href="async.html#custom-waitstrategy" class="xref page">Custom
<code>WaitStrategy</code></a> for an alternative way to configure the wait
strategy.</p>
+</div>
</div>
<div class="sect3">
<h4 id="log4j2.asyncLoggerConfigTimeout"><a class="anchor"
href="#log4j2.asyncLoggerConfigTimeout"></a><code>log4j2.asyncLoggerConfigTimeout</code></h4>
diff --git a/plugin-reference.html b/plugin-reference.html
index e0217dc76e..973fb6843a 100644
--- a/plugin-reference.html
+++ b/plugin-reference.html
@@ -1470,7 +1470,7 @@ Originally developed by Ceki Glc and Anders
Kristensen.</p>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>header</code></p></td>
-<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>String?</code></p></td>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>boolean?</code></p></td>
<td class="tableblock halign-left valign-top"></td>
<td class="tableblock halign-left valign-top"><div class="content"></div></td>
</tr>
diff --git a/release-notes.html b/release-notes.html
index 47d248edda..10f3025299 100644
--- a/release-notes.html
+++ b/release-notes.html
@@ -451,6 +451,9 @@
<p>Update <code>actions/upload-artifact</code> to version <code>4.3.2</code>
(<a href="https://github.com/apache/logging-log4j2/pull/2490";>2490</a>)</p>
</li>
<li>
+<p>Update <code>apache/logging-parent</code> to version `` (<a
href="https://github.com/apache/logging-log4j2/pull/2597";>2597</a>)</p>
+</li>
+<li>
<p>Update <code>co.elastic.clients:elasticsearch-java</code> to version
<code>8.13.4</code> (<a
href="https://github.com/apache/logging-log4j2/pull/2573";>2573</a>)</p>
</li>
<li>
diff --git a/sitemap.xml b/sitemap.xml
index e1f94a7f88..597b1962f8 100644
--- a/sitemap.xml
+++ b/sitemap.xml
@@ -2,282 +2,282 @@
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9";>
<url>
<loc>https://logging.apache.org/log4j/2.x/5min.html</loc>
-<lastmod>2024-05-21T08:44:47.769Z</lastmod>
+<lastmod>2024-05-21T11:18:53.506Z</lastmod>
</url>
<url>
<loc>https://logging.apache.org/log4j/2.x/articles.html</loc>
-<lastmod>2024-05-21T08:44:47.769Z</lastmod>
+<lastmod>2024-05-21T11:18:53.506Z</lastmod>
</url>
<url>
<loc>https://logging.apache.org/log4j/2.x/development.html</loc>
-<lastmod>2024-05-21T08:44:47.769Z</lastmod>
+<lastmod>2024-05-21T11:18:53.506Z</lastmod>
</url>
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