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@@ -241,7 +241,7 @@ document.write("Last Published: " + document.lastModified);
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<a href="#sc_rightLevel">Logging at the Right Level</a>
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</li>
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<li>
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-<a href="#sc_log4jIdioms">Use of Standard log4j Idioms</a>
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+<a href="#sc_slf4jIdioms">Use of Standard slf4j Idioms</a>
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</li>
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</ul>
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</li>
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@@ -677,27 +677,32 @@ hierarchy of groups.
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<h2 class="h3">Logging</h2>
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<div class="section">
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<p>
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-ZooKeeper uses
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-<a href="http://logging.apache.org/log4j">log4j</a>
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-version 1.2 as its logging infrastructure. For information on configuring log4j for
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+Zookeeper uses
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+<a href="http://www.slf4j.org/index.html">slf4j</a> as an abstraction layer for logging.
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+<a href="http://logging.apache.org/log4j">log4j</a> in version 1.2 is chosen as the final logging implementation for now.
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+For better embedding support, it is planned in the future to leave the decision of choosing the final logging implementation to the end user.
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+Therefore, always use the slf4j api to write log statements in the code, but configure log4j for how to log at runtime.
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+Note that slf4j has no FATAL level, former messages at FATAL level have been moved to ERROR level.
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+For information on configuring log4j for
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ZooKeeper, see the <a href="zookeeperAdmin.html#sc_logging">Logging</a> section
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of the <a href="zookeeperAdmin.html">ZooKeeper Administrator's Guide.</a>
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+
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</p>
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-<a name="N1015C"></a><a name="sc_developerGuidelines"></a>
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+<a name="N10160"></a><a name="sc_developerGuidelines"></a>
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<h3 class="h4">Developer Guidelines</h3>
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-<p>Please follow these guidelines when submitting code. Patch reviewers will look for the following:</p>
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-<a name="N10164"></a><a name="sc_rightLevel"></a>
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+<p>Please follow the
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+<a href="http://www.slf4j.org/manual.html">slf4j manual</a> when creating log statements within code.
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+Also read the
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+<a href="http://www.slf4j.org/faq.html#logging_performance">FAQ on performance</a>
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+, when creating log statements. Patch reviewers will look for the following:</p>
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+<a name="N10170"></a><a name="sc_rightLevel"></a>
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<h4>Logging at the Right Level</h4>
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<p>
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-There are <a href="http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/Level.html#FATAL">6 levels of logging in log4j</a>.
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+There are several levels of logging in slf4j.
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It's important to pick the right one. In order of higher to lower severity:</p>
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<ol>
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-<li>
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-<p> FATAL level designates very severe error events that will presumably lead the application to abort</p>
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-</li>
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-
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<li>
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<p>ERROR level designates error events that might still allow the application to continue running.</p>
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</li>
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@@ -711,7 +716,7 @@ It's important to pick the right one. In order of higher to lower severity:</p>
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</li>
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<li>
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-<p>EBUG Level designates fine-grained informational events that are most useful to debug an application.</p>
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+<p>DEBUG Level designates fine-grained informational events that are most useful to debug an application.</p>
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</li>
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<li>
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@@ -722,34 +727,29 @@ It's important to pick the right one. In order of higher to lower severity:</p>
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<p>
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ZooKeeper is typically run in production such that log messages of INFO level
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severity and higher (more severe) are output to the log.</p>
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-<a name="N1018F"></a><a name="sc_log4jIdioms"></a>
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-<h4>Use of Standard log4j Idioms</h4>
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+<a name="N10193"></a><a name="sc_slf4jIdioms"></a>
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+<h4>Use of Standard slf4j Idioms</h4>
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<p>
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<em>Static Message Logging</em>
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</p>
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<pre class="code">
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LOG.debug("process completed successfully!");
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</pre>
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-<p>However when creating a message from a number of components (string
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-concatenation), the log call should be wrapped with a "isXEnabled()" call. this
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-eliminates the string concatenation overhead when debug level logging is not enabled.
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+<p>
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+However when creating parameterized messages are required, use formatting anchors.
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</p>
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<pre class="code">
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-if (LOG.isDebugEnabled()) {
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- LOG.debug("got " + count + " messages in " + time + " minutes");
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-}
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+LOG.debug("got {} messages in {} minutes",new Object[]{count,time});
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</pre>
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<p>
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<em>Naming</em>
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</p>
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<p>
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-Loggers should be named after the class in which they are used. (See the
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-<a href="http://logging.apache.org/log4j/1.2/faq.html#2.4">log4j faq</a>
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-for reasons why this is a good idea.)
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+Loggers should be named after the class in which they are used.
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</p>
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<pre class="code">
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public class Foo {
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- private static final Logger LOG = Logger.getLogger(Foo.class);
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+ private static final Logger LOG = LoggerFactory.getLogger(Foo.class);
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....
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public Foo() {
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LOG.info("constructing Foo");
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Patrick D. Hunt