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| |
| <section> |
| <h2><a name="Log4j_2_API"></a>Log4j 2 API</h2> |
| <section> |
| <h3><a name="Log_Builder"></a>Log Builder</h3> |
| <a name="Building_Log_Messages"></a> |
| |
| <p> |
| Log4j has traditionally been used with logging statements like |
| </p> |
| <div> |
| <pre class="prettyprint linenums"> |
| logger.error("Unable to process request due to {}", code, exception);</pre></div> |
| This has resulted in some confusion as to whether the exception should be a parameter to the message or |
| if Log4j should handle it as a throwable. In order to make logging clearer a builder pattern has been |
| added to the API. Using the builder syntax the above would be handled as: |
| |
| <div> |
| <pre class="prettyprint linenums"> |
| logger.atError().withThrowable(exception).log("Unable to process request due to {}", code);</pre></div> |
| |
| <p> |
| With this syntax it is clear that the exception is to be treated as a Throwable by Log4j. |
| </p> |
| |
| <p> |
| The Logger class now returns a LogBuilder when any of the atTrace, atDebug, atInfo, atWarn, atError, |
| atFatal, always, or atLevel(Level) methods are called. The logBuilder then allows a Marker, Throwable, |
| and/or location to be added to the event before it is logged. A call to the log method always causes the |
| log event to be finalized and sent. |
| </p> |
| |
| <p> |
| A logging statement with a Marker, Throwable, and location would look like: |
| </p> |
| <div> |
| <pre class="prettyprint linenums"> |
| logger.atInfo().withMarker(marker).withLocation().withThrowable(exception).log("Login for user {} failed", userId);</pre></div> |
| |
| |
| <p> |
| Providing the location method on the LogBuilder provides two distinct advantages: |
| </p> |
| <ol style="list-style-type: decimal"> |
| |
| <li>Logging wrappers can use it to provide the location information to be used by Log4j.</li> |
| |
| <li>The overhead of capturing location information when using the location method with no |
| parameters is much better than having to calculate the location information when it is needed. Log4j |
| can simply ask for the stack trace entry at a fixed index instead of having to walk the stack trace |
| to determine the calling class. Of course, if the location information will not be used by the layout |
| this will result in slower performance.</li> |
| </ol> |
| |
| <section> |
| <h4><a name="Location_Performance"></a>Location Performance</h4> |
| |
| <p> |
| The table below shows some of the results from the FileAppenderBenchmark and FileAppenderWithLocationBenchmark |
| classes in the log4j-perf project when configured to use 4 threads. The results show that lazily including |
| the location information is about 8 times slower than not including location information. While using the |
| withLocation method of LogBuilder is about 3 times faster than lazily calculating the location information |
| it is still about 2.5 times slower than not including location information. |
| </p> |
| |
| <p> |
| The tests were run on a 2018 MacBook Pro with a |
| 2.9 GHz Intel Core i9 processor with 6 cores, 32 GB of memory and 1 TB of SSD storage on Java 11 using |
| Log4j 2.13.0 and Logback 1.2.3. |
| </p> |
| <img src="../images/LocationPerf.png" title="Location Performance" alt="Location Performance" /> |
| |
| <table border="0" class="table table-striped"> |
| |
| <tr class="a"> |
| |
| <th>Test</th> |
| |
| <th>Print Location Info</th> |
| |
| <th>No Location Info Printed</th> |
| </tr> |
| |
| <tr class="b"> |
| |
| <td>Log4j2 File</td> |
| |
| <td>191,509.724 ± 11339.978 ops/s</td> |
| |
| <td>1,407,329.130 ± 22595.997 ops/s</td> |
| </tr> |
| |
| <tr class="a"> |
| |
| <td>Log4j2 Log Builder withLocation()</td> |
| |
| <td>469,200.684 ± 50025.985 ops/s</td> |
| |
| <td>577,127.463 ± 11464.342 ops/s</td> |
| </tr> |
| |
| <tr class="b"> |
| |
| <td>Logback File</td> |
| |
| <td>159,116.538 ± 1884.969 ops/s</td> |
| |
| <td>1,240,438.384 ± 76619.873 ops/s</td> |
| </tr> |
| </table> |
| |
| <p> |
| As expected, when using LogBuilder with a call to the withLocation() method logging is much faster when |
| location information is used in the output but significantly slower when it is not. |
| </p> |
| |
| <p> |
| Note: Running the tests at various times provides varying results. Although some results have been as much |
| as 10% higher all results are generally affected similarly so the comparisons between them stay the same. |
| </p> |
| </section></section> |
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