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<li class="toctree-l2"><a class="reference internal" href="#how-much-impact-does-arthas-attach-have-on-the-performance-of-the-original-process">How much impact does Arthas attach have on the performance of the original process?</a></li>
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<li class="toctree-l2"><a class="reference internal" href="#can-commands-such-as-trace-watch-enhance-the-classes-in-jdk">Can commands such as trace/watch enhance the classes in jdk?</a></li>
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<li class="toctree-l2"><a class="reference internal" href="#how-to-view-the-result-in-json-format">How to view the result in <code class="docutils literal notranslate"><span class="pre">json</span></code> format</a></li>
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<li class="toctree-l2"><a class="reference internal" href="#can-arthas-trace-native-methods">Can arthas trace native methods</a></li>
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<li class="toctree-l2"><a class="reference internal" href="#can-arthas-view-the-value-of-a-variable-in-memory">Can arthas view the value of a variable in memory?</a></li>
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<li class="toctree-l2"><a class="reference internal" href="#java-lang-classformaterror-null-skywalking-arthas-compatible-use">java.lang.ClassFormatError: null, skywalking arthas compatible use</a></li>
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<div class="section" id="faq">
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<h1>FAQ<a class="headerlink" href="#faq" title="Permalink to this headline">¶</a></h1>
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<blockquote>
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<div><p>For questions that are not in this list, please search in issues. <a class="reference external" href="https://github.com/alibaba/arthas/issues">https://github.com/alibaba/arthas/issues</a></p>
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</div></blockquote>
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<div class="section" id="how-much-impact-does-arthas-attach-have-on-the-performance-of-the-original-process">
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<h2>How much impact does Arthas attach have on the performance of the original process?<a class="headerlink" href="#how-much-impact-does-arthas-attach-have-on-the-performance-of-the-original-process" title="Permalink to this headline">¶</a></h2>
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<p><a class="reference external" href="https://github.com/alibaba/arthas/issues/44">https://github.com/alibaba/arthas/issues/44</a></p>
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</div>
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<div class="section" id="can-commands-such-as-trace-watch-enhance-the-classes-in-jdk">
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<h2>Can commands such as trace/watch enhance the classes in jdk?<a class="headerlink" href="#can-commands-such-as-trace-watch-enhance-the-classes-in-jdk" title="Permalink to this headline">¶</a></h2>
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<p>By default, classes beginning with <code class="docutils literal notranslate"><span class="pre">java.</span></code> are filtered out, but they can be turned on:</p>
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<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">options unsafe true</pre></div>
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</div>
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<p>See more at <a class="reference internal" href="options.html"><span class="doc">options</span></a></p>
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</div>
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<div class="section" id="how-to-view-the-result-in-json-format">
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<h2>How to view the result in <code class="docutils literal notranslate"><span class="pre">json</span></code> format<a class="headerlink" href="#how-to-view-the-result-in-json-format" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">options json-format true</pre></div>
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</div>
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<p>See more at <a class="reference internal" href="options.html"><span class="doc">options</span></a></p>
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</div>
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<div class="section" id="can-arthas-trace-native-methods">
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<h2>Can arthas trace native methods<a class="headerlink" href="#can-arthas-trace-native-methods" title="Permalink to this headline">¶</a></h2>
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<p>No.</p>
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</div>
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<div class="section" id="can-arthas-view-the-value-of-a-variable-in-memory">
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<h2>Can arthas view the value of a variable in memory?<a class="headerlink" href="#can-arthas-view-the-value-of-a-variable-in-memory" title="Permalink to this headline">¶</a></h2>
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<p>No. But you can use some tricks to intercept the object with the <code class="docutils literal notranslate"><span class="pre">tt</span></code> command, or fetch it from a static method.</p>
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</div>
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<div class="section" id="how-to-filter-method-with-the-same-name">
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<h2>How to filter method with the same name?<a class="headerlink" href="#how-to-filter-method-with-the-same-name" title="Permalink to this headline">¶</a></h2>
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<p>You can used all variables in <a class="reference internal" href="advice-class.html"><span class="doc">fundamental fields in expressions</span></a> for the condition express to filter method with the same name, you can use the number of parameters <code class="docutils literal notranslate"><span class="pre">params.length</span> <span class="pre">==1</span></code>,parameter type <code class="docutils literal notranslate"><span class="pre">params[0]</span> <span class="pre">instanceof</span> <span class="pre">java.lang.Integer</span></code>,return value type <code class="docutils literal notranslate"><span class="pre">returnObj</span> <span class="pre">instanceof</span> <span class="pre">java.util.List</span></code> and so on in one or more combinations as condition express.</p>
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<p>You can use <code class="docutils literal notranslate"><span class="pre">-v</span></code> to view the condition express result <a class="reference external" href="https://github.com/alibaba/arthas/issues/1348">https://github.com/alibaba/arthas/issues/1348</a></p>
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<p>example <a class="reference internal" href="quick-start.html"><span class="doc">arthas-demo</span></a></p>
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<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">watch demo.MathGame primeFactors traceE '{params,returnObj,throwExp}' -v -n 5 -x 3 'params.length >0 && returnObj instanceof java.util.List'</pre></div>
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</div>
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</div>
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<div class="section" id="how-to-watch-or-trace-constructor">
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<h2>How to watch or trace constructor?<a class="headerlink" href="#how-to-watch-or-trace-constructor" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">watch demo.MathGame <init> '{params,returnObj,throwExp}' -v -n 5 -x 3 '1==1'</pre></div>
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</div>
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</div>
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<div class="section" id="java-lang-classformaterror-null-skywalking-arthas-compatible-use">
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<h2>java.lang.ClassFormatError: null, skywalking arthas compatible use<a class="headerlink" href="#java-lang-classformaterror-null-skywalking-arthas-compatible-use" title="Permalink to this headline">¶</a></h2>
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<p>When error log appear <code class="docutils literal notranslate"><span class="pre">java.lang.ClassFormatError:</span> <span class="pre">null</span></code>, it is usually modified by other bytecode tools that are not compatible with arthas modified bytecode.</p>
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<p>For example: use skywalking V8.1.0 below <a class="reference external" href="https://github.com/alibaba/arthas/issues/1141">cannot trace, watch classes enhanced by skywalking agent</a>, V8.1.0 or above is compatible, refer to skywalking configuration for more details. <a class="reference external" href="https://github.com/apache/skywalking/blob/v8.1.0/docs/en/FAQ/Compatible-with-other-javaagent-bytecode-processing">skywalking compatible with other javaagent bytecode processing</a>.</p>
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