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<!--
Google IO 2012 HTML5 Slide Template
Authors: Eric Bidelman <ebidel@gmail.com>
Luke Mahé <lukem@google.com>
URL: https://code.google.com/p/io-2012-slides
-->
<!DOCTYPE html>
<html>
<head>
<title>Deadsimple JRuby troubleshooting</title>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="chrome=1">
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<link rel="stylesheet" media="all" href="theme/css/default.css">
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<base target="_blank"> <!-- This amazingness opens all links in a new tab. -->
<script data-main="js/slides" src="js/require-1.0.8.min.js"></script>
<style>
span.highlight {background-color: #fff600;}
</style>
</head>
<body style="opacity: 0">
<slides class="layout-widescreen">
<!--
<slide class="segue dark quote nobackground">
<article class="flexbox auto-fadein vcenter">
<q>Does it Scale?</q>
</article>
</slide>
<slide class="segue dark quote nobackground">
<article class="flexbox auto-fadein vcenter">
<q>Does it <span style="text-decoration: line-through;">Scale</span> ThreadSafe?</q>
</article>
</slide>
-->
<slide class="nobackground">
<article class="flexbox vcenter">
<h1><span><img src="images/ruby-shift-logo.png"></span></h1>
<h3>Kiev 2012</h3>
</article>
</slide>
<slide class="title-slide segue nobackground">
<!-- The content of this hgroup is replaced programmatically through the slide_config.json. -->
<hgroup class="auto-fadein">
<h1 data-config-title><!-- populated from slide_config.json --></h1>
<h2 data-config-subtitle><!-- populated from slide_config.json --></h2>
<p data-config-presenter><!-- populated from slide_config.json --></p>
<br>
<br>
<br>
<br>
</hgroup>
</slide>
<slide>
<hgroup>
<h2>Agenda</h2>
</hgroup>
<article>
<ul>
<li>Why JRuby?</li>
<li>Unix and JVM tools for debugging JRuby</li>
<li>Our issues with JRuby in production</li>
<li>Current state of art</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>Why JRuby? Our Requirements</h2>
</hgroup>
<article>
<ul>
<li>Single-process application</li>
<li>Shared memory</li>
<li>Ability to use native-threads</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>Production Configuration</h2>
</hgroup>
<article>
<ul>
<li>JRuby 1.6.5(later updated to 1.6.7)</li>
<li>Kirk as application server(Jetty-based)<br>
<a href="https://github.com/strobecorp/kirk">https://github.com/strobecorp/kirk</a>
</li>
<li>Akka 1.3 - as Actor-library</li>
<li>Java - OpenJDK 6</li>
<li>Upstart for daemonizing</li>
<li>Ubuntu 10.04</li>
</ul>
</article>
</slide>
<!-- begin -->
<slide>
<hgroup>
<h2>Useful Unix-tools</h2>
</hgroup>
<article>
<p>Can be used for debugging any Unix-process:</p>
<ul>
<li><b>ps</b> and <b>top</b> - find information about required process(es)</li>
<li><b>strace</b> - tracing all kernel-calls from process</li>
<li><b>lsof</b> - observe all opened sockets/files</li>
<li><b>netstat</b> - monitoring all network activities(interfere with <b>lsof</b>)</li>
<li><b>tcpdump/wireshark</b> - dump and investigation of all network traffic</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>lsof - list open files</h2>
</hgroup>
<article>
<ul>
<li>Observe all open files/sockets for process</li>
<li>Observe all opened files in your system</li>
<li>Find-out where all your logs are written</li>
<li>Often used in combination with <b>strace</b></li>
</ul>
<p>Usage:
<pre class="prettyprint" data-lang="bash">
$ sudo lsof -p <PID></pre>
</p>
</article>
</slide>
<slide>
<hgroup>
<h2>lsof usage example</h2>
</hgroup>
<article>
<pre class="prettyprint" data-lang="bash">
$ sudo lsof -p 21647
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
java 21647 ubuntu cwd DIR 8,1 4096 321163 /home/ubuntu
java 21647 ubuntu rtd DIR 8,1 4096 2 /
java 21647 ubuntu txt REG 8,1 39584 9436 /usr/lib/jvm/java-6-openjdk/jre/bin/java
java 21647 ubuntu mem REG 8,1 105288 295079 /lib/x86_64-linux-gnu/libresolv-2.15.so
java 21647 ubuntu mem REG 8,1 31104 297067 /lib/x86_64-linux-gnu/libnss_dns-2.15.so
java 21647 ubuntu mem REG 8,1 424384 9408 /usr/lib/nss/libfreebl3.so
...
java 21647 ubuntu 0u CHR 1,3 0t0 735 /dev/null
java 21647 ubuntu <span style="background-color: #fff600">1w</span> REG 8,1 636410 297370 <span style="background-color: #fff600">/var/www/app/rails/log/kirk.log</span>
java 21647 ubuntu 2w CHR 1,3 0t0 735 /dev/null
....
java 21647 ubuntu <span style="background-color: #fff600">42u</span> IPv6 146353046 0t0 TCP 127.0.0.1:49872->127.0.0.1:postgresql (ESTABLISHED)
...
java 21647 ubuntu 64u IPv6 146353326 0t0 TCP localhost:3000 (LISTEN)
java 21647 ubuntu 65u IPv6 149554050 0t0 TCP 127.0.0.1:37047->127.0.0.1:6379 (CLOSE_WAIT)</pre>
</article>
</slide>
<slide>
<hgroup>
<h2>strace</h2>
</hgroup>
<article>
<ul>
<li>Trace system-calls
<ul>
<li>open/close file/socket</li>
<li>read/write to open file/socket</li>
<li>write to stdout/stderr</li>
</ul>
</li>
<li>Great for debugging process start-up issues</li>
<li>Get a clue why your process stuck</li>
<li>Can trace sub-process and threads</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>strace usage for JRuby</h2>
</hgroup>
<article>
<p>Usage:
<pre class="prettyprint" data-lang="bash">
$ sudo strace -e trace='!gettimeofday,clock_gettime,futex' -fp <PID>
#
# -e trace='!...' - skip trace of these calls
# -f - trace childs and threads
# -p - with PID
</pre>
</p>
</article>
</slide>
<slide>
<hgroup>
<h2>lsof + strace: demo</h2>
</hgroup>
<article>
<p>Run in <b>irb</b> next query:
<pre class="prettyprint" data-lang="sql">
ActiveRecord::Base.connection.execute('SELECT pg_sleep(10000)')</pre>
Find appropriate process PID:
<pre class="prettyprint" data-lang="bash">
$ jps -l
13690 sun.tools.jps.Jps
<span class="highlight">13356 org.jruby.Main</span></pre>
Run Strace:
<pre class="prettyprint" data-lang="bash">
$ sudo strace -fp <span class="highlight">13356</span> -e trace='!gettimeofday,futex,clock_gettime'
Process 13356 attached with 12 threads - interrupt to quit
[pid 13372] restart_syscall(<... resuming interrupted call ...> <unfinished ...>
[pid 13362] <span class="highlight">recv(15</span>, <unfinished ...>
[pid 13365] restart_syscall(<... resuming interrupted call ...> <unfinished ...>
[pid 13372] <... restart_syscall resumed> ) = -1 ETIMEDOUT (Connection timed out)</pre>
</p>
</article>
</slide>
<slide>
<hgroup>
<h2>lsof + strace: demo</h2>
</hgroup>
<article>
<p><b>lsof</b> in da house:
<pre class="prettyprint" data-lang="bash">
$ sudo lsof -p <span class="highlight">13356</span>
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
...
java 13356 cris 0u CHR 136,9 0t0 12 /dev/pts/9
java 13356 cris 1u CHR 136,9 0t0 12 /dev/pts/9
java 13356 cris 2u CHR 136,9 0t0 12 /dev/pts/9
java 13356 cris 3r REG 8,6 62447715 2232993 /usr/lib/jvm/java-7-oracle/jre/lib/rt.jar
java 13356 cris 4r REG 8,6 10017442 3419090 /home/cris/.rvm/rubies/jruby-1.6.7/lib/jruby.jar
java 13356 cris 5r REG 8,6 575675 2239123 /usr/lib/jvm/java-7-oracle/jre/lib/jsse.jar
java 13356 cris 6r CHR 1,8 0t0 5953 /dev/random
java 13356 cris 7u unix 0xefb78240 0t0 905568 socket
java 13356 cris 8r CHR 1,9 0t0 5954 /dev/urandom
...
java 13356 cris 14u unix 0xc583aac0 0t0 906952 socket
java 13356 cris <span class="highlight">15u</span> IPv6 906954 0t0 TCP <span class="highlight">localhost:59814->localhost:postgresql</span> (ESTABLISHED)
</pre>
</p>
</article>
</slide>
<slide>
<hgroup>
<h2>Issue #1: limited performance</h2>
</hgroup>
<article>
<ul>
<li>At first we started from Amazon Large instance</li>
<li>We didn't get required performance during load-testing</li>
<li>Next we tried XL-instance and it didn't help</li>
<li>Then we realized our Kirk-process used only 512Mb</li>
<li>Setting <b>JRUBY_OPTS="-J-Xmx2048m"</b> increased maximum allowed memory and resolved issue</li>
</ul>
<p><b>Tool for debug</b>: <b>top</b></p>
<p><b>Lessons learned</b>: learn JVM configuration parameters, it can be handy</p>
</article>
</slide>
<slide>
<hgroup>
<h2>Issue #2: slow connection to Postgres</h2>
</hgroup>
<article>
<b>Symptoms</b>:
<ul>
<li>Everything went good in development environment</li>
<li>In production environment our DB and Application were
on different hosting-platform</li>
<li>When we run application it looks like it totally stuck</li>
<li>But after ~20 seconds it started responding</li>
</ul>
<p><b>Tools for debug</b>: <b>tcpdump/wireshark</b></p>
<b>Debugging</b>:
<ul>
<li>plain traffic sniffing with <b>tcpdump</b> and analysis in <b>wireshark</b> showed JRuby sends many spam-selects to Postgres</li>
<li>This issue was known and update of postgres jdbc gem fixed it</li>
</ul>
<p><b>Lessons learned</b>: use updated gems and JRuby</p>
</article>
</slide>
<slide>
<hgroup>
<h2>JVM-toolbox</h2>
</hgroup>
<article>
<ul>
<li>Useful for debugging any JVM-language: Java, JRuby, Clojure, Scala, Groovy</li>
<li>Out of the box tools: jps, jconsole, jvisualvm, jstack, jdb, jmap, jhat, jstat, jstatd</li>
<li>Dozens of free and commercial third-party tools: MAT, YourKit, ...</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>Useful JVM-tools</h2>
</hgroup>
<article>
<ul>
<li><b>jps -l</b> - show all JVM-processes for current user</li>
<li><b>jstack</b> - get stacktrace of all running threads</li>
<li><b>jvisualvm</b> - monitoring different JVM activities: running threads, memory consumption, GC, and allow to obtain JRuby stacktraces</li>
<li><b>jdb</b> - Java Debugger</li>
<li><b>jmap</b> - obtain heap-dump of running JRuby process</li>
<li><b>MAT</b> - Eclipse Memory Analyzer. Incredible for debugging memory-leaks and other runtime-related issues</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>VisualVm (jvisualvm)</h2>
</hgroup>
<article>
<ul>
<li>One of the killer-app for JRuby</li>
<li>Get common information about JVM-process runtime</li>
<li>Work with local and remote JVM-process</li>
<li>Monitoring memory consumption and GC</li>
<li>Monitoring running threads activity</li>
<li>Can create HeapDump of running process</li>
<li>Charles Nutter wrote good introduction to VisualVM:<br> <a href="http://bit.ly/OsaFkA">http://bit.ly/OsaFkA</a></li>
<li>VisualVM deserves its own talk!</li>
<li><b>Obtaining JRuby stacktraces</b></li>
</ul>
</article>
</slide>
<slide>
<article>
<img src="images/screen/visualvm-memory.png">
</article>
</slide>
<slide>
<article>
<img src="images/screen/visualvm-threads.png">
</article>
</slide>
<slide>
<hgroup>
<h2>VisualVm: obtaining JRuby stacktrace </h2>
</hgroup>
<article>
<ul>
<li>Most useful VisualVM feature for troubleshooting!</li>
<li>JRuby stacktrace is incredebly useful when JRuby thread stuck</li>
<li>Stacktrace in 90% of cases is all you need to find the cause of issue!</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>Recipe: JRuby stacktrace in VisualVM</h2>
</hgroup>
<article>
<p>1. Run VisualVM:
<pre class="prettyprint" data-lang="bash">
# Run jvisualvm under the same user as for jruby-process
$ jvisualvm</pre></p>
<p>2. Install "VisualVM-MBeans" plugin:
<pre>
Tools > Plugins > Available Plugins
Check "VisualVM-MBeans" and click "Install"
Reload VisualVM</pre>
</p>
<p>3. Run JRuby with "--manage" option:
<pre class="prettyprint" data-lang="bash">
$ export JRUBY_OPTS="--manage"
$ rails s</pre></p>
</article>
</slide>
<slide>
<hgroup>
<h2>Recipe: JRuby stacktrace in VisualVM</h2>
</hgroup>
<article>
<p>4. Open appropriate JRuby-process in "Applications > Local" toolbar</p>
<p>5. Open "MBeans" in right-toolbar and select
<pre>
org.jruby > Runtime > SomeNumber > Runtime</pre></p>
<p>6. And last step:
<pre>Operations > Thread Dump</pre></p>
</article>
</slide>
<slide>
<img src="images/screen/visualvm-stacktrace.png">
</slide>
<slide>
<hgroup>
<h2>JRuby stacktrace via VisualVM!</h2>
</hgroup>
<article>
<img src="images/screen/visualvm-result.png">
</article>
</slide>
<slide>
<hgroup>
<h2>jstack or kill -QUIT</h2>
</hgroup>
<article>
<ul>
<li>Useful for obtaining Java-stacktrace of running JRuby thread</li>
<li>Requires some knowledge of Java and JRuby-internals</li>
<li><b>jstack</b> prints its output right into your console
<br>Run it under the same user as JRuby-process owner(or via su/sudo)!
</li>
<li><b>kill -QUIT <PID></b> prints its output into process <b>stdout</b></li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>Example: "jstack" or "kill -QUIT"</h2>
</hgroup>
<article class="smaller">
<pre class="prettyprint" data-lang="bash">
$ ps -aux | grep jruby
ubuntu <span class="highlight">20071</span> 0.0 2.6 718612 81360 pts/0 Sl+ Sep26 0:48 /usr/lib/jvm/java-7-oracle/bin/java ...
ubuntu 29775 0.0 0.0 4372 832 pts/8 S+ 16:15 0:00 grep jruby
$ kill -QUIT 20071
# OR
$ jstack <span class="highlight">20071</span>
2012-09-27 16:19:08
Full thread dump Java HotSpot(TM) Server VM (23.3-b01 mixed mode):
"RMI TCP Connection(16)-127.0.0.1" daemon prio=10 tid=0x8cc08400 nid=0x7451 runnable [0x8bbf9000]
java.lang.Thread.State: RUNNABLE
...
"main" prio=10 tid=0xb6506c00 nid=0x4e6d runnable [0xb68a4000]
java.lang.Thread.State: RUNNABLE
at <span class="highlight">java.io.FileInputStream.read(Native Method)</span>
at jline.Terminal.readCharacter(Terminal.java:99)
at jline.UnixTerminal.readVirtualKey(UnixTerminal.java:122)
at jline.ConsoleReader.readVirtualKey(ConsoleReader.java:1606)
at jline.ConsoleReader.readBinding(ConsoleReader.java:764)
at jline.ConsoleReader.readLine(ConsoleReader.java:511)
at jline.ConsoleReader.readLine(ConsoleReader.java:457)
at <span class="highlight">org.jruby.ext.Readline.s_readline(Readline.java:237)</span>
at org.jruby.ext.Readline$s$s_readline.call(Readline$s$s_readline.gen:65535)
at org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:332)
...
</pre>
</article>
</slide>
<slide>
<hgroup>
<h2>Issue #3: Rails 3.1 ain't thread-safe</h2>
</hgroup>
<article>
<b>Symptoms:</b>
<ul>
<li>All Rails-worker threads stuck</li>
<li>Kirk can't process any application requests</li>
<li>Only JVM-threads stay active</li>
</ul>
<p><b>Tools for debug</b>: <b>jstack</b>, <b>VisualVM</b></p>
<b>Debugging</b>:
<ul>
<li><b>jstack</b> showed that all JRuby threads are waiting for Mutex</li>
<li>We obtained JRuby-stacktrace via <b>VisualVm</b></li>
<li>Stacktrace points us to connection_pool.rb</li>
<li>Scrutiny code review of this file revealed nasty bugs in mutex logic</li>
<li>Gist with Fix: <a href="https://gist.github.com/2658680">https://gist.github.com/2658680</a></li>
</ul>
<p><b>Lessons learned</b>: pay closer attention to thread-safety in your gems</p>
</article>
</slide>
<slide class="segue dark quote nobackground">
<article class="flexbox auto-fadein vcenter">
<q>Dream about Magic Debugging Tool</q>
</article>
</slide>
<slide>
<hgroup>
<h2>Magic Debugging Tool</h2>
</hgroup>
<article>
<ul>
<li>Ability to investigate the whole running runtime</li>
<li>All running threads</li>
<li>Ability to obtain access to all objects and properties</li>
<li>Ability to jump into any JRuby Frame</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>jdb - Java Debugger</h2>
</hgroup>
<article>
<ul>
<li>Can sneak into any JVM-process</li>
<li>Can investigate all threads</li>
<li>But it require deep knowledge of JRuby-internals and it's hard to obtain access to complex data structure</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>MAT - Eclipse Memory Analyzer</h2>
</hgroup>
<article>
<ul>
<li>MAT - <a href="http://www.eclipse.org/mat/downloads.php">http://www.eclipse.org/mat/downloads.php</a>
<li>Real JRuby killep-app!</li>
<li>The simplest memory-leak detection tool</li>
<li>The simplest debugging tool
<ul>
<li>Shows all environment for running threads</li>
<li>Allows to observe any object on JVM heap</li>
<li>Require some basic knowledge of JRuby internals</li>
</ul>
</li>
<li>Deserves for two distinct talks</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>MAT usage</h2>
</hgroup>
<article>
<p>1. Obtain heap-dump via: <b>jmap</b> or <b>VisualVm</b>:
<pre class="prettyprint" data-lang="bash">
# normal way
$ jmap -dump:live,format=b,file=snapshot.hprof <PID>
# forced way(when process doesn't respond)
$ jmap -dump:format=b,file=snapshot.hprof -F <PID></pre></p>
<p>2. Feed it into MAT:
<pre>
File > Open Heap Dump</pre>
</p>
</article>
</slide>
<slide>
<img src="images/screen/mat-java-threads.png">
</slide>
<slide>
<img src="images/screen/mat-heap.png">
</slide>
<slide>
<hgroup>
<h2>Issue #4: Locks on Postgres transaction</h2>
</hgroup>
<article>
<b>Symptoms:</b>
<ul>
<li>One by one worker-threads became locked until all server stuck</li>
</ul>
<p><b>Tools for debug</b>: <b>jstack</b>, <b>jmap</b>, <b>MAT</b></p>
<b>Debugging</b>:
<ul>
<li><b>jstack</b> showed that part of JRuby threads are waiting for response from Postgres, and part of JRuby threads are waiting for mutex</li>
<li>But it was not clear, what kind of queries produce such behavior</li>
<li>We did HeapDump with <b>jmap</b> and fed it into <b>MAT</b></li>
<li>Going up by JRuby frames we managed to find actual SQL-query</li>
<li>Reason was in tricky deadlock with combination of PG-transaction and our mutex logic</li>
</ul>
<p><b>Lessons learned</b>: avoid using mutexes, prefer non-blocking actors</p>
</article>
</slide>
<slide>
<hgroup>
<h2>Issue #5: autoload isn't threadsafe</h2>
</hgroup>
<article>
<b>Symptoms:</b>
<ul>
<li>Time-to-time after deploy we got random errors with AR models</li>
<li>It looked like some part of model isn't presented at all</li>
</ul>
<p><b>Tools for debug</b>: <b>brain</b></p>
<b>Debugging</b>:
<ul>
<li>Having multithreaded environment we understood it can be a reason</li>
<li>Main issue can be when Ruby-class is under construction and some object is created in parallel thread</li>
<li>We reproduced this behavior even in MRI 1.9.3</li>
<li>The main reason was in gem with "autoload"-s</li>
</ul>
<p><b>Fix</b>: explicitly list all autoloaded classes in initializer</p>
<p><b>Lessons learned</b>: all Ruby-classes should be loaded before going into multithreaded mode</p>
</article>
</slide>
<slide>
<hgroup>
<h2>Summary: Why JRuby thread can stuck?</h2>
</hgroup>
<article>
<ul>
<li>Waiting on blocking system call [<b>jstack</b>/(<b>strace</b> + <b>lsof</b>)]
<ul>
<li>Waiting on response from Database</li>
<li>Trying to reach some file on broken FS</li>
<li>Trying to read/write from file/socket(operation without timeout)</li>
</ul>
</li>
<li>Waiting for Mutex [<b>jstack</b>, <b>jvisualvm</b>]</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>New Recommended Configuration</h2>
</hgroup>
<article>
<ul>
<li>JRuby 1.7.0(when it will be released)<br>
<ul><li>1.7.0preview2 is about 30% faster then 1.6.7</li></ul>
</li>
<li>Java - OpenJDK 7
<ul><li>invokedynamic on new Java doesn't show any speed improvements</li></ul>
</li>
<li>Actors via: Akka or Celluloid
<ul>
<li>Avoid writting home-made mutex-logic</li>
<li>Prefer using some non-blocking Actor-solution</li>
<li>We moved our Airbrake-notificator into actor</li>
</ul>
</li>
<li>Application server: Trinidad or Jetpack
<ul>
<li>Trinidad(Tomcat-based): <a href="http://thinkincode.net/trinidad/">http://thinkincode.net/trinidad/</a></li>
<li>Jetpack(Jetty-based): <a href="https://github.com/square/jetpack">https://github.com/square/jetpack</a></li>
</ul>
</li>
<li>Ubuntu 12.04
<ul><li>New Upstart with many appealing improvements</li></ul>
</li>
</ul>
</article>
</slide>
<slide>
<hgroup>
<h2>Current State of Business</h2>
</hgroup>
<article>
<ul>
<li>JRuby works very well and stable</li>
<li>Actors and threads benefeat us with lower latency on IO-waiting</li>
<li>No need to use background workers - instead we use actors</li>
<li>And you can try JRuby if it meets your requirements</li>
</ul>
</article>
</slide>
<slide class="thank-you-slide segue nobackground">
<article class="flexbox vleft auto-fadein">
<h2><Thank You!></h2>
</article>
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