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Note: Content on this page is subject to revision. For the most recent jHiccup documentation, please review the readme file included with the current jHiccup distribution.

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Using jHiccup
Supported/Tested Platforms
Running jHiccup
Reading and processing the jHiccup log with jHiccupLogProcessor
Using jHiccup to process latency log files
Hiccup charts
Using a control process

jHiccup is a widely-used open source tool from Azul Systems. jHiccup collects data to identify the frequency and duration of pause times (hiccups) that occur while a JVM runs a Java application. jHiccup works with any JVM, on any platfrom. Comparing this data with your overall Java application pause time performance helps isolate where your pause times are generated, so you can maximize solutions to reduce your Java application pause time.

jHiccup is issued as an addition to your JVM-Java application initiating command. It runs in the background for the duration of your active Java application. At regular reporting intervals, jHiccup saves data into two files. At any point during the running or after the Java application terminates, you can view the files directly or use the included Excel utility to view tracking charts created using the collected data.

jHiccup can be executed in one of three main ways:

  1. It can be run as a Java agent (using: java -javaagent=jHiccup.jar)
  2. It can be injected into a running application (using: jHiccup -p <pid>)
  3. It can also be run using a convenient wrapper command for your existing java application (using: jHiccup java myProg …)


Using jHiccup

1.   Using jHiccup as a Java agent:

jHiccup is most often used as a java agent. this is useful for platforms and environments where a java agent is simpler to integrate into launch scripts, or in environments where using the bash jHiccup wrapper script is not practical (e.g. Windows, and environments where java is not directly launched from the command line).

jHiccup.jar can be used as a java agent using the following launch syntax:

% java -javaagent:jHiccup.jar MyProgram


% java -javaagent:jHiccup.jar="<options>" MyProgram.jar -a -b -c

You can find the available options for the Java agent mode by running:

% java -javaagent:jHiccup.jar="-h"

Here is a Java agent usage example with explicit parameters:

% java -javaagent:jHiccup.jar="-d 0 -i 1000 -l hiccuplog -c" MyProgram.jar -a -b -c

This example will record hiccups experienced during the running of MyProgram.jar in log file hiccuplog, while at the same time recording the hiccups experienced by a control process running in a separate JVM in the log file c.hiccuplog. Measurement will start immediately upon startups (rather than the 30 second default delay), and interval data will be records every 1 second (rather than the default 5 seconds).

Useful java agent related notes:

Note 1: When used as a java agent, jHiccup will treat spaces, commas, and semicolons as delimiting characters ([ ,;]+). For example, the option string “-d 0 -i 1000” is equivalent to the option string “-d,0,-i,1000”. This is useful for environments where placing space delimiters into quoted strings is difficult or confusing.

Note 2: I find that a common way people add jHiccup as a java agent is by using the _JAVA_OPTIONS environment variable. This often allows one to add the jHiccup  java agent without significant launch script surgery. For example:

export _JAVA_OPTIONS='-javaagent:/path/to/jHiccup/target/jHiccup.jar="-d 20000 -i 1000"'

2.   Launching jHiccup by attaching it to an existing, running application:

The jHiccup agent can be injected into a live, running Java application if the environment supports the java attach API (which is typically available in java environments running Java SE 6 or later).

$ jHiccup -p <pid>

NOTE: In order to attach to a running java application, the running application needs to have ${JAVA_HOME}/lib/tools.jar in it’s classpath. While this is commonly the case already for many IDE and desktop environments, and for environments that involve or enable other attachable agents (such as profilers), you may find that it is not included in your application’s classpath, and that it needs to be added if attaching jHiccup at runtime is needed (launching jHiccup as a Java agent per the below may be a good alternative).

3.   Running jHiccup using the Wrapper Script form:

In the wrapper script form, all it takes is adding the word “jHiccup” in front of whatever the java invocation command line is. For example, if your program were normally executed as:

java MyProgram -a -b -c

The launch line would become:

jHiccup java MyProgram -a -b -c

or, for a program launched with:

/usr/bin/java -jar MyProgram.jar -a -b -c

The launch line would become:

jHiccup /usr/bin/java -jar MyProgram.jar -a -b -c

or, to override the defaults by making the recording start delay 60 seconds and log to hlog, it would become:

jHiccup -d 60000 -l hlog /usr/bin/java -jar MyProgram.jar -a -b -c

The jar file also includes a simple “Idle” class to facilitate sanity checks without an external program. Here is a simple sanity test example: jHiccup with a 4 sec delay on recording start, wrapping an Idle run that does nothing for 30 seconds and exits: % jHiccup -d 4000 /usr/bin/java org.jhiccup.Idle -t 30000 [Run jHiccup -h, or see comment in jHiccup script for more details.]

Supported/Tested Platforms

The jHiccup command is expected to work and has been tested on the following platforms:

  • Various Linux flavors (Tested on RHEL/CentOS 5.x and 6.x)
  • Mac OS X (tested on Lion, 10.7)
  • Windows with a Cygwin environment installed (tested on Windows 7)
  • Solaris (tested on both SPARC and x86)

jHiccup.jar is expected to work as a java agent and has been tested on the following platforms:

  • Various Linux flavors (Tested on RHEL/CentOS 5.x and 6.x)
  • Mac OS X (tested on Lion, 10.7)
  • Windows standard command shell (tested on Windows 7)
  • Solaris (tested on both SPARC and x86)

If you use jHiccup on other operating systems and setups, please report back on your experience so that we can expand the list.


Reading and processing the jHiccup log with jHiccupLogProcessor

jHiccup logs hiccup information in a histogram log (see HdrHistogram.org). This histogram log contains a full, high fidelity histogram of all collected result sin each interval, in a highly compressed form (typically using only ~200-400 bytes per interval). However, other than the timestamp and maximum hiccup magnitude found in the given interval, the rest of the log line for each interval is not human readable (it is a base64 encoding of a compressed HdrHistogram).

To translate the jHiccup log file to a more human-readable form (identical to the form that jHiccup versions before jHiccup 2.0 had used), the jHiccupLogProcessor utility is provided. In it’s simplest form, this utility can be used as such:

% jHiccupLogProcessor -i mylog.hlog -o mylog

Which will produce log file mylog and mylog.hgrm containing a human readable interval log (with selcted percentiles in each interval), as well as a human readable histogram percentile distribution log.

jHiccupLogProcessor can also be used to produce log files for an arbitrary section of the jHiccup log, by using the optional -start and -end parameters.

See jHiccupLogProcessor -h for more details.

Log file name recognizes and fills in %pid and %date terms

When a log file name is specified with the -l option, the terms %pid and %date will be filled in with the appropriate information. The default log file name setting is simply hiccup.%date.%pid.


Using jHiccup to process latency log files

jHiccup’s HiccupMeter class supports a mode (-f) that will take latency input from a file instead of recording it. This is useful for producing jHiccup-style text and graphical output for recorded latency data collected by some other means.

When provided to the -f option, an input file is expected to contain two white-space delimited values per line (in either integer or real number format), representing a time stamp and a measured latency, both in millisecond units.

It’s important to note that the default “expected interval between samples” resolution in jHiccup and HiccupMeter is 1 millisecond. When processing input files, it is imperative that an appropriate value be supplied to the -r option, and that this value correctly represent the expected interval between samples in the provided input file. HiccupMeter will use this parameter to determine whether additional, artificial values should be added to the histogram recording, between input samples that are farther apart in time than the expected interval specified to the -r option. This behavior corrects for “coordinated omission” situations (where long response times lead to “skipped” requests that would have typically correlated with “bad” response times). A “large” value (e.g. -r 100000) can easily be specified to avoid any correction of this situation.

Example: adding jHiccup to Tomcat runs:

In Tomcat’s catalina.sh script, replace the following line:





Hiccup Charts

Plotting jHiccup results

A jHiccupPlotter.xls Excel spreadsheet is included to conveniently plot jHiccup log files produced by jHiccupLogProcessor in “Hiccup Chart” form. To use the spreadsheet, load it into Excel, (make sure to enable macros), and follow the 2-step instructions in the main menu worksheet to automatically import the log files and produce the Hiccup Chart.

Note that jHiccupPlotter.xls reads the log files produced by jHiccupLogProcessor, (the interval log and the .hgrm histogram percentile distribution log), and not the .hlog log format that jHiccup outputs directly.


Using a Control Process to Concurrently Record Baseline Idle Load Hiccups

It is often useful to compare the hiccup behavior experienced by a running application with a “control” hiccup level of an idle workload, running on the same system and at the same time as the observed application. To make such control measurement convenient, jHiccup supports a “-c” option that will launch a concurrently executing “control process” and will separately log hiccup information of an idle workload running on a separate jvm for the duration of the instrumented application run. When selected, the control process log file name will match those used for the launching application, followed with a “.c”.

For example:

% jHiccup -l mylog -c /usr/bin/java <Java args> -jar MyProgram.jar -a -b -c

Will produce log file mylog detailing the hiccup behavior during the execution of MyProgram.jar, as well as a log file c.mylog detailing the hiccup behavior of an idle workload running on a separate JVM at the same time.


Note: Use of HdrHistogram

jHiccup depends on and makes systemic use of HdrHistogram to collected and report on the statistical distribution of hiccups. This package includes an HdrHistogram.jar jar file to support this functionality. HdrHistogram sources, documentation, and a ready to use jar file can all be found on GitHub, at http://giltene.github.com/HdrHistogram.

Building jHiccup

jHiccup can be (re)built from source files using Maven:

% mvn package

This file was modified by IntelliJ IDEA 12.1.6 for binding GitHub repository.

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