Telemetry Devices

You probably want to gain additional insights from a race. Therefore, we have added telemetry devices to Rally. If you invoke esrally list telemetry, it will show which telemetry devices are available:

dm@io:Projects/rally ‹master*›$ esrally list telemetry

    ____        ____
   / __ \____ _/ / /_  __
  / /_/ / __ `/ / / / / /
 / _, _/ /_/ / / / /_/ /
/_/ |_|\__,_/_/_/\__, /
                /____/


Available telemetry devices:

Command     Name                   Description
----------  ---------------------  -----------------------------------------------------
jit         JIT Compiler Profiler  Enables JIT compiler logs.
gc          GC log                 Enables GC logs.
jfr         Flight Recorder        Enables Java Flight Recorder (requires an Oracle JDK)
perf        perf stat              Reads CPU PMU counters (requires Linux and perf)
node-stats  Node Stats             Regularly samples node stats

Keep in mind that each telemetry device may incur a runtime overhead which can skew results.

You can attach one or more of these telemetry devices to the benchmarked cluster. Except for node-stats, this only works if Rally provisions the cluster (i.e. it does not work with --pipeline=benchmark-only).

jfr

The jfr telemetry device enables the Java Flight Recorder on the benchmark candidate. Up to JDK 11, Java flight recorder ships only with Oracle JDK, so Rally assumes that Oracle JDK is used for benchmarking. If you run benchmarks on JDK 11 or later, Java flight recorder is also available on OpenJDK.

To enable jfr, invoke Rally with esrally --telemetry jfr. jfr will then write a flight recording file which can be opened in Java Mission Control. Rally prints the location of the flight recording file on the command line.

Sample Java Flight Recording

Supported telemetry parameters:

  • recording-template: The name of a custom flight recording template. It is up to you to correctly install these recording templates on each target machine. If none is specified, the default recording template of Java flight recorder is used.

Note

Up to JDK 11 Java flight recorder ship only with Oracle JDK and the licensing terms do not allow you to run it in production environments without a valid license (for details, refer to the Oracle Java SE Advanced & Suite Products page). However, running in a QA environment is fine.

jit

The jit telemetry device enables JIT compiler logs for the benchmark candidate. If the HotSpot disassembler library is available, the logs will also contain the disassembled JIT compiler output which can be used for low-level analysis. We recommend to use JITWatch for analysis.

hsdis can be built for JDK 8 on Linux with (based on a description by Alex Blewitt):

curl -O -O -O -O https://raw.githubusercontent.com/dmlloyd/openjdk/jdk8u/jdk8u/hotspot/src/share/tools/hsdis/{hsdis.c,hsdis.h,Makefile,README}
mkdir -p build/binutils
curl http://ftp.gnu.org/gnu/binutils/binutils-2.27.tar.gz | tar --strip-components=1 -C build/binutils -z -x -f -
make BINUTILS=build/binutils ARCH=amd64

After it has been built, the binary needs to be copied to the JDK directory (see README of hsdis for details).

gc

The gc telemetry device enables GC logs for the benchmark candidate. You can use tools like GCViewer to analyze the GC logs.

perf

The perf telemetry device runs perf stat on each benchmarked node and writes the output to a log file. It can be used to capture low-level CPU statistics. Note that the perf tool, which is only available on Linux, must be installed before using this telemetry device.

node-stats

Warning

Using this telemetry device will skew your results because the node-stats API triggers additional refreshes. Additionally a lot of metrics get recorded impacting the measurement results even further.

The node-stats telemetry devices regularly calls the cluster node-stats API and records metrics from the following sections:

  • Indices stats (key indices in the node-stats API)
  • Thread pool stats (key jvm.thread_pool in the node-stats API)
  • JVM buffer pool stats (key jvm.buffer_pools in the node-stats API)
  • Circuit breaker stats (key breakers in the node-stats API)
  • Network-related stats (key transport in the node-stats API)
  • Process cpu stats (key process.cpu in the node-stats API)

Supported telemetry parameters:

  • node-stats-sample-interval (default: 1): A positive number greater than zero denoting the sampling interval in seconds.

  • node-stats-include-indices (default: false): A boolean indicating whether indices stats should be included.

  • node-stats-include-indices-metrics (default: docs,store,indexing,search,merges,query_cache,fielddata,segments,translog,request_cache): A comma-separated string specifying the Indices stats metrics to include. This is useful, for example, to restrict the collected Indices stats metrics. Specifying this parameter implicitly enables collection of Indices stats, so you don’t also need to specify node-stats-include-indices: true.

    Example: --telemetry-params="node-stats-include-indices-metrics:'docs'" will only collect the docs metrics from Indices stats. If you want to use multiple fields, pass a JSON file to telemetry-params (see the command line reference for details).

  • node-stats-include-thread-pools (default: true): A boolean indicating whether thread pool stats should be included.

  • node-stats-include-buffer-pools (default: true): A boolean indicating whether buffer pool stats should be included.

  • node-stats-include-breakers (default: true): A boolean indicating whether circuit breaker stats should be included.

  • node-stats-include-mem (default: true): A boolean indicating whether JVM heap stats should be included.

  • node-stats-include-network (default: true): A boolean indicating whether network-related stats should be included.

  • node-stats-include-process (default: true): A boolean indicating whether process cpu stats should be included.