Troubleshooting the Ruby Profiler

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Missing profiles in the profile search page

If you’ve configured the profiler and don’t see profiles in the profile search page, turn on debug mode and open a support ticket with debug files and the following information:

Operating system type and version (for example, Ubuntu Linux 22.04)
Runtime type, version, and vendor (for example, Ruby 2.7.3)

Missing profiles for Resque jobs

When profiling Resque jobs, you should set the RUN_AT_EXIT_HOOKS environment variable to 1, as described in the Resque documentation.

Without this flag, profiles for short-lived Resque jobs will be unavailable.

Profiling does not turn on because compilation of the Ruby VM just-in-time header failed

There is a known incompatibility between Ruby 2.7 and older GCC versions (4.8 and below) that impacts the profiler (upstream Ruby report, dd-trace-rb bug report). This can result in the following error message: “Your ddtrace installation is missing support for the Continuous Profiler because compilation of the Ruby VM just-in-time header failed. Your C compiler or Ruby VM just-in-time compiler seem to be broken.”

To fix this, update your operating system or Docker image so that the GCC version is something more recent than v4.8.

For further help with this issue, contact support and include the output of running DD_PROFILING_FAIL_INSTALL_IF_MISSING_EXTENSION=true gem install ddtrace and the resulting mkmf.log file.

Frames omitted when backtraces are very deep

The Ruby profiler truncates deep backtraces when collecting profiling data. Truncated backtraces are missing some of their caller functions, making it impossible to link them to the root call frame. As a result, truncated backtraces are grouped together under a N frames omitted frame.

You can increase the maximum depth with the DD_PROFILING_MAX_FRAMES environment variable, or in code:

Datadog.configure do |c|
  c.profiling.advanced.max_frames = 500
end

Unexpected failures or errors from Ruby gems that use native extensions in `dd-trace-rb` 1.11.0+

Starting from dd-trace-rb 1.11.0, the “CPU Profiling 2.0” profiler gathers data by sending SIGPROF unix signals to Ruby applications, enabling finer-grained data gathering.

Sending SIGPROF is a common profiling approach, and may cause system calls from native extensions/libraries to be interrupted with a system EINTR error code. Rarely, native extensions or libraries called by them may have missing or incorrect error handling for the EINTR error code.

The following incompatibilities are known:

Using the mysql2 gem together with versions of libmysqlclient older than 8.0.0. The affected libmysqlclient version is known to be present on Ubuntu 18.04, but not 20.04 or later releases.
Using the rugged gem.
Using the passenger gem/Phusion Passenger web server older than 6.0.19

In these cases, the latest version of the profiler automatically detects the incompatibility and applies a workaround.

If you encounter failures or errors from Ruby gems that use native extensions other than those listed above, you can manually enable the “no signals” workaround, which avoids the use of SIGPROF signals. To enable this workaround, set the DD_PROFILING_NO_SIGNALS_WORKAROUND_ENABLED environment variable to true, or in code:

Datadog.configure do |c|
  c.profiling.advanced.no_signals_workaround_enabled = true
end

Note: The above setting is only available starting in dd-trace-rb 1.12.0.

Let our team know if you find or suspect any incompatibilities by opening a support ticket. Doing this enables Datadog to add them to the auto-detection list, and to work with the gem/library authors to fix the issue.

Segmentation faults in `gc_finalize_deferred` in Ruby versions 2.6 to 3.2

A workaround for this issue is automatically applied since dd-trace-rb version 1.21.0. Datadog recommends upgrading to this version or later to fix this issue.

Prior to version 1.21.0, in rare situations the profiler could trigger Ruby VM Bug #19991 that manifests itself as a “Segmentation fault” with a crash stack trace including the gc_finalize_deferred function.

This bug has been fixed for Ruby 3.3 and above. For older Ruby versions (and prior to dd-trace-rb 1.21.0), you can use the “no signals” workaround to resolve this issue.

To enable this workaround, set the DD_PROFILING_NO_SIGNALS_WORKAROUND_ENABLED environment variable to true, or in code:

Datadog.configure do |c|
  c.profiling.advanced.no_signals_workaround_enabled = true
end