===================== Decoding Stack Traces

Topic: Decoding stack traces in ScyllaDB logs

Environment: Any ScyllaDB setup on any supported OS

Audience: All

Synopsis

This article describes how to decode the stack traces found in ScyllaDB logs.

What are Stack Traces?

Stack traces can appear in the logs due to various errors or in the course of regular database operation. It is useful to be able to decode the trace in order to understand what exactly happened. Decoding the stack trace requires the Debug binaries for the specific ScyllaDB build and OS in use are installed.

Note that sharing the stack trace as part of your support ticket or Github issue, helps the ScyllaDB support team to understand the issue better.

Install Debug Binary files

Install the Debug binaries according to your OS distribution

.. tabs::

.. group-tab:: RPM based distributions

  .. code-block:: none

     yum install scylla-debuginfo

.. group-tab:: DEB based distributions

  .. code-block:: none

     apt-get install scylla-server-dbg

Validate the debug binary file name

To later determine the actual debug binary, look in the /usr/lib/debug/ directory for a file named scylla.debug.

For example:

.. code-block:: none

find /usr/lib/debug/ | grep scylla.debug

/usr/lib/debug/usr/bin/scylla.debug

Locate and Analyze the Logs

Procedure

#. Copy the stack from the :doc:system log </getting-started/logging> and place it in a file (trace.txt, for example).

.. code-block:: none

  Jul 14 16:56:50 hostname01 scylla: Aborting on shard 8.
  Jul 14 16:56:50 hostname01 scylla: Backtrace:
  Jul 14 16:56:50 hostname01 scylla: 0x0000000000688602
  Jul 14 16:56:50 hostname01 scylla: 0x00000000005a36fc
  Jul 14 16:56:50 hostname01 scylla: 0x00000000005a39a5
  Jul 14 16:56:50 hostname01 scylla: 0x00000000005a3a53
  Jul 14 16:56:50 hostname01 scylla: /lib64/libpthread.so.0+0x000000000000f6cf
  Jul 14 16:56:50 hostname01 scylla: /lib64/libc.so.6+0x0000000000036276
  Jul 14 16:56:50 hostname01 scylla: /lib64/libc.so.6+0x0000000000037967
  Jul 14 16:56:50 hostname01 scylla: 0x00000000024ce37b
  Jul 14 16:56:50 hostname01 scylla: 0x00000000024d2a47
  Jul 14 16:56:50 hostname01 scylla: 0x00000000024df1d5
  Jul 14 16:56:50 hostname01 scylla: 0x00000000023dccec
  Jul 14 16:56:50 hostname01 scylla: 0x00000000023feac1
  Jul 14 16:56:50 hostname01 scylla: 0x00000000024324b9
  Jul 14 16:56:50 hostname01 scylla: 0x00000000024357e4
  Jul 14 16:56:50 hostname01 scylla: 0x0000000001eace90
  Jul 14 16:56:50 hostname01 scylla: 0x0000000001eaf944
  Jul 14 16:56:50 hostname01 scylla: 0x0000000000584ab6
  Jul 14 16:56:50 hostname01 scylla: 0x0000000000584c71
  Jul 14 16:56:50 hostname01 scylla: 0x00000000006522ff
  Jul 14 16:56:50 hostname01 scylla: 0x00000000006554e5
  Jul 14 16:56:50 hostname01 scylla: 0x000000000073d3cd
  Jul 14 16:56:50 hostname01 scylla: /lib64/libpthread.so.0+0x0000000000007e24
  Jul 14 16:56:50 hostname01 scylla: /lib64/libc.so.6+0x00000000000febac

#. Locate the files for backtrace.

.. code-block:: shell

  find . -name "scylla*.debug"

With ScyllaDB 4.1 for example, returns:

.. code-block:: shell

  /usr/lib/debug/opt/scylladb/libexec/scylla-4.1.1-0.20200703.1d9bbbc9577.x86_64.debug

#. Run the decoder:

.. code-block:: none

  ./seastar-addr2line -e /usr/lib/debug/usr/bin/scylla.debug -f trace.txt > trace_decoded.txt

trace_decoded.txt now contains the decoded version of the stack trace:

For example:

.. code-block:: none

  void seastar::backtrace<seastar::backtrace_buffer::append_backtrace()::{lambda(seastar::frame)#1}>(seastar::backtrace_buffer::append_backtrace()::{lambda(seastar::frame)#1}&&) at /usr/src/debug/scylla-4.1.1/seastar/util/backtrace.hh:56
  seastar::backtrace_buffer::append_backtrace() at /usr/src/debug/scylla-4.1.1/seastar/core/reactor.cc:390
  (inlined by) print_with_backtrace at /usr/src/debug/scylla-4.1.1/seastar/core/reactor.cc:411
  seastar::print_with_backtrace(char const*) at /usr/src/debug/scylla-4.1.1/seastar/core/reactor.cc:418
  sigabrt_action at /usr/src/debug/scylla-4.1.1/seastar/core/reactor.cc:3939
   (inlined by) operator() at /usr/src/debug/scylla-4.1.1/seastar/core/reactor.cc:3921
   (inlined by) _FUN at /usr/src/debug/scylla-4.1.1/seastar/core/reactor.cc:3917
  ...

  seastar::reactor::run_tasks(seastar::reactor::task_queue&) at /usr/src/debug/scylla-4.1.1/seastar/core/reactor.cc:2621
  seastar::reactor::run_some_tasks() at /usr/src/debug/scylla-4.1.1/seastar/core/reactor.cc:3033
  seastar::reactor::run_some_tasks() at /opt/scylladb/include/c++/7/chrono:377
   (inlined by) seastar::reactor::run() at /usr/src/debug/scylla-4.1.1/seastar/core/reactor.cc:3180