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<chapter>
  <header>
    <copyright>
      <year>2011</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
      Erlang Public License along with this software. If not, it can be
      retrieved online at http://www.erlang.org/.

      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
      the License for the specific language governing rights and limitations
      under the License.

    </legalnotice>

    <title>Observer</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
    <file>observer_ug.xml</file>
  </header>

  <section>
    <title>Introduction</title>
    <p>Observer, is a graphical tool for observing the characteristics of
    erlang systems.  Observer displays system information, application
    supervisor trees, process information, ets or mnesia tables and contains
    a frontend for erlang tracing.
    </p>
  </section>

  <section>
    <title>General</title>
    <p>Normally observer should be run from a standalone node to minimize
    the impact of the system being observed. Example:
    </p>
    <code>
 > erl -sname observer -hidden -setcookie MyCookie -run observer
    </code>
    <p>
      Choose which node to observe via <c>Nodes</c> menu. The <c>View/Refresh
      Interval</c> controls how frequent the view should be updated.
      The refresh interval is set per viewer so you can
      have different settings for each viewer. To minimize the system
      impact only the active viewer is updated and the other
      views will be updated when activated.
    </p>
    <note>
      <p>Only R15B nodes can be observed.</p>
    </note>

    <p> In general the mouse buttons behaves as expected, use left click
    to select objects, right click to pop up a menu with most used
    choices and double click to bring up information about the
    selected object. In most viewers with several columns you can change
    sort order by left clicking on column header.
    </p>
  </section>

  <section>
    <title>Applications</title>
    <p>The <c>Applications</c> view lists application information.
    Select an application in the left list to display its supervisor
    tree.
    </p>
    <p><c>Trace process</c> will add the selected process identifier
    to <c>Trace Overview</c> view and the node the process resides on
    will be added as well.
    </p>
    <p><c>Trace named process</c> will add the
    registered name of the process. This can be useful when tracing on
    several nodes, then processes with that name will be traced on all traced
    nodes.
    </p>
    <p><c>Trace process tree</c> and <c>Trace named process
    tree</c> will add the selected process and all processes below,
    right of, it to  the <c>Trace Overview</c> view.
    </p>
  </section>

  <section>
    <title>Processes</title>
    <p>The <c>Processes</c> view lists process information.
    For each process the following information is presented:
    </p>
    <taglist>
      <tag>Pid</tag>
      <item>The process identifier.</item>
      <tag>Reds</tag>
      <item>This is the number of reductions that has been executed
       on the process</item>
      <tag>Memory</tag>
      <item>This is the size of the process in bytes, obtained by a
       call to <c>process_info(Pid,memory)</c>.</item>
      <tag>MsgQ</tag>
      <item>This is the length of the message queue for the process.</item>
    </taglist>
    <note>
      <p><em>Reds</em> can be presented as accumulated values or as values since last update.</p>
    </note>
    <p><c>Trace Processes</c> will add the selected process identifiers to the <c>Trace Overview</c> view and the
    node the processes reside on will be added as well.
    <c>Trace Named Processes</c> will add the registered name of processes. This can be useful
    when tracing is done on several nodes, then processes with that name will be traced on all traced nodes.
    </p>
  </section>

  <section>
    <title>Table Viewer</title>
    <p>The <c>Table Viewer</c> view lists tables. By default ets tables
    are visible and unreadable, private ets, tables and tables created by the OTP
    applications are not visible.  Use <c>View</c> menu to view "system"
    ets tables, unreadable ets tables or mnesia tables.
    </p>
    <p>Double click to view the content of the table. Select table and activate <c>View/Table Information</c>
    menu to view table information.
    </p>
    <p>In the table viewer you can regexp search for objects, edit and delete objects.
    </p>
  </section>

  <section>
    <title>Trace Overview</title>
    <p>The <c>Trace Overview</c> view handles tracing. Tracing is done
    by selecting which processes to be traced and how to trace
    them. You can trace messages, function calls and events, where
    events are process related events such as <c>spawn</c>,
    <c>exit</c> and several others.
    </p>

    <p>When you want to trace function calls, you also need to setup
    <c>trace patterns</c>.  Trace patterns selects the function calls
    that will be traced. The number of traced function calls can be
    further reduced with <c>match specifications</c>.  Match
    specifications can also be used to trigger additional information
    in the trace messages.
    </p>
    <note><p>Trace patterns only applies to the traced processes.</p></note>

    <p>
      Processes are added from the <c>Applications</c> or <c>Processes</c> views.
      A special <c>new</c> identifier, meaning all processes spawned after trace start,
      can be added with the <c>Add 'new' Process</c> button.
    </p>
    <p>
      When adding processes, a window with trace options will pop up. The chosen options will
      be set for the selected processes.
      Process options can be changed by right clicking on a process.
    </p>
    <p>
      Processes added by process identifiers will add the nodes these
      processes resides on in the node list. Additional nodes can be added by the <c>Add
      Nodes</c> button.
    </p>
    <p>
      If function calls are traced, trace patterns must be added by <c>Add Trace Pattern</c> button.
      Select a module, function(s) and a match specification.
      If no functions are selected, all functions in the module will be traced.
      A few basic match specifications are provided in the tool, and
      you can provide your own match specifications. The syntax of match
      specifications are described in the <seealso
      marker="erts:match_spec">ERTS User's Guide</seealso>.  To simplify
      the writing of a match specification they can also be written as
      <c>fun/1</c> see <seealso marker="stdlib:ms_transform">ms_transform manual page</seealso> for
      further information.
    </p>

    <p>Use the <c>Start trace</c> button to start the trace.
    By default trace output is written to a new window, tracing is stopped when the
    window is closed, or with <c>Stop Trace</c> button.
    Trace output can be changed via <c>Options/Output</c> menu.
    The trace settings, including match specifications, can be saved to, or loaded from, a file.
    </p>
    <p>More information about tracing can be found in <seealso
    marker="runtime_tools:dbg">dbg</seealso> and in the chapter "Match
    specifications in Erlang" in <seealso marker="erts:match_spec">ERTS User's
    Guide</seealso> and the
    <seealso marker="stdlib:ms_transform">ms_transform manual page</seealso>.
    </p>
  </section>
</chapter>
