Adding Statistics
*****************

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This chapter describes how to add statistics to your plugins. Statistics
can be coupled or uncoupled; **coupled** statistics are quantities that
are related and must therefore be updated together. The Traffic Server
API statistics functions add your plugin's statistics to the Traffic
Server statistics system. You can view your plugin statistics as you
would any other Traffic Server statistic, using Traffic Line (Traffic
Server's command line interface). This chapter contains the following
topics:

.. toctree::
   :maxdepth: 2

   adding-statistics/coupled-statistics.en
   adding-statistics/viewing-statistics-using-traffic-line.en


Uncoupled Statistics
--------------------

A statistic is an object of type ``TSStat``. The value of the statistic
is of type ``TSStatType``. The possible ``TSStatTypes`` are:

-  ``TSSTAT_TYPE_INT64``

-  ``TSSTAT_TYPE_FLOAT``

There is *no* ``TSSTAT_TYPE_INT32``.

To add uncoupled statistics, follow the steps below:

1. Declare your statistic as a global variable in your plugin. For
   example:

   .. code-block:: c

      static TSStat my_statistic;

2. In ``TSPluginInit``, create new statistics using ``TSStatCreate``.
   When you create a new statistic, you need to give it an "external"
   name that the Traffic Server command line interface (Traffic Line)
   uses to access the statistic. For example:

   .. code-block:: c

      my_statistic = TSStatCreate ("my.statistic", TSSTAT_TYPE_INT64);

3. Modify (increment, decrement, or other modification) your statistic
   in plugin functions.