[[ml-configuring-categories]]
=== Categorizing log messages

Application log events are often unstructured and contain variable data. For
example:
//Obtained from it_ops_new_app_logs.json
[source,js]
----------------------------------
{"time":1454516381000,"message":"org.jdbi.v2.exceptions.UnableToExecuteStatementException: com.mysql.jdbc.exceptions.MySQLTimeoutException: Statement cancelled due to timeout or client request [statement:\"SELECT id, customer_id, name, force_disabled, enabled FROM customers\"]","type":"logs"}
----------------------------------
//NOTCONSOLE

You can use {ml} to observe the static parts of the message, cluster similar
messages together, and classify them into message categories.

NOTE: Categorization uses English tokenization rules and dictionary words in
order to identify log message categories. As such, only English language log
messages are supported.

The {ml} model learns what volume and pattern is normal for each category over
time. You can then detect anomalies and surface rare events or unusual types of
messages by using count or rare functions. For example:

//Obtained from it_ops_new_app_logs.sh
[source,js]
----------------------------------
PUT _xpack/ml/anomaly_detectors/it_ops_new_logs
{
  "description" : "IT Ops Application Logs",
  "analysis_config" : {
    "categorization_field_name": "message", <1>
    "bucket_span":"30m",
    "detectors" :[{
      "function":"count",
      "by_field_name": "mlcategory", <2>
      "detector_description": "Unusual message counts"
    }],
    "categorization_filters":[ "\\[statement:.*\\]"]
  },
  "analysis_limits":{
    "categorization_examples_limit": 5
  },
  "data_description" : {
    "time_field":"time",
    "time_format": "epoch_ms"
  }
}
----------------------------------
//CONSOLE
<1> The `categorization_field_name` property indicates which field will be
categorized.
<2> The resulting categories are used in a detector by setting `by_field_name`,
`over_field_name`, or `partition_field_name` to the keyword `mlcategory`. If you
do not specify this keyword in one of those properties, the API request fails.

The optional `categorization_examples_limit` property specifies the
maximum number of examples that are stored in memory and in the results data
store for each category. The default value is `4`. Note that this setting does
not affect the categorization; it just affects the list of visible examples. If
you increase this value, more examples are available, but you must have more
storage available. If you set this value to `0`, no examples are stored.

The optional `categorization_filters` property can contain an array of regular
expressions. If a categorization field value matches the regular expression, the
portion of the field that is matched is not taken into consideration when
defining categories. The categorization filters are applied in the order they
are listed in the job configuration, which allows you to disregard multiple
sections of the categorization field value. In this example, we have decided that
we do not want the detailed SQL to be considered in the message categorization.
This particular categorization filter removes the SQL statement from the categorization
algorithm.

If your data is stored in {es}, you can create an advanced job with these same
properties:

[role="screenshot"]
image::images/ml-category-advanced.jpg["Advanced job configuration options related to categorization"]

NOTE: To add the `categorization_examples_limit` property, you must use the
**Edit JSON** tab and copy the `analysis_limits` object from the API example.


After you open the job and start the {dfeed} or supply data to the job, you can
view the results in {kib}. For example:

[role="screenshot"]
image::images/ml-category-anomalies.jpg["Categorization example in the Anomaly Explorer"]

For this type of job, the **Anomaly Explorer** contains extra information for
each anomaly: the name of the category (for example, `mlcategory 11`) and
examples of the messages in that category. In this case, you can use these
details to investigate occurrences of unusually high message counts for specific
message categories.