Chapter 3. Logging
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## Chapter 3. Logging

Logging is an important means of gaining insight into your application's runtime behavior. Kodo provides a flexible logging system that integrates with many existing runtime systems, such as application servers and servlet runners.

There are four built-in logging plugins: a default logging framework that covers most needs, a Log4J delegate, an Apache Commons Logging delegate, and a no-op implementation for disabling logging.

| Warning
Logging can have a negative impact on performance. Disable verbose logging (such as logging of SQL statements) before running any performance tests. It is advisable to limit or disable logging for a production system. You can disable logging altogether by setting the `kodo.Log` property to `none`.

## 3.1. Logging Channels

Logging is done over a number of logging channels, each of which has a logging level which controls the verbosity of log messages recorded for the channel. Kodo uses the following logging channels:

- `kodo.Tool`: Messages issued by the Kodo command line and Ant tools. Most messages are basic statements detailing which classes or files the tools are running on. Detailed output is only available via the logging category the tool belongs to, such as `kodo.Enhance` for the enhancer (see Section 5.2, “Enhancement”) or `kodo.MetaData` for the mapping tool (see Section 7.1, “Forward Mapping”). This logging category is provided so that you can get a general idea of what a tool is doing without having to manipulate logging settings that might also affect runtime behavior.

- `kodo.Configuration`: Messages issued by the configuration framework.

- `kodo.Enhance`: Messages pertaining to enhancement and runtime class generation.

- `kodo.MetaData`: Details about the generation of metadata and object-relational mappings.

- `kodo.Runtime`: General Kodo runtime messages.

- `kodo.Query`: Messages about queries. Query strings and any parameter values, if applicable, will be logged to the `TRACE` level at execution time. Information about possible performance concerns will be logged to the `INFO` level.

- `kodo.Remote`: Remote connection and execution messages.

- `kodo.DataCache`: Messages from the L2 data cache plugins.

- `kodo.jdbc.JDBC`: JDBC connection information. General JDBC information will be logged to the `TRACE` level. Information about possible performance concerns will be logged to the `INFO` level.

- `kodo.jdbc.SQL`: This is the most common logging channel to use. Detailed information about the execution of SQL statements will be sent to the `TRACE` level. It is useful to enable this channel if you are curious about the exact SQL that Kodo issues to the datastore.

  When using the built-in Kodo logging facilities, you can enable SQL logging by adding `SQL=TRACE` to your `kodo.Log` property.

  Kodo can optionally reformat the logged SQL to make it easier to read. To enable pretty-printing, add `PrettyPrint=true` to the `kodo.ConnectionFactoryProperties` property. You can control how many columns wide the pretty-printed SQL will be with the `PrettyPrintLineLength` property. The default line length is 60 columns.

  While pretty printing makes things easier to read, it can make output harder to process with tools like grep.

  Pretty-printing properties configuration might look like so:

  JPA XML format:

      <property name="kodo.Log" value="SQL=TRACE"/>
      <property name="kodo.ConnectionFactoryProperties"
          value="MaxActive=100, PrettyPrint=true, PrettyPrintLineLength=72"/>

  JDO properties format:

      kodo.Log: SQL=TRACE
      kodo.ConnectionFactoryProperties: MaxActive=100, PrettyPrint=true, PrettyPrintLineLength=72

- `kodo.jdbc.Schema`: Details about operations on the database schema.

- `kodo.Manage`: JMX and management-related logging channel.

- `kodo.Profile`: Information related to Kodo's profiling framework.

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