| --- |
| title: Application-Defined and Custom Statistics |
| --- |
| |
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| <%=vars.product_name%> includes interfaces for defining and maintaining your own statistics. |
| |
| <a id="application_defined_statistics__section_88C31FA62A194947BF71AD54B5F9BAB3"></a> |
| The <%=vars.product_name%> package, `org.apache.geode`, includes the following interfaces for defining and maintaining your own statistics: |
| |
| - **StatisticDescriptor**. Describes an individual statistic. Each statistic has a name and information on the statistic it holds, such as its class type (long, int, etc.) and whether it is a counter that always increments, or a gauge that can vary in any manner. |
| - **StatisticsType**. Logical type that holds a list of `StatisticDescriptors` and provides access methods to them. The `StatisticDescriptors` contained by a `StatisticsType` are each assigned a unique ID within the list. `StatisticsType` is used to create a `Statistics` instance. |
| - **Statistics**. Instantiation of an existing `StatisticsType` object with methods for setting, incrementing, getting individual `StatisticDescriptor` values, and setting a callback which will recompute the statistic's value at configured sampling intervals. |
| - **StatisticsFactory**. Creates instances of `Statistics`. You can also use it to create instances of `StatisticDescriptor` and `StatisticsType`, because it implements `StatisticsTypeFactory`. `DistributedSystem` is an instance of `StatisticsFactory`. |
| - **StatisticsTypeFactory**. Creates instances of `StatisticDescriptor` and `StatisticsType`. |
| |
| The statistics interfaces are instantiated using statistics factory methods that are included in the package. For coding examples, see the online Java API documentation for `StatisticsFactory` and `StatisticsTypeFactory`. |
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| As an example, an application server might collect statistics on each client session in order to |
| gauge whether client requests are being processed in a satisfactory manner. Long request queues or |
| long server response times could prompt some capacity-management action such as starting additional |
| application servers. To set this up, each session-state data point is identified and defined in a |
| `StatisticDescriptor` instance. One instance might be a `RequestsInQueue` gauge, a non-negative |
| integer that increments and decrements. Another could be a `RequestCount` counter, an integer that |
| always increments. A list of these descriptors is used to instantiate a `SessionStateStats` |
| `StatisticsType`. When a client connects, the application server uses the `StatisticsType` object to |
| create a session-specific `Statistics` object. The server then uses the `Statistics` methods to |
| modify and retrieve the client’s statistics. The figures below illustrate the relationships between the |
| statistics interfaces and show the implementation of this use case. |
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| <img src="../../images/Statistics-interfaces.png" class="image" /> |
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| *The Statistics Interfaces* |
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| Each `StatisticDescriptor` contains one piece of statistical information. `StatisticalDesriptor` objects |
| are collected into a `StatisticsType`. The `StatisticsType` is instantiated to create a `Statistics` |
| object. |
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| <img src="../../images/Statistics-implementation.png" class="image" /> |
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| *Statistics Implementation* |
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| The `StatisticDescriptor` objects shown here hold three pieces of statistical information about client |
| session state. These are collected into a `SessionStateStats StatisticsType`. With this type, the |
| server creates a `Statistics` object for each client that connects. |
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