# Statistics

## Statistics Overview

Both Kea DHCP servers support statistics gathering. A working DHCP server encounters various events that can cause certain statistics to be collected. For example, a DHCPv4 server may receive a packet (pkt4-received statistic increases by one) that after parsing was identified as a DHCPDISCOVER (pkt4-discover-received). The Server processed it and decided to send a DHCPOFFER representing its answer (pkt4-offer-sent and pkt4-sent statistics increase by one). Such events happen frequently, so it is not uncommon for the statistics to have values in high thousands. They can serve as an easy and powerful tool for observing a server's and network's health. For example, if pkt4-received statistic stops growing, it means that the clients' packets are not reaching the server.

There are four types of statistics:

- integer - this is the most common type. It is implemented as 64 bit integer (int64_t in C++), so it can hold any value between -2^63 to 2^63 -1.

- floating point - this type is intended to store floating point precision. It is implemented as double C++ type.

- duration - this type is intended for recording time periods. It uses boost::posix_time::time_duration type, which stores hours, minutes, seconds and microseconds.

- string - this type is intended for recording statistics in textual form. It uses std::string C++ type.

During normal operation, DHCPv4 and DHCPv6 servers gather statistics. For a list of DHCPv4 and DHCPv6 statistics, see and , respectively.

To extract data from the statistics module, the control channel can be used. See for details. It is possible to retrieve a single or all statistics, reset statistics (i.e. set to neutral value, typically zero) or even remove completely a single or all statistics. See section for a list of statistic oriented commands.

## Statistics Lifecycle

It is useful to understand how the Statistics Manager module works. When the server starts operation, the manager is empty and does not have any statistics. When `statistic-get-all` is executed, an empty list is returned. Once the server performs an operation that causes a statistic to change, the related statistic will be created. In the general case, once a statistic is recorded even once, it is kept in the manager, until explicitly removed, by `statistic-remove` or `statistic-remove-all` being called or the server is shut down. Per subnet statistics are explicitly removed when reconfiguration takes place.

Statistics are considered run-time properties, so they are not retained after server restart.

Removing a statistic that is updated frequently makes little sense as it will be re-added when the server code next records that statistic. The `statistic-remove` and `statistic-remove-all` commands are intended to remove statistics that are not expected to be observed in the near future. For example, a misconfigured device in a network may cause clients to report duplicate addresses, so the server will report increasing values of pkt4-decline-received. Once the problem is found and the device is removed, the system administrator may want to remove the pkt4-decline-received statistic, so it won't be reported anymore. If a duplicate address is detected ever again, the server will add this statistic back.

## Commands for Manipulating Statistics

There are several commands defined that can be used for accessing (-get), resetting to zero or neutral value (-reset) or even removing a statistic completely (-remove). The difference between reset and remove is somewhat subtle. The reset command sets the value of the statistic to zero or neutral value. After this operation, the statistic will have a value of 0 (integer), 0.0 (float), 0h0m0s0us (duration) or "" (string). When asked for, a statistic with the values mentioned will be returned. `Remove` removes a statistic completely, so the statistic will not be reported anymore. Please note that the server code may add it back if there's a reason to record it.

The following sections describe commands that can be sent to the server: the examples are not fragments of a configuration file. For more information on sending commands to Kea, see .

### statistic-get command

statistic-get command retrieves a single statistic. It takes a single string parameter called `name` that specifies the statistic name. An example command may look like this:

    {
        "command": "statistic-get",
        "arguments": {
            "name": "pkt4-received"
        }
    }

The server will respond with details of the requested statistic, with result set to 0 indicating success and the specified statistic as the value of "arguments" parameter. If the requested statistic is not found, the response will contain an empty map, i.e. only { } as argument, but the status code will still be set to success (0).

### statistic-reset command

statistic-reset command sets the specified statistic to its neutral value: 0 for integer, 0.0 for float, 0h0m0s0us for time duration and "" for string type. It takes a single string parameter called `name` that specifies the statistic name. An example command may look like this:

    {
        "command": "statistic-reset",
        "arguments": {
            "name": "pkt4-received"
        }
    }

If the specific statistic is found and reset was successful, the server will respond with a status of 0, indicating success and an empty parameters field. If an error is encountered (e.g. requested statistic was not found), the server will return a status code of 1 (error) and the text field will contain the error description.

### statistic-remove command

statistic-remove command attempts to delete a single statistic. It takes a single string parameter called `name` that specifies the statistic name. An example command may look like this:

    {
        "command": "statistic-remove",
        "arguments": {
            "name": "pkt4-received"
        }
    }

If the specific statistic is found and its removal was successful, the server will respond with a status of 0, indicating success and an empty parameters field. If an error is encountered (e.g. requested statistic was not found), the server will return a status code of 1 (error) and the text field will contain the error description.

### statistic-get-all command

statistic-get-all command retrieves all statistics recorded. An example command may look like this:

    {
        "command": "statistic-get-all",
        "arguments": { }
    }

The server will respond with details of all recorded statistics, with result set to 0 indicating that it iterated over all statistics (even when the total number of statistics is zero).

### statistic-reset-all command

statistic-reset command sets all statistics to their neutral values: 0 for integer, 0.0 for float, 0h0m0s0us for time duration and "" for string type. An example command may look like this:

    {
        "command": "statistic-reset-all",
        "arguments": { }
    }

If the operation is successful, the server will respond with a status of 0, indicating success and an empty parameters field. If an error is encountered, the server will return a status code of 1 (error) and the text field will contain the error description.

### statistic-remove-all command

statistic-remove-all command attempts to delete all statistics. An example command may look like this:

    {
        "command": "statistic-remove-all",
        "arguments": { }
    }

If the removal of all statistics was successful, the server will respond with a status of 0, indicating success and an empty parameters field. If an error is encountered, the server will return a status code of 1 (error) and the text field will contain the error description.