# Activity Tracking

Starting with release 0.12, IRONdb supports tracking of metric activity without the expense of reading all known time series data to find active ranges. The activity of a metric is tracked at a 5 minute granularity. Any ingestion of a metric will mark that 5 minute period that the timestamp falls into as active for that metric. Activity periods are stored in the [surrogate database](https://docs.apica.io/platform-docs/getting-started/configuration#surrogate_database).

This activity tracking also coalesces nearby active ranges. Any activity on a metric within an 8 hour window marks that metric as active for that 8 hour span. For example, if you have a metric that arrived with the timestamp: `2018-07-03T11:00:01:123Z` and then nothing else arrived until `2018-07-03T19:00:02:123Z`, the metric would be considered *inactive* in the 8 hour span between these 2 timestamps. If, later, some late data arrives and we see a timestamp at: `2018-07-03T14:00:01:123Z`, then the entire 8 hour span is considered *active* for purposes of querying.

See [Searching Tags](https://docs.apica.io/platform-docs/metric-names-and-tags#tag-queries) on how to query activity periods for a given list of metrics.

This activity tracking only applies to data ingested after the upgrade to `0.12` or later. Any data ingested prior to installation of `0.12` will be invisible to the activity tracking code. However, IRONdb also ships with an API to rebuild activity tracking data by reading the actual datapoints for a metric to determine its activity ranges. Since this is an expensive operation it has to be triggered for a list of metrics by an operator.

## Rebuilding Activity Data

> Do not trigger this API until you have upgraded all IRONdb nodes to `0.12` or later.

### URI

* `/surrogate/activity_rebuild`

### Method

POST

### Inputs

A JSON document which lists the set of metrics to rebuild activity data for, with the syntax:

```
[
   {
      "check_uuid":"1fd7c873-0055-4bd3-a16a-2137b111e71a",
      "metric_name":"foo"
   },
   {
      "check_uuid":"1fd7c873-0055-4bd3-a16a-2137b111e71a",
      "metric_name":"bar"
   },
   {
      "check_uuid":"1fd7c873-0055-4bd3-a16a-2137b111e71a",
      "metric_name":"baz|ST[a:b,c:d]"
   }
]
```

> The above will rebuild activity for the 3 metrics listed in the document.