You can use the GetMetricData API to retrieve CloudWatch metric values. The operation can also include a CloudWatch Metrics Insights query, and one or more metric math functions.

A GetMetricData operation that does not include a query can retrieve as many as 500 different metrics in a single request, with a total of as many as 100,800 data points. You can also optionally perform metric math expressions on the values of the returned statistics, to create new time series that represent new insights into your data. For example, using Lambda metrics, you could divide the Errors metric by the Invocations metric to get an error rate time series. For more information about metric math expressions, see Metric Math Syntax and Functions in the Amazon CloudWatch User Guide.

If you include a Metrics Insights query, each GetMetricData operation can include only one query. But the same GetMetricData operation can also retrieve other metrics. Metrics Insights queries can query only the most recent three hours of metric data. For more information about Metrics Insights, see Query your metrics with CloudWatch Metrics Insights.

Calls to the GetMetricData API have a different pricing structure than calls to GetMetricStatistics. For more information about pricing, see Amazon CloudWatch Pricing.

Amazon CloudWatch retains metric data as follows:

• Data points with a period of less than 60 seconds are available for 3 hours. These data points are high-resolution metrics and are available only for custom metrics that have been defined with a StorageResolution of 1.

• Data points with a period of 60 seconds (1-minute) are available for 15 days.

• Data points with a period of 300 seconds (5-minute) are available for 63 days.

• Data points with a period of 3600 seconds (1 hour) are available for 455 days (15 months).

Data points that are initially published with a shorter period are aggregated together for long-term storage. For example, if you collect data using a period of 1 minute, the data remains available for 15 days with 1-minute resolution. After 15 days, this data is still available, but is aggregated and retrievable only with a resolution of 5 minutes. After 63 days, the data is further aggregated and is available with a resolution of 1 hour.

If you omit Unit in your request, all data that was collected with any unit is returned, along with the corresponding units that were specified when the data was reported to CloudWatch. If you specify a unit, the operation returns only data that was collected with that unit specified. If you specify a unit that does not match the data collected, the results of the operation are null. CloudWatch does not perform unit conversions.

Using Metrics Insights queries with metric math

You can't mix a Metric Insights query and metric math syntax in the same expression, but you can reference results from a Metrics Insights query within other Metric math expressions. A Metrics Insights query without a GROUP BY clause returns a single time-series (TS), and can be used as input for a metric math expression that expects a single time series. A Metrics Insights query with a GROUP BY clause returns an array of time-series (TS[]), and can be used as input for a metric math expression that expects an array of time series.