# Downsample an index

**POST /{index}/_downsample/{target_index}**

Downsamples a time series (TSDS) index and reduces its size by keeping the last value or by pre-aggregating metrics:

- When running in `aggregate` mode, it pre-calculates and stores statistical summaries (`min`, `max`, `sum`, `value_count` and `avg`)
for each metric field grouped by a configured time interval and their dimensions.
- When running in `last_value` mode, it keeps the last value for each metric in the configured interval and their dimensions.

For example, a TSDS index that contains metrics sampled every 10 seconds can be downsampled to an hourly index.
All documents within an hour interval are summarized and stored as a single document in the downsample index.

NOTE: Only indices in a time series data stream are supported.
Neither field nor document level security can be defined on the source index.
The source index must be read-only (`index.blocks.write: true`).


## Servers
- http://api.example.com: http://api.example.com ()


## Authentication methods
- Api key auth
- Basic auth
- Bearer auth


## Parameters

### Path parameters
- **index** (string)
  Name of the time series index to downsample.
- **target_index** (string)
  Name of the index to create.


### Body: application/json (object)

- **fixed_interval** (string)
  The interval at which to aggregate the original time series index.
- **sampling_method** (string)
  The sampling method used to reduce the documents; it can be either `aggregate` or `last_value`. Defaults to `aggregate`.


## Responses
### 200


#### Body: application/json (object)
object

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