---
title: Downsample
description: Phases allowed: hot, warm, cold. Aggregates a time series (TSDS) index and stores pre-computed statistical summaries (min, max, sum, and value_count)...
url: https://www.elastic.co/elastic/docs-builder/docs/2395/reference/elasticsearch/index-lifecycle-actions/ilm-downsample
---

# Downsample
Phases allowed: hot, warm, cold.
Aggregates a time series (TSDS) index and stores pre-computed statistical summaries (`min`, `max`, `sum`, and `value_count`) for each metric field grouped by a configured time interval. 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 and stored in the downsample index.
This action corresponds to the [downsample API](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-indices-downsample).
The name of the resulting downsample index is `downsample-<original-index-name>-<random-uuid>`. If ILM performs the `downsample` action on a backing index for a data stream, the downsample index becomes a backing index for the same stream and the source index is deleted.
To use the `downsample` action in the `hot` phase, the `rollover` action **must** be present. If no rollover action is configured, ILM will reject the policy.

## Options

<definitions>
  <definition term="fixed_interval">
    (Required, string) The [fixed time interval](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/2395/manage-data/lifecycle/rollup/understanding-groups#rollup-understanding-group-intervals) into which the data will be downsampled.
  </definition>
  <definition term="force_merge_index stack: ga 9.3">
    (Optional, boolean) When true, the downsampled index will be [force merged](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-indices-forcemerge) to one [segment](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-indices-segments). Defaults to `true`.
  </definition>
  <definition term="sampling_method stack: ga 9.3">
    (Optional, string) The sampling method that will be used to sample metrics; there are two methods available `aggregate` and
    the `last_value`. Defaults to `aggregate`.
  </definition>
</definitions>


## Example

```json

{
  "policy": {
    "phases": {
      "hot": {
        "actions": {
          "rollover": {
            "max_docs": 1
          },
          "downsample": {
  	          "fixed_interval": "1h",
  	          "force_merge_index": false
  	      }
        }
      }
    }
  }
}
```