Data streams

A data stream lets you store append-only time series data across multiple indices while giving you a single named resource for requests. Data streams are well-suited for logs, events, metrics, and other continuously generated data.

You can submit indexing and search requests directly to a data stream. The stream automatically routes the request to backing indices that store the stream’s data. You can use index lifecycle management (ILM) to automate the management of these backing indices. For example, you can use ILM to automatically move older backing indices to less expensive hardware and delete unneeded indices. ILM can help you reduce costs and overhead as your data grows.

A data stream consists of one or more hidden, auto-generated backing indices.

Each data stream requires a matching index template. The template contains the mappings and settings used to configure the stream’s backing indices.

Every document indexed to a data stream must contain a @timestamp field, mapped as a date or date_nanos field type. If the index template doesn’t specify a mapping for the @timestamp field, Elasticsearch maps @timestamp as a date field with default options.

The same index template can be used for multiple data streams. You cannot delete an index template in use by a data stream.

When you submit a read request to a data stream, the stream routes the request to all its backing indices.

The most recently created backing index is the data stream’s write index. The stream adds new documents to this index only.

You cannot add new documents to other backing indices, even by sending requests directly to the index.

You also cannot perform operations on a write index that may hinder indexing, such as:

When you create a data stream, Elasticsearch automatically creates a backing index for the stream. This index also acts as the stream’s first write index. A rollover creates a new backing index that becomes the stream’s new write index.

We recommend using ILM to automatically roll over data streams when the write index reaches a specified age or size. If needed, you can also manually roll over a data stream.

Each data stream tracks its generation: a six-digit, zero-padded integer that acts as a cumulative count of the stream’s rollovers, starting at 000001.

When a backing index is created, the index is named using the following convention:

.ds-<data-stream>-<generation>

Backing indices with a higher generation contain more recent data. For example, the web-server-logs data stream has a generation of 34. The stream’s most recent backing index is named .ds-web-server-logs-000034.

Some operations, such as a shrink or restore, can change a backing index’s name. These name changes do not remove a backing index from its data stream.

Data streams are designed for use cases where existing data is rarely, if ever, updated. You cannot send update or deletion requests for existing documents directly to a data stream. Instead, use the update by query and delete by query APIs.

If needed, you can update or delete documents by submitting requests directly to the document’s backing index.