147 lines
5.4 KiB
Plaintext
147 lines
5.4 KiB
Plaintext
[[data-streams-overview]]
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== Data streams overview
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++++
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<titleabbrev>Overview</titleabbrev>
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++++
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A data stream consists of one or more _backing indices_. Backing indices are
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<<index-hidden,hidden>>, auto-generated indices used to store a stream's
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documents.
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image::images/data-streams/data-streams-diagram.svg[align="center"]
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The creation of a data stream requires a matching
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<<indices-templates,index template>>. This template acts as a blueprint for
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the stream's backing indices. It contains:
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* A name or wildcard (`*`) pattern for the data stream.
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* The data stream's _timestamp field_. This field must be mapped as a
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<<date,`date`>> or <<date_nanos,`date_nanos`>> field datatype and must be
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included in every document indexed to the data stream.
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* The mappings and settings applied to each backing index when it's created.
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The same index template can be used to create multiple data streams.
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See <<set-up-a-data-stream>>.
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[discrete]
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[[data-streams-generation]]
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=== Generation
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Each data stream tracks its _generation_: a six-digit, zero-padded integer
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that acts as a cumulative count of the data stream's backing indices. This count
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includes any deleted indices for the stream. The generation is incremented
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whenever a new backing index is added to the stream.
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When a backing index is created, the index is named using the following
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convention:
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[source,text]
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----
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.ds-<data-stream>-<generation>
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----
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.*Example*
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[%collapsible]
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====
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The `web_server_logs` data stream has a generation of `34`. The most recently
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created backing index for this data stream is named
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`.ds-web_server_logs-000034`.
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====
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Because the generation increments with each new backing index, backing indices
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with a higher generation contain more recent data. Backing indices with a lower
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generation contain older data.
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A backing index's name can change after its creation due to a
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<<indices-shrink-index,shrink>>, <<snapshots-restore-snapshot,restore>>, or
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other operations.
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[discrete]
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[[data-stream-write-index]]
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=== Write index
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When a read request is sent to a data stream, it routes the request to all its
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backing indices. For example, a search request sent to a data stream would query
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all its backing indices.
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image::images/data-streams/data-streams-search-request.svg[align="center"]
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However, the most recently created backing index is the data stream’s only
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_write index_. The data stream routes all indexing requests for new documents to
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this index.
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image::images/data-streams/data-streams-index-request.svg[align="center"]
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You cannot add new documents to a stream's other backing indices, even by
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sending requests directly to the index. This means you cannot submit the
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following requests directly to any backing index except the write index:
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* An <<docs-index_,index API>> request with an
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<<docs-index-api-op_type,`op_type`>> of `create`. The `op_type` parameter
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defaults to `create` when adding new documents.
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* A <<docs-bulk,bulk API>> request using a `create` action
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Because it's the only index capable of ingesting new documents, you cannot
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perform operations on a write index that might hinder indexing. These
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prohibited operations include:
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* <<indices-clone-index,Clone>>
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* <<indices-close,Close>>
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* <<indices-delete-index,Delete>>
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* <<freeze-index-api,Freeze>>
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* <<indices-shrink-index,Shrink>>
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* <<indices-split-index,Split>>
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[discrete]
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[[data-streams-rollover]]
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=== Rollover
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When a data stream is created, one backing index is automatically created.
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Because this single index is also the most recently created backing index, it
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acts as the stream's write index.
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A <<indices-rollover-index,rollover>> creates a new backing index for a data
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stream. This new backing index becomes the stream's write index, replacing
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the current one, and increments the stream's generation.
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In most cases, we recommend using <<index-lifecycle-management,{ilm}
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({ilm-init})>> to automate rollovers for data streams. This lets you
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automatically roll over the current write index when it meets specified
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criteria, such as a maximum age or size.
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However, you can also use the <<indices-rollover-index,rollover API>> to
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manually perform a rollover. See <<manually-roll-over-a-data-stream>>.
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[discrete]
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[[data-streams-append-only]]
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=== Append-only
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For most time-series use cases, existing data is rarely, if ever, updated.
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Because of this, data streams are designed to be append-only. This means you can
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send indexing requests for new documents directly to a data stream. However, you
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cannot send update or deletion requests for existing documents to a data stream.
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To update or delete specific documents in a data stream, submit one of the
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following requests to the backing index containing the document:
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* An <<docs-index_,index API>> request with an
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<<docs-index-api-op_type,`op_type`>> of `index`.
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These requests must include valid <<optimistic-concurrency-control,`if_seq_no`
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and `if_primary_term`>> arguments.
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* A <<docs-bulk,bulk API>> request using the `delete`, `index`, or `update`
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action. If the action type is `index`, the action must include valid
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<<bulk-optimistic-concurrency-control,`if_seq_no` and `if_primary_term`>>
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arguments.
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* A <<docs-delete,delete API>> request
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See <<update-delete-docs-in-a-data-stream>>.
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TIP: If you frequently update or delete existing documents,
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we recommend using an <<indices-add-alias,index alias>> and
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<<indices-templates,index template>> instead of a data stream. You can still
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use <<index-lifecycle-management,{ilm-init}>> to manage indices for the alias.
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