
[[index-modules]]
= Index modules

Index Modules are modules created per index and control all aspects related to
an index.

[discrete]
[[index-modules-settings]]
== Index Settings

[[index-modules-settings-description]]
// tag::index-modules-settings-description-tag[]
Index level settings can be set per-index. Settings may be:

_static_::

They can only be set at index creation time or on a
<<indices-open-close,closed index>>.

_dynamic_::

They can be changed on a live index using the
<<indices-update-settings,update-index-settings>> API.
// end::index-modules-settings-description-tag[]

WARNING: Changing static or dynamic index settings on a closed index could
result in incorrect settings that are impossible to rectify without deleting
and recreating the index.

[discrete]
=== Static index settings

Below is a list of all _static_ index settings that are not associated with any
specific index module:

[[index-number-of-shards]]
// tag::index-number-of-shards-tag[]
`index.number_of_shards`::
The number of primary shards that an index should have. Defaults to `1`. This setting can only be set at index creation time. It cannot be changed on a closed index.
+
NOTE: The number of shards are limited to `1024` per index. This limitation is a safety limit to prevent accidental creation of indices that can destabilize a cluster due to resource allocation. The limit can be modified by specifying `export ES_JAVA_OPTS="-Des.index.max_number_of_shards=128"` system property on every node that is part of the cluster.

// end::index-number-of-shards-tag[]

[[index-number-of-routing-shards]]
`index.number_of_routing_shards`::
+
====
Integer value used with <<index-number-of-shards,`index.number_of_shards`>> to
route documents to a primary shard. See <<mapping-routing-field>>.

{es} uses this value when <<indices-split-index,splitting>> an index.
For example, a 5 shard index with `number_of_routing_shards` set to `30` (`5 x
2 x 3`) could be split by a factor of `2` or `3`. In other words, it could be
split as follows:

* `5` -> `10` -> `30`  (split by 2, then by 3)
* `5` -> `15` -> `30` (split by 3, then by 2)
* `5` -> `30` (split by 6)

This setting's default value depends on the number of primary shards in the
index. The default is designed to allow you to split by factors of 2 up
to a maximum of 1024 shards.

NOTE: In {es} 7.0.0 and later versions, this setting affects how documents are
distributed across shards. When reindexing an older index with custom routing,
you must explicitly set `index.number_of_routing_shards` to maintain the same
document distribution. See the
{ref-70}/breaking-changes-7.0.html#_document_distribution_changes[related
breaking change].
====

[[index-codec]] `index.codec`::

    The +default+ value compresses stored data with LZ4
    compression, but this can be set to +best_compression+
    which uses {wikipedia}/DEFLATE[DEFLATE] for a higher
    compression ratio, at the expense of slower stored fields performance.
    If you are updating the compression type, the new one will be applied
    after segments are merged. Segment merging can be forced using
    <<indices-forcemerge,force merge>>.

[[routing-partition-size]] `index.routing_partition_size`::

    The number of shards a custom <<mapping-routing-field,routing>> value can go to.
    Defaults to 1 and can only be set at index creation time. This value must be less
    than the `index.number_of_shards` unless the `index.number_of_shards` value is also 1.
    See <<routing-index-partition>> for more details about how this setting is used.

[[ccr-index-soft-deletes]]
// tag::ccr-index-soft-deletes-tag[]
`index.soft_deletes.enabled`::
deprecated:[7.6.0, Creating indices with soft-deletes disabled is deprecated and will be removed in future Elasticsearch versions.]
Indicates whether soft deletes are enabled on the index. Soft deletes can only
be configured at index creation and only on indices created on or after
{es} 6.5.0. Defaults to `true`.
// end::ccr-index-soft-deletes-tag[]

[[ccr-index-soft-deletes-retention-period]]
//tag::ccr-index-soft-deletes-retention-tag[]
`index.soft_deletes.retention_lease.period`::
The maximum period to retain a shard history retention lease before it is
considered expired. Shard history retention leases ensure that soft deletes are
retained during merges on the Lucene index. If a soft delete is merged away
before it can be replicated to a follower the following process will fail due
to incomplete history on the leader. Defaults to `12h`.
//end::ccr-index-soft-deletes-retention-tag[]

[[load-fixed-bitset-filters-eagerly]] `index.load_fixed_bitset_filters_eagerly`::

    Indicates whether <<query-filter-context, cached filters>> are pre-loaded for
    nested queries. Possible values are `true` (default) and `false`.

[[index-shard-check-on-startup]] `index.shard.check_on_startup`::
+
====
WARNING: Expert users only. This setting enables some very expensive processing
at shard startup and is only ever useful while diagnosing a problem in your
cluster. If you do use it, you should do so only temporarily and remove it
once it is no longer needed.

{es} automatically performs integrity checks on the contents of shards at
various points during their lifecycle. For instance, it verifies the checksum
of every file transferred when recovering a replica or taking a snapshot. It
also verifies the integrity of many important files when opening a shard, which
happens when starting up a node and when finishing a shard recovery or
relocation. You can therefore manually verify the integrity of a whole shard
while it is running by taking a snapshot of it into a fresh repository or by
recovering it onto a fresh node.

This setting determines whether {es} performs additional integrity checks while
opening a shard. If these checks detect corruption then they will prevent the
shard from being opened. It accepts the following values:

`false`::: Don't perform additional checks for corruption when opening a shard.
This is the default and recommended behaviour.

`checksum`::: Verify that the checksum of every file in the shard matches its
contents. This will detect cases where the data read from disk differ from the
data that {es} originally wrote, for instance due to undetected disk corruption
or other hardware failures. These checks require reading the entire shard from
disk which takes substantial time and IO bandwidth and may affect cluster
performance by evicting important data from your filesystem cache.

`true`::: Performs the same checks as `checksum` and also checks for logical
inconsistencies in the shard, which could for instance be caused by the data
being corrupted while it was being written due to faulty RAM or other hardware
failures. These checks require reading the entire shard from disk which takes
substantial time and IO bandwidth, and then performing various checks on the
contents of the shard which take substantial time, CPU and memory.
====

[discrete]
[[dynamic-index-settings]]
=== Dynamic index settings

Below is a list of all _dynamic_ index settings that are not associated with any
specific index module:

[[dynamic-index-number-of-replicas]]
`index.number_of_replicas`::

    The number of replicas each primary shard has. Defaults to 1.

[[dynamic-index-auto-expand-replicas]]
`index.auto_expand_replicas`::
Auto-expand the number of replicas based on the number of data nodes in the
cluster. Set to a dash delimited lower and upper bound (e.g. `0-5`) or use `all`
for the upper bound (e.g. `0-all`). Defaults to `false` (i.e. disabled). Note
that the auto-expanded number of replicas only takes
<<shard-allocation-filtering,allocation filtering>> rules into account, but
ignores other allocation rules such as <<allocation-total-shards,total shards
per node>>, and this can lead to the cluster health becoming `YELLOW` if the
applicable rules prevent all the replicas from being allocated.
+
If the upper bound is `all` then <<shard-allocation-awareness,shard allocation
awareness>> and
<<cluster-routing-allocation-same-shard-host,`cluster.routing.allocation.same_shard.host`>>
are ignored for this index.

[[dynamic-index-search-idle-after]]
`index.search.idle.after`::
    How long a shard can not receive a search or get request until it's considered
    search idle. (default is `30s`)

[[index-refresh-interval-setting]]
`index.refresh_interval`::

    How often to perform a refresh operation, which makes recent changes to the
    index visible to search. Defaults to `1s`. Can be set to `-1` to disable
    refresh. If this setting is not explicitly set, shards that haven't seen
    search traffic for at least `index.search.idle.after` seconds will not receive
    background refreshes until they receive a search request. Searches that hit an
    idle shard where a refresh is pending will wait for the next background
    refresh (within `1s`). This behavior aims to automatically optimize bulk
    indexing in the default case when no searches are performed. In order to opt
    out of this behavior an explicit value of `1s` should set as the refresh
    interval.

[[index-max-result-window]]
`index.max_result_window`::

    The maximum value of `from + size` for searches to this index. Defaults to
    `10000`. Search requests take heap memory and time proportional to
    `from + size` and this limits that memory. See
    <<scroll-search-results,Scroll>> or <<search-after,Search After>> for a more efficient alternative
    to raising this.

`index.max_inner_result_window`::

    The maximum value of `from + size` for inner hits definition and top hits aggregations to this index. Defaults to
    `100`. Inner hits and top hits aggregation take heap memory and time proportional to `from + size` and this limits that memory.

`index.max_rescore_window`::

    The maximum value of `window_size` for `rescore` requests in searches of this index.
    Defaults to `index.max_result_window` which defaults to `10000`. Search
    requests take heap memory and time proportional to
    `max(window_size, from + size)` and this limits that memory.

`index.max_docvalue_fields_search`::

    The maximum number of `docvalue_fields` that are allowed in a query.
    Defaults to `100`. Doc-value fields are costly since they might incur
    a per-field per-document seek.

`index.max_script_fields`::

    The maximum number of `script_fields` that are allowed in a query.
    Defaults to `32`.

[[index-max-ngram-diff]]
`index.max_ngram_diff`::

    The maximum allowed difference between min_gram and max_gram for NGramTokenizer and NGramTokenFilter.
    Defaults to `1`.

[[index-max-shingle-diff]]
`index.max_shingle_diff`::

    The maximum allowed difference between max_shingle_size and min_shingle_size
    for the <<analysis-shingle-tokenfilter,`shingle` token filter>>. Defaults to
    `3`.

`index.max_refresh_listeners`::

    Maximum number of refresh listeners available on each shard of the index.
    These listeners are used to implement <<docs-refresh,`refresh=wait_for`>>.

 `index.analyze.max_token_count`::

    The maximum number of tokens that can be produced using _analyze API.
    Defaults to `10000`.

[[index-max-analyzed-offset]]
 `index.highlight.max_analyzed_offset`::

     The maximum number of characters that will be analyzed for a highlight request.
     This setting is only applicable when highlighting is requested on a text that was indexed without offsets or term vectors.
     Defaults to `1000000`.

[[index-max-terms-count]]
 `index.max_terms_count`::

    The maximum number of terms that can be used in Terms Query.
    Defaults to `65536`.

[[index-max-regex-length]]
 `index.max_regex_length`::

    The maximum length of regex that can be used in Regexp Query.
    Defaults to `1000`.


`index.query.default_field`::
+
--
(string or array of strings)
Wildcard (`*`) patterns matching one or more fields. The following query types
search these matching fields by default:

* <<query-dsl-mlt-query>>
* <<query-dsl-multi-match-query>>
* <<query-dsl-query-string-query>>
* <<query-dsl-simple-query-string-query>>

Defaults to `*`, which matches all fields eligible for
<<term-level-queries,term-level queries>>, excluding metadata fields.
--

 `index.routing.allocation.enable`::

    Controls shard allocation for this index. It can be set to:
    * `all` (default) - Allows shard allocation for all shards.
    * `primaries` - Allows shard allocation only for primary shards.
    * `new_primaries` - Allows shard allocation only for newly-created primary shards.
    * `none` - No shard allocation is allowed.

 `index.routing.rebalance.enable`::

    Enables shard rebalancing for this index. It can be set to:
    * `all` (default) - Allows shard rebalancing for all shards.
    * `primaries` - Allows shard rebalancing only for primary shards.
    * `replicas` - Allows shard rebalancing only for replica shards.
    * `none` - No shard rebalancing is allowed.

 `index.gc_deletes`::

    The length of time that a <<delete-versioning,deleted document's version number>> remains available for <<index-versioning,further versioned operations>>.
    Defaults to `60s`.

[[index-default-pipeline]]
 `index.default_pipeline`::

    Default <<ingest,ingest pipeline>> for the index. Index requests will fail
    if the default pipeline is set and the pipeline does not exist. The default may be
    overridden using the `pipeline` parameter. The special pipeline name `_none` indicates
    no ingest pipeline should be run.

[[index-final-pipeline]]
`index.final_pipeline`::
Final <<ingest,ingest pipeline>> for the index. Indexing requests
will fail if the final pipeline is set and the pipeline does not exist.
The final pipeline always runs after the request pipeline (if specified) and
the default pipeline (if it exists). The special pipeline name `_none`
indicates no ingest pipeline will run.
+
NOTE: You can't use a final pipeline to change the `_index` field. If the
pipeline attempts to change the `_index` field, the indexing request will fail.

[[index-hidden]] `index.hidden`::

    Indicates whether the index should be hidden by default. Hidden indices are not
    returned by default when using a wildcard expression. This behavior is controlled
    per request through the use of the `expand_wildcards` parameter. Possible values are
    `true` and `false` (default).

[discrete]
=== Settings in other index modules

Other index settings are available in index modules:

<<analysis,Analysis>>::

    Settings to define analyzers, tokenizers, token filters and character
    filters.

<<index-modules-allocation,Index shard allocation>>::

    Control over where, when, and how shards are allocated to nodes.

<<index-modules-mapper,Mapping>>::

    Enable or disable dynamic mapping for an index.

<<index-modules-merge,Merging>>::

    Control over how shards are merged by the background merge process.

<<index-modules-similarity,Similarities>>::

    Configure custom similarity settings to customize how search results are
    scored.

<<index-modules-slowlog,Slowlog>>::

    Control over how slow queries and fetch requests are logged.

<<index-modules-store,Store>>::

    Configure the type of filesystem used to access shard data.

<<index-modules-translog,Translog>>::

    Control over the transaction log and background flush operations.

<<index-modules-history-retention,History retention>>::

    Control over the retention of a history of operations in the index.

<<index-modules-indexing-pressure,Indexing pressure>>::

    Configure indexing back pressure limits.

[discrete]
[[x-pack-index-settings]]
=== [xpack]#{xpack} index settings#

<<ilm-settings,{ilm-cap}>>::

    Specify the lifecycle policy and rollover alias for an index.

include::index-modules/analysis.asciidoc[]

include::index-modules/allocation.asciidoc[]

include::index-modules/blocks.asciidoc[]

include::index-modules/mapper.asciidoc[]

include::index-modules/merge.asciidoc[]

include::index-modules/similarity.asciidoc[]

include::index-modules/slowlog.asciidoc[]

include::index-modules/store.asciidoc[]

include::index-modules/translog.asciidoc[]

include::index-modules/history-retention.asciidoc[]

include::index-modules/index-sorting.asciidoc[]

include::index-modules/indexing-pressure.asciidoc[]
