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Index modules

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Index modules

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

Index Settings

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Index level settings can be set per-index. Settings may be:

static: They can only be set at index creation time or on a closed index.
dynamic: They can be changed on a live index using the update-index-settings API.

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.

Static index settings

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

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.

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.

index.number_of_routing_shards

Number of routing shards used to split 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.

index.shard.check_on_startup

Whether or not shards should be checked for corruption before opening. When corruption is detected, it will prevent the shard from being opened. Accepts:

false: (default) Don’t check for corruption when opening a shard.
checksum: Check for physical corruption.
true: Check for both physical and logical corruption. This is much more expensive in terms of CPU and memory usage.

Expert only. Checking shards may take a lot of time on large indices.

index.codec

The default value compresses stored data with LZ4 compression, but this can be set to best_compression which uses 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 force merge.

index.routing_partition_size

The number of shards a custom 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 to an index partition for more details about how this setting is used.

index.soft_deletes.enabled: [7.6.0] Deprecated in 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 Elasticsearch 6.5.0. Defaults to true.

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.
index.load_fixed_bitset_filters_eagerly: Indicates whether cached filters are pre-loaded for nested queries. Possible values are true (default) and false.
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).

Dynamic index settings

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

index.number_of_replicas: The number of replicas each primary shard has. Defaults to 1.
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 allocation filtering rules into account, but ignores any other allocation rules such as shard allocation awareness and 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.
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: 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: 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 or 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: The maximum allowed difference between min_gram and max_gram for NGramTokenizer and NGramTokenFilter. Defaults to 1.

index.max_shingle_diff: The maximum allowed difference between max_shingle_size and min_shingle_size for the shingle token filter. Defaults to 3.
index.blocks.read_only: Set to true to make the index and index metadata read only, false to allow writes and metadata changes.
index.blocks.read_only_allow_delete: Similar to index.blocks.read_only, but also allows deleting the index to make more resources available. The disk-based shard allocator may add and remove this block automatically.

Deleting documents from an index to release resources - rather than deleting the index itself - can increase the index size over time. When index.blocks.read_only_allow_delete is set to true, deleting documents is not permitted. However, deleting the index itself releases the read-only index block and makes resources available almost immediately.

Elasticsearch adds and removes the read-only index block automatically when the disk utilization falls below the high watermark, controlled by cluster.routing.allocation.disk.watermark.flood_stage.

index.blocks.read: Set to true to disable read operations against the index.
index.blocks.write: Set to true to disable data write operations against the index. Unlike read_only, this setting does not affect metadata. For instance, you can close an index with a write block, but not an index with a read_only block.
index.blocks.metadata: Set to true to disable index metadata reads and writes.
index.max_refresh_listeners: Maximum number of refresh listeners available on each shard of the index. These listeners are used to implement refresh=wait_for.
index.analyze.max_token_count: The maximum number of tokens that can be produced using _analyze API. Defaults to 10000.
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: The maximum number of terms that can be used in Terms Query. Defaults to 65536.

index.max_regex_length

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

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 deleted document’s version number remains available for further versioned operations. Defaults to 60s.

index.default_pipeline

The default ingest node pipeline for this 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

The final ingest node pipeline for this index. Index 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.

Settings in other index modules

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Other index settings are available in index modules:

Analysis: Settings to define analyzers, tokenizers, token filters and character filters.
Index shard allocation: Control over where, when, and how shards are allocated to nodes.
Mapping: Enable or disable dynamic mapping for an index.
Merging: Control over how shards are merged by the background merge process.
Similarities: Configure custom similarity settings to customize how search results are scored.
Slowlog: Control over how slow queries and fetch requests are logged.
Store: Configure the type of filesystem used to access shard data.
Translog: Control over the transaction log and background flush operations.
History retention: Control over the retention of a history of operations in the index.

X-Pack index settings

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Index lifecycle management: Specify the lifecycle policy and rollover alias for an index.

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