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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 5. 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.

index.shard.check_on_startup

[preview] This functionality is in technical preview and may be changed or removed in a future release. Elastic will work to fix any issues, but features in technical preview are not subject to the support SLA of official GA features. 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.

fix

Check for both physical and logical corruption. Segments that were reported as corrupted will be automatically removed. This option may result in data loss. Use with extreme caution!

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.

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 available nodes. 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).
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.
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_rescore_window: The maximum value of window_size for rescore`s 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.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: Set to true to disable read operations against the index.
index.blocks.write: Set to true to disable write operations against the index.
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.

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.

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