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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

Integer value used with index.number_of_shards to route documents to a primary shard. See _routing field.

Elasticsearch uses this value when 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.

In Elasticsearch 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 related breaking change.

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. Experiments with indexing log datasets have shown that best_compression gives up to ~18% lower storage usage in the most ideal scenario compared to default while only minimally affecting indexing throughput (~2%).

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.shard.check_on_startup

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.

Elasticsearch 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 Elasticsearch 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 Elasticsearch 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.

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.

WARNING: Configuring it to 0 may lead to temporary availability loss
during node restarts or permanent data loss in case of data corruption.

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 other allocation rules such as 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 and cluster.routing.allocation.same_shard.host are ignored for this index.

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.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.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:

Defaults to *, which matches all fields eligible for 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 deleted document’s version number remains available for further versioned operations. Defaults to 60s.

index.default_pipeline: Default 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: Final 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.

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: 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).

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.
Indexing pressure: Configure indexing back pressure limits.

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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