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Shrink index

The shrink index API operation moves all of your data in an existing index into a new index with fewer primary shards.

Example

POST /my-old-index/_shrink/my-new-index
{
  "settings": {
    "index.number_of_replicas": 4,
    "index.number_of_shards": 3
  },
  "aliases":{
    "new-index-alias": {}
  }
}

Path and HTTP methods

POST /<index-name>/_shrink/<target-index>
PUT /<index-name>/_shrink/<target-index>

When creating new indices with this operation, remember that OpenSearch indices have the following naming restrictions:

  • All letters must be lowercase.
  • Index names can’t begin with underscores (_) or hyphens (-).

  • Index names can’t contain spaces, commas, or the following characters:

    :, ", *, +, /, \, |, ?, #, >, or <

URL parameters

The shrink index API operation requires you to specify both the source index and the target index. All other parameters are optional.

Parameter Type description
<index-name> String The index to shrink.
<target-index> String The target index to shrink the source index into.
wait_for_active_shards String Specifies the number of active shards that must be available before OpenSearch processes the request. Default is 1 (only the primary shard). Set to all or a positive integer. Values greater than 1 require replicas. For example, if you specify a value of 3, the index must have two replicas distributed across two additional nodes for the request to succeed.
master_timeout Time How long to wait for a connection to the master node. Default is 30s.
timeout Time How long to wait for the request to return a response. Default is 30s.

Request body

You can use the request body to configure some index settings for the target index. All fields are optional.

Field Type Description
alias Object Sets an alias for the target index. Can have the fields filter, index_routing, is_hidden, is_write_index, routing, or search_routing. See Index Aliases.
settings Object Index settings you can apply to your target index. See Index Settings.
max_shard_size Bytes Specifies the maximum size of a primary shard in the target index. Because max_shard_size conflicts with the index.number_of_shards setting, you cannot set both of them at the same time.

The max_shard_size parameter

The max_shard_size parameter specifies the maximum size of a primary shard in the target index. OpenSearch uses max_shard_size and the total storage for all primary shards in the source index to calculate the number of primary shards and their size for the target index.

The primary shard count of the target index is the smallest factor of the source index’s primary shard count for which the shard size does not exceed max_shard_size. For example, if the source index has 8 primary shards, they occupy a total of 400 GB of storage, and the max_shard_size is equal to 150 GB, OpenSearch calculates the number of primary shards in the target index using the following algorithm:

  1. Calculate the minimum number of primary shards as 400/150, rounded to the nearest whole integer. The minimum number of primary shards is 3.
  2. Calculate the number of primary shards as the smallest factor of 8 that is greater than 3. The number of primary shards is 4.

The maximum number of primary shards for the target index is equal to the number of primary shards in the source index because the shrink operation is used to reduce the primary shard count. As an example, consider a source index with 5 primary shards that occupy a total of 600 GB of storage. If max_shard_size is 100 GB, the minimum number of primary shards is 600/100, which is 6. However, because the number of primary shards in the source index is smaller than 6, the number of primary shards in the target index is set to 5.

The minimum number of primary shards for the target index is 1.

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