145 lines
5.6 KiB
Plaintext
145 lines
5.6 KiB
Plaintext
[[indices-shrink-index]]
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== Shrink Index
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The shrink index API allows you to shrink an existing index into a new index
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with fewer primary shards. The requested number of primary shards in the target index
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must be a factor of the number of shards in the source index. For example an index with
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`8` primary shards can be shrunk into `4`, `2` or `1` primary shards or an index
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with `15` primary shards can be shrunk into `5`, `3` or `1`. If the number
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of shards in the index is a prime number it can only be shrunk into a single
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primary shard. Before shrinking, a (primary or replica) copy of every shard
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in the index must be present on the same node.
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Shrinking works as follows:
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* First, it creates a new target index with the same definition as the source
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index, but with a smaller number of primary shards.
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* Then it hard-links segments from the source index into the target index. (If
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the file system doesn't support hard-linking, then all segments are copied
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into the new index, which is a much more time consuming process.)
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* Finally, it recovers the target index as though it were a closed index which
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had just been re-opened.
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[float]
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=== Preparing an index for shrinking
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In order to shrink an index, the index must be marked as read-only, and a
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(primary or replica) copy of every shard in the index must be relocated to the
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same node and have <<cluster-health,health>> `green`.
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These two conditions can be achieved with the following request:
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[source,js]
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--------------------------------------------------
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PUT /my_source_index/_settings
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{
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"settings": {
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"index.routing.allocation.require._name": "shrink_node_name", <1>
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"index.blocks.write": true <2>
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}
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}
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--------------------------------------------------
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<1> Forces the relocation of a copy of each shard to the node with name
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`shrink_node_name`. See <<shard-allocation-filtering>> for more options.
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<2> Prevents write operations to this index while still allowing metadata
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changes like deleting the index.
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It can take a while to relocate the source index. Progress can be tracked
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with the <<cat-recovery,`_cat recovery` API>>, or the <<cluster-health,
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`cluster health` API>> can be used to wait until all shards have relocated
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with the `wait_for_relocating_shards` parameter.
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[float]
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=== Shrinking an index
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To shrink `my_source_index` into a new index called `my_target_index`, issue
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the following request:
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[source,js]
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--------------------------------------------------
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POST my_source_index/_shrink/my_target_index
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--------------------------------------------------
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The above request returns immediately once the target index has been added to
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the cluster state -- it doesn't wait for the shrink operation to start.
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[IMPORTANT]
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=====================================
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Indices can only be shrunk if they satisfy the following requirements:
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* the target index must not exist
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* The index must have more primary shards than the target index.
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* The number of primary shards in the target index must be a factor of the
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number of primary shards in the source index. The source index must have
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more primary shards than the target index.
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* The index must not contain more than `2,147,483,519` documents in total
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across all shards that will be shrunk into a single shard on the target index
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as this is the maximum number of docs that can fit into a single shard.
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* The node handling the shrink process must have sufficient free disk space to
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accommodate a second copy of the existing index.
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=====================================
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The `_shrink` API is similar to the <<indices-create-index, `create index` API>>
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and accepts `settings` and `aliases` parameters for the target index:
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[source,js]
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--------------------------------------------------
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POST my_source_index/_shrink/my_target_index
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{
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"settings": {
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"index.number_of_replicas": 1,
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"index.number_of_shards": 1, <1>
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"index.codec": "best_compression" <2>
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},
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"aliases": {
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"my_search_indices": {}
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}
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}
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--------------------------------------------------
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<1> The number of shards in the target index. This must be a factor of the
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number of shards in the source index.
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<2> Best compression will only take affect when new writes are made to the
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index, such as when <<indices-forcemerge,force-merging>> the shard to a single
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segment.
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NOTE: Mappings may not be specified in the `_shrink` request, and all
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`index.analysis.*` and `index.similarity.*` settings will be overwritten with
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the settings from the source index.
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[float]
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=== Monitoring the shrink process
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The shrink process can be monitored with the <<cat-recovery,`_cat recovery`
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API>>, or the <<cluster-health, `cluster health` API>> can be used to wait
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until all primary shards have been allocated by setting the `wait_for_status`
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parameter to `yellow`.
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The `_shrink` API returns as soon as the target index has been added to the
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cluster state, before any shards have been allocated. At this point, all
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shards are in the state `unassigned`. If, for any reason, the target index
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can't be allocated on the shrink node, its primary shard will remain
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`unassigned` until it can be allocated on that node.
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Once the primary shard is allocated, it moves to state `initializing`, and the
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shrink process begins. When the shrink operation completes, the shard will
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become `active`. At that point, Elasticsearch will try to allocate any
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replicas and may decide to relocate the primary shard to another node.
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[float]
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=== Wait For Active Shards
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Because the shrink operation creates a new index to shrink the shards to,
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the <<create-index-wait-for-active-shards,wait for active shards>> setting
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on index creation applies to the shrink index action as well.
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