135 lines
4.2 KiB
Plaintext
135 lines
4.2 KiB
Plaintext
[[indices-clone-index]]
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=== Clone Index
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The clone index API allows you to clone an existing index into a new index,
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where each original primary shard is cloned into a new primary shard in
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the new index.
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[float]
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==== How does cloning work?
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Cloning 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.
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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 cloning
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Create a new index:
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[source,console]
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--------------------------------------------------
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PUT my_source_index
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{
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"settings": {
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"index.number_of_shards" : 5
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}
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}
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--------------------------------------------------
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In order to clone an index, the index must be marked as read-only,
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and have <<cluster-health,health>> `green`.
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This can be achieved with the following request:
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[source,console]
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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.blocks.write": true <1>
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}
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}
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--------------------------------------------------
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// TEST[continued]
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<1> Prevents write operations to this index while still allowing metadata
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changes like deleting the index.
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[float]
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==== Cloning an index
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To clone `my_source_index` into a new index called `my_target_index`, issue
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the following request:
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[source,console]
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--------------------------------------------------
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POST my_source_index/_clone/my_target_index
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--------------------------------------------------
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// TEST[continued]
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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 clone operation to start.
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[IMPORTANT]
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=====================================
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Indices can only be cloned if they satisfy the following requirements:
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* the target index must not exist
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* The source index must have the same number of primary shards as the target index.
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* The node handling the clone 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 `_clone` 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,console]
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--------------------------------------------------
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POST my_source_index/_clone/my_target_index
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{
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"settings": {
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"index.number_of_shards": 5 <1>
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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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// TEST[s/^/PUT my_source_index\n{"settings": {"index.blocks.write": true, "index.number_of_shards": "5"}}\n/]
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<1> The number of shards in the target index. This must be equal to the
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number of shards in the source index.
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NOTE: Mappings may not be specified in the `_clone` request. The mappings of
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the source index will be used for the target index.
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[float]
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==== Monitoring the clone process
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The clone 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 `_clone` 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, its primary shard will remain `unassigned` until it
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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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clone process begins. When the clone 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 clone operation creates a new index to clone 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 clone index action as well.
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