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