Shrink an index

Shrink an index into a new index with fewer primary shards.

Before you can shrink an index:

  • The index must be read-only.
  • A copy of every shard in the index must reside on the same node.
  • The index must have a green health status.

To make shard allocation easier, we recommend you also remove the index's replica shards. You can later re-add replica shards as part of the shrink operation.

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.

The current write index on a data stream cannot be shrunk. In order to shrink the current write index, the data stream must first be rolled over so that a new write index is created and then the previous write index can be shrunk.

A shrink operation:

  • Creates a new target index with the same definition as the source index, but with a smaller number of primary shards.
  • Hard-links segments from the source index into the target index. If the file system does not 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 do not work across disks.
  • Recovers the target index as though it were a closed index which had just been re-opened. Recovers shards to the .routing.allocation.initial_recovery._id index setting.
Important

Indices can only be shrunk if they satisfy the following requirements:

  • The target index must not exist.
  • The source 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.

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