Package co.elastic.clients.elasticsearch.indices

Class ForcemergeRequest

java.lang.Object
co.elastic.clients.elasticsearch._types.RequestBase
co.elastic.clients.elasticsearch.indices.ForcemergeRequest
public class ForcemergeRequest extends RequestBase
Force a merge. Perform the force merge operation on the shards of one or more indices. For data streams, the API forces a merge on the shards of the stream's backing indices.

Merging reduces the number of segments in each shard by merging some of them together and also frees up the space used by deleted documents. Merging normally happens automatically, but sometimes it is useful to trigger a merge manually.

WARNING: We recommend force merging only a read-only index (meaning the index is no longer receiving writes). When documents are updated or deleted, the old version is not immediately removed but instead soft-deleted and marked with a "tombstone". These soft-deleted documents are automatically cleaned up during regular segment merges. But force merge can cause very large (greater than 5 GB) segments to be produced, which are not eligible for regular merges. So the number of soft-deleted documents can then grow rapidly, resulting in higher disk usage and worse search performance. If you regularly force merge an index receiving writes, this can also make snapshots more expensive, since the new documents can't be backed up incrementally.

Blocks during a force merge

Calls to this API block until the merge is complete (unless request contains wait_for_completion=false). If the client connection is lost before completion then the force merge process will continue in the background. Any new requests to force merge the same indices will also block until the ongoing force merge is complete.

Running force merge asynchronously

If the request contains wait_for_completion=false, Elasticsearch performs some preflight checks, launches the request, and returns a task you can use to get the status of the task. However, you can not cancel this task as the force merge task is not cancelable. Elasticsearch creates a record of this task as a document at _tasks/<task_id>. When you are done with a task, you should delete the task document so Elasticsearch can reclaim the space.

Force merging multiple indices

You can force merge multiple indices with a single request by targeting:

  • One or more data streams that contain multiple backing indices
  • Multiple indices
  • One or more aliases
  • All data streams and indices in a cluster

Each targeted shard is force-merged separately using the force_merge threadpool. By default each node only has a single force_merge thread which means that the shards on that node are force-merged one at a time. If you expand the force_merge threadpool on a node then it will force merge its shards in parallel

Force merge makes the storage for the shard being merged temporarily increase, as it may require free space up to triple its size in case max_num_segments parameter is set to 1, to rewrite all segments into a new one.

Data streams and time-based indices

Force-merging is useful for managing a data stream's older backing indices and other time-based indices, particularly after a rollover. In these cases, each index only receives indexing traffic for a certain period of time. Once an index receive no more writes, its shards can be force-merged to a single segment. This can be a good idea because single-segment shards can sometimes use simpler and more efficient data structures to perform searches. For example: 

 POST /.ds-my-data-stream-2099.03.07-000001/_forcemerge?max_num_segments=1
See Also:

  • Field Details

  • Method Details

    • of

      public static ForcemergeRequest of(Function<ForcemergeRequest.Builder,ObjectBuilder<ForcemergeRequest>> fn)

    • allowNoIndices

      @Nullable public final Boolean allowNoIndices()
      Whether to ignore if a wildcard indices expression resolves into no concrete indices. (This includes _all string or when no indices have been specified)

      API name: allow_no_indices

    • expandWildcards

      public final List<ExpandWildcard> expandWildcards()
      Whether to expand wildcard expression to concrete indices that are open, closed or both.

      API name: expand_wildcards

    • flush

      @Nullable public final Boolean flush()
      Specify whether the index should be flushed after performing the operation (default: true)

      API name: flush

    • ignoreUnavailable

      @Nullable public final Boolean ignoreUnavailable()
      Whether specified concrete indices should be ignored when unavailable (missing or closed)

      API name: ignore_unavailable

    • index

      public final List<String> index()
      A comma-separated list of index names; use _all or empty string to perform the operation on all indices

      API name: index

    • maxNumSegments

      @Nullable public final Long maxNumSegments()
      The number of segments the index should be merged into (default: dynamic)

      API name: max_num_segments

    • onlyExpungeDeletes

      @Nullable public final Boolean onlyExpungeDeletes()
      Specify whether the operation should only expunge deleted documents

      API name: only_expunge_deletes

    • waitForCompletion

      @Nullable public final Boolean waitForCompletion()
      Should the request wait until the force merge is completed.

      API name: wait_for_completion