Force a merge | Elasticsearch API (v8)

Force a merge Added in 2.1.0

POST /_forcemerge

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.

External documentation

Query parameters

allow_no_indices boolean

Whether to ignore if a wildcard indices expression resolves into no concrete indices. (This includes _all string or when no indices have been specified)
expand_wildcards string | array[string]

Whether to expand wildcard expression to concrete indices that are open, closed or both.
flush boolean

Specify whether the index should be flushed after performing the operation (default: true)
ignore_unavailable boolean

Whether specified concrete indices should be ignored when unavailable (missing or closed)
max_num_segments number

The number of segments the index should be merged into (default: dynamic)
only_expunge_deletes boolean

Specify whether the operation should only expunge deleted documents
wait_for_completion boolean

Should the request wait until the force merge is completed.

Responses

200 application/json
Hide response attributes Show response attributes object
- _shards object
  
  Additional properties are allowed.
  
  Hide _shards attributes Show _shards attributes object
  
  failed number Required
  
  successful number Required
  
  total number Required
  
  failures array[object]
  
  Hide failures attributes Show failures attributes object
  
  index string
  
  node string
  
  reason object Required
  
  Additional properties are allowed.
  
  Hide reason attributes Show reason attributes object
  
  type string Required
  
  The type of error
  
  reason string
  
  A human-readable explanation of the error, in english
  
  stack_trace string
  
  The server stack trace. Present only if the error_trace=true parameter was sent with the request.
  
  caused_by object
  
  Additional properties are allowed.
  
  root_cause array[object]
  
  suppressed array[object]
  
  shard number Required
  
  status string
  
  skipped number
- task string
  
  task contains a task id returned when wait_for_completion=false, you can use the task_id to get the status of the task at _tasks/

POST /_forcemerge

curl \
 -X POST http://api.example.com/_forcemerge

Response examples (200)

{
  "_shards": {
    "failed": 42.0,
    "successful": 42.0,
    "total": 42.0,
    "failures": [
      {
        "index": "string",
        "node": "string",
        "reason": {
          "type": "string",
          "reason": "string",
          "stack_trace": "string",
          "caused_by": {},
          "root_cause": [
            {}
          ],
          "suppressed": [
            {}
          ]
        },
        "shard": 42.0,
        "status": "string"
      }
    ],
    "skipped": 42.0
  },
  "task": "string"
}