Flush data streams or indices

POST /_flush

Flushing a data stream or index is the process of making sure that any data that is currently only stored in the transaction log is also permanently stored in the Lucene index. When restarting, Elasticsearch replays any unflushed operations from the transaction log into the Lucene index to bring it back into the state that it was in before the restart. Elasticsearch automatically triggers flushes as needed, using heuristics that trade off the size of the unflushed transaction log against the cost of performing each flush.

After each operation has been flushed it is permanently stored in the Lucene index. This may mean that there is no need to maintain an additional copy of it in the transaction log. The transaction log is made up of multiple files, called generations, and Elasticsearch will delete any generation files when they are no longer needed, freeing up disk space.

It is also possible to trigger a flush on one or more indices using the flush API, although it is rare for users to need to call this API directly. If you call the flush API after indexing some documents then a successful response indicates that Elasticsearch has flushed all the documents that were indexed before the flush API was called.

Query parameters

  • allow_no_indices boolean

    If false, the request returns an error if any wildcard expression, index alias, or _all value targets only missing or closed indices. This behavior applies even if the request targets other open indices.

  • expand_wildcards string | array[string]

    Type of index that wildcard patterns can match. If the request can target data streams, this argument determines whether wildcard expressions match hidden data streams. Supports comma-separated values, such as open,hidden. Valid values are: all, open, closed, hidden, none.

  • force boolean

    If true, the request forces a flush even if there are no changes to commit to the index.

  • ignore_unavailable boolean

    If false, the request returns an error if it targets a missing or closed index.

  • wait_if_ongoing boolean

    If true, the flush operation blocks until execution when another flush operation is running. If false, Elasticsearch returns an error if you request a flush when another flush operation is running.

Responses

  • 200 application/json
    Hide response attribute Show response attribute 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]

            Additional properties are allowed.

          • suppressed array[object]

            Additional properties are allowed.

        • shard number Required
        • status string
      • skipped number
POST /_flush 
curl \
 -X POST http://api.example.com/_flush
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
  }
}