[[plugins-delete-by-query]]
== Delete By Query Plugin

The delete by query plugin adds support for deleting all of the documents
(from one or more indices) which match the specified query. It is a
replacement for the problematic _delete-by-query_ functionality which has been
removed from Elasticsearch core.

Internally, it uses the <<scroll-scan, Scan/Scroll>> and <<docs-bulk, Bulk>>
APIs to delete documents in an efficient and safe manner. It is slower than
the old _delete-by-query_ functionality, but fixes the problems with the
previous implementation.

TIP: Queries which match large numbers of documents may run for a long time,
as every document has to be deleted individually.  Don't use _delete-by-query_
to clean out all or most documents in an index.  Rather create a new index and
perhaps reindex the documents you want to keep.

=== Installation

This plugin can be installed using the plugin manager:

[source,sh]
----------------------------------------------------------------
bin/plugin install elasticsearch/elasticsearch-delete-by-query
----------------------------------------------------------------

The plugin must be installed on every node in the cluster, and each node must
be restarted after installation.

=== Removal

The plugin can be removed with the following command:

[source,sh]
----------------------------------------------------------------
bin/plugin remove elasticsearch/elasticsearch-delete-by-query
----------------------------------------------------------------

The node must be stopped before removing the plugin.

=== Usage

The query can either be provided using a simple query string as
a parameter:

[source,shell]
--------------------------------------------------
curl -XDELETE 'http://localhost:9200/twitter/tweet/_query?q=user:kimchy'
--------------------------------------------------

or using the <<query-dsl,Query DSL>> defined within the request body:

[source,js]
--------------------------------------------------
curl -XDELETE 'http://localhost:9200/twitter/tweet/_query' -d '{
    "query" : { <1>
        "term" : { "user" : "kimchy" }
    }
}
'
--------------------------------------------------
<1> The query must be passed as a value to the `query` key, in the same way as
the <<search-search,search api>>.

Both of the above examples end up doing the same thing, which is to delete all
tweets from the twitter index for the user `kimchy`.

Delete-by-query supports deletion across <<search-multi-index-type,multiple indices and multiple types>>.

==== Query-string parameters

The following query string parameters are supported:

`q`::

Instead of using the <<query-dsl,Query DSL>> to pass a `query` in the request
body, you can use the `q` query string parameter to  specify a query using
<<query-string-syntax,`query_string` syntax>>. In this case, the following
additional parameters are supported: `df`, `analyzer`, `default_operator`,
 `lowercase_expanded_terms`, `analyze_wildcard` and `lenient`.
See <<search-uri-request>> for details.

`size`::

The number of hits returned *per shard* by the <<scroll-scan,scroll/scan>>
request.  Defaults to 10.  May also be specified in the request body.

`timeout`::

The maximum execution time of the delete by query process. Once expired, no
more documents will be deleted.

`routing`::

A comma separated list of routing values to control which shards the delete by
query request should be executed on.

When using the `q` parameter, the following additional parameters are
supported (as explained in <<search-uri-request>>): `df`, `analyzer`,
`default_operator`.


==== Response body

The JSON response looks like this:

[source,js]
--------------------------------------------------
{
  "took" : 639,
  "timed_out" : false,
  "_indices" : {
    "_all" : {
      "found" : 5901,
      "deleted" : 5901,
      "missing" : 0,
      "failed" : 0
    },
    "twitter" : {
      "found" : 5901,
      "deleted" : 5901,
      "missing" : 0,
      "failed" : 0
    }
  },
  "failures" : [ ]
}
--------------------------------------------------

Internally, the query is used to execute an initial
<<scroll-scan,scroll/scan>> request. As hits are pulled from the scroll API,
they are passed to the <<bulk,Bulk API>> for deletion.

IMPORTANT: Delete by query will only delete the version of the document that
was visible to search at the time the request was executed.  Any documents
that have been reindexed or updated during execution will not be deleted.

Since documents can be updated or deleted by external operations during the
_scan-scroll-bulk_ process, the plugin keeps track of different counters for
each index, with the totals displayed under the `_all` index.  The counters
are as follows:

`found`::

The number of documents matching the query for the given index.

`deleted`::

The number of documents successfully deleted for the given index.

`missing`::

The number of documents that were missing when the plugin tried to delete
them. Missing documents were present when the original query was run, but have
already been deleted by another process.

`failed`::

The number of documents that failed to be deleted for the given index. A
document may fail to be deleted if it has been updated to a new version by
another process, or if the shard containing the document has gone missing due
to hardware failure, for example.
