Update By Query APIedit

The simplest usage of _update_by_query just performs an update on every document in the index without changing the source. This is useful to pick up a new property or some other online mapping change. Here is the API:

POST twitter/_update_by_query?conflicts=proceed

That will return something like this:

{
  "took" : 147,
  "timed_out": false,
  "updated": 120,
  "deleted": 0,
  "batches": 1,
  "version_conflicts": 0,
  "noops": 0,
  "retries": {
    "bulk": 0,
    "search": 0
  },
  "throttled_millis": 0,
  "requests_per_second": -1.0,
  "throttled_until_millis": 0,
  "total": 120,
  "failures" : [ ]
}

_update_by_query gets a snapshot of the index when it starts and indexes what it finds using internal versioning. That means that you’ll get a version conflict if the document changes between the time when the snapshot was taken and when the index request is processed. When the versions match the document is updated and the version number is incremented.

Note

Since internal versioning does not support the value 0 as a valid version number, documents with version equal to zero cannot be updated using _update_by_query and will fail the request.

All update and query failures cause the _update_by_query to abort and are returned in the failures of the response. The updates that have been performed still stick. In other words, the process is not rolled back, only aborted. While the first failure causes the abort, all failures that are returned by the failing bulk request are returned in the failures element; therefore it’s possible for there to be quite a few failed entities.

If you want to simply count version conflicts not cause the _update_by_query to abort you can set conflicts=proceed on the url or "conflicts": "proceed" in the request body. The first example does this because it is just trying to pick up an online mapping change and a version conflict simply means that the conflicting document was updated between the start of the _update_by_query and the time when it attempted to update the document. This is fine because that update will have picked up the online mapping update.

Back to the API format, you can limit _update_by_query to a single type. This will only update tweet documents from the twitter index:

POST twitter/tweet/_update_by_query?conflicts=proceed

You can also limit _update_by_query using the Query DSL. This will update all documents from the twitter index for the user kimchy:

POST twitter/_update_by_query?conflicts=proceed
{
  "query": { 
    "term": {
      "user": "kimchy"
    }
  }
}

The query must be passed as a value to the query key, in the same way as the Search API. You can also use the q parameter in the same way as the search api.

So far we’ve only been updating documents without changing their source. That is genuinely useful for things like picking up new properties but it’s only half the fun. _update_by_query supports a script object to update the document. This will increment the likes field on all of kimchy’s tweets:

POST twitter/_update_by_query
{
  "script": {
    "source": "ctx._source.likes++",
    "lang": "painless"
  },
  "query": {
    "term": {
      "user": "kimchy"
    }
  }
}

Just as in Update API you can set ctx.op to change the operation that is executed:

noop
Set ctx.op = "noop" if your script decides that it doesn’t have to make any changes. That will cause _update_by_query to omit that document from its updates. This no operation will be reported in the noop counter in the response body.
delete
Set ctx.op = "delete" if your script decides that the document must be deleted. The deletion will be reported in the deleted counter in the response body.

Setting ctx.op to anything else is an error. Setting any other field in ctx is an error.

Note that we stopped specifying conflicts=proceed. In this case we want a version conflict to abort the process so we can handle the failure.

This API doesn’t allow you to move the documents it touches, just modify their source. This is intentional! We’ve made no provisions for removing the document from its original location.

It’s also possible to do this whole thing on multiple indexes and multiple types at once, just like the search API:

POST twitter,blog/tweet,post/_update_by_query

If you provide routing then the routing is copied to the scroll query, limiting the process to the shards that match that routing value:

POST twitter/_update_by_query?routing=1

By default _update_by_query uses scroll batches of 1000. You can change the batch size with the scroll_size URL parameter:

POST twitter/_update_by_query?scroll_size=100

_update_by_query can also use the Ingest Node feature by specifying a pipeline like this:

PUT _ingest/pipeline/set-foo
{
  "description" : "sets foo",
  "processors" : [ {
      "set" : {
        "field": "foo",
        "value": "bar"
      }
  } ]
}
POST twitter/_update_by_query?pipeline=set-foo

URL Parametersedit

In addition to the standard parameters like pretty, the Update By Query API also supports refresh, wait_for_completion, wait_for_active_shards, and timeout.

Sending the refresh will update all shards in the index being updated when the request completes. This is different than the Index API’s refresh parameter which causes just the shard that received the new data to be indexed.

If the request contains wait_for_completion=false then Elasticsearch will perform some preflight checks, launch the request, and then return a task which can be used with Tasks APIs to cancel or get the status of the task. Elasticsearch will also create a record of this task as a document at .tasks/task/${taskId}. This is yours to keep or remove as you see fit. When you are done with it, delete it so Elasticsearch can reclaim the space it uses.

wait_for_active_shards controls how many copies of a shard must be active before proceeding with the request. See here for details. timeout controls how long each write request waits for unavailable shards to become available. Both work exactly how they work in the Bulk API.

requests_per_second can be set to any positive decimal number (1.4, 6, 1000, etc) and throttles the number of requests per second that the update-by-query issues or it can be set to -1 to disabled throttling. The throttling is done waiting between bulk batches so that it can manipulate the scroll timeout. The wait time is the difference between the time it took the batch to complete and the time requests_per_second * requests_in_the_batch. Since the batch isn’t broken into multiple bulk requests large batch sizes will cause Elasticsearch to create many requests and then wait for a while before starting the next set. This is "bursty" instead of "smooth". The default is -1.

Response bodyedit

The JSON response looks like this:

{
  "took" : 639,
  "updated": 0,
  "batches": 1,
  "version_conflicts": 2,
  "retries": {
    "bulk": 0,
    "search": 0
  }
  "throttled_millis": 0,
  "failures" : [ ]
}
took
The number of milliseconds from start to end of the whole operation.
updated
The number of documents that were successfully updated.
batches
The number of scroll responses pulled back by the the update by query.
version_conflicts
The number of version conflicts that the update by query hit.
retries
The number of retries attempted by update-by-query. bulk is the number of bulk actions retried and search is the number of search actions retried.
throttled_millis
Number of milliseconds the request slept to conform to requests_per_second.
failures
Array of all indexing failures. If this is non-empty then the request aborted because of those failures. See conflicts for how to prevent version conflicts from aborting the operation.

Works with the Task APIedit

You can fetch the status of all running update-by-query requests with the Task API:

GET _tasks?detailed=true&actions=*byquery

The responses looks like:

{
  "nodes" : {
    "r1A2WoRbTwKZ516z6NEs5A" : {
      "name" : "r1A2WoR",
      "transport_address" : "127.0.0.1:9300",
      "host" : "127.0.0.1",
      "ip" : "127.0.0.1:9300",
      "attributes" : {
        "testattr" : "test",
        "portsfile" : "true"
      },
      "tasks" : {
        "r1A2WoRbTwKZ516z6NEs5A:36619" : {
          "node" : "r1A2WoRbTwKZ516z6NEs5A",
          "id" : 36619,
          "type" : "transport",
          "action" : "indices:data/write/update/byquery",
          "status" : {    
            "total" : 6154,
            "updated" : 3500,
            "created" : 0,
            "deleted" : 0,
            "batches" : 4,
            "version_conflicts" : 0,
            "noops" : 0,
            "retries": {
              "bulk": 0,
              "search": 0
            }
            "throttled_millis": 0
          },
          "description" : ""
        }
      }
    }
  }
}

this object contains the actual status. It is just like the response json with the important addition of the total field. total is the total number of operations that the reindex expects to perform. You can estimate the progress by adding the updated, created, and deleted fields. The request will finish when their sum is equal to the total field.

With the task id you can look up the task directly:

GET /_tasks/taskId:1

The advantage of this API is that it integrates with wait_for_completion=false to transparently return the status of completed tasks. If the task is completed and wait_for_completion=false was set on it them it’ll come back with a results or an error field. The cost of this feature is the document that wait_for_completion=false creates at .tasks/task/${taskId}. It is up to you to delete that document.

Works with the Cancel Task APIedit

Any Update By Query can be canceled using the Task Cancel API:

POST _tasks/task_id:1/_cancel

The task_id can be found using the tasks API above.

Cancellation should happen quickly but might take a few seconds. The task status API above will continue to list the task until it is wakes to cancel itself.

Rethrottlingedit

The value of requests_per_second can be changed on a running update by query using the _rethrottle API:

POST _update_by_query/task_id:1/_rethrottle?requests_per_second=-1

The task_id can be found using the tasks API above.

Just like when setting it on the _update_by_query API requests_per_second can be either -1 to disable throttling or any decimal number like 1.7 or 12 to throttle to that level. Rethrottling that speeds up the query takes effect immediately but rethrotting that slows down the query will take effect on after completing the current batch. This prevents scroll timeouts.

Manual slicingedit

Update-by-query supports Sliced Scroll allowing you to manually parallelize the process relatively easily:

POST twitter/_update_by_query
{
  "slice": {
    "id": 0,
    "max": 2
  },
  "script": {
    "source": "ctx._source['extra'] = 'test'"
  }
}
POST twitter/_update_by_query
{
  "slice": {
    "id": 1,
    "max": 2
  },
  "script": {
    "source": "ctx._source['extra'] = 'test'"
  }
}

Which you can verify works with:

GET _refresh
POST twitter/_search?size=0&q=extra:test&filter_path=hits.total

Which results in a sensible total like this one:

{
  "hits": {
    "total": 120
  }
}

Automatic slicingedit

You can also let update-by-query automatically parallelize using Sliced Scroll to slice on _uid:

POST twitter/_update_by_query?refresh&slices=5
{
  "script": {
    "source": "ctx._source['extra'] = 'test'"
  }
}

Which you also can verify works with:

POST twitter/_search?size=0&q=extra:test&filter_path=hits.total

Which results in a sensible total like this one:

{
  "hits": {
    "total": 120
  }
}

Adding slices to _update_by_query just automates the manual process used in the section above, creating sub-requests which means it has some quirks:

  • You can see these requests in the Tasks APIs. These sub-requests are "child" tasks of the task for the request with slices.
  • Fetching the status of the task for the request with slices only contains the status of completed slices.
  • These sub-requests are individually addressable for things like cancellation and rethrottling.
  • Rethrottling the request with slices will rethrottle the unfinished sub-request proportionally.
  • Canceling the request with slices will cancel each sub-request.
  • Due to the nature of slices each sub-request won’t get a perfectly even portion of the documents. All documents will be addressed, but some slices may be larger than others. Expect larger slices to have a more even distribution.
  • Parameters like requests_per_second and size on a request with slices are distributed proportionally to each sub-request. Combine that with the point above about distribution being uneven and you should conclude that the using size with slices might not result in exactly size documents being `_update_by_query`ed.
  • Each sub-requests gets a slightly different snapshot of the source index though these are all taken at approximately the same time.

Picking the number of slicesedit

At this point we have a few recommendations around the number of slices to use (the max parameter in the slice API if manually parallelizing):

  • Don’t use large numbers. 500 creates fairly massive CPU thrash.
  • It is more efficient from a query performance standpoint to use some multiple of the number of shards in the source index.
  • Using exactly as many shards as are in the source index is the most efficient from a query performance standpoint.
  • Indexing performance should scale linearly across available resources with the number of slices.
  • Whether indexing or query performance dominates that process depends on lots of factors like the documents being reindexed and the cluster doing the reindexing.

Pick up a new propertyedit

Say you created an index without dynamic mapping, filled it with data, and then added a mapping value to pick up more fields from the data:

PUT test
{
  "mappings": {
    "test": {
      "dynamic": false,   
      "properties": {
        "text": {"type": "text"}
      }
    }
  }
}

POST test/test?refresh
{
  "text": "words words",
  "flag": "bar"
}
POST test/test?refresh
{
  "text": "words words",
  "flag": "foo"
}
PUT test/_mapping/test   
{
  "properties": {
    "text": {"type": "text"},
    "flag": {"type": "text", "analyzer": "keyword"}
  }
}

This means that new fields won’t be indexed, just stored in _source.

This updates the mapping to add the new flag field. To pick up the new field you have to reindex all documents with it.

Searching for the data won’t find anything:

POST test/_search?filter_path=hits.total
{
  "query": {
    "match": {
      "flag": "foo"
    }
  }
}
{
  "hits" : {
    "total" : 0
  }
}

But you can issue an _update_by_query request to pick up the new mapping:

POST test/_update_by_query?refresh&conflicts=proceed
POST test/_search?filter_path=hits.total
{
  "query": {
    "match": {
      "flag": "foo"
    }
  }
}
{
  "hits" : {
    "total" : 1
  }
}

You can do the exact same thing when adding a field to a multifield.