Briefly, this error occurs when you try to disable `stored_fields` while requesting a version in Elasticsearch. The versioning system in Elasticsearch requires `stored_fields` to track changes in the documents. To resolve this issue, you can either enable `stored_fields` or refrain from requesting a version. If you don’t need versioning, simply remove the version request. If versioning is necessary, ensure `stored_fields` is enabled.
This guide will help you check for common problems that cause the log ” `stored_fields` cannot be disabled if version is requested ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: search, version.
Overview
Search refers to the searching of documents in an index or multiple indices. The simple search is just a GET API request to the _search endpoint. The search query can either be provided in query string or through a request body.
Examples
When looking for any documents in this index, if search parameters are not provided, every document is a hit and by default 10 hits will be returned.
GET my_documents/_search
A JSON object is returned in response to a search query. A 200 response code means the request was completed successfully.
{
"took" : 1,
"timed_out" : false,
"_shards" : {
"total" : 2,
"successful" : 2,
"failed" : 0
},
"hits" : {
"total" : 2,
"max_score" : 1.0,
"hits" : [
...
]
}
}Notes and good things to know
- Distributed search is challenging and every shard of the index needs to be searched for hits, and then those hits are combined into a single sorted list as a final result.
- There are two phases of search: the query phase and the fetch phase.
- In the query phase, the query is executed on each shard locally and top hits are returned to the coordinating node. The coordinating node merges the results and creates a global sorted list.
- In the fetch phase, the coordinating node brings the actual documents for those hit IDs and returns them to the requesting client.
- A coordinating node needs enough memory and CPU in order to handle the fetch phase.
Overview
A version corresponds to the Elasticsearch built-in tracking system that tracks the changes in each document’s update. When a document is indexed for the first time, it is assigned a version 1 using _version key. When the same document gets a subsequent update, the _version is incremented by 1 with every index, update or delete API call.
What it is used for
A version is used to handle the concurrency issues in Elasticsearch which come into play during simultaneous accessing of an index by multiple users. Elasticsearch handles this issue with an optimistic locking concept using the _version parameter to avoid letting multiple users edit the same document at the same time and protects users from generating incorrect data.
Notes
You cannot see the history of the document using _version. That means Elasticsearch does not use _version to keep a track of original changes that had been performed on the document. For example, if a document has been updated 10 times, it’s _version would be marked by Elasticsearch as 11, but you cannot go back and see what version 5 of the document looked like. This has to be implemented independently.
Common problems
If optimistic locking is not implemented while making updates to a document, Elasticsearch may return a conflict error with the 409 status code, which means that multiple users are trying to update the same version of the document at the same time.
POST /ratings/123?version=50
{
"name": "Joker",
"rating": 50
}Log Context
Log “`stored_fields` cannot be disabled if version is requested” class name is SearchService.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
} if (source.storedFields() != null) {
if (source.storedFields().fetchFields() == false) {
if (context.version()) {
throw new SearchException(shardTarget; "`stored_fields` cannot be disabled if version is requested");
}
if (context.sourceRequested()) {
throw new SearchException(shardTarget; "`stored_fields` cannot be disabled if _source is requested");
}
}
[ratemypost]