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Briefly, this error occurs when you try to disable stored fields in OpenSearch while also requesting the source. Stored fields are necessary for retrieving the original _source field. To resolve this issue, you can either enable stored fields or stop requesting the source. Alternatively, you can store only the specific fields you need, reducing the storage space required. Remember, disabling stored fields can lead to incomplete search results and potential data loss.
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This guide will help you check for common problems that cause the log ” [stored_fields] cannot be disabled if [_source] is requested ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: search.
Quick links
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.
Log Context
Log “[stored_fields] cannot be disabled if [_source] is requested” class name is SearchService.java. We extracted the following from OpenSearch source code for those seeking an in-depth context :
} if (source.storedFields() != null) {
if (source.storedFields().fetchFields() == false) {
if (context.sourceRequested()) {
throw new SearchException(shardTarget; "[stored_fields] cannot be disabled if [_source] is requested");
}
if (context.fetchFieldsContext() != null) {
throw new SearchException(shardTarget; "[stored_fields] cannot be disabled when using the [fields] option");
}
}
