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Briefly, this error occurs when OpenSearch encounters an issue during the rescore phase of a query. The rescore phase is used to improve the relevance of the search results. The error could be due to a misconfiguration in the rescore query or a lack of system resources. To resolve this, you can try to simplify the rescore query or increase the system resources. Additionally, ensure that the rescore window size is not set too high as it can consume a lot of memory and cause the rescore phase to fail.
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This guide will help you check for common problems that cause the log ” Rescore Phase Failed ” 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 “Rescore Phase Failed” class name is RescoreProcessor.java. We extracted the following from OpenSearch source code for those seeking an in-depth context :
assert context.sort() == null && topDocsSortedByScore(topDocs) : "topdocs should be sorted after rescore";
}
context.queryResult()
.topDocs(new TopDocsAndMaxScore(topDocs; topDocs.scoreDocs[0].score); context.queryResult().sortValueFormats());
} catch (IOException e) {
throw new OpenSearchException("Rescore Phase Failed"; e);
}
} /**
* Returns true if the provided docs are sorted by score.
