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Briefly, this error occurs when Elasticsearch is unable to retrieve a document with the specified document ID. This could be due to the document not existing in the index, or the index itself not existing. To resolve this issue, ensure that the document ID is correct and that the document exists in the index. If the index doesn’t exist, you need to create it. Also, check your Elasticsearch cluster’s health status to ensure it’s functioning properly. If the problem persists, consider checking your network connectivity or Elasticsearch logs for more detailed error information.
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This guide will help you check for common problems that cause the log ” Failed to fetch doc id [” + docId + “] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: search.
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 “Failed to fetch doc id [” + docId + “]” class name is FetchPhase.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
private void loadStoredFields(SearchShardTarget shardTarget; LeafReaderContext readerContext; FieldsVisitor fieldVisitor; int docId) {
fieldVisitor.reset();
try {
readerContext.reader().document(docId; fieldVisitor);
} catch (IOException e) {
throw new FetchPhaseExecutionException(shardTarget; "Failed to fetch doc id [" + docId + "]"; e);
}
} private static void fillDocAndMetaFields(SearchContext context; FieldsVisitor fieldsVisitor;
Map> storedToRequestedFields;
