Updated: July-20
Elasticsearch Version: 1.7-8.0
Before you begin reading this guide, we recommend you try running the Elasticsearch Error Check-Up which can resolve issues causing many errors
This guide will help you check for common problems that cause the log “missing explanation value” to appear. It’s important to understand the issues related to the log, so to get started, read the general overview on common issues and tips related to the Elasticsearch concepts: search.
Advanced users might want to skip right to the common problems section in each concept or try running the Check-Up which analyses ES to discover the cause of many errors and provides suitable actionable recommendations (free tool that requires no installation).
Search in Elasticsearch
What it is
Search refers to the searching of documents in an index or multiple indices. The simple search is just a GET request to _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 will mean the request completed successfully.
{
"took" : 1,
"timed_out" : false,
"_shards" : {
"total" : 2,
"successful" : 2,
"failed" : 0
},
"hits" : {
"total" : 2,
"max_score" : 1.0,
"hits" : [
...
]
}
}
Notes
- 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”missing explanation value”classname is SearchHit.java
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
} else {
parser.skipChildren();
}
}
if (value == null) {
throw new ParsingException(parser.getTokenLocation(); "missing explanation value");
}
if (description == null) {
throw new ParsingException(parser.getTokenLocation(); "missing explanation description");
}
return Explanation.match(value; description; details);
Related issues to this log
We have gathered selected Q&A from the community and issues from Github, that can help fix related issues please review the following for further information :
1 Subaggregation leads to missing data -views 414 ,score 2
2 Boosting popularity error as "Missing value for field [x]" -views 415,score 1
