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Briefly, this error occurs when Elasticsearch expects a JSON object (denoted by XContentParser.Token.START_OBJECT) but doesn’t find it in the request body. This usually happens due to incorrect or malformed JSON syntax. To resolve this issue, you can: 1) Validate your JSON syntax using a JSON validator. 2) Ensure that your JSON starts with a ‘{‘ and ends with a ‘}’. 3) Check that all keys and string values are enclosed in double quotes. 4) Make sure that all nested JSON objects and arrays are correctly formatted and closed.
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This guide will help you check for common problems that cause the log ” Expected [” + XContentParser.Token.START_OBJECT + “] in [ ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: parser, 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 “Expected [” + XContentParser.Token.START_OBJECT + “] in [” class name is SearchSourceBuilder.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
}
this.ignoreFailure = ignoreFailure;
this.fieldName = scriptFieldName;
this.script = script;
} else {
throw new ParsingException(parser.getTokenLocation(); "Expected [" + XContentParser.Token.START_OBJECT + "] in ["
+ parser.currentName() + "] but found [" + token + "]"; parser.getTokenLocation());
}
} public String fieldName() {
