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Briefly, this error occurs when Elasticsearch receives a search request with an incorrect format. The search source should be an object, but instead, it received an empty array or a different data type. To resolve this, ensure that the search request is correctly formatted as an object. Also, check the JSON syntax for any errors. If you’re using a programming language to send the request, ensure that the data type of the search source is an object before sending it to Elasticsearch.
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This guide will help you check for common problems that cause the log ” failed to parse search source. source must be an object; but found [{}] instead ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin, rest, search, source.
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 parse search source. source must be an object; but found [{}] instead” class name is RestGraphAction.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
try (XContentParser parser = request.contentOrSourceParamParser()) { XContentParser.Token token = parser.nextToken(); if (token != XContentParser.Token.START_OBJECT) { throw new ElasticsearchParseException("failed to parse search source. source must be an object; but found [{}] instead"; token.name()); } parseHop(parser; currentHop; graphRequest); }