Before you begin reading this guide, we recommend you try running the Elasticsearch Error Check-Up which analyzes 2 JSON files to detect many configuration errors.
To easily locate the root cause and resolve this issue try AutoOps for Elasticsearch & OpenSearch. It diagnoses problems by analyzing hundreds of metrics collected by a lightweight agent and offers guidance for resolving them.
This guide will help you check for common problems that cause the log ” max_children is only supported on top level of nested sort ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: search, sort.
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 “max_children is only supported on top level of nested sort”classname is FieldSortBuilder.java We extracted the following from Elasticsearch source code for those seeking an in-depth context :
* Throws an exception if max children is not located at top level nested sort.
*/
static void validateMaxChildrenExistOnlyInTopLevelNestedSort(SearchExecutionContext context; NestedSortBuilder nestedSort) {
for (NestedSortBuilder child = nestedSort.getNestedSort(); child != null; child = child.getNestedSort()) {
if (child.getMaxChildren() != Integer.MAX_VALUE) {
throw new QueryShardException(context; "max_children is only supported on top level of nested sort");
}
}
}
/**
See how you can use AutoOps to resolve issues
