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Briefly, this error occurs when OpenSearch tries to execute a reverse nested aggregation on a field that is not nested. This means that the field you’re trying to aggregate is not within a nested data type. To resolve this issue, you can either change your query to target a nested field, or modify your index mapping to make the target field nested. Additionally, ensure that the path specified in the reverse nested aggregation is correct and refers to a nested field.
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This guide will help you check for common problems that cause the log ” [reverse_nested] nested path [” + path + “] is not nested ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: aggregations, search.
Quick links
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 “[reverse_nested] nested path [” + path + “] is not nested” class name is ReverseNestedAggregationBuilder.java. We extracted the following from OpenSearch source code for those seeking an in-depth context :
parentObjectMapper = queryShardContext.getObjectMapper(path);
if (parentObjectMapper == null) {
return new ReverseNestedAggregatorFactory(name; true; null; queryShardContext; parent; subFactoriesBuilder; metadata);
}
if (parentObjectMapper.nested().isNested() == false) {
throw new AggregationExecutionException("[reverse_nested] nested path [" + path + "] is not nested");
}
} NestedScope nestedScope = queryShardContext.nestedScope();
try {
