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Briefly, this error occurs when OpenSearch expects a list or an entry of context mapping, but it doesn’t find one. This usually happens when there’s a mismatch between the data type provided and the data type expected by the context mapping. To resolve this issue, you can either modify your data to match the expected data type or adjust the context mapping to accept the current data type. Additionally, ensure that your data is correctly formatted and doesn’t contain any unexpected values or types.
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This guide will help you check for common problems that cause the log ” expected a list or an entry of context mapping ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: mapping, search.
Quick links
Overview
Mapping is similar to database schemas that define the properties of each field in the index. These properties may contain the data type of each field and how fields are going to be tokenized and indexed. In addition, the mapping may also contain various advanced level properties for each field to define the options exposed by Lucene and OpenSearch. You can create a mapping of an index using the _mappings REST endpoint. The very first time OpenSearch finds a new field whose mapping is not pre-defined inside the index, it automatically tries to guess the data type and analyzer of that field and set its default value. For example, if you index an integer field without pre-defining the mapping, OpenSearch sets the mapping of that field as long.
Examples
Create an index with predefined mapping:
PUT /my_index?pretty
{
"settings": {
"number_of_shards": 1
},
"mappings": {
"properties": {
"name": {
"type": "text"
},
"age": {
"type": "integer"
}
}
}
}Create mapping in an existing index:
PUT /my_index/_mapping?pretty
{
"properties": {
"email": {
"type": "keyword"
}
}
}View the mapping of an existing index:
GET my_index/_mapping?pretty
View the mapping of an existing field:
GET /my_index/_mapping/field/name?pretty
Notes
- It is not possible to update the mapping of an existing field. If the mapping is set to the wrong type, re-creating the index with updated mapping and re-indexing is the only option available.
Common problems
- The most common problem in OpenSearch is incorrectly defined mapping which limits the functionality of the field. For example, if the data type of a string field is set as text, you cannot use that field for aggregations, sorting or exact match filters. Similarly, if a string field is dynamically indexed without predefined mapping, OpenSearch automatically creates two fields internally. One as a text type for full-text search and another as keyword type, which in most cases is a waste of space.
- The mapping of each index is part of the cluster state and is managed by master nodes. If the mapping is too big, meaning there are thousands of fields in the index, the cluster state grows too large to be handled and creates the issue of mapping explosion, resulting in the slowness of the cluster.
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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 “expected a list or an entry of context mapping” class name is ContextMappings.java. We extracted the following from OpenSearch source code for those seeking an in-depth context :
throw new OpenSearchParseException("expected at least one context mapping");
}
} else if (configuration instanceof Map) {
contextMappings = Collections.singletonList(load(((Map) configuration); indexVersionCreated));
} else {
throw new OpenSearchParseException("expected a list or an entry of context mapping");
}
return new ContextMappings(contextMappings);
} private static ContextMapping load(Map contextConfig; Version indexVersionCreated) {
