Briefly, this error occurs when the `from` parameter in an Elasticsearch query is not set to 0 while using the `search_after` parameter. The `search_after` parameter is used for pagination of results, and the `from` parameter must be set to 0 to ensure correct pagination. To resolve this issue, you should set the `from` parameter to 0 in your query when using `search_after`. Alternatively, if you need to use the `from` parameter with a value other than 0, you should not use `search_after` in the same query.
This guide will help you check for common problems that cause the log ” `from` parameter must be set to 0 when `search_after` is used. ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: 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 “`from` parameter must be set to 0 when `search_after` is used.” class name is SearchService.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
if (CollectionUtils.isEmpty(source.searchAfter()) == false) {
if (context.scrollContext() != null) {
throw new SearchException(shardTarget; "`search_after` cannot be used in a scroll context.");
}
if (context.from() > 0) {
throw new SearchException(shardTarget; "`from` parameter must be set to 0 when `search_after` is used.");
} String collapseField = source.collapse() != null ? source.collapse().getField() : null;
FieldDoc fieldDoc = SearchAfterBuilder.buildFieldDoc(context.sort(); source.searchAfter(); collapseField);
context.searchAfter(fieldDoc);
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