Briefly, this error occurs when Elasticsearch encounters an issue while executing a progress listener during the reduce phase of a search operation. This could be due to a variety of reasons such as insufficient resources, network issues, or a bug in the code. To resolve this issue, you could try increasing the resources allocated to Elasticsearch, checking the network connectivity between nodes, or reviewing the code for potential bugs. Additionally, ensure that your Elasticsearch version is up-to-date as this could also be a bug that has been fixed in a newer version.
This log is related to search problems, in addition to reading the guide below you can use the free Search Log Analyzer. With Opster’s Analyzer, you can easily locate slow searches and understand what led to them adding additional load to your system. The tool is free and takes just 2 minutes to run.
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 execute progress listener on reduce” classname is SearchProgressListener.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
protected final void notifyFinalReduce(List shards; TotalHits totalHits; InternalAggregations aggs; int reducePhase) {
try {
onFinalReduce(shards; totalHits; aggs; reducePhase);
} catch (Exception e) {
logger.warn("Failed to execute progress listener on reduce"; e);
}
}
final void notifyFetchResult(int shardIndex) {
try {
