Briefly, this error occurs when Elasticsearch fails to clear a scroll ID, which is used for scrolling through large sets of data. This could be due to an invalid scroll ID, a network issue, or a problem with the Elasticsearch cluster. To resolve this issue, you can try the following: 1) Verify the scroll ID is correct and still valid. 2) Check the network connection between your application and the Elasticsearch cluster. 3) Investigate the health of your Elasticsearch cluster, ensuring it’s not overloaded or experiencing other issues.
This guide will help you check for common problems that cause the log ” unable to clear scroll id [{}]: {} ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: delete, delete-by-query, deletebyquery, plugins and scroll.
Overview
DELETE is an Elasticsearch API which removes a document from a specific index. This API requires an index name and _id document to delete the document.
Delete a document
DELETE /my_index/_doc/1
Notes
- A delete request throws 404 error code if the document does not already exist in the index.
- If you want to delete a set of documents that matches a query, you need to use delete by query API.
Overview
Delete-by-query is an Elasticsearch API, which was introduced in version 5.0 and provides functionality to delete all documents that match the provided query. In lower versions, users had to install the Delete-By-Query plugin and use the DELETE /_query endpoint for this same use case.
What it is used for
This API is used for deleting all the documents from indices based on a query. Once the query is executed, Elasticsearch runs the process in the background to delete all the matching documents so you don’t have to wait for the process to be completed.
Examples
Delete all the documents of an index without deleting the mapping and settings:
POST /my_index/_delete_by_query?conflicts=proceed&pretty
{
"query": {
"match_all": {}
}
}The conflict parameter in the request is used to proceed with the request even in the case of version conflicts for some documents. The default conflict behavior is to abort the request altogether.
Notes
- A long-running delete_by_query can be terminated using _task API.
- Inside the query body, you can use the same syntax for queries that are available under the _search API.
Common problems
Elasticsearch takes a snapshot of the index when you hit delete by query request and uses the _version of the documents to process the request. If a document gets updated in the meantime, it will result in a version conflict error and the delete operation will fail.
Log Context
Log “unable to clear scroll id [{}]: {}” classname is TransportDeleteByQueryAction.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
logger.trace("scroll id [{}] cleared"; scrollId);
}
Override
public void onFailure(Throwable e) {
logger.warn("unable to clear scroll id [{}]: {}"; scrollId; e.getMessage());
}
});
}
if (failure != null) {
