Briefly, this error occurs when Elasticsearch is unable to send an error response for a specific action, in this case, ‘clear sc’. This could be due to network issues, insufficient permissions, or a problem with the Elasticsearch cluster itself. To resolve this issue, you can check the network connectivity, ensure the user has the necessary permissions, or investigate the health of the Elasticsearch cluster. Additionally, checking the Elasticsearch logs for more detailed error messages can help identify the root cause of the problem.
This guide will help you check for common problems that cause the log ” Failed to send error response for action [clear_sc] and request [ ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: request, response, scroll and search.
Overview
In Elasticsearch, the concept of scroll comes into play when you have a large set of search results. Large search results are exhaustive for both the Elasticsearch cluster and the requesting client in terms of memory and processing. The scroll API enables you to take a snapshot of a large number of results from a single search request.
Examples
To perform a scroll search, you need to add the scroll parameter to a search query and specify how long Elasticsearch should keep the search context viable.
GET mydocs-2019/_search?scroll=40s
{
"size": 5000,
"query": {
"match_all": {}
},
"sort": [
{
"_doc": {
"order": "asc"
}
}
]
}This query will return a maximum of 5000 hits. If the scroll is idle for more than 40 seconds, it will be deleted. The response will return the first page of the results and a scroll ID. You can use the scroll ID to get additional documents from the scroll. You’ll be able to keep retrieving the documents until you have all of them.
Notes
- Changes made to documents after the scroll will not show up in your results.
- When you are done with the scroll, you can delete it manually using the scroll ID.
DELETE _search/scroll/<scroll_id>
Log Context
Log “Failed to send error response for action [clear_sc] and request [” classname is TransportClearScrollAction.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
Override
public void onFailure(Throwable e) {
try {
channel.sendResponse(e);
} catch (Exception e1) {
logger.warn("Failed to send error response for action [clear_sc] and request [" + request + "]"; e1);
}
}
});
}
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