Briefly, this error occurs when Elasticsearch fails to execute a query template due to an issue with flushing the writer. This could be due to a lack of disk space, a corrupted index, or a network connectivity issue. To resolve this, you can try freeing up disk space, checking the health of your indices and repairing if necessary, or ensuring stable network connectivity. Additionally, check your Elasticsearch logs for more specific details about the error.
In addition we recommend you run the Elasticsearch Template Optimizer to fix problems in your data modeling.
It will analyze your templates to detect issues and improve search performance, reduce indexing bottlenecks and optimize storage utilization. The Template Optimizer is free and requires no installation.
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 “Could not execute query template (failed to flush writer):” classname is MustacheScriptEngineService.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
UTF8StreamWriter writer = utf8StreamWriter().setOutput(result);
((Mustache) template).execute(writer; vars);
try {
writer.flush();
} catch (IOException e) {
logger.error("Could not execute query template (failed to flush writer): "; e);
} finally {
try {
writer.close();
} catch (IOException e) {
logger.error("Could not execute query template (failed to close writer): "; e);
