Failed to notify callback – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch encounters an issue while executing a callback function. This could be due to a variety of reasons such as a network issue, a problem with the callback function itself, or a resource constraint. To resolve this issue, you can try the following: 1) Check the network connectivity and ensure it’s stable. 2) Review the callback function for any errors or issues. 3) Check the system resources and ensure there’s enough memory and CPU available for Elasticsearch to operate efficiently.

This guide will help you check for common problems that cause the log ” failed to notify callback ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: .

Log Context

Log “failed to notify callback” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

        for (Tuple> tuple : candidates) {
            Consumer consumer = tuple.v2();
            try {
            } catch (Exception ex) {
                logger.warn("failed to notify callback"; ex);

    private Consumer preserveContext(Consumer consumer) {


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