Exception thrown by listener while notifying on ack timeout – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-2.9

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Briefly, this error occurs when a listener in OpenSearch fails to receive an acknowledgment (ack) within a specified timeout period. This could be due to network issues, overloaded system, or a slow listener. To resolve this, you can increase the timeout period to allow more time for the ack to be received. Alternatively, you can investigate the listener to ensure it’s functioning properly and not being slowed down by other processes. Lastly, check your network connection and system load to ensure they are not causing delays.

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This guide will help you check for common problems that cause the log ” exception thrown by listener while notifying on ack timeout ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: cluster.

Log Context

Log “exception thrown by listener while notifying on ack timeout” classname is MasterService.java.
We extracted the following from OpenSearch source code for those seeking an in-depth context :

        public void onAckTimeout() {
            try (ThreadContext.StoredContext ignore = context.get()) {
            } catch (Exception e) {
                logger.error("exception thrown by listener while notifying on ack timeout"; e);

        public TimeValue ackTimeout() {


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