Failed to properly stop client thread – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch is unable to terminate a client thread correctly. This could be due to a variety of reasons such as a long-running query, a heavy load on the server, or a bug in the Elasticsearch software. To resolve this issue, you can try to identify and stop the long-running query, reduce the load on the server, or upgrade Elasticsearch to the latest version. If the problem persists, consider increasing the thread pool size or optimizing your queries for better performance.

This guide will help you check for common problems that cause the log ” Failed to properly stop client thread [{}] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: client, reindex, thread.

Log Context

Log “Failed to properly stop client thread [{}]” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

            super.finishHim(failure; indexingFailures; searchFailures; timedOut);
            // A little extra paranoia so we log something if we leave any threads running
            for (Thread thread : createdThreads) {
                if (thread.isAlive()) {
                    assert false : "Failed to properly stop client thread [" + thread.getName() + "]";
                    logger.error("Failed to properly stop client thread [{}]"; thread.getName());



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