Unexpectedly failed to clear cache – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 8.3-8.9

Briefly, this error occurs when Elasticsearch is unable to clear its cache due to issues like insufficient permissions, disk space, or a network problem. To resolve this, you can try increasing the disk space, checking the network connectivity, or ensuring that Elasticsearch has the necessary permissions to perform the operation. Additionally, check for any underlying system issues that might be causing this error.

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

Log Context

Log “unexpectedly failed to clear cache” classname is JoinValidationService.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :


    private final AbstractRunnable cacheClearer = new AbstractRunnable() {
        public void onFailure(Exception e) {
            logger.error("unexpectedly failed to clear cache"; e);
            assert false : e;

        protected void doRun() {