Failed to flush after merge has finished – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch is unable to flush data to disk after a merge operation has completed. This could be due to insufficient disk space, I/O issues, or a problem with the underlying file system. To resolve this issue, you can try freeing up disk space, checking the health of your disk, or investigating if there are any issues with your file system. Additionally, ensure that your Elasticsearch version is up-to-date as this could also be a bug that has been fixed in a newer version.

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

Log Context

Log “failed to flush after merge has finished” classname is InternalEngine.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

                // we deadlock on engine#close for instance.
                engineConfig.getThreadPool().executor(ThreadPool.Names.FLUSH).execute(new AbstractRunnable() {
                    @Override
                    public void onFailure(Exception e) {
                        if (isClosed.get() == false) {
                            logger.warn("failed to flush after merge has finished");
                        }
                    }

                    @Override
                    protected void doRun() {

 

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