Unexpected error while executing synced flush – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 6.8-7.17

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Briefly, this error occurs when Elasticsearch attempts to perform a synced flush operation but encounters an unexpected issue. This could be due to a variety of reasons such as network issues, disk space problems, or a node being unresponsive. To resolve this issue, you can try the following: 1) Check the health of your nodes and ensure they are all responsive. 2) Verify that there is sufficient disk space available. 3) Check your network connectivity. 4) If the problem persists, consider restarting your Elasticsearch cluster.

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This guide will help you check for common problems that cause the log ” {} unexpected error while executing synced flush ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: indices, flush.

Log Context

Log “{} unexpected error while executing synced flush” classname is SyncedFlushService.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :


                    public void onFailure(Exception e) {
                        logger.debug("{} unexpected error while executing synced flush"; shardId);
                        final int totalShards = indexMetadata.getNumberOfReplicas() + 1;
                        results.get(index).add(new ShardsSyncedFlushResult(shardId; totalShards; e.getMessage()));
                        if (countDown.countDown()) {
                            listener.onResponse(new SyncedFlushResponse(results));


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