%s failed to execute %s sync – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 8.4-8.9

Briefly, this error occurs when Elasticsearch struggles to synchronize data across its nodes. This could be due to network issues, heavy load, or insufficient resources. To resolve this, you can try increasing the timeout settings, ensuring all nodes are reachable and functioning properly, or scaling up your resources. Additionally, consider optimizing your queries to reduce the load on the server.

This guide will help you check for common problems that cause the log ” %s failed to execute %s sync ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: index.

Log Context

Log “%s failed to execute %s sync” classname is IndexService.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

                        try {
                            shard.runUnderPrimaryPermit(() -> sync.accept(shard); e -> {
                                if (e instanceof AlreadyClosedException == false
                                    && e instanceof IndexShardClosedException == false
                                    && e instanceof ShardNotInPrimaryModeException == false) {
                                    logger.warn(() -> format("%s failed to execute %s sync"; shard.shardId(); source); e);
                            }; ThreadPool.Names.SAME);
                        } catch (final AlreadyClosedException | IndexShardClosedException e) {
                            // the shard was closed concurrently; continue


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