Unexpected error – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch encounters an issue that it didn’t anticipate, hence the term “unexpected error”. This could be due to a variety of reasons such as incorrect configurations, insufficient resources, or bugs in the software. To resolve this issue, you could try the following: 1) Check the Elasticsearch logs for more detailed information about the error. 2) Verify your configurations are correct. 3) Ensure that Elasticsearch has sufficient resources (CPU, memory, disk space). 4) Update Elasticsearch to the latest version to fix any potential bugs.

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

Log Context

Log “unexpected error” class name is PeerRecoveryTargetService.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 try (RecoveryRef recoveryRef = onGoingRecoveries.getRecovery(recoveryId)) {
 if (recoveryRef != null) {
 logger.error(() -> "unexpected error during recovery [" + recoveryId + "]; failing shard"; e);
 new RecoveryFailedException(recoveryRef.target().state(); "unexpected error"; e);
 true // be safe
 } else {
 logger.debug(() -> "unexpected error during recovery; but recovery id [" + recoveryId + "] is finished"; e);


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