Unexpected failure while fetching – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 2.4-2.6

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Briefly, this error occurs when OpenSearch encounters an unexpected issue while trying to retrieve data. This could be due to a variety of reasons such as network issues, corrupted data, or a problem with the OpenSearch cluster. To resolve this issue, you could try restarting the OpenSearch service, checking the network connection, or investigating the integrity of the data. If the problem persists, you may need to look into the health of your OpenSearch cluster and consider reindexing your data.

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This guide will help you check for common problems that cause the log ” unexpected failure while fetching [{}] ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: index.

Log Context

Log “unexpected failure while fetching [{}]” classname is OnDemandBlockSnapshotIndexInput.java.
We extracted the following from OpenSearch source code for those seeking an in-depth context :

        try {
            return transferManager.asyncFetchBlob(blobFetchRequest).get();
        } catch (InterruptedException | ExecutionException e) {
            logger.error(() -> new ParameterizedMessage("unexpected failure while fetching [{}]"; blobFetchRequest); e);
            throw new IllegalStateException(e);



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