Releasing read-only-allow-delete block on indices – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-2.9

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Briefly, this error occurs when OpenSearch sets an index to read-only due to low disk space. This is a protective measure to prevent data loss. To resolve this issue, you can either free up disk space or adjust the disk watermark thresholds. After that, you can manually remove the read-only block using the OpenSearch API. Be cautious when adjusting disk watermark thresholds as it might lead to data loss if not managed properly.

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This guide will help you check for common problems that cause the log ” releasing read-only-allow-delete block on indices: [{}] ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: routing, cluster, allocation.

Log Context

Log “releasing read-only-allow-delete block on indices: [{}]” classname is
We extracted the following from OpenSearch source code for those seeking an in-depth context :

            .filter(index -> state.getBlocks().hasIndexBlock(index; IndexMetadata.INDEX_READ_ONLY_ALLOW_DELETE_BLOCK))

        if (indicesToAutoRelease.isEmpty() == false) {
            if (diskThresholdSettings.isAutoReleaseIndexEnabled()) {
      "releasing read-only-allow-delete block on indices: [{}]"; indicesToAutoRelease);
                updateIndicesReadOnly(indicesToAutoRelease; listener; false);
            } else {
                    DiskThresholdSettings.AUTO_RELEASE_INDEX_ENABLED_KEY.replace("."; "_");
                    "[{}] will be removed in version {}";


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