Failed to prepare warm – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-2.9

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Briefly, this error occurs when OpenSearch fails to prepare or warm up the necessary caches before executing a query. This could be due to insufficient memory, high load, or a configuration issue. To resolve this, you can increase the memory allocation for OpenSearch, reduce the load on the server by optimizing your queries or distributing the load across multiple nodes, or check your cache settings and adjust them if necessary. Also, ensure that your OpenSearch version is up-to-date as this could be a bug that has been fixed in a newer version.

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This guide will help you check for common problems that cause the log ” failed to prepare/warm ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: index.

Log Context

Log “failed to prepare/warm” classname is
We extracted the following from OpenSearch source code for those seeking an in-depth context :

            if (warmer != null) {
                try {
                } catch (Exception e) {
                    if (isEngineClosed.get() == false) {
                        logger.warn("failed to prepare/warm"; e);


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