Block until refresh ran out of slots and forced a refresh – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1.2-2.9

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Briefly, this error occurs when OpenSearch is unable to allocate more slots for indexing operations due to a high volume of data being indexed concurrently. This forces an automatic refresh to free up slots. To resolve this issue, you can increase the refresh interval, reduce the bulk size of indexing operations, or scale up your OpenSearch cluster to handle more concurrent indexing operations. Additionally, optimizing your indexing process by using bulk requests or asynchronous indexing can also help to mitigate this issue.

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This guide will help you check for common problems that cause the log ” block until refresh ran out of slots and forced a refresh: [{}] ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: refresh, replication.

Log Context

Log “block until refresh ran out of slots and forced a refresh: [{}]” classname is
We extracted the following from OpenSearch source code for those seeking an in-depth context :

            if (waitUntilRefresh) {
                assert pendingOps.get() > 0;
                indexShard.addRefreshListener(location; forcedRefresh -> {
                    if (forcedRefresh) {
                        logger.warn("block until refresh ran out of slots and forced a refresh: [{}]"; request);


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