Failed to acquire reader – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 7.1-8.9

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Briefly, this error occurs when Elasticsearch is unable to obtain a reader for a specific index segment. This could be due to a corrupted index, insufficient system resources, or a problem with the underlying storage system. To resolve this issue, you can try to restore the index from a backup, increase system resources, or check the health of your storage system. If the index is not critical, you could also consider deleting and recreating it.

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

Log Context

Log “failed to acquire reader” class name is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 throw ex;
 } catch (Exception ex) {
 maybeFailEngine("acquire_reader"; ex);
 ensureOpen(ex); // throw EngineCloseException here if we are already closed
 logger.error("failed to acquire reader"; ex);
 throw new EngineException(shardId; "failed to acquire reader"; ex);
 } finally {


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