Failed to acquire reader – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 7.1-8.9

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.

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 {