Failed to acquire reader – How to solve this Elasticsearch error

Opster Team

Aug-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 disk I/O issue. To resolve this, you can try to restore the index from a backup, increase system resources, or check the disk for errors. If the index is not critical, deleting and recreating it might be an option. Also, ensure that your Elasticsearch version is up-to-date as this could be a bug that has been fixed in a newer version.

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” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

        } catch (AlreadyClosedException ex) {
            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 {