Exception failing batch on rejection %s – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 8.8-8.9

Briefly, this error occurs when Elasticsearch is unable to process a batch of requests due to rejection, often caused by resource constraints like memory or CPU. To resolve this, you can increase the thread pool size or the queue size. Alternatively, you can optimize your indexing by reducing the batch size or increasing the refresh interval. Also, consider upgrading your hardware or adding more nodes to your cluster to handle the load. Lastly, ensure your queries are optimized to prevent unnecessary load on the system.

This guide will help you check for common problems that cause the log ” exception failing batch on rejection [%s] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: cluster.

Log Context

Log “exception failing batch on rejection [%s]” classname is MasterService.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

            assert currentlyExecutingBatch == nextBatch;
            try {
            } catch (Exception e2) {
                logger.error(() -> format("exception failing batch on rejection [%s]"; nextBatch); e2);
                assert false : e2;
            } finally {
                currentlyExecutingBatch = null;
        } while (totalQueueSize.decrementAndGet() > 0);


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