Now throttling indexing numMergesInFlight= maxNumMerges= – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-2.9

Before you dig into reading this guide, have you tried asking OpsGPT what this log means? You’ll receive a customized analysis of your log.

Try OpsGPT now for step-by-step guidance and tailored insights into your OpenSearch operation.

Briefly, this error occurs when the number of merges in flight exceeds the maximum number of merges allowed in OpenSearch. This is a mechanism to prevent the system from being overwhelmed by too many indexing operations. To resolve this issue, you can consider reducing the indexing load, increasing the maximum number of merges allowed, or optimizing your indexing strategy to reduce the need for merges. Additionally, ensure your hardware resources are sufficient and properly allocated to handle the indexing load.

For a complete solution to your to your search operation, try for free AutoOps for Elasticsearch & OpenSearch . With AutoOps and Opster’s proactive support, you don’t have to worry about your search operation – we take charge of it. Get improved performance & stability with less hardware.

This guide will help you check for common problems that cause the log ” now throttling indexing: numMergesInFlight={}; maxNumMerges={} ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: index.

Log Context

Log “now throttling indexing: numMergesInFlight={}; maxNumMerges={}” classname is
We extracted the following from OpenSearch source code for those seeking an in-depth context :

        public synchronized void beforeMerge(OnGoingMerge merge) {
            int maxNumMerges = mergeScheduler.getMaxMergeCount();
            if (numMergesInFlight.incrementAndGet() > maxNumMerges) {
                if (isThrottling.getAndSet(true) == false) {
          "now throttling indexing: numMergesInFlight={}; maxNumMerges={}"; numMergesInFlight; maxNumMerges);


How helpful was this guide?

We are sorry that this post was not useful for you!

Let us improve this post!

Tell us how we can improve this post?

Get expert answers on Elasticsearch/OpenSearch