Starting segment upgrade – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 1.5-1.5

Briefly, this error occurs when Elasticsearch is upgrading the Lucene index segments to a newer version. This is a normal process when you upgrade Elasticsearch and it’s not necessarily an error, but an informational message. However, it can cause performance issues due to increased I/O operations. To resolve this, you can schedule the upgrade during off-peak hours, or increase your hardware resources. Also, ensure you have a backup of your data before starting the upgrade process to prevent data loss in case of any issues.

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

Log Context

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

         ElasticsearchMergePolicy mp = (ElasticsearchMergePolicy) indexWriter.getConfig().getMergePolicy();
        try {
            if (upgrade) {
      "starting segment upgrade");
            store.incRef(); // increment the ref just to ensure nobody closes the store while we optimize
            try {
                if (onlyExpungeDeletes) {


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