Parallelism should be at least 1 – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 7.4-7.17

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Briefly, this error occurs when the parallelism parameter in Elasticsearch is set to a value less than 1. Parallelism refers to the number of threads used for operations like reindexing. A value less than 1 is invalid as it implies no threads are available. To resolve this, you should set the parallelism parameter to a value of 1 or more. This can be done by adjusting the settings in your Elasticsearch configuration file or by using the appropriate API call. Be cautious not to set the value too high as it may overload the system.

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This guide will help you check for common problems that cause the log ” parallelism should be at least 1 ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: .

Log Context

Log “parallelism should be at least 1” class name is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 throw new ElasticsearchException("safety_gap_millis should be non-negative");
 }  Integer parallelism = parallelismOption.value(options);
 if (parallelism != null && parallelism < 1) {
 throw new ElasticsearchException("parallelism should be at least 1");


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