Failed to serialise ml metadata – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 6.8-6.8

Briefly, this error occurs when Elasticsearch is unable to serialize Machine Learning metadata due to issues like data corruption, incompatible data types, or insufficient memory. To resolve this, you can try the following: 1) Check for data corruption and restore from a backup if necessary. 2) Ensure that all data types are compatible with the serialization process. 3) Increase the memory allocation for Elasticsearch if it’s insufficient. 4) Update Elasticsearch to the latest version as it might be a bug that has been fixed in newer versions.

This guide will help you check for common problems that cause the log ” Failed to serialise ml_metadata ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin.

Log Context

Log “Failed to serialise ml_metadata” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

             mlMetadata.toXContent(builder; params);

        } catch (IOException e) {
            logger.error("failed to serialise ml_metadata"; e);

        AnomalyDetectorsIndex.createStateIndexAndAliasIfNecessary(client; clusterService.state(); ActionListener.wrap(


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