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

Opster Team

Aug-23, Version: 6.8-7.17

Briefly, this error occurs when Elasticsearch is unable to serialize machine learning (ML) metadata due to issues like incompatible data types or corrupted data. To resolve this, you can try the following: 1) Check the data types of your ML metadata to ensure they are compatible with Elasticsearch’s serialization process. 2) Inspect your ML metadata for any signs of corruption or inconsistencies. 3) If the problem persists, consider reindexing your data or recreating your ML jobs. Always ensure to backup your data before making any major changes.

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);



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