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system.iceberg_metadata_log

The system.iceberg_metadata_log table records metadata access and parsing events for Iceberg tables read by ClickHouse. It provides detailed information about each metadata file or entry processed, which is useful for debugging, auditing, and understanding Iceberg table structure evolution.

Purpose​

This table logs every metadata file and entry read from Iceberg tables, including root metadata files, manifest lists, and manifest entries. It helps users trace how ClickHouse interprets Iceberg table metadata and diagnose issues related to schema evolution, file resolution, or query planning.

Note

This table is primarily intended for debugging purposes.

Columns​

NameTypeDescription
event_dateDateDate of the log entry.
event_timeDateTimeTimestamp of the event.
query_idStringQuery ID that triggered the metadata read.
content_typeEnum8Type of metadata content (see below).
table_pathStringPath to the Iceberg table.
file_pathStringPath to the root metadata JSON file, Avro manifest list, or manifest file.
contentStringContent in JSON format (raw metadata from .json, Avro metadata, or Avro entry).
row_in_fileNullable(UInt64)Row number in the file, if applicable. Present for ManifestListEntry and ManifestFileEntry content types.

content_type values​

  • None: No content.
  • Metadata: Root metadata file.
  • ManifestListMetadata: Manifest list metadata.
  • ManifestListEntry: Entry in a manifest list.
  • ManifestFileMetadata: Manifest file metadata.
  • ManifestFileEntry: Entry in a manifest file.
Querying in ClickHouse Cloud

The data in this system table is held locally on each node in ClickHouse Cloud. Obtaining a complete view of all data, therefore, requires the clusterAllReplicas function. See here for further details.

Controlling log verbosity​

You can control which metadata events are logged using the iceberg_metadata_log_level setting.

To log all metadata used in the current query:

SELECT * FROM my_iceberg_table SETTINGS iceberg_metadata_log_level = 'manifest_file_entry';

SYSTEM FLUSH LOGS iceberg_metadata_log;

SELECT content_type, file_path, row_in_file
FROM system.iceberg_metadata_log
WHERE query_id = '{previous_query_id}';

To log only the root metadata JSON file used in the current query:

SELECT * FROM my_iceberg_table SETTINGS iceberg_metadata_log_level = 'metadata';

SYSTEM FLUSH LOGS iceberg_metadata_log;

SELECT content_type, file_path, row_in_file
FROM system.iceberg_metadata_log
WHERE query_id = '{previous_query_id}';

See more information in the description of the iceberg_metadata_log_level setting.

Good To Know​

  • Use iceberg_metadata_log_level at the query level only when you need to investigate your Iceberg table in detail. Otherwise, you may populate the log table with excessive metadata and experience performance degradation.
  • The table may contain duplicate entries, as it is intended primarily for debugging and does not guarantee uniqueness per entity.
  • If you use a content_type more verbose than ManifestListMetadata, the Iceberg metadata cache is disabled for manifest lists.
  • Similarly, if you use a content_type more verbose than ManifestFileMetadata, the Iceberg metadata cache is disabled for manifest files.

See also​