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system.metric_log

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.

Contains history of metrics values from tables system.metrics and system.events, periodically flushed to disk.

Columns:

  • hostname (LowCardinality(String)) — Hostname of the server executing the query.
  • event_date (Date) — Event date.
  • event_time (DateTime) — Event time.
  • event_time_microseconds (DateTime64) — Event time with microseconds resolution.

Example

SELECT * FROM system.metric_log LIMIT 1 FORMAT Vertical;

Row 1:
──────
hostname:                                                        clickhouse.eu-central1.internal
event_date:                                                      2020-09-05
event_time:                                                      2020-09-05 16:22:33
event_time_microseconds:                                         2020-09-05 16:22:33.196807
milliseconds:                                                    196
ProfileEvent_Query:                                              0
ProfileEvent_SelectQuery:                                        0
ProfileEvent_InsertQuery:                                        0
ProfileEvent_FailedQuery:                                        0
ProfileEvent_FailedSelectQuery:                                  0
...
...
CurrentMetric_Revision:                                          54439
CurrentMetric_VersionInteger:                                    20009001
CurrentMetric_RWLockWaitingReaders:                              0
CurrentMetric_RWLockWaitingWriters:                              0
CurrentMetric_RWLockActiveReaders:                               0
CurrentMetric_RWLockActiveWriters:                               0
CurrentMetric_GlobalThread:                                      74
CurrentMetric_GlobalThreadActive:                                26
CurrentMetric_LocalThread:                                       0
CurrentMetric_LocalThreadActive:                                 0
CurrentMetric_DistributedFilesToInsert:                          0

Schema This table can be configured with different schema types using the XML tag <schema_type>. The default schema type is wide, where each metric or profile event is stored as a separate column. This schema is the most performant and efficient for single-column reads.

The transposed schema stores data in a format similar to system.asynchronous_metric_log, where metrics and events are stored as rows. This schema is useful for low-resource setups because it reduces resource consumption during merges.

There is also a compatibility schema, transposed_with_wide_view, which stores actual data in a table with the transposed schema (system.transposed_metric_log) and creates a view on top of it using the wide schema. This view queries the transposed table, making it useful for migrating from the wide schema to the transposed schema.

See also