system.metric_log
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
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
- metric_log setting — Enabling and disabling the setting.
- system.asynchronous_metrics — Contains periodically calculated metrics.
- system.events — Contains a number of events that occurred.
- system.metrics — Contains instantly calculated metrics.
- Monitoring — Base concepts of ClickHouse monitoring.