asynchronous_metric_log

Description

Contains the historical values for system.asynchronous_metrics, which are saved once per time interval (one second by default). Enabled by default.

Key-value metrics of system.asynchronous_metrics (those broken down per CPU core, block device, network interface, or disk) are logged as one row per key, with the key in the key column. For scalar metrics the key column is empty.

Before version 26.8 every key was a separate scalar metric with the key mangled into its name (BlockReadBytes_sda). The asynchronous_metrics_key_values_mode server setting switches back to that form (legacy_names), or logs both forms at the same time (both) while the monitoring is being migrated.

It is safe to truncate or drop this table at any time.

Columns

• hostname (LowCardinality(String)) — Hostname of the server executing the query.
• clickhouse_version (LowCardinality(String)) — Version of the ClickHouse server that produced the row.
• system_processor (LowCardinality(String)) — CPU architecture of the ClickHouse server that produced the row.
• event_date (Date) — Event date.
• event_time (DateTime) — Event time.
• metric (LowCardinality(String)) — Metric name.
• key (LowCardinality(String)) — The key of a key-value metric, e.g. the CPU core number or the block device name. Empty for scalar metrics.
• value (Float64) — Metric value.

Examples

SELECT * FROM system.asynchronous_metric_log LIMIT 3 \G

Row 1:
──────
hostname:   clickhouse.eu-central1.internal
event_date: 2023-11-14
event_time: 2023-11-14 14:39:07
metric:     AsynchronousHeavyMetricsCalculationTimeSpent
key:
value:      0.001

Row 2:
──────
hostname:   clickhouse.eu-central1.internal
event_date: 2023-11-14
event_time: 2023-11-14 14:39:08
metric:     AsynchronousHeavyMetricsCalculationTimeSpent
key:
value:      0

Row 3:
──────
hostname:   clickhouse.eu-central1.internal
event_date: 2023-11-14
event_time: 2023-11-14 14:39:09
metric:     AsynchronousHeavyMetricsCalculationTimeSpent
key:
value:      0

See also

• asynchronous_metric_log setting — Enabling and disabling the setting.
• system.asynchronous_metrics — Contains metrics, calculated periodically in the background.
• system.metric_log — Contains history of metrics values from tables system.metrics and system.events, periodically flushed to disk.