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Events

Events shows changes, failures, and server activity recorded by ClickHouse. It helps explain what happened before or during a problem without requiring a manual search across several system tables.

What Is an Event?​

An event records a change or problem at a specific time. Examples include a server restart, a query running out of memory, a table change, or a replication failure.

Events are shown alongside the CPU, memory, network, and disk charts in Time Travel. Normal changes in those charts are not treated as events, and this page does not replace an alerting system.

The list focuses on supported events that can help explain a problem. It does not include every ClickHouse log entry and is not exhaustive.

Event Categories​

Events are grouped into broad categories:

  • Server lifecycle
  • Query execution
  • Replication
  • Keeper and coordination
  • Storage
  • Schema and configuration changes
  • Maintenance

Some events happen at one moment, such as a failed query, table change, or server crash. Others last for a period, such as a replica remaining read-only until it recovers.

Finding an Event​

The chart groups similar events together over the selected time range. Available actions include:

  • Drag across the chart to focus on a shorter time range
  • Search by message, host, table, or query ID
  • Filter by severity, category, and event type
  • Expand a group to see each event
  • Select an event to see its details and what was happening nearby

Event Details​

The details panel shows when the event happened, how serious it was, where the information came from, and any useful query, host, or table details. Query events can also open the standard Query Details view.

The page also shows what was happening around the event:

  • Queries that were active at the event time
  • Host CPU and memory before and after the event
  • Related log messages
  • Other nearby events

If one source is unavailable, the page still shows information from the sources it can read.

Open in Time Travel​

Select Open in Time Travel to open the chart at the event time. The event can then be compared with the CPU, memory, network, and disk charts, as well as the queries, merges, and mutations that were active.

From Time Travel, select an event marker and use View details to open it on the Events page.

Data Availability​

TraceHouse reads events from ClickHouse system logs and saved metrics. Available events depend on which system tables are accessible and how long their data is kept.

The source indicator shows when some information is missing.

Some ClickHouse tables only show the current state. Because of this, TraceHouse may not be able to show every past replication problem.

For the complete list of supported events and their ClickHouse sources, see Time Travel Events.