system.trace_log 

Contains stack traces collected by the sampling query profiler.

ClickHouse creates this table when the trace_log server configuration section is set. Also the query_profiler_real_time_period_ns and query_profiler_cpu_time_period_ns settings should be set.

To analyze logs, use the addressToLine, addressToSymbol and demangle introspection functions.

Columns:

• event_date (Date) — Date of sampling moment.

• event_time (DateTime) — Timestamp of the sampling moment.

• timestamp_ns (UInt64) — Timestamp of the sampling moment in nanoseconds.

• revision (UInt32) — ClickHouse server build revision.

  When connecting to server by clickhouse-client, you see the string similar to Connected to ClickHouse server version 19.18.1 revision 54429.. This field contains the revision, but not the version of a server.

• timer_type (Enum8) — Timer type:

  • Real represents wall-clock time.
  • CPU represents CPU time.

• thread_number (UInt32) — Thread identifier.

• query_id (String) — Query identifier that can be used to get details about a query that was running from the query_log system table.

• trace (Array(UInt64)) — Stack trace at the moment of sampling. Each element is a virtual memory address inside ClickHouse server process.

Example

SELECT * FROM system.trace_log LIMIT 1 \G

Row 1:
──────
event_date:    2019-11-15
event_time:    2019-11-15 15:09:38
revision:      54428
timer_type:    Real
thread_number: 48
query_id:      acc4d61f-5bd1-4a3e-bc91-2180be37c915
trace:         [94222141367858,94222152240175,94222152325351,94222152329944,94222152330796,94222151449980,94222144088167,94222151682763,94222144088167,94222151682763,94222144088167,94222144058283,94222144059248,94222091840750,94222091842302,94222091831228,94222189631488,140509950166747,140509942945935]

Original article