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55 lines
2.9 KiB
Markdown
55 lines
2.9 KiB
Markdown
# system.trace_log {#system_tables-trace_log}
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Contains stack traces collected by the sampling query profiler.
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ClickHouse creates this table when the [trace_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-trace_log) server configuration section is set. Also the [query_profiler_real_time_period_ns](../../operations/settings/settings.md#query_profiler_real_time_period_ns) and [query_profiler_cpu_time_period_ns](../../operations/settings/settings.md#query_profiler_cpu_time_period_ns) settings should be set.
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To analyze logs, use the `addressToLine`, `addressToSymbol` and `demangle` introspection functions.
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Columns:
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- `event_date` ([Date](../../sql-reference/data-types/date.md)) — Date of sampling moment.
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- `event_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — Timestamp of the sampling moment.
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- `event_time_microseconds` ([DateTime64](../../sql-reference/data-types/datetime64.md)) — Timestamp of the sampling moment with microseconds precision.
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- `timestamp_ns` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Timestamp of the sampling moment in nanoseconds.
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- `revision` ([UInt32](../../sql-reference/data-types/int-uint.md)) — ClickHouse server build revision.
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When connecting to the 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.
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- `timer_type` ([Enum8](../../sql-reference/data-types/enum.md)) — Timer type:
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- `Real` represents wall-clock time.
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- `CPU` represents CPU time.
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- `thread_number` ([UInt32](../../sql-reference/data-types/int-uint.md)) — Thread identifier.
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- `query_id` ([String](../../sql-reference/data-types/string.md)) — Query identifier that can be used to get details about a query that was running from the [query_log](#system_tables-query_log) system table.
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- `trace` ([Array(UInt64)](../../sql-reference/data-types/array.md)) — Stack trace at the moment of sampling. Each element is a virtual memory address inside ClickHouse server process.
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**Example**
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``` sql
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SELECT * FROM system.trace_log LIMIT 1 \G
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```
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``` text
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Row 1:
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──────
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event_date: 2020-09-10
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event_time: 2020-09-10 11:23:09
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event_time_microseconds: 2020-09-10 11:23:09.872924
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timestamp_ns: 1599762189872924510
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revision: 54440
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trace_type: Memory
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thread_id: 564963
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query_id:
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trace: [371912858,371912789,371798468,371799717,371801313,371790250,624462773,566365041,566440261,566445834,566460071,566459914,566459842,566459580,566459469,566459389,566459341,566455774,371993941,371988245,372158848,372187428,372187309,372187093,372185478,140222123165193,140222122205443]
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size: 5244400
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```
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[Original article](https://clickhouse.tech/docs/en/operations/system_tables/trace_log) <!--hide--> |