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59 lines
4.3 KiB
Markdown
59 lines
4.3 KiB
Markdown
---
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slug: /en/operations/system-tables/trace_log
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---
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# trace_log
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Contains stack traces collected by the [sampling query profiler](../../operations/optimizing-performance/sampling-query-profiler.md).
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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 see settings: [query_profiler_real_time_period_ns](../../operations/settings/settings.md#query_profiler_real_time_period_ns), [query_profiler_cpu_time_period_ns](../../operations/settings/settings.md#query_profiler_cpu_time_period_ns), [memory_profiler_step](../../operations/settings/settings.md#memory_profiler_step),
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[memory_profiler_sample_probability](../../operations/settings/settings.md#memory_profiler_sample_probability), [trace_profile_events](../../operations/settings/settings.md#trace_profile_events).
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To analyze logs, use the `addressToLine`, `addressToLineWithInlines`, `addressToSymbol` and `demangle` introspection functions.
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Columns:
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- `hostname` ([LowCardinality(String)](../../sql-reference/data-types/string.md)) — Hostname of the server executing the query.
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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.`. This field contains the `revision`, but not the `version` of a server.
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- `trace_type` ([Enum8](../../sql-reference/data-types/enum.md)) — Trace type:
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- `Real` represents collecting stack traces by wall-clock time.
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- `CPU` represents collecting stack traces by CPU time.
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- `Memory` represents collecting allocations and deallocations when memory allocation exceeds the subsequent watermark.
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- `MemorySample` represents collecting random allocations and deallocations.
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- `MemoryPeak` represents collecting updates of peak memory usage.
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- `ProfileEvent` represents collecting of increments of profile events.
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- `thread_id` ([UInt64](../../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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- `size` ([Int64](../../sql-reference/data-types/int-uint.md)) - For trace types `Memory`, `MemorySample` or `MemoryPeak` is the amount of memory allocated, for other trace types is 0.
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- `event` ([LowCardinality(String)](../../sql-reference/data-types/lowcardinality.md)) - For trace type `ProfileEvent` is the name of updated profile event, for other trace types is an empty string.
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- `increment` ([UInt64](../../sql-reference/data-types/int-uint.md)) - For trace type `ProfileEvent` is the amount of increment of profile event, for other trace types is 0.
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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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hostname: clickhouse.eu-central1.internal
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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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