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6.0 KiB
Markdown
90 lines
6.0 KiB
Markdown
---
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slug: /en/operations/system-tables/query_views_log
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---
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# query_views_log
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Contains information about the dependent views executed when running a query, for example, the view type or the execution time.
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To start logging:
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1. Configure parameters in the [query_views_log](../../operations/server-configuration-parameters/settings.md#query_views_log) section.
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2. Set [log_query_views](../../operations/settings/settings.md#log-query-views) to 1.
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The flushing period of data is set in `flush_interval_milliseconds` parameter of the [query_views_log](../../operations/server-configuration-parameters/settings.md#query_views_log) server settings section. To force flushing, use the [SYSTEM FLUSH LOGS](../../sql-reference/statements/system.md#query_language-system-flush_logs) query.
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ClickHouse does not delete data from the table automatically. See [Introduction](../../operations/system-tables/index.md#system-tables-introduction) for more details.
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You can use the [log_queries_probability](../../operations/settings/settings.md#log-queries-probability) setting to reduce the number of queries, registered in the `query_views_log` table.
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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)) — The date when the last event of the view happened.
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- `event_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — The date and time when the view finished execution.
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- `event_time_microseconds` ([DateTime](../../sql-reference/data-types/datetime.md)) — The date and time when the view finished execution with microseconds precision.
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- `view_duration_ms` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Duration of view execution (sum of its stages) in milliseconds.
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- `initial_query_id` ([String](../../sql-reference/data-types/string.md)) — ID of the initial query (for distributed query execution).
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- `view_name` ([String](../../sql-reference/data-types/string.md)) — Name of the view.
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- `view_uuid` ([UUID](../../sql-reference/data-types/uuid.md)) — UUID of the view.
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- `view_type` ([Enum8](../../sql-reference/data-types/enum.md)) — Type of the view. Values:
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- `'Default' = 1` — [Default views](../../sql-reference/statements/create/view.md#normal). Should not appear in this log.
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- `'Materialized' = 2` — [Materialized views](../../sql-reference/statements/create/view.md#materialized).
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- `'Live' = 3` — [Live views](../../sql-reference/statements/create/view.md#live-view).
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- `view_query` ([String](../../sql-reference/data-types/string.md)) — The query executed by the view.
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- `view_target` ([String](../../sql-reference/data-types/string.md)) — The name of the view target table.
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- `read_rows` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Number of read rows.
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- `read_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Number of read bytes.
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- `written_rows` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Number of written rows.
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- `written_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Number of written bytes.
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- `peak_memory_usage` ([Int64](../../sql-reference/data-types/int-uint.md)) — The maximum difference between the amount of allocated and freed memory in context of this view.
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- `ProfileEvents` ([Map(String, UInt64)](../../sql-reference/data-types/array.md)) — ProfileEvents that measure different metrics. The description of them could be found in the table [system.events](../../operations/system-tables/events.md#system_tables-events).
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- `status` ([Enum8](../../sql-reference/data-types/enum.md)) — Status of the view. Values:
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- `'QueryStart' = 1` — Successful start the view execution. Should not appear.
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- `'QueryFinish' = 2` — Successful end of the view execution.
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- `'ExceptionBeforeStart' = 3` — Exception before the start of the view execution.
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- `'ExceptionWhileProcessing' = 4` — Exception during the view execution.
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- `exception_code` ([Int32](../../sql-reference/data-types/int-uint.md)) — Code of an exception.
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- `exception` ([String](../../sql-reference/data-types/string.md)) — Exception message.
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- `stack_trace` ([String](../../sql-reference/data-types/string.md)) — [Stack trace](https://en.wikipedia.org/wiki/Stack_trace). An empty string, if the query was completed successfully.
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**Example**
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Query:
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``` sql
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SELECT * FROM system.query_views_log LIMIT 1 \G;
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```
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Result:
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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: 2021-06-22
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event_time: 2021-06-22 13:23:07
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event_time_microseconds: 2021-06-22 13:23:07.738221
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view_duration_ms: 0
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initial_query_id: c3a1ac02-9cad-479b-af54-9e9c0a7afd70
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view_name: default.matview_inner
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view_uuid: 00000000-0000-0000-0000-000000000000
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view_type: Materialized
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view_query: SELECT * FROM default.table_b
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view_target: default.`.inner.matview_inner`
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read_rows: 4
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read_bytes: 64
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written_rows: 2
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written_bytes: 32
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peak_memory_usage: 4196188
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ProfileEvents: {'FileOpen':2,'WriteBufferFromFileDescriptorWrite':2,'WriteBufferFromFileDescriptorWriteBytes':187,'IOBufferAllocs':3,'IOBufferAllocBytes':3145773,'FunctionExecute':3,'DiskWriteElapsedMicroseconds':13,'InsertedRows':2,'InsertedBytes':16,'SelectedRows':4,'SelectedBytes':48,'ContextLock':16,'RWLockAcquiredReadLocks':1,'RealTimeMicroseconds':698,'SoftPageFaults':4,'OSReadChars':463}
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status: QueryFinish
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exception_code: 0
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exception:
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stack_trace:
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```
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**See Also**
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- [system.query_log](../../operations/system-tables/query_log.md#system_tables-query_log) — Description of the `query_log` system table which contains common information about queries execution.
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- [system.query_thread_log](../../operations/system-tables/query_thread_log.md#system_tables-query_thread_log) — This table contains information about each query execution thread.
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