---
description: 'System table containing information about threads that execute queries,
  for example, thread name, thread start time, duration of query processing.'
keywords: ['system table', 'query_thread_log']
slug: /operations/system-tables/query_thread_log
title: 'system.query_thread_log'
---

import SystemTableCloud from '@site/docs/_snippets/_system_table_cloud.md';

# system.query_thread_log

<SystemTableCloud/>

Contains information about threads that execute queries, for example, thread name, thread start time, duration of query processing.

To start logging:

1.  Configure parameters in the [query_thread_log](/operations/server-configuration-parameters/settings#query_thread_log) section.
2.  Set [log_query_threads](/operations/settings/settings#log_query_threads) to 1.

The flushing period of data is set in `flush_interval_milliseconds` parameter of the [query_thread_log](/operations/server-configuration-parameters/settings#query_thread_log) server settings section. To force flushing, use the [SYSTEM FLUSH LOGS](/sql-reference/statements/system#flush-logs) query.

ClickHouse does not delete data from the table automatically. See [Introduction](/operations/system-tables/overview#system-tables-introduction) for more details.

You can use the [log_queries_probability](/operations/settings/settings#log_queries_probability)) setting to reduce the number of queries, registered in the `query_thread_log` table.

Columns:

- `hostname` ([LowCardinality(String)](../../sql-reference/data-types/string.md)) — Hostname of the server executing the query.
- `event_date` ([Date](../../sql-reference/data-types/date.md)) — The date when the thread has finished execution of the query.
- `event_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — The date and time when the thread has finished execution of the query.
- `event_time_microseconds` ([DateTime](../../sql-reference/data-types/datetime.md)) — The date and time when the thread has finished execution of the query with microseconds precision.
- `query_start_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — Start time of query execution.
- `query_start_time_microseconds` ([DateTime64](../../sql-reference/data-types/datetime64.md)) — Start time of query execution with microsecond precision.
- `query_duration_ms` ([UInt64](/sql-reference/data-types/int-uint#integer-ranges)) — Duration of query execution.
- `read_rows` ([UInt64](/sql-reference/data-types/int-uint#integer-ranges)) — Number of read rows.
- `read_bytes` ([UInt64](/sql-reference/data-types/int-uint#integer-ranges)) — Number of read bytes.
- `written_rows` ([UInt64](/sql-reference/data-types/int-uint#integer-ranges)) — For `INSERT` queries, the number of written rows. For other queries, the column value is 0.
- `written_bytes` ([UInt64](/sql-reference/data-types/int-uint#integer-ranges)) — For `INSERT` queries, the number of written bytes. For other queries, the column value is 0.
- `memory_usage` ([Int64](../../sql-reference/data-types/int-uint.md)) — The difference between the amount of allocated and freed memory in context of this thread.
- `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 thread.
- `thread_name` ([String](../../sql-reference/data-types/string.md)) — Name of the thread.
- `thread_id` ([UInt64](../../sql-reference/data-types/int-uint.md)) — OS thread ID.
- `master_thread_id` ([UInt64](/sql-reference/data-types/int-uint#integer-ranges)) — OS initial ID of initial thread.
- `query` ([String](../../sql-reference/data-types/string.md)) — Query string.
- `is_initial_query` ([UInt8](/sql-reference/data-types/int-uint#integer-ranges)) — Query type. Possible values:
  - 1 — Query was initiated by the client.
  - 0 — Query was initiated by another query for distributed query execution.
- `user` ([String](../../sql-reference/data-types/string.md)) — Name of the user who initiated the current query.
- `query_id` ([String](../../sql-reference/data-types/string.md)) — ID of the query.
- `address` ([IPv6](../../sql-reference/data-types/ipv6.md)) — IP address that was used to make the query.
- `port` ([UInt16](/sql-reference/data-types/int-uint#integer-ranges)) — The client port that was used to make the query.
- `initial_user` ([String](../../sql-reference/data-types/string.md)) — Name of the user who ran the initial query (for distributed query execution).
- `initial_query_id` ([String](../../sql-reference/data-types/string.md)) — ID of the initial query (for distributed query execution).
- `initial_address` ([IPv6](../../sql-reference/data-types/ipv6.md)) — IP address that the parent query was launched from.
- `initial_port` ([UInt16](/sql-reference/data-types/int-uint#integer-ranges)) — The client port that was used to make the parent query.
- `interface` ([UInt8](/sql-reference/data-types/int-uint#integer-ranges)) — Interface that the query was initiated from. Possible values:
  - 1 — TCP.
  - 2 — HTTP.
- `os_user` ([String](../../sql-reference/data-types/string.md)) — OS's username who runs [clickhouse-client](../../interfaces/cli.md).
- `client_hostname` ([String](../../sql-reference/data-types/string.md)) — Hostname of the client machine where the [clickhouse-client](../../interfaces/cli.md) or another TCP client is run.
- `client_name` ([String](../../sql-reference/data-types/string.md)) — The [clickhouse-client](../../interfaces/cli.md) or another TCP client name.
- `client_revision` ([UInt32](../../sql-reference/data-types/int-uint.md)) — Revision of the [clickhouse-client](../../interfaces/cli.md) or another TCP client.
- `client_version_major` ([UInt32](../../sql-reference/data-types/int-uint.md)) — Major version of the [clickhouse-client](../../interfaces/cli.md) or another TCP client.
- `client_version_minor` ([UInt32](../../sql-reference/data-types/int-uint.md)) — Minor version of the [clickhouse-client](../../interfaces/cli.md) or another TCP client.
- `client_version_patch` ([UInt32](../../sql-reference/data-types/int-uint.md)) — Patch component of the [clickhouse-client](../../interfaces/cli.md) or another TCP client version.
- `http_method` ([UInt8](/sql-reference/data-types/int-uint#integer-ranges)) — HTTP method that initiated the query. Possible values:
  - 0 — The query was launched from the TCP interface.
  - 1 — `GET` method was used.
  - 2 — `POST` method was used.
- `http_user_agent` ([String](../../sql-reference/data-types/string.md)) — The `UserAgent` header passed in the HTTP request.
- `quota_key` ([String](../../sql-reference/data-types/string.md)) — The "quota key" specified in the [quotas](../../operations/quotas.md) setting (see `keyed`).
- `revision` ([UInt32](../../sql-reference/data-types/int-uint.md)) — ClickHouse revision.
- `ProfileEvents` ([Map(String, UInt64)](../../sql-reference/data-types/array.md)) — ProfileEvents that measure different metrics for this thread. The description of them could be found in the table [system.events](/operations/system-tables/events).

**Example**

```sql
 SELECT * FROM system.query_thread_log LIMIT 1 \G
```

```text
Row 1:
──────
hostname:                      clickhouse.eu-central1.internal
event_date:                    2020-09-11
event_time:                    2020-09-11 10:08:17
event_time_microseconds:       2020-09-11 10:08:17.134042
query_start_time:              2020-09-11 10:08:17
query_start_time_microseconds: 2020-09-11 10:08:17.063150
query_duration_ms:             70
read_rows:                     0
read_bytes:                    0
written_rows:                  1
written_bytes:                 12
memory_usage:                  4300844
peak_memory_usage:             4300844
thread_name:                   TCPHandler
thread_id:                     638133
master_thread_id:              638133
query:                         INSERT INTO test1 VALUES
is_initial_query:              1
user:                          default
query_id:                      50a320fd-85a8-49b8-8761-98a86bcbacef
address:                       ::ffff:127.0.0.1
port:                          33452
initial_user:                  default
initial_query_id:              50a320fd-85a8-49b8-8761-98a86bcbacef
initial_address:               ::ffff:127.0.0.1
initial_port:                  33452
interface:                     1
os_user:                       bharatnc
client_hostname:               tower
client_name:                   ClickHouse
client_revision:               54437
client_version_major:          20
client_version_minor:          7
client_version_patch:          2
http_method:                   0
http_user_agent:
quota_key:
revision:                      54440
ProfileEvents:        {'Query':1,'SelectQuery':1,'ReadCompressedBytes':36,'CompressedReadBufferBlocks':1,'CompressedReadBufferBytes':10,'IOBufferAllocs':1,'IOBufferAllocBytes':89,'ContextLock':15,'RWLockAcquiredReadLocks':1}
```

**See Also**

- [system.query_log](/operations/system-tables/query_log) — Description of the `query_log` system table which contains common information about queries execution.
- [system.query_views_log](/operations/system-tables/query_views_log) — This table contains information about each view executed during a query.
