ClickHouse/docs/en/operations/system-tables/part_log.md
Ivan Blinkov 7170f3c534
[docs] split aggregate function and system table references (#11742)
* prefer relative links from root

* wip

* split aggregate function reference

* split system tables
2020-06-18 11:24:31 +03:00

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# system.part\_log {#system_tables-part-log}
The `system.part_log` table is created only if the [part\_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-part-log) server setting is specified.
This table contains information about events that occurred with [data parts](../../engines/table-engines/mergetree-family/custom-partitioning-key.md) in the [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) family tables, such as adding or merging data.
The `system.part_log` table contains the following columns:
- `event_type` (Enum) — Type of the event that occurred with the data part. Can have one of the following values:
- `NEW_PART` — Inserting of a new data part.
- `MERGE_PARTS` — Merging of data parts.
- `DOWNLOAD_PART` — Downloading a data part.
- `REMOVE_PART` — Removing or detaching a data part using [DETACH PARTITION](../../sql-reference/statements/alter.md#alter_detach-partition).
- `MUTATE_PART` — Mutating of a data part.
- `MOVE_PART` — Moving the data part from the one disk to another one.
- `event_date` (Date) — Event date.
- `event_time` (DateTime) — Event time.
- `duration_ms` (UInt64) — Duration.
- `database` (String) — Name of the database the data part is in.
- `table` (String) — Name of the table the data part is in.
- `part_name` (String) — Name of the data part.
- `partition_id` (String) — ID of the partition that the data part was inserted to. The column takes the all value if the partitioning is by `tuple()`.
- `rows` (UInt64) — The number of rows in the data part.
- `size_in_bytes` (UInt64) — Size of the data part in bytes.
- `merged_from` (Array(String)) — An array of names of the parts which the current part was made up from (after the merge).
- `bytes_uncompressed` (UInt64) — Size of uncompressed bytes.
- `read_rows` (UInt64) — The number of rows was read during the merge.
- `read_bytes` (UInt64) — The number of bytes was read during the merge.
- `error` (UInt16) — The code number of the occurred error.
- `exception` (String) — Text message of the occurred error.
The `system.part_log` table is created after the first inserting data to the `MergeTree` table.