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:
-`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.
