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ClickHouse/docs/en/operations/system-tables/parts_columns.md
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DOCSUP-1830: Describe the system.parts_columns table (#16531) 
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# system.parts_columns {#system_tables-parts_columns}
Contains information about parts and columns of [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) tables.
Each row describes one data part.
Columns:
- `partition` ([String](../../sql-reference/data-types/string.md)) — The partition name. To learn what a partition is, see the description of the [ALTER](../../sql-reference/statements/alter/index.md#query_language_queries_alter) query.
Formats:
- `YYYYMM` for automatic partitioning by month.
- `any_string` when partitioning manually.
- `name` ([String](../../sql-reference/data-types/string.md)) — Name of the data part.
- `part_type` ([String](../../sql-reference/data-types/string.md)) — The data part storing format.
Possible values:
- `Wide` — Each column is stored in a separate file in a filesystem.
- `Compact` — All columns are stored in one file in a filesystem.
Data storing format is controlled by the `min_bytes_for_wide_part` and `min_rows_for_wide_part` settings of the [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) table.
- `active` ([UInt8](../../sql-reference/data-types/int-uint.md)) — Flag that indicates whether the data part is active. If a data part is active, it’s used in a table. Otherwise, it’s deleted. Inactive data parts remain after merging.
- `marks` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The number of marks. To get the approximate number of rows in a data part, multiply `marks` by the index granularity (usually 8192) (this hint doesn’t work for adaptive granularity).
- `rows` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The number of rows.
- `bytes_on_disk` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of all the data part files in bytes.
- `data_compressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of compressed data in the data part. All the auxiliary files (for example, files with marks) are not included.
- `data_uncompressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of uncompressed data in the data part. All the auxiliary files (for example, files with marks) are not included.
- `marks_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The size of the file with marks.
- `modification_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — The time the directory with the data part was modified. This usually corresponds to the time of data part creation.
- `remove_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — The time when the data part became inactive.
- `refcount` ([UInt32](../../sql-reference/data-types/int-uint.md)) — The number of places where the data part is used. A value greater than 2 indicates that the data part is used in queries or merges.
- `min_date` ([Date](../../sql-reference/data-types/date.md)) — The minimum value of the date key in the data part.
- `max_date` ([Date](../../sql-reference/data-types/date.md)) — The maximum value of the date key in the data part.
- `partition_id` ([String](../../sql-reference/data-types/string.md)) — ID of the partition.
- `min_block_number` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The minimum number of data parts that make up the current part after merging.
- `max_block_number` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The maximum number of data parts that make up the current part after merging.
- `level` ([UInt32](../../sql-reference/data-types/int-uint.md)) — Depth of the merge tree. Zero means that the current part was created by insert rather than by merging other parts.
- `data_version` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Number that is used to determine which mutations should be applied to the data part (mutations with a version higher than `data_version`).
- `primary_key_bytes_in_memory` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The amount of memory (in bytes) used by primary key values.
- `primary_key_bytes_in_memory_allocated` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The amount of memory (in bytes) reserved for primary key values.
- `database` ([String](../../sql-reference/data-types/string.md)) — Name of the database.
- `table` ([String](../../sql-reference/data-types/string.md)) — Name of the table.
- `engine` ([String](../../sql-reference/data-types/string.md)) — Name of the table engine without parameters.
- `disk_name` ([String](../../sql-reference/data-types/string.md)) — Name of a disk that stores the data part.
- `path` ([String](../../sql-reference/data-types/string.md)) — Absolute path to the folder with data part files.
- `column` ([String](../../sql-reference/data-types/string.md)) — Name of the column.
- `type` ([String](../../sql-reference/data-types/string.md)) — Column type.
- `column_position` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Ordinal position of a column in a table starting with 1.
- `default_kind` ([String](../../sql-reference/data-types/string.md)) — Expression type (`DEFAULT`, `MATERIALIZED`, `ALIAS`) for the default value, or an empty string if it is not defined.
- `default_expression` ([String](../../sql-reference/data-types/string.md)) — Expression for the default value, or an empty string if it is not defined.
- `column_bytes_on_disk` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of the column in bytes.
- `column_data_compressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of compressed data in the column, in bytes.
- `column_data_uncompressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Total size of the decompressed data in the column, in bytes.
- `column_marks_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The size of the column with marks, in bytes.
- `bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Alias for `bytes_on_disk`.
- `marks_size` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Alias for `marks_bytes`.
**Example**
``` sql
SELECT * FROM system.parts_columns LIMIT 1 FORMAT Vertical;
```
``` text
Row 1:
──────
partition: tuple()
name: all_1_2_1
part_type: Wide
active: 1
marks: 2
rows: 2
bytes_on_disk: 155
data_compressed_bytes: 56
data_uncompressed_bytes: 4
marks_bytes: 96
modification_time: 2020-09-23 10:13:36
remove_time: 2106-02-07 06:28:15
refcount: 1
min_date: 1970-01-01
max_date: 1970-01-01
partition_id: all
min_block_number: 1
max_block_number: 2
level: 1
data_version: 1
primary_key_bytes_in_memory: 2
primary_key_bytes_in_memory_allocated: 64
database: default
table: 53r93yleapyears
engine: MergeTree
disk_name: default
path: /var/lib/clickhouse/data/default/53r93yleapyears/all_1_2_1/
column: id
type: Int8
column_position: 1
default_kind:
default_expression:
column_bytes_on_disk: 76
column_data_compressed_bytes: 28
column_data_uncompressed_bytes: 2
column_marks_bytes: 48
```
**See Also**
- [MergeTree family](../../engines/table-engines/mergetree-family/mergetree.md)
[Original article](https://clickhouse.tech/docs/en/operations/system_tables/parts_columns) <!--hide-->
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