# 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 does not 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)