ClickHouse/docs/en/operations/system-tables/parts_columns.md

system.parts_columns

Contains information about parts and columns of MergeTree tables.

Each row describes one data part.

Columns:

• partition (String) — The partition name. To learn what a partition is, see the description of the ALTER query.

  Formats:

  • YYYYMM for automatic partitioning by month.
  • any_string when partitioning manually.

• name (String) — Name of the data part.

• part_type (String) — 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 table.

• active (UInt8) — 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) — 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) — The number of rows.

• bytes_on_disk (UInt64) — Total size of all the data part files in bytes.

• data_compressed_bytes (UInt64) — 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) — Total size of uncompressed data in the data part. All the auxiliary files (for example, files with marks) are not included.

• marks_bytes (UInt64) — The size of the file with marks.

• modification_time (DateTime) — The time the directory with the data part was modified. This usually corresponds to the time of data part creation.

• remove_time (DateTime) — The time when the data part became inactive.

• refcount (UInt32) — 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) — The minimum value of the date key in the data part.

• max_date (Date) — The maximum value of the date key in the data part.

• partition_id (String) — ID of the partition.

• min_block_number (UInt64) — The minimum number of data parts that make up the current part after merging.

• max_block_number (UInt64) — The maximum number of data parts that make up the current part after merging.

• level (UInt32) — Depth of the merge tree. Zero means that the current part was created by insert rather than by merging other parts.

• data_version (UInt64) — 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) — The amount of memory (in bytes) used by primary key values.

• primary_key_bytes_in_memory_allocated (UInt64) — The amount of memory (in bytes) reserved for primary key values.

• database (String) — Name of the database.

• table (String) — Name of the table.

• engine (String) — Name of the table engine without parameters.

• disk_name (String) — Name of a disk that stores the data part.

• path (String) — Absolute path to the folder with data part files.

• column (String) — Name of the column.

• type (String) — Column type.

• column_position (UInt64) — Ordinal position of a column in a table starting with 1.

• default_kind (String) — Expression type (DEFAULT, MATERIALIZED, ALIAS) for the default value, or an empty string if it is not defined.

• default_expression (String) — Expression for the default value, or an empty string if it is not defined.

• column_bytes_on_disk (UInt64) — Total size of the column in bytes.

• column_data_compressed_bytes (UInt64) — Total size of compressed data in the column, in bytes.

• column_data_uncompressed_bytes (UInt64) — Total size of the decompressed data in the column, in bytes.

• column_marks_bytes (UInt64) — The size of the column with marks, in bytes.

• bytes (UInt64) — Alias for bytes_on_disk.

• marks_size (UInt64) — Alias for marks_bytes.

Example

SELECT * FROM system.parts_columns LIMIT 1 FORMAT Vertical;

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

Original article