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system.parts_columns

Description​

Contains information about parts and columns of MergeTree tables. Each row describes one data part.

Columns​

  • partition (String) — The partition name.
  • name (String) — Name of the data part.
  • uuid (UUID) — The parts UUID.
  • 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.
  • 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 does not 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 for the Date column if that is included in the partition key.
  • max_date (Date) — The maximum value for the Date column if that is included in the partition key.
  • min_time (DateTime) — The minimum value for the DateTime column if that is included in the partition key.
  • max_time (DateTime) — The maximum value for the DateTime column if that is included in the partition key.
  • partition_id (String) — ID of the partition.
  • min_block_number (Int64) — The minimum number of data parts that make up the current part after merging.
  • max_block_number (Int64) — 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 the 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 marks for column, in bytes.
  • column_modification_time (Nullable(DateTime)) — The last time the column was modified.
  • column_ttl_min (Nullable(DateTime)) — The minimum value of the calculated TTL expression of the column.
  • column_ttl_max (Nullable(DateTime)) — The maximum value of the calculated TTL expression of the column.
  • statistics (Array(String)) — The statistics of the column.
  • estimates.min (Nullable(String)) — Estimated minimum value of the column.
  • estimates.max (Nullable(String)) — Estimated maximum value of the column.
  • estimates.cardinality (Nullable(UInt64)) — Estimated cardinality of the column.
  • serialization_kind (String) — Kind of serialization of a column
  • substreams (Array(String)) — Names of substreams to which column is serialized
  • filenames (Array(String)) — Names of files for each substream of a column respectively
  • subcolumns.names (Array(String)) — Names of subcolumns of a column
  • subcolumns.types (Array(String)) — Types of subcolumns of a column
  • subcolumns.serializations (Array(String)) — Kinds of serialization of subcolumns of a column
  • subcolumns.bytes_on_disk (Array(UInt64)) — Sizes in bytes for each subcolumn
  • subcolumns.data_compressed_bytes (Array(UInt64)) — Sizes of the compressed data for each subcolumn, in bytes
  • subcolumns.data_uncompressed_bytes (Array(UInt64)) — Sizes of the decompressed data for each subcolumn, in bytes
  • subcolumns.marks_bytes (Array(UInt64)) — Sizes of the marks for each subcolumn of a column, in 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​