chunk_columnstore_stats()

Since 2.18.0

chunk_columnstore_stats() replaces chunk_compression_stats(), deprecated in 2.18.0. The parameters are the same.

Retrieve statistics about the chunks in the columnstore

chunk_columnstore_stats returns the size of chunks in the columnstore, these values are computed when you call either:

• CREATE TABLE: create a hypertable with a default job that automatically moves chunks in a hypertable to the columnstore at a specific time interval.
• add_columnstore_policy: create a job on an existing hypertable that automatically moves chunks in a hypertable to the columnstore at a specific time interval.
• convert_to_columnstore: manually add a specific chunk in a hypertable to the columnstore.

Inserting into a chunk in the columnstore does not change the chunk size. For more information about how to compute chunk sizes, see chunks_detailed_size.

Samples

To retrieve statistics about chunks:

• Show the status of the first two chunks in the conditions hypertable:

  SELECT * FROM chunk_columnstore_stats('conditions')
    ORDER BY chunk_name LIMIT 2;

  Returns:

  -[ RECORD 1 ]------------------+----------------------
  chunk_schema                   | _timescaledb_internal
  chunk_name                     | _hyper_1_1_chunk
  compression_status             | Uncompressed
  before_compression_table_bytes |
  before_compression_index_bytes |
  before_compression_toast_bytes |
  before_compression_total_bytes |
  after_compression_table_bytes  |
  after_compression_index_bytes  |
  after_compression_toast_bytes  |
  after_compression_total_bytes  |
  node_name                      |
  -[ RECORD 2 ]------------------+----------------------
  chunk_schema                   | _timescaledb_internal
  chunk_name                     | _hyper_1_2_chunk
  compression_status             | Compressed
  before_compression_table_bytes | 8192
  before_compression_index_bytes | 32768
  before_compression_toast_bytes | 0
  before_compression_total_bytes | 40960
  after_compression_table_bytes  | 8192
  after_compression_index_bytes  | 32768
  after_compression_toast_bytes  | 8192
  after_compression_total_bytes  | 49152
  node_name                      |

• Use pg_size_pretty to return a more human friendly format:

  SELECT pg_size_pretty(after_compression_total_bytes) AS total
    FROM chunk_columnstore_stats('conditions')
    WHERE compression_status = 'Compressed';

  Returns:

  -[ RECORD 1 ]--+------
  total | 48 kB

Arguments

The syntax is:

SELECT * FROM chunk_columnstore_stats('<hypertable_name>');

Name	Type	Default	Required	Description
hypertable	REGCLASS	-	✔	The name of a hypertable

Returns

Column	Type	Description
chunk_schema	NAME	Schema name of the chunk.
chunk_name	NAME	Name of the chunk.
compression_status	TEXT	Current compression status of the chunk.
before_compression_table_bytes	BIGINT	Size of the heap before compression. Returns NULL if compression_status == Uncompressed.
before_compression_index_bytes	BIGINT	Size of all the indexes before compression. Returns NULL if compression_status == Uncompressed.
before_compression_toast_bytes	BIGINT	Size the TOAST table before compression. Returns NULL if compression_status == Uncompressed.
before_compression_total_bytes	BIGINT	Size of the entire chunk table (before_compression_table_bytes + before_compression_index_bytes + before_compression_toast_bytes) before compression. Returns NULL if compression_status == Uncompressed.
after_compression_table_bytes	BIGINT	Size of the heap after compression. Returns NULL if compression_status == Uncompressed.
after_compression_index_bytes	BIGINT	Size of all the indexes after compression. Returns NULL if compression_status == Uncompressed.
after_compression_toast_bytes	BIGINT	Size the TOAST table after compression. Returns NULL if compression_status == Uncompressed.
after_compression_total_bytes	BIGINT	Size of the entire chunk table (after_compression_table_bytes + after_compression_index_bytes + after_compression_toast_bytes) after compression. Returns NULL if compression_status == Uncompressed.
node_name	NAME	DEPRECATED: nodes the chunk is located on, applicable only to distributed hypertables.