Contents
pg_column_compression()
A function returning the compression algorithm used on a TOAST value
pg_column_compression() is a system function returning the compression algorithm used to compress a TOAST value.
pg_column_compression() was added in PostgreSQL 14.
Usage
pg_column_compression ( "any" ) → text
If a value was not compressed, NULL is returned.
Change history
- PostgreSQL 14
- added (commit bbe0a81d)
Examples
Example of pg_column_compression(), with a value where no compression took place, a value which was compressed with the default pglz algorithm, and a column compressed with lz4:
postgres=# CREATE TABLE foo (id INT, val TEXT);
CREATE TABLE
postgres=# INSERT INTO foo values (1, 'bar');
INSERT 0 1
postgres=# INSERT INTO foo values (2, REPEAT('bar', 3072));
INSERT 0 1
postgres=# ALTER TABLE foo ALTER COLUMN val SET COMPRESSION lz4;
ALTER TABLE
postgres=# INSERT INTO foo values (3, REPEAT('baz', 3072));
INSERT 0 1
postgres=# SELECT id, pg_column_compression(val) FROM foo;
id | pg_column_compression
----+-----------------------
1 |
2 | pglz
3 | lz4
(3 rows)
References
- PostgreSQL documentation: Database Object Management Functions