The compression is enabled per table for all disk-based tables inside the database. The default behavior is controlled by a setting in solid.ini file setting

This setting defines whether the compression is enabled by default. The default behavior can be overridden by table specific property COMPRESSED/NONCOMPRESSED that can be set by CREATE TABLE / ALTER TABLE commands. Note that if CompressAllTableS=YES, all tables are compressed regardless of ALTER TABLE commands. If CompressAllTableS=NO, compression can be turned on per table by ALTER TABLE.

In HotStandby environments, it is recommended to have the same setting in both databases.

The physical disk block size [IndexFile] BlockSize defines the node size in B+tree. Since node size is the size of compression unit, this setting has potentially significant impact on compression rate of the database.

Typically compression is defined when table is created. It is also possible to enable compression after the table is created. In that case existing pages are not compressed. Hence, compressing an existing populated table or full database is not a simple operation. When new data is added to the table then also old pages get compressed when they get full.