DB2 uses a dictionary based algorithm for compressing data records. DB2 9 will scan tables, and search for duplicate occurrences, then assign a short numeric key to each entries. You will understand better with a picture:

Compress data

Each new occurences of “Sophie”, “New York”, “IBM US”, will be respectively assign to “(01)”, “(19)” and “(09)”. This is very useful on large table. Each time a new row is added to the table, DB2 will automatically compress these new data.

Seems to be good, let’s try on our DB2 now. To enable the compression,  we should turn on the “COMPRESS” option on the table.

CREATE TABLE Users COMPRESS YES

or use alter if the table is already created:

ALTER TABLE Users COMPRESS YES

Typically, we can save an average ratio of 45 to 75 percent of our storage space. Next time, we’ll see how to use the inspect tool, to determine the compression ratio.