How to shrink pg_toast table?

You can use one of the two types of vacuuming: standard or full.

standard:

VACUUM table_name;

full:

VACUUM FULL table_name; 

Keep in mind that VACUUM FULL locks the table it is working on until it's finished.

You may want to perform standard vacuum more frequently on your tables which have frequent upload/delete activity, it may not give you as much space as vacuum full does but you will be able to run operations like SELECT, INSERT, UPDATE and DELETE and it will take less time to complete.

In my case, when pg_toast (along with other tables) got out of control, standard VACUUM made a slight difference but was not enough. I used VACUUM FULL to reclaim more disk space which was very slow on large relations. I decided to tune autovacuum and use standard VACUUM more often on my tables which are updated frequently.

If you need to use VACUUM FULL, you should do it when your users are less active. Also, do not turn off autovacuum.

You can get some additional information by adding verbose to your commands:

VACUUM FULL VERBOSE table_name;

Try the following:

vacuum full