Introduction

All large objects are stored in a single system table named pg_largeobject . Each large object also has an entry in the system table pg_largeobject_metadata . Large objects can be created, modified, and deleted using a read/write API that is similar to standard operations on files.

PostgreSQL also supports a storage system called " TOAST " , which automatically stores values larger than a single database page into a secondary storage area per table. This makes the large object facility partially obsolete. One remaining advantage of the large object facility is that it allows values up to 4 TB in size, whereas TOAST ed fields can be at most 1 GB. Also, reading and updating portions of a large object can be done efficiently, while most operations on a TOAST ed field will read or write the whole value as a unit.