50.30. pg_largeobject
The catalogpg_largeobject holds the data making up“large objects”. A large object is identified by an OID assigned when it is created. Each large object is broken into segments or“pages” small enough to be conveniently stored as rows inpg_largeobject. The amount of data per page is defined to beLOBLKSIZE (which is currentlyBLCKSZ/4, or typically 2 kB).
Prior toPostgreSQL 9.0, there was no permission structure associated with large objects. As a result,pg_largeobject was publicly readable and could be used to obtain the OIDs (and contents) of all large objects in the system. This is no longer the case; usepg_largeobject_metadata to obtain a list of large object OIDs.
Table 50.30. pg_largeobject Columns
| Name | Type | References | Description |
|---|---|---|---|
loid | oid | | Identifier of the large object that includes this page |
pageno | int4 | Page number of this page within its large object (counting from zero) | |
data | bytea | Actual data stored in the large object. This will never be more thanLOBLKSIZE bytes and might be less. |
Each row ofpg_largeobject holds data for one page of a large object, beginning at byte offset (pageno * LOBLKSIZE) within the object. The implementation allows sparse storage: pages might be missing, and might be shorter thanLOBLKSIZE bytes even if they are not the last page of the object. Missing regions within a large object read as zeroes.