pg_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 in
pg_largeobject. The amount of data per page is defined to be
LOBLKSIZE (which is currently
BLCKSZ/4, or typically 2 kB).
Prior to PostgreSQL 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; use
pg_largeobject_metadata to obtain a list of large object OIDs.
|Identifier of the large object that includes this page
|Page number of this page within its large object (counting from zero)
|Actual data stored in the large object. This will never be more than
LOBLKSIZE bytes and might be less.
Each row of
pg_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 than
LOBLKSIZE bytes even if they are not the last page of the object. Missing regions within a large object read as zeroes.
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