PostgreSQL
51.30. pg_largeobject
The catalog pg_largeobject holds the data making up “[.quote]#large objects”. A large object is identified by an OID assigned when it is created. Each large object is broken into segments or [.quote]“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.
Table 51.30. pg_largeobject Columns
| Name | Type | References | Description |
|---|---|---|---|
|
|
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 |
+
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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