pg_largeobject

PostgreSQL 9.1.2 Documentation
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# 45.28. `pg_largeobject`

The catalog `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.

Table 45-28. `pg_largeobject` Columns

Name | Type | References | Description
--- | --- | --- | ---
`loid` | `oid` | ``pg_largeobject_metadata`.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 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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