35.2. Implementation Features

35.2. Implementation Features
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+ The large object implementation breaks large + objects up into “chunks” and stores the chunks in + rows in the database. A B-tree index guarantees fast + searches for the correct chunk number when doing random + access reads and writes. +

+ The chunks stored for a large object do not have to be contiguous. + For example, if an application opens a new large object, seeks to offset + 1000000, and writes a few bytes there, this does not result in allocation + of 1000000 bytes worth of storage; only of chunks covering the range of + data bytes actually written. A read operation will, however, read out + zeroes for any unallocated locations preceding the last existing chunk. + This corresponds to the common behavior of “sparsely allocated” + files in Unix file systems. +

+ As of PostgreSQL 9.0, large objects have an owner + and a set of access permissions, which can be managed using + GRANT and + REVOKE. + SELECT privileges are required to read a large + object, and + UPDATE privileges are required to write or + truncate it. + Only the large object's owner (or a database superuser) can delete, + comment on, or change the owner of a large object. + To adjust this behavior for compatibility with prior releases, see the + lo_compat_privileges run-time parameter. +

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35.1. Introduction	Home	35.3. Client Interfaces