pg_lo_read_all() reads a large
object and passes it straight through to the browser after
sending all pending headers. Mainly intended for sending
binary data like images or sound. It returns number of bytes
read. It returns FALSE, if
an error occurred.
To use the large object (lo) interface, it is necessary
to enclose it within a transaction block.
注: This function used to be called pg_loreadall().
See also pg_lo_read().