|PostgreSQL Programmer's Guide|
pg_lo_read conn fd bufVar len
Specifies a valid database connection.
File descriptor for the large object from pg_lo_open.
Specifies a valid buffer variable to contain the large object segment.
Specifies the maximum allowable size of the large object segment.
pg_lo_read reads at most len bytes from a large object into a variable named bufVar.
bufVar must be a valid variable name.