|PostgreSQL Programmer's Guide|
pg_lo_write conn fd buf len
Specifies a valid database connection.
File descriptor for the large object from pg_lo_open.
Specifies a valid string variable to write to the large object.
Specifies the maximum size of the string to write.
pg_lo_write writes at most len bytes to a large object from a variable buf.
buf must be the actual string to write, not a variable name.