The handle of a connection to the database in which the large object exists.
A descriptor for the large object from pg_lo_open.
The name of a buffer variable to contain the large object segment.
The maximum number of bytes to read.
The number of bytes actually read is returned; this could be less than the number requested if the end of the large object is reached first.
If an error occurs reading from the large object, a negative number will be returned. Other errors result in a Tcl error being thrown. Note that error handling for this command is different from most of the other Large Object commands.