ObjectOutputStream currently records replaced objects (i.e., those which have
been returned by a call to ObjectOutputStream.replaceObject() or a
class-defined writeReplace() method) in the object array replaceObjects[]. In
order to determine whether or not an object has a replacement,
ObjectOutputStream performs a linear scan of the table (see
ObjectOutputStream.lookupReplace()). If the number of replaced objects is
large, the overhead of this search becomes prohibitively expensive--for each
new object serialized, ObjectOutputStream will scan the entire array for a
match before concluding that there is none.

The replacement table should be replaced with a hash table similar to the one
used for wire handle lookup.