Here is a new patch set @ 10b5bb3bffaee8
As previously stated, the patch set implements the concept of saving the
"difference" between page offsets in order to save disc space.
The second significant change was that I decided to modify the
pg_upgrade portion as suggested by Heikki above.
At the very least, the logic becomes much simpler and completely
replicates what is done in the multxact.c module and provide some
optimization.
Perhaps this will be easier to comprehend and analyse than attempting
to correctly convert bytes from one format to another.
In the near future, I intend to focus on testing and implement a test
suite.
-- Best regards,
Maxim Orlov.