ctid & updates

1#
I saw a post from Jan Wieck about how ctid can be used for a fast update.
I noticed that ctid changes on update (as expected since it's really a new
row). Is there anyway to get the new ctid from the update so later
updates to the row can continue to use ctid to zero in on the row
location?

2#
Also, is ctid unique for each row? I would guess so since it looks like
(and I'm guessing) that ctid is a page/row offset. So there should be only
one thing at each ctid address. Is that correct that ctid is unique to a
table? Can anything interesting be done with the empty space? Is there any
way to find the maximum ctid and look for quantities of empty space? I
assume a user-side program could use that data to see how much unused,
yet allocated space there is in a table?

That might be the "You don't have to be a PostgreSQL hacker" version of
looking for compressible (via relocation) tables.

Joshua b. Jore ; http://www.greentechnologist.org ; 1121 1233 1311 200
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