Re: [HACKERS] postgres inode q's

Jan,

Thanks for the explanation, that does help to explain, and adds a lot to my
postgres knowledge in general ..

Based on your explanation, I understand how running VACUUM wiped out the new
tuples that did not have a corresponding XID in pg_log.

However, there is one aspect of this I still do not quite grasp ..

What happens if the INSERT/DELETE is done without a transaction
(BEGIN/COMMIT)? Is an XID still generated for that particular tuple, or is the
tuple instantly commited with no XID stamped into the beginning/ending fields?

Also, I  don't understand why vacuum didn't wipe out all tuples in the
database, rather than just the new ones.  Here's why:

When I updated the "new" database with the new records I used the  DELETE then
INSERT trick to avoid having to write logic to first see if there was an
existing record and then to update only the changing fields.  Since I actually
deleted, then inserted,  I'm guessing that the XID would change so that when I
moved the database over to the other server, ALL of the XIDs would be
different, not just the newly added rows.  In which case, I would expect
VACUUM to wipe everything.  Instead, it only wiped the new rows, which tells
me that even though I DELETED/INSERTED all existing rows, that somehow the
XID's still sync with the XID's on the other server.

Assuming the XIDs did change, I'd guess that though I had exactly the same
number of rows I started with (666730 instead of +1400000) it is because the
XIDs happened to correspond, but not necessarily with their original
relationships.  Which would mean that I still had 666730 rows, but not the
original ones.  Probably a smattering of new and old ones.

I'm just theorizing off of the top of my head .. please let me know where I
have gone wrong!

Much Thanks,
Bryan










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