Tom Lane wrote:
Heikki Linnakangas <[EMAIL PROTECTED]> writes:
We wouldn't clean up tuples that are visible to a transaction, but if you have one long-running transaction like pg_dump in a database with otherwise short transaction, you'll have a lot of tuples that are not vacuumable because of the long-running process, but are not in fact visible to any transaction.

It sounds to me like you are proposing to remove the middles of update
chains, which would break READ-COMMITTED updates initiated by the older
transactions.  Now admittedly pg_dump isn't going to issue any such
updates, but VACUUM doesn't know that.

You could restrict this to serializable transactions, or even to
read-only transactions. Or maybe the tuple could be reduced to
just it's header - doesn't HOT do something similar?

greetings, Florian Pflug

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