Jim Nasby <decibel@decibel.org> writes:
> On Jan 26, 2007, at 4:48 PM, Tom Lane wrote:
>> I don't actually see that it buys you a darn thing ... you still won't
>> be able to delete dead updated tuples because of the possibility of
>> the LRT deciding to chase ctid chains up from the tuples it can see.
> Well, Simon was talking about a serialized LRT, which ISTM shouldn't
> be hunting down ctid chains past the point it serialized at.
How you figure that? If the LRT wants to update a tuple, it's got to
chase the ctid chain to see whether the head update committed or not.
It's not an error for a serializable transaction to update a tuple that
was tentatively updated by a transaction that rolled back.
> Even if that's not the case, there is also the possibility if a LRT
> publishing information about what tables it will hit.
I think we already bought 99% of the possible win there by fixing
vacuum. Most ordinary transactions aren't going to be able to predict
which other tables the user might try to touch.
regards, tom lane