Re: TOAST performance (was Re: [GENERAL] Delete Performance)

Bruce Momjian <pgman@candle.pha.pa.us> writes:
>> I don't see how that reduces the total amount of disk traffic?

> Well, right now we write the pre-image to WAL, then write the new page
> over the old one.  In my case, you just write the new, and somewhere
> record that the old page is no longer active.

The devil is in the details of that last little bit.  How is "mark a
page inactive" cheaper than "mark a tuple dead"?  More specifically,
how do you propose to avoid WAL-logging the page you are going to do
this marking in?  Seems you still end up with a WAL page image for
something.
        regards, tom lane