On 30.05.2013 15:12, Andres Freund wrote:
Now, I am far from being convinced its a good idea to get rid of PD_ALL_VISIBLE, but I don't think it does. Except that it currently is legal for the page level ALL_VISIBLE being set while the corresponding visibilitymap one isn't there's not much prohibiting us fundamentally from looking in the vm when we need to know whether the page is all visible, is there?
Hmm, so you're suggesting that the visibility map would be *required* to interpret the pages correctly. Ie. if you just zapped the visibility map, you'd lose critical information and the heap would appear to be corrupt. I guess that's possible, but it makes me quite uneasy. At the moment, it's relieving to know that it's always safe to just truncate the visibility map in case of emergency.
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