On Fri, Nov 02, 2007 at 06:12:37PM +0530, Gokulakannan Somasundaram wrote: > I am especially interested in the case of continuing the HOT chain across > pages. When we are actually reclaiming space, we should check the snapshot > and reclaim it. If it is HOT updated, we will leave the top most tuple and > take the rest. So then the top most tuple will remain always and any index > scan now has to make read two heap pages to reach the target entry.Is this > the only reason, it was left out?
It's not that simple. At any point in time there may be dozens of active snapshots, each of which might see a different tuple in the chain. So to clear any tuple you have to wait until all active snapshots are gone. You will almost never be able to reduce the chain to just one. As for your original question and jumping across pages, why stop at one. Why not chain HOT tuples down 100 pages? Because then it gets very expensive. Not to mention the locking considerations. Better keep it simple. Have a nice day, -- Martijn van Oosterhout <[EMAIL PROTECTED]> http://svana.org/kleptog/ > Those who make peaceful revolution impossible will make violent revolution > inevitable. > -- John F Kennedy
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