On Thu, Oct 1, 2009 at 5:08 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Robert Haas <robertmh...@gmail.com> writes: >> The elephant in the room here is that if the relation is a million >> pages of which 1-100,000 and 1,000,000 are in use, no amount of bias >> is going to help us truncate the relation unless every tuple on page >> 1,000,000 gets updated or deleted. > > Well, there is no way to move a tuple across pages in a user-invisible, > non-blocking fashion, so our ability to do something automatic about the > above scenario is limited. The discussion at the moment is about ways > of reducing the probability of getting into that situation in the first > place. That doesn't preclude also providing some more-invasive tools > that people can use when they do get into that situation; but let's > not let I-want-a-magic-pony syndrome prevent us from doing anything > at all.
That's fair enough, but it's our usual practice to consider, before implementing a feature or code change, what fraction of the people it will actually help and by how much. If there's a way that we can improve the behavior of the system in this area, I am all in favor of it, but I have pretty modest expectations for how much real-world benefit will ensue. I suspect that it's pretty common for large tables to contain a core of infrequently-updated records, and even a very light smattering of those, distributed randomly, will be enough to stop table shrinkage before it can get very far. ...Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
