On Fri, Dec 7, 2012 at 9:21 AM, Pavan Deolasee <pavan.deola...@gmail.com> wrote: > On Thu, Dec 6, 2012 at 11:31 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > >> >> I think taking a second whack at setting the visibility bit is a fine >> idea, but let's drop all the rest of this premature optimization. >> > > Fair enough. I thought about doing it that way but was worried that an > additional page scan will raise eyebrows. While it does not affect the > common case because we would have done that scan anyways in the > subsequent vacuum, but in the worst case where most of the pages not > remain all-visible by the time we come back to the second phase of > vacuum, this additional line pointer scan will add some overhead. With > couple of pluses for the approach, I won't mind doing it this way > though. >
Revised patch attached. This time much less invasive. I added a new function heap_page_is_all_visible() to check if the given page is all-visible and also return the visibility cutoff xid. Couple of things: - We use the same OldestXmin computed in the first phase for visibility checks. We can potentially recompute this at the start of second phase. I wasn't convinced thats needed or even correct - It will be a good idea to consolidate the page scanning in a single place to avoid code duplication. But may be will do that some other day. Thanks, Pavan -- Pavan Deolasee http://www.linkedin.com/in/pavandeolasee
vacuum-secondphase-setvm-v2.patch
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