On Sat, Sep 24, 2005 at 07:19:10PM -0400, Tom Lane wrote: > "Jim C. Nasby" <jnasby@xxxxxxxxxxxxx> writes: > > I can't seem to find info about this in the docs, or on the web. > > http://developer.postgresql.org/docs/postgres/storage-page-layout.html > > Currently, when a tuple is reclaimed by VACUUM, we just mark its item > pointer as unused (and hence recyclable). I think it might be safe to > decrease pd_lower if there are unused pointers at the end of the page's > pointer array, but we don't currently do that. In any case there could > still be unused pointers embedded within the array. I suspect that if the free space in pages isn't collapsed during vacuum then it probably doesn't matter, but I don't know if that's the case. If it is collapsed then my intuition is that tables that are fairly narrow would benefit from adjusting pd_lower because it wouldn't take too many item pointers to equate to a tuple. This would probably be even more pronounced if the tuples were generally small but could vary to a larger size. Sounds like a good newbie TODO? -- Jim C. Nasby, Sr. Engineering Consultant jnasby@xxxxxxxxxxxxx Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461 ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
