Tom Lane wrote: > Alvaro Herrera <[EMAIL PROTECTED]> writes: > > I think what Tom is concerned about is that this hasn't been tested > > enough with big datasets. Also there a little loss of index pages but > > it's much less (orders of magnitude, I think) than what was before. > > This is because the index won't shrink "vertically". > > The fact that we won't remove levels shouldn't be meaningful at all --- > I mean, if the index was once big enough to require a dozen btree > levels, and you delete everything, are you going to be upset that it > drops to 13 pages rather than 2? I doubt it. > > The reason I'm waffling about whether the problem is completely fixed or > not is that the existing code will only remove-and-recycle completely > empty btree pages. As long as you have one key left on a page it will > stay there. So you could end up with ridiculously low percentage-filled > situations. This could be fixed by collapsing together adjacent > more-than-half-empty pages, but we ran into a lot of problems trying to > do that in a concurrent fashion. So I'm waiting to find out if real > usage patterns have a significant issue with this or not.
Though the new code will put empty index pages into the free-space map, will it also shrink the index file to remove those pages? For example, if I have 200M rows in a table, and I delete all of them except 100, does the index shrink, or the pages just become available for reuse. With VACUUM FULL, we have a way to shrink the heap. Do we shrink the index? -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
