Alvaro Herrera <alvherre@dcc.uchile.cl> writes:
> On Wed, May 14, 2003 at 12:42:17PM -0400, Tom Lane wrote:
>> In CVS tip we keep track of that information in the index's metapage
>> (page zero). But in so-far-released versions it's not explicitly
>> tracked anywhere. You'd have to actually chase down the tree from the
>> root to a leaf to count the levels.
> Does this level count takes into consideration the fast root of the
> tree? I think it doesn't.
IIRC we store the levels of both the true root and the fast root in
the metapage.
> If this is so, the number of disk accesses will be overestimated by
> reading only the level count. One should traverse levels down from the
> true root to the fast root and substract that from the level count.
You're correct, the fast-root level is the interesting one for
performance estimates.
regards, tom lane
