cost_index()

Hi!

Some fragment of code (src/backend/optimizer/path/costsize.c, lineno ~400):
/*
* Normal case: apply the Mackert and Lohman formula, and then
* interpolate between that and the correlation-derived result.
*/
pages_fetched = index_pages_fetched(tuples_fetched,
baserel->pages,
(double) index->pages,
root);
if (indexonly)
pages_fetched = ceil(pages_fetched * (1.0 - baserel->allvisfrac));

As I understand the code, index_pages_fetched() returns summary of page's read
for index and heap together. But on next line this recalculates with "all
visible fraction" of heap. After recent vacuum it could be 1.0 and then
pages_fetches will be zero. It seems to me obviously wrong, because it's for
index only scan it could be true only for heap, not for index pages.

Am I wrong or miss something?

--
Teodor Sigaev E-mail: teodor(at)sigaev(dot)ru
WWW: http://www.sigaev.ru/