Tom Lane wrote: > I wanted to enumerate my concerns while yesterday's > events are still fresh in mind. (Andres or Robert might have more.) > > * I do not understand why this feature is on-by-default in the first > place. It can only be a win for expression indexes that are many-to-one > mappings; for indexes that are one-to-one or few-to-one, it's a pretty > big loss. I see no reason to assume that most expression indexes fall > into the first category. I suggest that the design ought to be to use > this optimization only for indexes for which the user has explicitly > enabled recheck_on_update. That would allow getting rid of the cost check > in IsProjectionFunctionalIndex, about which we'd otherwise have to have > an additional fight: I do not like its ad-hoc-ness, nor the modularity > violation (and potential circularity) involved in having the relcache call > cost_qual_eval.
That was my impression too when I had a closer look at this feature. What about an option "hot_update_check" with values "off" (default), "on" and "always"? Yours, Laurenz Albe
