On Wed, Dec 3, 2014 at 11:19 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Atri Sharma <atri.j...@gmail.com> writes: > > Is it possible to only replan part of the plan in case of this > > optimization? I think that we might need to only replan parts of the > > original plan (as you mentioned, join search and above). So we could > reuse > > the original plan in part and not do a lot of replanning (an obvious case > > is scan strategy, which we can assume will not change for the two plans). > > I think you assume wrong; or at least, I certainly would not wish to > hard-wire any such assumption. Skipping some joins could change the > shape of the join tree *completely*, because the cost estimates will > change so much. And that could in turn lead to making different choices > of scan methods, eg, we might or might not care about sort order of > a scan result if we change join methods. > > regards, tom lane > Agreed, but in some cases, we could possibly make some assumptions (if there is no index, if a large fraction of table will be returned in scan, FunctionScan).
