2018-07-30 1:00 GMT+02:00 Tom Lane <t...@sss.pgh.pa.us>: > David Rowley <david.row...@2ndquadrant.com> writes: > > On 29 July 2018 at 17:38, Dinesh Kumar <dns98...@gmail.com> wrote: > >> I found performance variance between accessing int1 and int200 column > which > >> is quite large. > > > Have a look at slot_deform_tuple and heap_deform_tuple. You'll see > > that tuples are deformed starting at the first attribute. If you ask > > for attribute 200 then it must deform 1-199 first. > > Note that that can be optimized away in some cases, though evidently > not the one the OP is testing. From memory, you need a tuple that > contains no nulls, and all the columns to the left of the target > column have to be fixed-width datatypes. Otherwise, the offset to > the target column is uncertain, and we have to search for it. >
JIT decrease a overhead of this. Regards Pavel > regards, tom lane > >
