On Wed, Sep 5, 2018 at 12:00 PM Jeff Janes <jeff.ja...@gmail.com> wrote:
> On Wed, Sep 5, 2018 at 12:21 AM Dinesh Kumar <dns98...@gmail.com> wrote: > >> Hi All, >> I was wondering whether the case is solved or still continuing. As a >> Postgres newbie, I can't understand any of the terms (JIT, tuple >> deformation) as you mentioned above. Please anyone let me know , what is >> the current scenario. >> >> > JIT is a just-in-time compilation, which will be new in v11. Tuple > deforming is how you get the row from the on-disk format to the in-memory > format. > > Some people see small improvements in tuple deforming using JIT in your > situation, some see large decreases, depending on settings and apparently > on hardware. But regardless, JIT is not going to reduce your particular > use case (many nullable and actually null columns, referencing a > high-numbered column) down to being constant-time operation in the number > of preceding columns. Maybe JIT will reduce the penalty for accessing a > high-numbered column by 30%, but won't reduce the penalty by 30 fold. Put > your NOT NULL columns first and then most frequently accessed NULLable > columns right after them, if you can. > Correction: NOT NULL columns with fixed width types first. Then of the columns which are either nullable or variable width types, put the most frequently accessed earlier.
