Re: Performance difference in accessing differrent columns in a Postgres Table

On Wed, Sep 5, 2018 at 12:21 AM Dinesh Kumar <dns98944(at)gmail(dot)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.

Cheers,

Jeff

>