Re: Performance difference in accessing differrent columns in aPostgres Table

On Wed, Sep 5, 2018 at 12:21 AM Dinesh Kumar <dns98944@gmail.com> wrote:

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