Re: pg_upgarde: The control data check for equal max_index_keys in old and new version

Thanks, I understand now.
I should read the code comments properly too :).

Regards,
Neha

Cheers,
Neha

On Fri, Apr 22, 2016 at 1:45 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> neha khatri <nehakhatri5(at)gmail(dot)com> writes:
> > I have recently started working on Postgresql and I was looking in the
> the
> > pg_upgrade code. pg_upgrade checks index control data(max_index_keys) to
> be
> > equal in the old and new version.
>
> > I would like to understand why the number of index columns should be
> equal
> > in new and old versions.
>
> Because that changes the size of index tuple headers, see
> src/include/access/itup.h
>
> > Can the number of maximum index columns not be
> > changed from one release to another release.
>
> Sure, as long as you don't care about on-disk database compatibility.
> The checks associated with pg_control are meant to ensure exactly
> that, though.
>
> regards, tom lane
>