Re: _bt_check_unique checks every row in table when doing update?? - Mailing list pgsql-bugs

Tom Lane wrote:
> > (In my case, I think the call to _bt_check_unique could be
> > avoided altogether since the update isn't changing any of
> > the columns present in the unique key.
>
> It's fairly difficult for the index AM to know that; in general we don't
> have access to the old tuple to check, at the time the index update is
> running.

We do have a TODO item:

* Prevent index uniqueness checks when UPDATE does not modifying column

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