Re: HOT update: why must ALL indexes should be update?

On Fri, Apr 21, 2023 at 10:19:42AM -0400, Tom Lane wrote:
> Daniel Wu <staywithpin@gmail.com> writes:
> > We have many indexes on a table. The chance is that any column could be
> > some part of an index. I understand that when an index has a column that is
> > updated, we can't use HOT, because the index entry could point to a totally
> > different row. But if I have 10 indexes, if only 1 index will be updated,
> > why the rest 9 indexes couldn't use HOT update?
> 
> Whether it's a HOT update is a property of the table row, not of
> individual indexes.

Right, specifically the item pointer on the heap/table page can't be
reused because _one_ of the indexes needs a new item pointer to point
to.  See the later sections of this talk for diagrams:

    https://momjian.us/main/presentations/internals.html#mvcc

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Embrace your flaws.  They make you human, rather than perfect,
  which you will never be.