On Fri, Feb 24, 2017 at 2:13 PM, Robert Haas <robertmh...@gmail.com> wrote:

> On Thu, Feb 23, 2017 at 9:21 PM, Bruce Momjian <br...@momjian.us> wrote:
> >
> > I have what might be a supid question.  As I remember, WARM only allows
> > a single index-column change in the chain.  Why are you seeing such a
> > large performance improvement?  I would have thought it would be that
> > high if we allowed an unlimited number of index changes in the chain.
> I'm not sure how the test case is set up.  If the table has multiple
> indexes, each on a different column, and only one of the indexes is
> updated, then you figure to win because now the other indexes need
> less maintenance (and get less bloated).  If you have only a single
> index, then I don't see how WARM can be any better than HOT, but maybe
> I just don't understand the situation.
That's correct. If you have just one index and if the UPDATE modifies
indexed indexed, the UPDATE won't be a WARM update and the patch gives you
no benefit. OTOH if the UPDATE doesn't modify any indexed columns, then it
will be a HOT update and again the patch gives you no benefit. It might be
worthwhile to see if patch causes any regression in these scenarios, though
I think it will be minimal or zero.


 Pavan Deolasee                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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