Re: Patch: Write Amplification Reduction Method (WARM)

On Fri, Feb 24, 2017 at 2:13 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> On Thu, Feb 23, 2017 at 9:21 PM, Bruce Momjian <bruce(at)momjian(dot)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.

Thanks,
Pavan

--
Pavan Deolasee http://www.2ndQuadrant.com/
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