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