Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)

Поиск
Список
Период
Сортировка
От Pavan Deolasee
Тема Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)
Дата
Msg-id CABOikdP+PrqVrKeVSPb2M5kT9r0wmpsPuicserbJKJ6eG1vRCg@mail.gmail.com
обсуждение исходный текст
Ответ на Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)  (Bruce Momjian <bruce@momjian.us>)
Ответы Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)  (Bruce Momjian <bruce@momjian.us>)
Список pgsql-hackers
Дерево обсуждения


On Thu, Feb 23, 2017 at 11:53 PM, Bruce Momjian <bruce@momjian.us> wrote:
On Thu, Feb 23, 2017 at 03:03:39PM -0300, Alvaro Herrera wrote:
> Bruce Momjian wrote:
>
> > 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.
>
> The second update in a chain creates another non-warm-updated tuple, so
> the third update can be a warm update again, and so on.

Right, before this patch they would be two independent HOT chains.  It
still seems like an unexpectedly-high performance win.  Are two
independent HOT chains that much more expensive than joining them via
WARM?

In these tests, there are zero HOT updates, since every update modifies some index column. With WARM, we could reduce regular updates to half, even when we allow only one WARM update per chain (chain really has a single tuple for this discussion). IOW approximately half updates insert new index entry in *every* index and half updates 
insert new index entry *only* in affected index. That itself does a good bit for performance.

So to answer your question: yes, joining two HOT chains via WARM is much cheaper because it results in creating new index entries just for affected indexes.

Thanks,
Pavan

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

В списке pgsql-hackers по дате отправления:

Предыдущее
От: Robert Haas
Дата:
Сообщение: Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)
Следующее
От: Pavan Deolasee
Дата:
Сообщение: Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)