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

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От Pavan Deolasee
Тема Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)
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Msg-id CABOikdNqzSPgFqxmvO6UwNmNfVw78yn+LBCJi5_dvh=JN4yf_w@mail.gmail.com
обсуждение исходный текст
Ответ на Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)  (Peter Geoghegan <pg@bowt.ie>)
Ответы Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)  (Robert Haas <robertmhaas@gmail.com>)
In-place index updates and HOT (Was: [HACKERS] Patch: WriteAmplification Reduction Method (WARM))  (Peter Geoghegan <pg@bowt.ie>)
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On Fri, Jul 28, 2017 at 5:57 AM, Peter Geoghegan <pg@bowt.ie> wrote:
Pavan Deolasee <pavan.deolasee@gmail.com> wrote:
> I'll be happy if someone wants to continue hacking the patch further and
> get it in a committable shape. I can stay actively involved. But TBH the
> amount of time I can invest is far as compared to what I could during the
> last cycle.

That's disappointing.


Yes, it is even more for me. But I was hard pressed to choose between Postgres-XL 10 and WARM. Given ever increasing interest in XL and my ability to control the outcome, I thought it makes sense to focus on XL for now. 
 
I personally find it very difficult to assess something like this.

One good thing is that the patch is ready and fully functional. So that allows those who are keen to run real performance tests and see the actual impact of the patch. 
 
The
problem is that even if you can demonstrate that the patch is strictly
better than what we have today, the risk of reaching a local maxima
exists.  Do we really want to double-down on HOT?

Well HOT has served us well for over a decade now. So I won't hesitate to place my bets on WARM.
 

If I'm not mistaken, the goal of WARM is, roughly speaking, to make
updates that would not be HOT-safe today do a "partial HOT update".  My
concern with that idea is that it doesn't do much for the worst case.

I see your point. But I would like to think this way: does the technology significantly help many common use cases, that are currently not addressed by HOT? It probably won't help all workloads, that's given. Also, we don't have any credible alternative while this patch has progressed quite a lot. May be Robert will soon present the pluggable storage/UNDO patch and that will cover everything and more that is currently covered by HOT/WARM. That will probably make many other things redundant. 

Thanks,
Pavan

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

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