Re: Patch: Write Amplification Reduction Method (WARM)

On Tue, Mar 28, 2017 at 08:04:34AM +0530, Pavan Deolasee wrote:
> And I've answered it so many times by now :-) 

LOL

> Just to add more to what I just said in another email, note that HOT/WARM
> chains are created when a new root line pointer is created in the heap (a line
> pointer that has an index pointing to it). And a new root line pointer is
> created when a non-HOT/non-WARM update is performed. As soon as you do a
> non-HOT/non-WARM update, the next update can again be a WARM update even when
> everything fits in a single block. 
>
> That's why for a workload which doesn't do HOT updates and where not all index
> keys are updated, you'll find every alternate update to a row to be a WARM
> update, even when there is no chain conversion. That itself can save lots of
> index bloat, reduce IO on the index and WAL.
>
> Let me know if its still not clear and I can draw some diagrams to explain it.

Ah, yes, that does help to explain the 50% because 50% of updates are
now HOT/WARM.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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