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From Øystein Grøvlen <Oystein.Grov...@Sun.COM>
Subject Re: Discussion of incremental checkpointing----Added some new content
Date Sat, 11 Feb 2006 19:51:47 GMT
Very good analysis, Suresh.  I agree with you that we should keep this 
simple and not introduce a lot of overhead to determine the constants.

--
Øystein

Suresh Thalamati wrote:
> 
> My two cents:
> If the goal is do to auto-tune the checkpoint interval , I think amount 
> of log generated is a good indication of how fast the
> system is. By finding out how fast log is getting generated,
> one can predict with in reasonable error how long the recovery
> will take on that system.
> 
> It might be worth to find a simple solution to start with, than trying 
> to get it perfect. How about some  simple solution to tune the 
> checkpoint interval like the following:
> 
> Say on a particular system:
> 
> 1) we can generate N amount of log in X amount time on a running system.
> 
> 2) R is fraction of time it takes to recover a log generated in X amount 
> of time. One can pre calculate this factor by doing some tests instead 
> of trying to find on each boot.
> 
> 3) Y is the recovery time, derby users likely to see by
> default in the worst case.
> 
> 4) C is after how much log generation a checkpoint should be scheduled
> 
> ideal checkpoint interval log size should be some thing like :
> 
>    C = (N / X) * (Y * R)
> 
> 
> For example :
> 
> X = 5 min,   N  = 50 MB., Y =  1 min, R = 0.5
> 
> C = (50 / 5 ) * ( 1 / 0.5)    = 20 MB.
> 
> 
> One could use some formula like above at checkpoint to tune when should 
> the next checkpoint should occur , I understand first time it will be 
> completely Off,  but the interval will stabilize after a few checkpoints.
> 
> I think irrespective of whatever approach is finally implemented, we 
> have to watch  for overhead introduced to get it exactly right, I don't 
> think user will really care if recovery takes few seconds
> less or more.
> 
> Aside from tuning the checkpoint interval, I think we should find ways 
> to minimize the effect of checkpoint on the system throughput.
> I guess that is a different topic.
> 
> 
> 
> Thanks
> -suresht
> 

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