reducing n_val

Christopher Meiklejohn cmeiklejohn at basho.com
Tue Jul 16 09:23:07 EDT 2013


On Tuesday, July 16, 2013 at 8:32 AM, Simon Effenberg wrote:
> is it possible to reduce the n_val? I mean you can change it but what
> happens then?
> 
> - is old data removed or is it laying around? (or maybe deleted after
> some time thanks to AAE?)

Changing the n_val setting in the default bucket properties will only affect new PUT operations moving forward. Older replicas will not be removed, and the AAE process will not purge older, unneeded replicas.

> 
> - is it causing problems like:
> - reducing n_val from 3 to 2
> - update data
> - sleep 10minutes
> - read data but second primary is borked => is the first fallback
> vnode on the place where the 3rd n_val vnode was before? So is this
> reading old crappy data (maybe the vclock is rescuing there but
> that's only one edge case I can think off right now)?

It's possible that the fallback virtual node will be started on the same physical node that originally hosted the third primary, however, it will be a different virtual node and backend directory as these are parameterized based on partition identifier and node.

- Chris

-- 
Christopher Meiklejohn
Software Engineer

Basho Technologies, Inc. 





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