[openstack-dev] [nova] Distributed Database

Mike Bayer mbayer at redhat.com
Fri Apr 29 03:16:54 UTC 2016

On 04/28/2016 08:25 PM, Edward Leafe wrote:

> Your own tests showed that a single RDBMS instance doesn’t even break a sweat
> under your test loads. I don’t see why we need to shard it in the first
> place, especially if in doing so we add another layer of complexity and
> another dependency in order to compensate for that choice. Cells are a useful
> concept, but this proposed implementation is adding way too much complexity
> and debt to make it worthwhile.

now that is a question I have also.  Horizontal sharding is usually for 
the case where you need to store say, 10B rows, and you'd like to split 
it up among different silos.  Nothing that I've seen about Nova suggests 
this is a system with any large data requirements, or even medium size 
data (a few million rows in relational databases is nothing).    I 
didn't have the impression that this was the rationale behind Cells, it 
seems like this is more of some kind of logical separation of some kind 
that somehow suits some environments (but I don't know how). 
Certainly, if you're proposing a single large namespace of data across a 
partition of nonrelational databases, and then the data size itself is 
not that large, as long as "a single namespace" is appropriate then 
there's no reason to break out of more than one MySQL database.  There's 
not much reason to transparently shard unless you are concerned about 
adding limitless storage capacity.   The Cells sharding seems to be 
intentionally explicit and non-transparent.

> -- Ed Leafe
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