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Re: [Xen-API] [MirageOS-devel] xen dev summit talk slides: Branch Consistency for Xenstore

On 17 Aug 2014, at 11:01, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:

> I'm giving a talk at the Xen Developer Summit at Linuxcon tomorrow on the 
> work that we've (primarily Dave Scott and Thomas Gazagnaire) on improving the 
> Xenstore via Irmin features.
> Slides here: http://decks.openmirage.org/xendevsummit14#/
> Repo: https://github.com/mirage/mirage-decks as usual

[+xen-api-devel] Talk went well, quick notes here:

- git workflow very popular. Lots of people twigged onto the maintainability 
benefits of `git bisect` automation in particular.

- questions about why Xenstore transactions are still necessary in the modern 
world.  Can replace with consensus protocols instead?  Maybe time for an ABI 
bump to deprecate the ancient xenstore protocol.

- space usage is a concern -- building an RRD-style constant size library to 
maintain progressive history would be a big win.

- *excellent* talk from Felipe Huici (CCed) from NEC about building much denser 
VM workloads, and he observed that Xenstored/xenconsoled are a big bottleneck 
at ~10000 VMs.  Are your slides available Felipe?  Some sub notes:

 - we could write a mirage xenconsoled to log to irmin and drain guest console 
rings much faster.
 - a distributed xenstored+irmin would allow significantly more scalability 
than attempting to build a serially fast version.
 - felipe has the beginning of a simple c++ xenstored that doesn't implement 
the full semantics, but is enough for MiniOS.
 - it may be useful to negotiate a xenstore v2 protocol and use that for new 
guests.  It could use a simple fixed-length binary protocol (protobuf-style?), 
and eliminate the need for transactions perhaps.

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