[openstack-dev] Scheduler proposal

Joshua Harlow harlowja at fastmail.com
Sun Oct 11 17:00:05 UTC 2015

Clint Byrum wrote:
> Excerpts from Boris Pavlovic's message of 2015-10-11 00:02:39 -0700:
>> 2Everybody,
>> Just curios why we need such complexity.
>> Let's take a look from other side:
>> 1) Information about all hosts (even in case of 100k hosts) will be less
>> then 1 GB
>> 2) Usually servers that runs scheduler service have at least 64GB RAM and
>> more on the board
>> 3) math.log(100000)<  12  (binary search per rule)
>> 4) We have less then 20 rules for scheduling
>> 5) Information about hosts is updated every 60 seconds (no updates host is
>> dead)
>> According to this information:
>> 1) We can store everything in RAM of single server
>> 2) We can use Python
>> 3) Information about hosts is temporary data and shouldn't be stored in
>> persistence storage
>> Simplest architecture to cover this:
>> 1) Single RPC service that has two methods: find_host(rules),
>> update_host(host, data)
>> 2) Store information about hosts  like a dict (host_name->data)
>> 3) Create for each rule binary tree and update it on each host update
>> 4) Make a algorithm that will use binary trees to find host based on rules
>> 5) Each service like compute node, volume node, or neutron will send
>> updates about host
>>     that they managed (cross service scheduling)
>> 6) Make a algorithm that will sync host stats in memory between different
>> schedulers
> I'm in, except I think this gets simpler with an intermediary service
> like ZK/Consul to keep track of this 1GB of data and replace the need
> for 6, and changes the implementation of 5 to "updates its record and
> signals its presence".
> What you've described is where I'd like to experiment, but I don't want
> to reinvent ZK or Consul or etcd when they already exist and do such a
> splendid job keeping observers informed of small changes in small data
> sets. You still end up with the same in-memory performance, and this is
> in line with some published white papers from Google around their use
> of Chubby, which is their ZK/Consul.

+1 let's not recreate this; the code @ paste.openstack.org/show/475941/ 
basically does 1-6 and within about ~100 lines, it doesn't optimize 
things into a binary tree, but thats easily doable... for all I care put 
the information received into N trees (perhaps even using 
and do searches across those as desired (and this is where u can get 
into considering something like numpy to help).

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