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From Andor Molnar <an...@cloudera.com.INVALID>
Subject Re: Interesting FB article on CM at scale; LAD
Date Fri, 20 Jul 2018 08:49:22 GMT
Great article, thanks Pat.

There're 2 things which I found particularly interesting:

- Is Zeus going to be decod as part of the migration? Are the
patches/improvements in it going to be open sources and possibly backported
to ZooKeeper?

- "Independent data store: ZooKeeper couples a data store with its
distribution framework."

I believe that decoupling the data store from the coordination framework
wouldn't be too much of a hassle in ZooKeeper by introducing a plugin-based
data store replacing current ZkDatabase. In addition to that I wonder if we
could make client libraries "datastore-aware" letting them serve read
requests directly from the database. e.g. from HDFS data nodes. It might
successfully decouple the load generated by large number of read requests
from writes.

In which case will ZooKeeper be in any aspects different from an HDFS
cluster? It adds strong consistency and ordering guarantees.
Which parts of ZooKeeper do we still need after such change, because the
distributed data store guarantees a consistent view of the data tree across
participants so what would be the gain of dealing with consensus?

Going back to Fb's original problem in terms of data/metadata decoupling:
they wanted to distribute large files like 100MB whereas they already 5MB
files present in Zk. I think 5MB is already too much data in a single znode
and ZooKeeper is not designed to deal with such load of data distribution.
So maybe it was originally a use case problem which eventually escalated to
a new system design.

Propagating metadata updates to millions of subscribers sounds to me more
of an IoT / pubsub problem. Which Facebook has presented a very promising
answer to. Using a tree of subscribers combined with sharding has very
strong scalability potential.

Dealing with the distribution of large files triggered by metadata change:
bittorrent? :)


On Fri, Jul 20, 2018 at 8:07 AM, Patrick Hunt <phunt@apache.org> wrote:

> "Location-Aware Distribution (LAD), a new peer-to-peer system that handles
> the distribution of configuration changes to millions of servers."
> https://code.fb.com/data-infrastructure/location-aware-
> distribution-configuring-servers-at-scale/
> Previously Facebook’s configuration management system (called Configerator)
> used ZooKeeper. SOSP 2015 paper:
> https://research.fb.com/publications/holistic-configuration-management-at-
> facebook/
> Patrick

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