Chris Trezzo commented on YARN-1492:

Thanks [~kasha]! A couple of questions:

bq. 2. The choice of SCM store should be transparent to the rest of SCM code. 
It would be better to define an interface for the SCMStore similar to the 
RMStateStore today.

To clarify the above point. An interface does exist in the current 
implementation (see SCMStore.java in YARN-2180), and all SCMStore 
implementations should be based off of that. Unfortunately some implementation 
details from the in-memory store have leaked through via the SCMContext object. 
I am working on an update to improve the interface so that an SCMContext object 
is no longer needed and all implementation details are hidden behind 
SCMStore.java. Does your above point mean that you are looking for a state 
machine-based interface like RMStateStore, or do you see additional issues with 
the SCMStore interface outside of the SCMContext fix?

bq. 3. Defaulting to the in-memory store requires providing a way to initialize 
the store with currently running applications and cached jars, which is quite 
involved and not so elegant either. I propose implementing leveldb and zk 
stores. We could default to leveldb on non-HA clusters, and ZK store for HA 
clusters if we choose to embed the SCM in the RM.

Do you see the leveldb and zk stores as blockers to merging into trunk/2.6 or 
would an in-memory store with the interface fixes mentioned above be enough 
initially? Leveldb and ZK stores could be easily added post-merge in an 
incremental way as additional SCMStore implementations.

> truly shared cache for jars (jobjar/libjar)
> -------------------------------------------
>                 Key: YARN-1492
>                 URL: https://issues.apache.org/jira/browse/YARN-1492
>             Project: Hadoop YARN
>          Issue Type: New Feature
>    Affects Versions: 2.0.4-alpha
>            Reporter: Sangjin Lee
>            Assignee: Chris Trezzo
>         Attachments: YARN-1492-all-trunk-v1.patch, 
> YARN-1492-all-trunk-v2.patch, YARN-1492-all-trunk-v3.patch, 
> YARN-1492-all-trunk-v4.patch, YARN-1492-all-trunk-v5.patch, 
> shared_cache_design.pdf, shared_cache_design_v2.pdf, 
> shared_cache_design_v3.pdf, shared_cache_design_v4.pdf, 
> shared_cache_design_v5.pdf, shared_cache_design_v6.pdf
> Currently there is the distributed cache that enables you to cache jars and 
> files so that attempts from the same job can reuse them. However, sharing is 
> limited with the distributed cache because it is normally on a per-job basis. 
> On a large cluster, sometimes copying of jobjars and libjars becomes so 
> prevalent that it consumes a large portion of the network bandwidth, not to 
> speak of defeating the purpose of "bringing compute to where data is". This 
> is wasteful because in most cases code doesn't change much across many jobs.
> I'd like to propose and discuss feasibility of introducing a truly shared 
> cache so that multiple jobs from multiple users can share and cache jars. 
> This JIRA is to open the discussion.

This message was sent by Atlassian JIRA

Reply via email to