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From Andrew Melo <>
Subject Re: [DISCUSS] Remove multiple workers on the same host support from Standalone backend
Date Fri, 13 Mar 2020 23:33:03 GMT
Hi Xingbo, Sean,

On Fri, Mar 13, 2020 at 12:31 PM Xingbo Jiang <> wrote:

> Andrew, could you provide more context of your use case please? Is it like
> you deploy homogeneous containers on hosts with available resources, and
> each container launches one worker? Or you deploy workers directly on hosts
> thus you could have multiple workers from the same application on the same
> host?

Sure, I describe a bit more detail about the actual workload below [*], but
the short version is that our computing resources/infrastructure are all
built around batch submission into (usually) the HTCondor scheduler, and
we've got a PoC using pyspark to replace the interactive portion of data
analysis. To run pyspark on our main resources, we use some scripts around
the standalone mode to spin up N slaves per-user**, which may or may not
end up on the same host. I understood Xingbo's original mail to mean that
wouldn't be allowed in the future, but from Sean's response, it seems like
I'm incorrect.

That being said, our use-case is very bursty, and it would be very good if
there was a way we could have one pool of JVMs that could be shared between
N different concurrent users instead of having N different pools of JVMs
that each serve one person. We're already resource constrained, and we're
expecting our data rates to increase 10x in 2026, so the less idle CPU, the
better for us.


* I work for one of the LHC experiments at CERN (
and there's two main "phases" of our data pipeline: production and
analysis. The analysis half is currently implemented by having users
writing some software, splitting the input dataset(s) into N parts and then
submitting those jobs to the batch system (combining the outputs in a
manual postprocessing step). In terms of scale, there are currently ~100
users running ~900 tasks over ~50k cpus. The use case relevant to this
context is the terminal analysis phase which involves calculating some
additional columns, applying calibrations, filtering out the 'interesting'
events and extracting histograms describing those events. Conceptually,
it's an iterative process of "extract plots, look at plots, change
parameters", but running in a batch system means the latency is bad, so it
can take a long time to converge to the right set of params.

** though we have much smaller, dedicated k8s/mesos/yarn clusters we use
for prototyping

> Thanks,
> Xingbo
> On Fri, Mar 13, 2020 at 10:23 AM Sean Owen <> wrote:
>> You have multiple workers in one Spark (standalone) app? this wouldn't
>> prevent N apps from each having a worker on a machine.
>> On Fri, Mar 13, 2020 at 11:51 AM Andrew Melo <>
>> wrote:
>> >
>> > Hello,
>> >
>> > On Fri, Feb 28, 2020 at 13:21 Xingbo Jiang <>
>> wrote:
>> >>
>> >> Hi all,
>> >>
>> >> Based on my experience, there is no scenario that necessarily requires
>> deploying multiple Workers on the same node with Standalone backend. A
>> worker should book all the resources reserved to Spark on the host it is
>> launched, then it can allocate those resources to one or more executors
>> launched by this worker. Since each executor runs in a separated JVM, we
>> can limit the memory of each executor to avoid long GC pause.
>> >>
>> >> The remaining concern is the local-cluster mode is implemented by
>> launching multiple workers on the local host, we might need to re-implement
>> LocalSparkCluster to launch only one Worker and multiple executors. It
>> should be fine because local-cluster mode is only used in running Spark
>> unit test cases, thus end users should not be affected by this change.
>> >>
>> >> Removing multiple workers on the same host support could simplify the
>> deploy model of Standalone backend, and also reduce the burden to support
>> legacy deploy pattern in the future feature developments. (There is an
>> example in , where we
>> designed a complex approach to coordinate resource requirements from
>> different workers launched on the same host).
>> >>
>> >> The proposal is to update the document to deprecate the support of
>> system environment `SPARK_WORKER_INSTANCES` in Spark 3.0, and remove the
>> support in the next major version (Spark 3.1).
>> >>
>> >> Please kindly let me know if you have use cases relying on this
>> feature.
>> >
>> >
>> > When deploying spark on batch systems (by wrapping the standalone
>> deployment in scripts that can be consumed by the batch scheduler), we
>> typically end up with >1 worker per host. If I understand correctly, this
>> proposal would make our use case unsupported.
>> >
>> > Thanks,
>> > Andrew
>> >
>> >
>> >
>> >>
>> >> Thanks!
>> >>
>> >> Xingbo
>> >
>> > --
>> > It's dark in this basement.
>> ---------------------------------------------------------------------
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