Hi, all,
Thanks for all the inputs! Finally I got some time to go through the
discussion thread and digest most of the points made above. Here is my
personal summary:
Consensus on requirements:
1. ApplicationRunner needs async APIs.
2. ApplicationRunner can be hidden from user (except maybe in config)
3. StreamApplication is the direct wrapper for the programming interface
(i.e. removing StreamGraph from the user API and allow users to call
input() and output() from the StreamApplication) in main()
4. There has to be a serialization format of the StreamApplication
itself, s.t. the tasks can just deserialize and create the user logic
included in StreamApplication in multiple TaskContext.
5. JobRunner seems to be a very thin layer on-top-of StreamProcessor or
YarnJob, and it is always a LocalJob in a LocalApplitionRunner and a
RemoteJob in a RemoteApplicationRunner. There is a desire to remove it
6. StreamApplication needs to have some methods to allow user-injected
global objects for the whole application, such as JmxServer,
MetricsReporter, etc.
Some additional discussion points:
1. In StreamApplication#input()/output(), what should be the input /
output parameter? The StreamSpec? Or the actual implementation I/O object
to provide messages (i.e. similar to socket reader/file reader object)? In
the later case, we will need to define an abstract layer of StreamReader
and StreamWriter in the user-facing API that supports read/write of
partitioned streams on top of the SystemConsumer/SystemProducer/SystemAdmin
objects. Also, the number of I/O streams via the StreamReader/StreamWriter
can not be pre-determined (i.e. depending on input stream partitions and
the groupers). Hence, I am leaning toward to expose StreamSpec in the API
and let user builds the StreamSpec via SpecBuilder. The actual I/O objects
will be instantiated when SystemConsumer/SystemProducer are instantiated,
with the number of physical partitions in each container.
2. There is a need to support task-level programs via the same launch
model as well.
Some ideas to implement the above requirements:
1. StreamGraph#write() should be used internally to generate and persist
the serialized format of user logic. Then, StreamGraph#read() should give
back a deserialized version of user logic. This would implies that the user
functions defined in APIs are mandated to be serializable.
2. StreamApplication should include a SpecBuilder provides the
instantiation of MessageStream/Stores, which is passed to
StreamApplication#input() / StreamApplication#output()
3. StreamApplication should also include an internal ApplicationRunner
instance (config driven, class loaded) to be able to switch between local
vs remote execution
4. Implementation of LocalApplicationRunner should directly instantiate
and manage StreamProcessor instances for each job, removing the
LocalJobRunnner
5. Implementation of RemoteApplicationRunner should instantiate a remote
JobFactory, create the remote job and submitted it for each job, removing
the current JobRunner interface
6. We also need a StreamTaskApplication class that allows user to create
task-level applications, by mandate the constructor with a parameter of
StreamTaskFactory
One more opinion around the status and the waitForFinish(): I would think
that waitForFinish() is just waiting for the local Runtime to complete, not
to wait for the remote job to be completed.
I will be working on revision of SEP-2 and some example user code example
for now and will share it soon.
Thanks!
-Yi
On Wed, May 3, 2017 at 8:08 AM, Chris Pettitt <cpett...@linkedin.com.invalid
> wrote:
> Hi Xinyu,
>
> I took a second look at the registerStore API. Would it be possible to call
> register storeDirectly on the app, similar to what we're doing with
> app.input (possible with the restriction registerStore must be called
> before we add an operator that uses the store)? Otherwise we'll end up
> having to do two passes on the graph again - similar to the way we had to
> do a pass to init stream config and then hook up the graph.
>
> Thanks,
> Chris
>
>
> On Fri, Apr 28, 2017 at 8:55 PM, xinyu liu <xinyuliu...@gmail.com> wrote:
>
> > Right, option #2 seems redundant for defining streams after further
> > discussion here. StreamSpec itself is flexible enough to achieve both
> > static and programmatic specification of the stream. Agree it's not
> > convenient for now (pretty obvious after looking at your bsr
> > beam.runners.samza.wrapper), and we should provide similar predefined
> > convenient wrappers for user to create the StreamSpec. In your case
> > something like BoundedStreamSpec.file(....) which will generate the
> system
> > and serialize the data as you did.
> >
> > We're still thinking the callback proposed in #2 can be useful for
> > requirement #6: injecting other user objects in run time, such as stores
> > and metrics. To simplify the user understanding further, I think we might
> > hide the ApplicationRunner and expose the StreamApplication instead,
> which
> > will make requirement #3 not user facing. So the API becomes like:
> >
> > StreamApplication app = StreamApplication.local(config)
> > .init (env -> {
> > env.registerStore("my-store", new MyStoreFactory());
> > env.registerMetricsReporter("my-reporte", new
> > MyMetricsReporterFactory());
> > })
> > .withLifeCycleListener(myListener);
> >
> > app.input(BoundedStreamSpec.create("/sample/input.txt"))
> > .map(...)
> > .window(...)
> >
> > app.run();
> >
> > For requirement #5, I add a .withLifeCycleListener() in the API, which
> can
> > trigger the callbacks with life cycle events.
> >
> > For #4: distribution of the jars will be what we have today using the
> Yarn
> > localization with a remote store like artifactory or http server. We
> > discussed where to put the graph serialization. The current thinking is
> to
> > define a general interface which can backed by a remote store, like
> Kafka,
> > artifactory or http server. For Kafka, it's straightforward but we will
> > have the size limit or cut it by ourselves. For the other two, we need to
> > investigate whether we can easily upload jars to our artifactory and
> > localizing it with Yarn. Any opinions on this?
> >
> > Thanks,
> > Xinyu
> >
> > On Fri, Apr 28, 2017 at 11:34 AM, Chris Pettitt <
> > cpett...@linkedin.com.invalid> wrote:
> >
> > > Your proposal for #1 looks good.
> > >
> > > I'm not quite how to reconcile the proposals for #1 and #2. In #1 you
> add
> > > the stream spec straight onto the runner while in #2 you do it in a
> > > callback. If it is either-or, #1 looks a lot better for my purposes.
> > >
> > > For #4 what mechanism are you using to distribute the JARs? Can you use
> > the
> > > same mechanism to distribute the serialized graph?
> > >
> > > On Fri, Apr 28, 2017 at 12:14 AM, xinyu liu <xinyuliu...@gmail.com>
> > wrote:
> > >
> > > > btw, I will get to SAMZA-1246 as soon as possible.
> > > >
> > > > Thanks,
> > > > Xinyu
> > > >
> > > > On Thu, Apr 27, 2017 at 9:11 PM, xinyu liu <xinyuliu...@gmail.com>
> > > wrote:
> > > >
> > > > > Let me try to capture the updated requirements:
> > > > >
> > > > > 1. Set up input streams outside StreamGraph, and treat graph
> building
> > > as
> > > > a
> > > > > library (*Fluent, Beam*).
> > > > >
> > > > > 2. Improve ease of use for ApplicationRunner to avoid complex
> > > > > configurations such as zkCoordinator, zkCoordinationService.
> > > > (*Standalone*).
> > > > > Provide some programmatic way to tweak them in the API.
> > > > >
> > > > > 3. Clean up ApplicationRunner into a single interface (*Fluent*).
> We
> > > can
> > > > > have one or more implementations but it's hidden from the users.
> > > > >
> > > > > 4. Separate StreamGraph from runtime environment so it can be
> > > serialized
> > > > (*Beam,
> > > > > Yarn*)
> > > > >
> > > > > 5. Better life cycle management of application, parity with
> > > > > StreamProcessor (*Standalone, Beam*). Stats should include
> exception
> > in
> > > > > case of failure (tracked in SAMZA-1246).
> > > > >
> > > > > 6. Support injecting user-defined objects into ApplicationRunner.
> > > > >
> > > > > Prateek and I iterate on the ApplilcationRunner API based on these
> > > > > requirements. To support #1, we can set up input streams on the
> > runner
> > > > > level, which returns the MessageStream and allows graph building
> > > > > afterwards. The code looks like below:
> > > > >
> > > > > ApplicationRunner runner = ApplicationRunner.local();
> > > > > runner.input(streamSpec)
> > > > > .map(..)
> > > > > .window(...)
> > > > > runner.run();
> > > > >
> > > > > StreamSpec is the building block for setting up streams here. It
> can
> > be
> > > > > set up in different ways:
> > > > >
> > > > > - Direct creation of stream spec, like runner.input(new
> > > StreamSpec(id,
> > > > > system, stream))
> > > > > - Load from streamId from env or config, like
> > > > runner.input(runner.env().
> > > > > getStreamSpec(id))
> > > > > - Canned Spec which generates the StreamSpec with id, system and
> > > stream
> > > > > to minimize the configuration. For example,
> CollectionSpec.create(new
> > > > > ArrayList[]{1,2,3,4}), which will auto generate the system and
> stream
> > > in
> > > > > the spec.
> > > > >
> > > > > To support #2, we need to be able to set up StreamSpec-related
> > objects
> > > > and
> > > > > factories programmatically in env. Suppose we have the following
> > before
> > > > > runner.input(...):
> > > > >
> > > > > runner.setup(env /* a writable interface of env*/ -> {
> > > > > env.setStreamSpec(streamId, streamSpec);
> > > > > env.setSystem(systemName, systemFactory);
> > > > > })
> > > > >
> > > > > runner.setup(->) also provides setup for stores and other runtime
> > stuff
> > > > > needed for the execution. The setup should be able to serialized to
> > > > config.
> > > > > For #6, I haven't figured out a good way to inject user-defined
> > objects
> > > > > here yet.
> > > > >
> > > > > With this API, we should be able to also support #4. For remote
> > > > > runner.run(), the operator user classes/lamdas in the StreamGraph
> > need
> > > to
> > > > > be serialized. As today, the existing option is to serialize to a
> > > stream,
> > > > > either the coordinator stream or the pipeline control stream, which
> > > will
> > > > > have the size limit per message. Do you see RPC as an option?
> > > > >
> > > > > For this version of API, seems we don't need the StreamApplication
> > > > wrapper
> > > > > as well as exposing the StreamGraph. Do you think we are on the
> right
> > > > path?
> > > > >
> > > > > Thanks,
> > > > > Xinyu
> > > > >
> > > > >
> > > > > On Thu, Apr 27, 2017 at 6:09 AM, Chris Pettitt <
> > > > > cpett...@linkedin.com.invalid> wrote:
> > > > >
> > > > >> That should have been:
> > > > >>
> > > > >> For #1, Beam doesn't have a hard requirement...
> > > > >>
> > > > >> On Thu, Apr 27, 2017 at 9:07 AM, Chris Pettitt <
> > cpett...@linkedin.com
> > > >
> > > > >> wrote:
> > > > >>
> > > > >> > For #1, I doesn't have a hard requirement for any change from
> > > Samza. A
> > > > >> > very nice to have would be to allow the input systems to be set
> up
> > > at
> > > > >> the
> > > > >> > same time as the rest of the StreamGraph. An even nicer to have
> > > would
> > > > >> be to
> > > > >> > do away with the callback based approach and treat graph
> building
> > > as a
> > > > >> > library, a la Beam and Flink.
> > > > >> >
> > > > >> > For the moment I've worked around the two pass requirement (once
> > for
> > > > >> > config, once for StreamGraph) by introducing an IR layer between
> > > Beam
> > > > >> and
> > > > >> > the Samza Fluent translation. The IR layer is convenient
> > independent
> > > > of
> > > > >> > this problem because it makes it easier to switch between the
> > Fluent
> > > > and
> > > > >> > low-level APIs.
> > > > >> >
> > > > >> >
> > > > >> > For #4, if we had parity with StreamProcessor for lifecycle we'd
> > be
> > > in
> > > > >> > great shape. One additional issue with the status call that I
> may
> > > not
> > > > >> have
> > > > >> > mentioned is that it provides you no way to get at the cause of
> > > > failure.
> > > > >> > The StreamProcessor API does allow this via the callback.
> > > > >> >
> > > > >> >
> > > > >> > Re. #2 and #3, I'm a big fan of getting rid of the extra
> > > configuration
> > > > >> > indirection you currently have to jump through (this is also
> > related
> > > > to
> > > > >> > system consumer configuration from #1. It makes it much easier
> to
> > > > >> discover
> > > > >> > what the configurable parameters are too, if we provide some
> > > > >> programmatic
> > > > >> > way to tweak them in the API - which can turn into config under
> > the
> > > > >> hood.
> > > > >> >
> > > > >> > On Wed, Apr 26, 2017 at 9:20 PM, xinyu liu <
> xinyuliu...@gmail.com
> > >
> > > > >> wrote:
> > > > >> >
> > > > >> >> Let me give a shot to summarize the requirements for
> > > > ApplicationRunner
> > > > >> we
> > > > >> >> have discussed so far:
> > > > >> >>
> > > > >> >> - Support environment for passing in user-defined objects
> > (streams
> > > > >> >> potentially) into ApplicationRunner (*Beam*)
> > > > >> >>
> > > > >> >> - Improve ease of use for ApplicationRunner to avoid complex
> > > > >> >> configurations
> > > > >> >> such as zkCoordinator, zkCoordinationService. (*Standalone*)
> > > > >> >>
> > > > >> >> - Clean up ApplicationRunner into a single interface
> (*Fluent*).
> > We
> > > > can
> > > > >> >> have one or more implementations but it's hidden from the
> users.
> > > > >> >>
> > > > >> >> - Separate StreamGraph from environment so it can be
> serializable
> > > > >> (*Beam,
> > > > >> >> Yarn*)
> > > > >> >>
> > > > >> >> - Better life cycle management of application, including
> > > > >> >> start/stop/stats (*Standalone,
> > > > >> >> Beam*)
> > > > >> >>
> > > > >> >>
> > > > >> >> One way to address 2 and 3 is to provide pre-packaged runner
> > using
> > > > >> static
> > > > >> >> factory methods, and the return type will be the
> > ApplicationRunner
> > > > >> >> interface. So we can have:
> > > > >> >>
> > > > >> >> ApplicationRunner runner = ApplicationRunner.zk() /
> > > > >> >> ApplicationRunner.local()
> > > > >> >> / ApplicationRunner.remote() / ApplicationRunner.test().
> > > > >> >>
> > > > >> >> Internally we will package the right configs and run-time
> > > environment
> > > > >> with
> > > > >> >> the runner. For example, ApplicationRunner.zk() will define all
> > the
> > > > >> >> configs
> > > > >> >> needed for zk coordination.
> > > > >> >>
> > > > >> >> To support 1 and 4, can we pass in a lambda function in the
> > runner,
> > > > and
> > > > >> >> then we can run the stream graph? Like the following:
> > > > >> >>
> > > > >> >> ApplicationRunner.zk().env(config ->
> > > > environment).run(streamGraph);
> > > > >> >>
> > > > >> >> Then we need a way to pass the environment into the
> StreamGraph.
> > > This
> > > > >> can
> > > > >> >> be done by either adding an extra parameter to each operator,
> or
> > > > have a
> > > > >> >> getEnv() function in the MessageStream, which seems to be
> pretty
> > > > hacky.
> > > > >> >>
> > > > >> >> What do you think?
> > > > >> >>
> > > > >> >> Thanks,
> > > > >> >> Xinyu
> > > > >> >>
> > > > >> >>
> > > > >> >>
> > > > >> >>
> > > > >> >>
> > > > >> >> On Sun, Apr 23, 2017 at 11:01 PM, Prateek Maheshwari <
> > > > >> >> pmaheshw...@linkedin.com.invalid> wrote:
> > > > >> >>
> > > > >> >> > Thanks for putting this together Yi!
> > > > >> >> >
> > > > >> >> > I agree with Jake, it does seem like there are a few too many
> > > > moving
> > > > >> >> parts
> > > > >> >> > here. That said, the problem being solved is pretty broad, so
> > let
> > > > me
> > > > >> >> try to
> > > > >> >> > summarize my current understanding of the requirements.
> Please
> > > > >> correct
> > > > >> >> me
> > > > >> >> > if I'm wrong or missing something.
> > > > >> >> >
> > > > >> >> > ApplicationRunner and JobRunner first, ignoring test
> > environment
> > > > for
> > > > >> the
> > > > >> >> > moment.
> > > > >> >> > ApplicationRunner:
> > > > >> >> > 1. Create execution plan: Same in Standalone and Yarn
> > > > >> >> > 2. Create intermediate streams: Same logic but different
> leader
> > > > >> election
> > > > >> >> > (ZK-based or pre-configured in standalone, AM in Yarn).
> > > > >> >> > 3. Run jobs: In JVM in standalone. Submit to the cluster in
> > Yarn.
> > > > >> >> >
> > > > >> >> > JobRunner:
> > > > >> >> > 1. Run the StreamProcessors: Same process in Standalone &
> Test.
> > > > >> Remote
> > > > >> >> host
> > > > >> >> > in Yarn.
> > > > >> >> >
> > > > >> >> > To get a single ApplicationRunner implementation, like Jake
> > > > >> suggested,
> > > > >> >> we
> > > > >> >> > need to make leader election and JobRunner implementation
> > > > pluggable.
> > > > >> >> > There's still the question of whether ApplicationRunner#run
> API
> > > > >> should
> > > > >> >> be
> > > > >> >> > blocking or non-blocking. It has to be non-blocking in YARN.
> We
> > > > want
> > > > >> it
> > > > >> >> to
> > > > >> >> > be blocking in standalone, but seems like the main reason is
> > ease
> > > > of
> > > > >> use
> > > > >> >> > when launched from main(). I'd prefer making it consitently
> > > > >> non-blocking
> > > > >> >> > instead, esp. since in embedded standalone mode (where the
> > > > processor
> > > > >> is
> > > > >> >> > running in another container) a blocking API would not be
> > > > >> user-friendly
> > > > >> >> > either. If not, we can add both run and runBlocking.
> > > > >> >> >
> > > > >> >> > Coming to RuntimeEnvironment, which is the least clear to me
> so
> > > > far:
> > > > >> >> > 1. I don't think RuntimeEnvironment should be responsible for
> > > > >> providing
> > > > >> >> > StreamSpecs for streamIds - they can be obtained with a
> > > config/util
> > > > >> >> class.
> > > > >> >> > The StreamProcessor should only know about logical streamIds
> > and
> > > > the
> > > > >> >> > streamId <-> actual stream mapping should happen within the
> > > > >> >> > SystemProducer/Consumer/Admins provided by the
> > > RuntimeEnvironment.
> > > > >> >> > 2. There's also other components that the user might be
> > > interested
> > > > in
> > > > >> >> > providing implementations of in embedded Standalone mode
> (i.e.,
> > > not
> > > > >> >> just in
> > > > >> >> > tests) - MetricsRegistry and JMXServer come to mind.
> > > > >> >> > 3. Most importantly, it's not clear to me who creates and
> > manages
> > > > the
> > > > >> >> > RuntimeEnvironment. It seems like it should be the
> > > > ApplicationRunner
> > > > >> or
> > > > >> >> the
> > > > >> >> > user because of (2) above and because StreamManager also
> needs
> > > > >> access to
> > > > >> >> > SystemAdmins for creating intermediate streams which users
> > might
> > > > >> want to
> > > > >> >> > mock. But it also needs to be passed down to the
> > StreamProcessor
> > > -
> > > > >> how
> > > > >> >> > would this work on Yarn?
> > > > >> >> >
> > > > >> >> > I think we should figure out how to integrate
> > RuntimeEnvironment
> > > > with
> > > > >> >> > ApplicationRunner before we can make a call on one vs.
> multiple
> > > > >> >> > ApplicationRunner implementations. If we do keep
> > > > >> LocalApplicationRunner
> > > > >> >> and
> > > > >> >> > RemoteApplication (and TestApplicationRunner) separate, agree
> > > with
> > > > >> Jake
> > > > >> >> > that we should remove the JobRunners and roll them up into
> the
> > > > >> >> respective
> > > > >> >> > ApplicationRunners.
> > > > >> >> >
> > > > >> >> > - Prateek
> > > > >> >> >
> > > > >> >> > On Thu, Apr 20, 2017 at 10:06 AM, Jacob Maes <
> > > jacob.m...@gmail.com
> > > > >
> > > > >> >> wrote:
> > > > >> >> >
> > > > >> >> > > Thanks for the SEP!
> > > > >> >> > >
> > > > >> >> > > +1 on introducing these new components
> > > > >> >> > > -1 on the current definition of their roles (see Design
> > > feedback
> > > > >> >> below)
> > > > >> >> > >
> > > > >> >> > > *Design*
> > > > >> >> > >
> > > > >> >> > > - If LocalJobRunner and RemoteJobRunner handle the
> > different
> > > > >> >> methods
> > > > >> >> > of
> > > > >> >> > > launching a Job, what additional value do the different
> > > types
> > > > of
> > > > >> >> > > ApplicationRunner and RuntimeEnvironment provide? It
> seems
> > > > like
> > > > >> a
> > > > >> >> red
> > > > >> >> > > flag
> > > > >> >> > > that all 3 would need to change from environment to
> > > > >> environment. It
> > > > >> >> > > indicates that they don't have proper modularity. The
> > > > >> >> > > call-sequence-figures
> > > > >> >> > > support this; LocalApplicationRunner and
> > > > RemoteApplicationRunner
> > > > >> >> make
> > > > >> >> > > the
> > > > >> >> > > same calls and the diagram only varies after
> > > jobRunner.start()
> > > > >> >> > > - As far as I can tell, the only difference between
> Local
> > > and
> > > > >> >> Remote
> > > > >> >> > > ApplicationRunner is that one is blocking and the other
> is
> > > > >> >> > > non-blocking. If
> > > > >> >> > > that's all they're for then either the names should be
> > > changed
> > > > >> to
> > > > >> >> > > reflect
> > > > >> >> > > this, or they should be combined into one
> > ApplicationRunner
> > > > and
> > > > >> >> just
> > > > >> >> > > expose
> > > > >> >> > > separate methods for run() and runBlocking()
> > > > >> >> > > - There isn't much detail on why the main() methods for
> > > > >> >> Local/Remote
> > > > >> >> > > have such different implementations, how they receive
> the
> > > > >> >> Application
> > > > >> >> > > (direct vs config), and concretely how the deployment
> > > scripts,
> > > > >> if
> > > > >> >> any,
> > > > >> >> > > should interact with them.
> > > > >> >> > >
> > > > >> >> > >
> > > > >> >> > > *Style*
> > > > >> >> > >
> > > > >> >> > > - nit: None of the 11 uses of the word "actual" in the
> doc
> > > are
> > > > >> >> > > *actually*
> > > > >> >> > > needed. :-)
> > > > >> >> > > - nit: Colors of the runtime blocks in the diagrams are
> > > > >> >> unconventional
> > > > >> >> > > and a little distracting. Reminds me of nai won bao. Now
> > I'm
> > > > >> >> hungry.
> > > > >> >> > :-)
> > > > >> >> > > - Prefer the name "ExecutionEnvironment" over
> > > > >> "RuntimeEnvironment".
> > > > >> >> > The
> > > > >> >> > > term "execution environment" is used
> > > > >> >> > > - The code comparisons for the ApplicationRunners are
> not
> > > > >> >> > apples-apples.
> > > > >> >> > > The local runner example is an application that USES the
> > > local
> > > > >> >> runner.
> > > > >> >> > > The
> > > > >> >> > > remote runner example is the just the runner code
> itself.
> > > So,
> > > > >> it's
> > > > >> >> not
> > > > >> >> > > readily apparent that we're comparing the main() methods
> > and
> > > > not
> > > > >> >> the
> > > > >> >> > > application itself.
> > > > >> >> > >
> > > > >> >> > >
> > > > >> >> > > On Mon, Apr 17, 2017 at 5:02 PM, Yi Pan <
> nickpa...@gmail.com
> > >
> > > > >> wrote:
> > > > >> >> > >
> > > > >> >> > > > Made some updates to clarify the role and functions of
> > > > >> >> > RuntimeEnvironment
> > > > >> >> > > > in SEP-2.
> > > > >> >> > > >
> > > > >> >> > > > On Fri, Apr 14, 2017 at 9:30 AM, Yi Pan <
> > nickpa...@gmail.com
> > > >
> > > > >> >> wrote:
> > > > >> >> > > >
> > > > >> >> > > > > Hi, everyone,
> > > > >> >> > > > >
> > > > >> >> > > > > In light of new features such as fluent API and
> > standalone
> > > > that
> > > > >> >> > > introduce
> > > > >> >> > > > > new deployment / application launch models in Samza, I
> > > > created
> > > > >> a
> > > > >> >> new
> > > > >> >> > > > SEP-2
> > > > >> >> > > > > to address the new use cases. SEP-2 link:
> > > > https://cwiki.apache
> > > > >> .
> > > > >> >> > > > > org/confluence/display/SAMZA/
> SEP-2%3A+ApplicationRunner+
> > > > Design
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> > > > >> >> > > > > Please take a look and give feedbacks!
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> > > > >> >> > > > > Thanks!
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> > > > >> >> > > > > -Yi
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