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From rahul gidwani <rahul.gidw...@gmail.com>
Subject Re: Allowing clients to set priorities
Date Fri, 22 Apr 2016 22:41:29 GMT

For the first item.  Yes that was implemented but there were a few issues.

It is related to PHOENIX-938, but also had this desire back in the
days at Flurry, I recall us always wishing for a way that we could
reserve a group of handlers for specific users or tables.

The other issue with the approach that PHOENIX-938 takes it has a
custom RpcScheduler implementation, which has a LimitedPrivate API,
thus only guaranteeing binary and source compatibility between source
versions.   The API changed between hbase 1.1 and 1.2.  That was one
issue the other was  a custom RpcController is for the clients, which
is also bad because that is IA.Private.

Additionally the client might know which handler pool it wants to go
to, but the current method of doing custom controller implementation
is the fact it isin't configurable.  If I wanted to add a new group of
regionserver handlers, I would have to update all the client and
server jars to do this.  In addition to that we have to infer what the
intent of the rpc call is by the time we get to the RpcController
instead of knowing if we did it at the Operation level.  The
DelegatingPayloadCarryingRpcController doesn't know much about the
intent of the request either, you end up having to hard code static
maps for special tables in your custom controller implementation.

For the exposing priority to the client I was thinking this work goes
into OperationWithAttributes or Operation we can add a setPriority()
and getPriority() and by default they are set to normal priority
unless explicitly overridden.  For things like Meta table I am
assuming there will be some resolution system we come up with that
wont be exposed but documented.  Maybe the logic can go into
Operation.getPriority() and then you would simply call
controller.setProperty(operation.getPriority).  The batch operations
could do something like take the highest priority individual operation
and that become the priority at the entire batch level.

Another option is to piggy back on Matteo's great work on Quotas and
we could add a reservation type system.  Maybe similar functionality
and behavior as quotas but phase 1 is to only be able to reserve
handlers for (tables, users, namespaces)  - If we go that route, no
need to expose priorities to the clients, they will just refer to some
reservation cache and route them to the appropriate group of handlers.
Because this information would probably be stored in the Quota  table
and we need this prior to starting up handlers - this might require
discussions or a design discussion.

I think going the reservation route might be more elegant (but I need
to hash out a few things before getting a design ready)  but I would
love to hear what you guys think.

Thanks for discussing this,

> On Apr 22, 2016, at 10:35 AM, Stack <stack@duboce.net> wrote:
> A few things:
> + Our Matteo reminded me of the HBASE-11048 "Support setting custom
> priority per client RPC"/PHOENIX-938 "Use higher priority queue for index
> updates to prevent deadlock" work which adds in a factory so clients can do
> their rpccontroller. You'd build on this or controllers will always pass
> priority regardless of the rpccontroller implementation? How would your
> work and it relate? You'd surface priority on each method?
> + What are you thinking regards priority on meta? How to not preempt the
> internal workings of hbase itself?
> Answers to above can wait till design time, np.
> Is there an associated phoenix issue other than PHOENIX-938 that goes w/
> this work?
> Thanks Rahul,
> St.Ack
> On Fri, Apr 22, 2016 at 9:53 AM, rahul gidwani <rahul.gidwani@gmail.com>
> wrote:
>> Sure sorry didn't provide a good example.
>> There are two situations where I have thought this feature might be
>> useful.   Maybe more...
>> 1.  For something like Phoenix, there are situations where you want
>> certain operations for tables / users to always have handlers
>> available to do work.  For example any write to an index table should
>> never block.  One way to almost guarantee this is to give it its own
>> special set of handlers and allow from a client call to denote that
>> this call is meant for this specific handler pool.
>> 2.  Suppose you have a large cluster with 1 really large table.  You
>> can't really use regionserver groups and there are clients doing all
>> sorts of operations on this cluster.  Map/Reduce jobs (long scans,
>> heavy reduces), processing pipeline, random reads, etc.  There are
>> features already to de-prioritize long running scanners and there is
>> rpc throttling and we can split up the handlers into read, write.
>> Currently there is no easy way to say I want to reserve 10 handlers on
>> each regionserver for the processing pipeline and from the client you
>> can pass something along that would tell the server to use this
>> special handler pool.
>> Also Stack, I saw your TODO and I believe we could get rid of the
>> AnnotatinoReadingPriorityFunction.
>> We can talk about design if folks are interested.
>> Thanks
>> rahul
>>>> On Apr 21, 2016, at 12:05 AM, Mikhail Antonov <olorinbant@gmail.com>
>>> wrote:
>>> This is interesting idea. Sorry if I missed some context - what's the
>>> primary incentive here? What's examples of those categorized thread
>> pools?
>>> Sounds intersecting a bit with HBASE-15136
>>> <https://issues.apache.org/jira/browse/HBASE-15136> (deadline scheduling
>>> for RPC requests) in the area of rpc prioritizing.
>>> -Mikhail
>>>> On Wed, Apr 20, 2016 at 11:21 PM, Stack <stack@duboce.net> wrote:
>>>> On Wed, Apr 20, 2016 at 1:47 PM, rahul gidwani <rahul.gidwani@gmail.com
>>>> wrote:
>>>>> I was wondering if people would be interested in allowing the client
>>>>> specify priorities?  I really think we are good responsible adults and
>>>> wont
>>>>> abuse this feature.   :)
>>>>> This would not just be for one particular operation but all operations.
>>>>> I'll make it feature complete.
>>>> Sounds sweet.
>>>> RPC passes priority in the header already IIRC.
>>>> We could then purge our ugly decompose of the request just to figure
>> what
>>>> it is so we can prioritize based off annotation.
>>>> St.Ack
>>>>> As for batch operations prioirites would be at batch level.
>>>>> I know the phoenix guys would really like this feature as it would
>> really
>>>>> help with their indexing work.
>>>>> Eventually I think it would be nice to get to a point where we can have
>>>>> some sort of configurable reservation system.  Where regionservers
>> could
>>>>> have handler groups and we could send a little bit more info with the
>> rpc
>>>>> call to specify the reserved set of handlers they would like to
>> utilize.
>>>>> thanks
>>>>> rahul
>>> --
>>> Thanks,
>>> Michael Antonov

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