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From kishore g <g.kish...@gmail.com>
Subject Re: Message throttling of controller behavior unexpectedly when there are multiple constraints
Date Sun, 17 May 2015 13:19:46 GMT
Got it, that should be fixed. Would be great to get a patch to fix it. Good

Kishore G
On May 16, 2015 11:50 PM, "Hang Qi" <hangq.1985@gmail.com> wrote:

> Hi Kishore,
> Thanks for your reply.
> I am not saying I want Offline->Slave higher priority than Slave->Master.
> I agree with you, one master is more important than two slaves, and that
> one only applies to one partition. What I am saying is during p0, p1, p2
> Offline->Slave transition on node A, I also want p3, p4, p5 performing
> Offline->Slave transition on node B at the same time, but not wait until
> p0, p1, p2 becomes Master on node A, there begins to have partition
> transition on node B, that's kind of waste here.
> The reason to have one transition per partition at a time is summarized in
> following thread.
> http://mail-archives.apache.org/mod_mbox/helix-user/201503.mbox/%3CCAJ2%3DoXxBWF1VoCm%3DjjyhuFCWHuxw3wYPotGz8VRkEnzVhrmgwQ%40mail.gmail.com%3E
> Thanks
> Hang Qi
> On Sat, May 16, 2015 at 8:23 PM, kishore g <g.kishore@gmail.com> wrote:
>> Thanks Hang for the detailed explanation.
>> Before the MessageSelectionStage, there is a stage that orders the
>> messages according to the state transition priority list. I think
>> Slave-Master is always higher priority than offline-slave which makes sense
>> because in general having a master is probably more important than two
>> slaves.
>> Can you provide the state transition priority list in your state model
>> definition. If you think that its important to get node B to Slave state
>> before promoting node A from Slave to Master, you can change the priority
>> order. Note: this can be changed dynamically and does not require re
>> starting the servers.
>> Another question is what is the reason to have constraint #2 i.e only one
>> transition per partition at a time.
>> thanks,
>> Kishore G
>> On Sat, May 16, 2015 at 4:48 PM, Hang Qi <hangq.1985@gmail.com> wrote:
>>> Hi folks,
>>> We found a very strange behavior on message throttling of controller
>>> when there is multiple constraints. Here is our setup ( we are using
>>> helix-0.6.4, only one resource )
>>>    - constraint 1: per node constraint, we only allow 3 state
>>>    transitions happens on one node concurrently.
>>>    - constraint 2: per partition constraint, we define the state
>>>    transition priorities in the state model, and only allow one state
>>>    transition happens on one single partition concurrently.
>>> We are using MasterSlave state model, suppose we have two nodes A, B,
>>> each has 8 partitions (p0-p7) respectively, and initially both A and B are
>>> shutdown, and now we start them at the same time (say A is slightly earlier
>>> than B).
>>> The expected behavior might be
>>>    1. p0, p1, p2 on A starts from Offline -> Slave; p3, p4, p5 on B
>>>    starts from Offline -> Slave
>>> But the real result is:
>>>    1. p0, p1, p2 on A starts from Offline -> Slave, nothing happens on B
>>>    2. until p0, p1, p2 all transited to Master state, p3, p4, p5 on A
>>>    starts from Offline -> Slave; p0, p1, p2 on B starts from Offline ->
>>> As step Offline -> Slave might take long time, this behavior result in
>>> very long time to bring up these two nodes (long down time result in long
>>> catch up time as well), though ideally we should not let both nodes down at
>>> the same time.
>>> Looked at the controller code, the stage and pipeline based
>>> implementation is well design, very easy to understand and to reason about.
>>> The logic of MessageThrottleStage#throttle,
>>>    1. it goes through each messages selected by MessageSelectionStage,
>>>    2. for each message, it goes through all selected matched
>>>    constraints, and decrease the quota of each constraints
>>>    1. if any constraint's quota is less than 0, this message will be
>>>       marked as throttled.
>>> I think there is something wrong here, the message will take the quota
>>> of constraints even it is not going to be sent out (throttled). That
>>> explains our case,
>>>    - all the messages have been generated by the beginning, (p0, A,
>>>    Offline->Slave), ... (p7, A, Offline->Slave), (p0, B, Offline->Slave),
>>>    (p7, B, Offline->Slave)
>>>    - in the messageThrottleStage#throttle
>>>       - (p0, A, Offline->Slave), (p1, A, Offline->Slave), (p2, A,
>>>       Offline->Slave) are good, and constraint 1 on A reaches 0, constraint
2 on
>>>       p0, p1, p2 reaches 0 as well
>>>       - (p3, A, Offline->Slave), ... (p7, A, Offline->Slave) throttled
>>>       by constraint 1 on A, also takes the quota of constraint 2 on those
>>>       partitions as well.
>>>       - (p0, B, Offline->Slave), ... (p7, B, Offline->Slave) throttled
>>>       by constraint 2
>>>       - thus only (p0, A, Offline->Slave), (p1, A, Oflline->Slave),
>>>       (p2, A, Offline->Slave) has been sent out by controller.
>>> Does that make sense, or is there anything else you can think of to
>>> result in this unexpected behavior? And is there any work around for it?
>>> One thing comes into my mind is update constraint 2 to be only one state
>>> transition is allowed of single partition on certain state transitions.
>>> Thanks very much.
>>> Thanks
>>> Hang Qi
> --
> Qi hang

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