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Zookeeper, mail # dev - RFC: Behavior of QuotaExceededException


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Thawan Kooburat 2013-02-27, 00:41
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Re: RFC: Behavior of QuotaExceededException
Flavio Junqueira 2013-02-27, 08:10
It wouldn't be very nice to allow holes in the sequence of operations of a client, it would violate session semantics. I'm also wondering about a couple of things:

- What does QuotaExceedException convey to the application? That the application client won't ever be able to send operations again with that session? That it won't be able to submit new operations for up to x amount of time, where x is computed somehow? Expiring the session will have the side-effect that all the ephemeral nodes will be gone, I'm not sure that's desirable, but as a punishment it might work out fine. ;-)
- Have you consider limiting the rate of client operations instead of failing operations? Shaping the traffic of operations of a client might be way nicer from the client perspective, but perhaps a bit harder to implement.

-Flavio

On Feb 27, 2013, at 1:41 AM, Thawan Kooburat <[EMAIL PROTECTED]> wrote:

> Hi,
> I am currently working on ZOOKEEPER-1383. One of the main feature introduced in this change is to allow ZooKeeper to enforce hard limit (e.g.  Txn per sec) per folder .
>
> With hard limit, we need to introduce a new exception/error code (QuotaExceeded) for ZooKeeper operations that modify the DataTree.  If a client get this error, it means that the particular operation is definitely failed.
>
> From our internal discussion, this may make it harder for a user to write an application.  The thought is that this can possibly introduce a hole in sequence of operations that the client application performs, since some operation may success but some may be not.  One of the idea is to also  trigger session expire (or at least trigger disconnect) on the server-side in addition to QuotaExceed error.  This will cause all subsequent operations from that client to fail and allow the application to use existing error handling logic to recover from QuotaExceed.  Typically, the application that exceeded the quota is already doing something wrong from administrator's perspective, but we also want to fail gracefully and able to recover when the problem is fixed or quota is increased.
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> Let me know if you have any suggestion.
>
> --
> Thawan Kooburat
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Thawan Kooburat 2013-02-27, 19:12
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Camille Fournier 2013-03-01, 17:15
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Thawan Kooburat 2013-03-02, 01:21