Re: [Postgres-xc-developers] Random failures in the regression test.

[Koichi S. <koi...@gm...>]

I think it hits the point.   I tested this patch several times and it
seems to work fine.   The delay time (at present 10ms) is short enough
and it is applied only when we need to cancel a statement.

We should check this into all the master and STABLE branches improving
magic number with some meaningful name.

Any thoughts?
---
Koichi Suzuki


2014-01-24 18:25 GMT+09:00 Masataka Saito <pg...@gm...>:
> Hello,
>
> As I've been exasperated by random failures, I'm willing to whip the cause
> of the issue.
>
> This issue is related to cancel of the failed query.
> When a datanode reports an error of a query, a coordinator sends a cancel
> request to non-idle nodes, waits the node to get ready and requests nodes to
> rollback the transaction.
>
> Where's the problem? Consider the next case.
> 1. Datanode A (PID 1) reports an error to coordinator A. ([1] 'E' message)
> 2. Coordinator A receives [1] and reports an error to a frontend. ([2] 'E'
> message)
> 3. Coordinator A starts aborting process and it thinks datanode A (PID 1) is
> not idle.
> 4. Coordinator A sends a cancel request about PID 1 to datanode A (PID 2).
> ([3] cancel message)
> 5. Datanode A (PID 1) reports ready to coordinator A. ([4] 'Z' message)
> 6. Coordinator A receives [4] and sends "ROLLBACK TRANSACTION" immediately.
> ([5] 'Q' message)
> 7. Datanode A (PID 1) receives [5] and starts processing the query.
> 8. Datanode A (PID 2) receives [3].
> 9. Datanode A (PID 2) notify PID 1 of [3].
> 10. Datanode A (PID 1) cancel processing [5] and reports an error to
> Coordinator A. ([6] 'E' message)
> 11. Coordinator A receives [6] and reports an error to a frontend. ([7] 'E'
> message)
>
> [7] makes unexpected output and a test fails.
>
> Saying an extreme thing, it could occur that the next query of [5] is
> cancelled by [3].
>
> As far as I know, there's no way to know when to the cancel request get to
> be processed, I think we can't not wait an experimental duration after
> cancelling like the attached patch.
>
> Does anyone have another cool idea to solve this issue?
>
> Regards.
>
> ------------------------------------------------------------------------------
> CenturyLink Cloud: The Leader in Enterprise Cloud Services.
> Learn Why More Businesses Are Choosing CenturyLink Cloud For
> Critical Workloads, Development Environments & Everything In Between.
> Get a Quote or Start a Free Trial Today.
> http://pubads.g.doubleclick.net/gampad/clk?id=119420431&iu=/4140/ostg.clktrk
> _______________________________________________
> Postgres-xc-developers mailing list
> Pos...@li...
> https://lists.sourceforge.net/lists/listinfo/postgres-xc-developers
>