Re: [Postgres-xc-developers] XC Stuck in a Loop

[Abbas B. <abb...@en...>]

Can you share the query and table structure that you are using to perform
the test? You can obscure the column/table names if they are part of some
proprietary application.
The comment you mentioned in execRemote.c is relevant for DMLs only but you
said that your's is a SELECT, isn't it?


On Fri, Aug 30, 2013 at 1:30 AM, Matt Warner <MW...@xi...> wrote:

> Short version: it looks like there’s a problem with ExecNestLoop and
> ExecProcNode recursively calling each other and getting stuck in a loop
> that never completes.****
>
> ** **
>
> Details:****
>
> I’ve been experimenting with XC using fairly large tables. In this case
> it’s 4 tables, 2 replicated, 2 distributed by hash. The select statement is
> a mere 31 lines long and contains a group by on 2 columns of one of the
> tables. The query never completes, even days later.****
>
> ** **
>
> I’m using dtrace and a “git clone” version of XC from a few days ago
> compiled with the debug flag (-g). I see that ExecNestLoop and ExecProcNode
> appear to be calling each other heavily, as in thousands of times per
> second. That is, I am seeing stack traces where one calls the other, but
> also vice versa.****
>
> ** **
>
> In researching further, I see a note in execRemote.c that seems to
> indicate that recursively calling ExecProcNode is happening by design:****
>
> ** **
>
>         /*****
>
>          * The current implementation of DMLs with RETURNING when run on
> replicated****
>
>          * tables returns row from one of the datanodes. In order to
> achieve this****
>
> *         * ExecProcNode is repeatedly called saving one tuple and
> rejecting the rest.*
>
>          * Do we have a DML on replicated table with RETURNING?****
>
>          */****
>
> ** **
>
> I don’t know about the accuracy of the debugging and certainly I’m out of
> my element when poring through the XC source code, so my guess as to the
> source of the problem should be questioned.****
>
> ** **
>
> What additional debugging information can I provide to assist with the
> correct identification and debugging of this problem?****
>
> ** **
>
> Regards,****
>
> ** **
>
> Matt****
>
> ** **
>
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*Abbas*
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