[Postgres-xl-developers] bug about parallel execution

Tomas Vondra tomas.vondra at 2ndquadrant.com
Wed Jun 21 13:17:55 PDT 2017


On 6/21/17 8:42 AM, senhu(胡森) wrote:
> Hello, all:
>     I ran TPCH queries on PG-XL 9.6 a few days ago, and I have found 
> there is something wrong with parallel execution.
> Here is the SQL:
> ...
> When I ran this sql, I got error message like this:
> ERROR:  Invalid Datanode number
> CONTEXT:  parallel worker
> I think the reason is that the parallel execution happened on 
> coordinators, not on datanodes. I have a patch to fix this, and the 
> patch is to make the parallel execution only happen on datanodes.
> We can have further discussion about this, and to find if there are some 
> more better sulotions about this.

I agree we should disable parallel execution on coordinators, at least 
for now - and indeed that's what we tried to do in commit b6c7a69c. I'm 
not sure why it did not affect this particular plan.

We may allow parallelism on coordinators in the future, but at this 
point it may interfere with connection pooling for example (which I 
think might be the cause of your issue).


Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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