Re: asynchronous and vectorized execution

On Fri, Sep 23, 2016 at 8:45 AM, Amit Khandekar <amitdkhan.pg@gmail.com> wrote:
> For e.g., in the above plan which you specified, suppose :
> 1. Hash Join has called ExecProcNode() for the child foreign scan b, and so
> is
> waiting in ExecAsyncWaitForNode(foreign_scan_on_b).
> 2. The event wait list already has foreign scan on a that is on a different
> subtree.
> 3. This foreign scan a happens to be ready, so in
> ExecAsyncWaitForNode (), ExecDispatchNode(foreign_scan_a) is called,
> which returns with result_ready.
> 4. Since it returns result_ready, it's parent node is now inserted in the
> callbacks array, and so it's parent (Append) is executed.
> 5. But, this Append planstate is already in the middle of executing Hash
> join, and is waiting for HashJoin.

Ah, yeah, something like that could happen.  I've spent much of this
week working on a new design for this feature which I think will avoid
this problem.  It doesn't work yet - in fact I can't even really test
it yet.  But I'll post what I've got by the end of the day today so
that anyone who is interested can look at it and critique.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company