Re: [PoC] Asynchronous execution again (which is not parallel)

Hi!

On 2016/01/21 18:26, Kyotaro HORIGUCHI wrote:
>>> Then, suppose we add a function bool ExecStartAsync(PlanState *target,
>>> ExecCallback callback, PlanState *cb_planstate, void *cb_context).
>>> For non-async-aware plan nodes, this just returns false.  async-aware
>>> plan nodes should initiate some work, register some callbacks, and
>>> return.  The callback that get registered should arrange in turn to
>>> register the callback passed as an argument when a tuple becomes
>>> available, passing the planstate and context provided by
>>> ExecStartAsync's caller, plus the TupleTableSlot containing the tuple.
>>
>> Although I don't imagine clearly about the case of
>> async-aware-nodes under non-aware-nodes, it seems to have a high
>> affinity with (true) parallel execution framework.
> 
> The ExecStartAsync is similar to ExecStartNode of my old
> patch. One of the most annoying things of that is that it needs
> to walk down to their descendents and in turn it needs garbageous
> corresponding additional codes for all type of nodes which can
> have children.

Unless I am missing something, I wonder if this is where
planstate_tree_walker() introduced by commit 8dd401aa is useful. For
example, I see that it's used in ExecShutdownNode() in a manner that looks
interesting for this discussion.

Thanks,
Amit