Re: numbering plan nodes

On Fri, Sep 18, 2015 at 5:24 AM, Kouhei Kaigai <kaigai@ak.jp.nec.com> wrote:
>> On Thu, Sep 17, 2015 at 9:01 PM, Kouhei Kaigai <kaigai@ak.jp.nec.com> wrote:
>> > I entirely agree with the idea of plan-node identifier, however,
>> > uncertain whether the node-id shall represent physical location on
>> > the dynamic shared memory segment, because
>> > (1) Relatively smaller number of node type needs shared state,
>> >     thus most of array items are empty.
>> > (2) Extension that tries to modify plan-tree using planner_hook
>> >     may need to adjust node-id also.
>> >
>> > Even though shm_toc_lookup() has to walk on the toc entries to find
>> > out the node-id, it happens at once on beginning of the executor at
>> > background worker side. I don't think it makes a significant problem.
>>
>> Yes, I was thinking that what would make sense is to have each
>> parallel-aware node call shm_toc_insert() using its ID as the key.
>> Then, we also need Instrumentation nodes.  For those, I thought we
>> could use some fixed, high-numbered key, and Tom's idea.
>>
> Hmm, indeed, run-time statistics are needed for every node.
> If an array indexed by node-id would be a hash slot, we can treat
> non-contiguous node-id with no troubles.

Yeah, we could do that, but it seems more complex than we really need.

>> Are there extensions that use planner_hook to do surgery on the plan
>> tree?  What do they do, exactly?
>>
> (Even though it will not work under Funnel,) PG-Strom often inject
> a preprocessor node under Agg-node to produce partial aggregation
> to reduce number of rows to be processed by CPU.

OK.  So, if you wanted to make it work under a Funnel, you'd need to
stick a node ID on it that was higher than any assigned to any plan
node thus far.  Doesn't seem like a big deal.

> Also, I have seen a paper published by Fujitsu folks. Their module
> modifies plan-tree to replace built-in scan node with their own
> columnar storage scan node.
>   http://db-event.jpn.org/deim2015/paper/195.pdf
> This paper is written in Japanese, however, figure-3 in page.4 shows
> what I explain above.

If you replaced a node, you'd just copy the ID from the existing node.
That seems simple enough.

-- 
Robert Haas
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