Re: auto_explain vs. parallel query

On 11/01/2016 08:32 PM, Robert Haas wrote:
> On Tue, Nov 1, 2016 at 10:58 AM, Tomas Vondra
> <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>> Damn! You're right of course. Who'd guess I need more coffee this early?
>>
>> Attached is a fix replacing the flag with an array of flags, indexed by
>> ParallelMasterBackendId. Hopefully that makes it work with multiple
>> concurrent parallel queries ... still, I'm not sure this is the right
>> solution.
>
> I feel like it isn't. I feel like this ought to go in the DSM for
> that parallel query, not the main shared memory segment, but I'm not
> sure how to accomplish that offhand. Also, if we do solve it this
> way, surely we don't need the locking. The flag's only set before any
> workers have started and never changes thereafter.
>

I'm not sure what you mean by "DSM for that parallel query" - I thought
the segments are created for Gather nodes, no? Or is there a DSM for the
whole query that we could use?

Another thing is that maybe we don't really want to give extensions
access to any of those segments - my impression was those segments are
considered internal (is there RequestAddinShmemSpace for them?). And
hacking something just for auto_explain seems a big ugly.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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