Re: Logic behind parallel default? WAS: Rename max_parallel_degree?

On 05/31/2016 11:05 AM, Josh berkus wrote:
> On 05/31/2016 11:00 AM, Tom Lane wrote:
>> !          If this occurs, the plan will run with fewer workers than expected,
>> !          which may be inefficient.  The default value is 2.  Setting this
>> !          value to 0 disables parallel query execution.
>
> Is there a thread on how we determined this default of 2?  I can't find
> one under likely search terms.
>
> I'm concerned about the effect of overallocating parallel workers on
> systems which are already running out of cores (e.g. AWS instances), and
> run with default settings.  Possibly max_parallel_workers takes care of
> this, which is why I want to understand the logic here.
>

I don't remember the thread but I seem to recall that the default of 2 
is explicitly during Beta, RC etc... so that we can see what happens. 
Robert could speak better to that.

JD

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