Re: enable parallel query by default?

On 02/08/2016 01:07 PM, Robert Haas wrote:
> Hi,
>
> One of the questions I have about parallel query is whether it should
> be enabled by default. That is, should we make the default value of
> max_parallel_degree to a value higher than 0? Perhaps 1, say?

O.k. after some googling where I found your fantastic blog on the
subject, max_parallel_degree looks like it should be
max_parallel_workers. Am I correct in assuming that given the
opportunity to use parallel workers, postgres will launch N number of
workers up to the value of max_parallel_degree ?

If so, then I think 1 or 2 would be reasonable. By far the majority of
servers are going to have at least two cores.

>
> There are some good reasons why this might be a bad idea, such as:
>
> - As discussed on a nearby thread, there is every possibility of nasty bugs.

Which we won't find if it doesn't get turned on.

> - Parallel query uses substantially more resources than a regular
> query, which might overload your system.

How much of a reality is that? Isn't this something we could just cover
in the release notes?

>
> On the other hand:
>
> - Features that are on by default get more testing and thus might get
> less buggy more quickly.

Correct.

> - A lot of people don't change the default configuration and thus
> wouldn't get any benefit from the feature if it's not on by default.
>

Correct.

> Thoughts?
>

+1 on enabling by default.

Sincerely,

JD

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