On 02/08/2016 01:07 PM, Robert Haas wrote:

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.


- 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.



+1 on enabling by default.



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