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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