Re: [HACKERS] CREATE TABLE with parallel workers, 10.0?

Hi,

On 2017-02-15 08:48:44 -0500, Robert Haas wrote:
> We got rid of the major existing use of page locks in
> 6d46f4783efe457f74816a75173eb23ed8930020, which extirpated them from
> hash indexes, and I was kind of hoping they could go away altogether,
> but we can't do that as long as GIN is using them.

Learned a new word today.


> Anyway, if we solve those problems, we can allow inserts (not updates
> or deletes, those have other problems, principally relating to combo
> CIDs) in parallel mode, which would make it possible to allow the
> kinds of things you are asking about here.

I don't think general INSERTs are safe, if you consider unique indexes
and foreign keys (both setting xmax in the simple cases and multixacts
are likely to be problematic).


> The other way of fixing this problem is to have each worker generate a
> subset of the tuples and funnel them all back to the leader through a
> Gather node; the leader then does all the inserts.  That avoids having
> to solve the problems mentioned above, but it probably doesn't perform
> nearly as well.

I think it'd already be tremendously useful however.  I think it'd not
be an unreasonable first step. It'd be a good fallback that'd be useful
for !insert and such anyway.


Regards,

Andres