Re: Creating multiple indexes in one table scan.

* Gurjeet Singh (singh(dot)gurjeet(at)gmail(dot)com) wrote:
> Bruce points out the even simpler case is to build several indexes in
> parallel over the same scan.
>
> I thought I had posted a patch to that effect long back, but upon searching
> my emails apparently I forgot about the patch.
>
> Attached is the patch that I developed in Nov. 2010, so expect a lot of bit
> rot. I had tried to make it elegant, but I have to admit its a hack. This
> patch does not imply that it is using any kind of parallelism, the context
> in which that above statement was made. It just helps to avoid scanning the
> same relation multiple times. I performed some tests on it and AFAICR, this
> did not produce a net win. But those tests may have been performed in a
> virtual machine and not on a bare metal, I forget.

I'm not too surprised that it didn't help all that much since you're
doing everything in one backend. My guess at what Bruce was talking
about is being able to actually have multiple CREATE INDEX's going in
parallel in different backends. If they didn't all grab an
AccessExclusive lock, wouldn't they be able to use the same ring buffer
to read through the table anyway? And with CREATE INDEX CONCURRENTLY,
isn't this supported already?

I haven't tried this yet, but it sure seems like something we could
probably already claim to support..

Thanks,

Stephen