Re: Atomics for heap_parallelscan_nextpage()

On 05/06/2017 04:57 PM, David Rowley wrote:
> Andres mentioned in [2] that it might be worth exploring using atomics
> to do the same job. So I went ahead and did that, and came up with the
> attached, which is a slight variation on what he mentioned in the
> thread.
>
> To keep things a bit more simple, and streamline, I ended up pulling
> out the logic for setting the startblock into another function, which
> we only call once before the first call to
> heap_parallelscan_nextpage(). I also ended up changing phs_cblock and
> replacing it with a counter that always starts at zero. The actual
> block is calculated based on that + the startblock modulo nblocks.
> This makes things a good bit more simple for detecting when we've
> allocated all the blocks to the workers, and also works nicely when
> wrapping back to the start of a relation when we started somewhere in
> the middle due to piggybacking with a synchronous scan.
Looks reasonable. I edited the comments and the variable names a bit, to
my liking, and committed. Thanks!

- Heikki