Re: Atomics for heap_parallelscan_nextpage()

On 08/16/2017 04:20 PM, Heikki Linnakangas wrote:
> 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!

A couple of 32-bit x86 buildfarm members don't seem to be happy with
this. I'll investigate, but if anyone has a clue, I'm all ears...

- Heikki