Re: [v9.5] Custom Plan API

On Thu, May 8, 2014 at 6:34 AM, Kouhei Kaigai <kaigai@ak.jp.nec.com> wrote:
> Umm... I'm now missing the direction towards my goal.
> What approach is the best way to glue PostgreSQL and PGStrom?

I haven't really paid any attention to PGStrom. Perhaps it's just that
I missed it, but I would find it useful if you could direct me towards
a benchmark or something like that, that demonstrates a representative
scenario in which the facilities that PGStrom offers are compelling
compared to traditional strategies already implemented in Postgres and
other systems.

If I wanted to make joins faster, personally, I would look at
opportunities to optimize our existing hash joins to take better
advantage of modern CPU characteristics. A lot of the research
suggests that it may be useful to implement techniques that take
better advantage of available memory bandwidth through techniques like
prefetching and partitioning, perhaps even (counter-intuitively) at
the expense of compute bandwidth. It's possible that it just needs to
be explained to me, but, with respect, intuitively I have a hard time
imagining that offloading joins to the GPU will help much in the
general case. Every paper on joins from the last decade talks a lot
about memory bandwidth and memory latency. Are you concerned with some
specific case that I may have missed? In what scenario might a
cost-based optimizer reasonably prefer a custom join node implemented
by PgStrom, over any of the existing join node types? It's entirely
possible that I simply missed relevant discussions here.

-- 
Peter Geoghegan