Re: Hmmm... why does CPU-intensive pl/pgsql code parallelise so badly when queries parallelise fine? Anyone else seen this? - Mailing list pgsql-performance

On 07/07/2015 08:05 PM, Craig James wrote:

No ideas, but I ran into the same thing. I have a set of C/C++ functions
that put some chemistry calculations into Postgres as extensions (things
like, "calculate the molecular weight of this molecule"). As SQL
functions, the whole thing bogged down, and we never got the scalability
we needed. On our 8-CPU setup, we couldn't get more than 2 CPUs busy at
the same time, even with dozens of clients.

When I moved these same functions into an Apache fast-CGI HTTP service
(exact same code, same network overhead), I could easily scale up and
use the full 100% of all eight CPUs.

I have no idea why, and never investigated further. The convenience of
having the functions in SQL wasn't that important.

I admit that I haven't read this whole thread but:

Using Apache Fast-CGI, you are going to fork a process for each instance of the function being executed and that in turn will use all CPUs up to the max available resource.

With PostgreSQL, that isn't going to happen unless you are running (at least) 8 functions across 8 connections.

JD

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