Re: PG18 GIN parallel index build crash - invalid memory alloc request size

I like (a) more, because it's more consistent with how I understand m_w_m. It's weird
to say "use up to 20GB of memory" and then the system overrides that with "1GB". 
I don't think it affects performance, though.

There wasn't really that much gain from 1GB -> 20GB, I was using that setting for QA purposes more than measured performance.  During the early parts of an OSM build, you need to have a big Node Cache to hit max speed, 1/2 or more of a ~90GB file.  Once that part finishes, the 45GB+ cache block frees up and index building starts.  I just looked at how much was just freed and thought "ehhh...split it in half and maybe 20GB maintenance mem?"  Results seemed a little better than the 1GB setting I started at, so I've ran with that 20GB setting since.  

That was back in PG14 and so many bottlenecks have moved around.  Since reporting this bug I've done a set of PG18 tests with m_w_m=256MB, and one of them just broke my previous record time running PG17.  So even that size setting seems fine.