Re: Using quicksort for every external sort run

On Mon, Nov 30, 2015 at 5:12 PM, Greg Stark <stark(at)mit(dot)edu> wrote:
> I think the take-away is that this is outside the domain where any interesting break points occur.

I think that these are representative of what people want to do with
external sorts. We have already had Jeff look for a regression. He
found one only with less than 4MB of work_mem (the default), with over
100 million tuples.

What exactly are we looking for?

> And can you calculate an estimate where the domain would be where multiple passes would be needed for this table at these work_mem sizes? Is it feasible to test around there?

Well, you said that 1GB of work_mem was enough to avoid that within
about 4TB - 8TB of data. So, I believe the answer is "no":

[pg(at)hydra ~]$ df -h
Filesystem Size Used Avail Use% Mounted on
rootfs 20G 19G 519M 98% /
devtmpfs 31G 128K 31G 1% /dev
tmpfs 31G 384K 31G 1% /dev/shm
/dev/mapper/vg_hydra-root 20G 19G 519M 98% /
tmpfs 31G 127M 31G 1% /run
tmpfs 31G 0 31G 0% /sys/fs/cgroup
tmpfs 31G 0 31G 0% /media
/dev/md0 497M 145M 328M 31% /boot
/dev/mapper/vg_hydra-data 1023G 322G 651G 34% /data

--
Peter Geoghegan