Re: [HACKERS] A Better External Sort?

Jeffrey,

> I guess database reads are different, but I remain unconvinced that they
> are *fundamentally* different. After all, a tab-delimited file (my sort
> workload) is a kind of database.

Unfortunately, they are ... because of CPU overheads. I'm basing what's
"reasonable" for data writes on the rates which other high-end DBs can
make. From that, 25mb/s or even 40mb/s for sorts should be achievable
but doing 120mb/s would require some kind of breakthrough.

> On a single disk you wouldn't notice, but XFS scales much better when
> you throw disks at it. I get a 50MB/sec boost from the 24th disk,
> whereas ext3 stops scaling after 16 disks. For writes both XFS and ext3
> top out around 8 disks, but in this case XFS tops out at 500MB/sec while
> ext3 can't break 350MB/sec.

That would explain it. I seldom get more than 6 disks (and 2 channels) to
test with.

--
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco