Re: xfs: does mkfs.xfs require fancy switches to get decent performance? (was Tux3 Report: How fast can we fsync?)

From: Howard Chu
Date: Tue May 12 2015 - 09:26:19 EST

Daniel Phillips wrote:
On 05/12/2015 02:03 AM, Pavel Machek wrote:
I'd call system with 65 tasks doing heavy fsync load at the some time
"embarrassingly misconfigured" :-). It is nice if your filesystem can
stay fast in that case, but...

Well, Tux3 wins the fsync race now whether it is 1 task, 64 tasks or
10,000 tasks. At the high end, maybe it is just a curiosity, or maybe
it tells us something about how Tux3 is will scale on the big machines
that XFS currently lays claim to. And Java programmers are busy doing
all kinds of wild and crazy things with lots of tasks. Java almost
makes them do it. If they need their data durable then they can easily
create loads like my test case.

Suppose you have a web server meant to serve 10,000 transactions
simultaneously and it needs to survive crashes without losing client
state. How will you do it? You could install an expensive, finicky
database, or you could write some Java code that happens to work well
because Linux has a scheduler and a filesystem that can handle it.
Oh wait, we don't have the second one yet, but maybe we soon will.

I will not claim that stupidly fast and scalable fsync is the main
reason that somebody should want Tux3, however, the lack of a high
performance fsync was in fact used as a means of spreading FUD about
Tux3, so I had some fun going way beyond the call of duty to answer
that. By the way, I am still waiting for the original source of the
FUD to concede the point politely, but maybe he is waiting for the
code to land, which it still has not as of today, so I guess that is
fair. Note that it would have landed quite some time ago if Tux3 was
already merged.

Well, stupidly fast and scalable fsync sounds wonderful to me; it's the primary pain point in LMDB write performance now.

I look forward to testing Tux3 when usable code shows up in a public repo.

-- Howard Chu
CTO, Symas Corp.
Director, Highland Sun
Chief Architect, OpenLDAP
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