Mailinglist Archive: opensuse (1470 mails)

< Previous Next >
Re: [opensuse] Why Is Leap 42.1 Benchmarking Poorly?
  • From: Vojtěch Zeisek <vojtech.zeisek@xxxxxxxxxxxx>
  • Date: Thu, 25 Feb 2016 12:56:08 +0100
  • Message-id: <2566929.8lNnOIM7Fd@veles>
Dne Čt 25. února 2016 14:40:00, Andrei Borzenkov napsal(a):
On Thu, Feb 25, 2016 at 2:28 PM, Vojtěch Zeisek
<vojtech.zeisek@xxxxxxxxxxxx> wrote:
Copy-on-write is terribly slowing down any DB.

btrfs does not do any copy on write. It does "redirect on write" which

https://btrfs.wiki.kernel.org/index.php/Main_Page „Btrfs is a new copy on
write (CoW) filesystem for Linux...“ Did I misunderstand something? :-)

is quite different. This does cause fragmentation; it is impossible to
give blanket statement what effect it will have. It will likely impact
sequential IO; it is much less likely impact random IO (unless your
database is very small and would not be affected by seek latency
otherwise).

I don't know the theoretical background. But many tests show Btrfs with CoW
and subvolumes has bad performance impact to DB. See also
https://btrfs.wiki.kernel.org/index.php/SysadminGuide#Copy_on_Write_.28CoW.29

Also snapshots don't make sense
for DB (use DB's tools).

If you have suggestions how to make point in time online copies
without impacting normal activity (terribly slowing down client access

Client access is what is counted, right? ;-)

:) ) *and* revert to them in seconds for multiterabyte database (in
order of several dozens TB) without using snapshots I am all ears.

I don't say it is a bug. It just isn't the best for all user cases...

--
Vojtěch Zeisek

Komunita openSUSE GNU/Linuxu
Community of the openSUSE GNU/Linux

https://www.opensuse.org/
https://trapa.cz/
< Previous Next >
Follow Ups