I got same problem with squid when squid exit normally (/etc/rc.d/squid stop), when mass squid disk cache is written, there is a one min freeze on the server. (OpenBSD 5.2). The problem was also here under OpenBSD 5.1. CPU is also OK (10% of a big xeon quad). But for me softdeps aren't activated. The temporary solution i used, kill -9 squid process when stop/restart is done.
-- Cordialement, Loïc BLOT, UNIX systems, security and network expert http://www.unix-experience.fr Le dimanche 06 janvier 2013 à 16:08 +0100, Federico Giannici a écrit : > You was right: turning off softdep made the freezes much shorter. > > Thanks. > > > On 01/06/13 13:49, Stefan Sperling wrote: > > On Sun, Jan 06, 2013 at 12:22:44PM +0100, Federico Giannici wrote: > >> We have an OpenBSD 5.2 amd64 where every 5 minutes a few thousand of > >> ".rrd" files from MRTG are written (actually, updated) to disk. > >> > >> The problem is that for a few seconds (15-20) every other access to > >> the disk is totally blocked. So during those 15-20 seconds the > >> access to the graphs is freezed! And this is really annoying for a > >> graphs server... > >> > >> It's not a problem of CPU load (it's a quadruple core AMD Athlon II > >> X4 630 Processor). Processes run smoothly, they freeze only when > >> they try to access the disk. Disk is a normal SATA, and the > >> partition is FFS with softdep. > > > > It's probably the bug in the buffer cache where the kernel would allow > > userland to queue up so many writes that eventually the kernel is starved > > out of buffers. Everything else (for example, read operations on your > > graph files) then sleeps until enough writes have been spilled out to disk. > > > >> Is there anything (some system tuning?) I can do to get rid of the > >> freezes, or at least to mitigate them? > > > > The best solution is an upgrade to -current where this has been fixed. > > See http://marc.info/?l=openbsd-cvs&m=135231065926430&w=2 and other > > related commits by Bob Beck. > > > > If you'd rather stick to 5.2 you can try turning off softdep. softdep delays > > some write operations so turning it off might help somewhat by allowing more > > read operations to interleave with write operations. While the bug was > > affecting -current I found that my systems where much more responsive with > > softdep turned off.
