Vanrish 2.1.5 eating memory, hit % decrease
kbrownfield at google.com
Fri Apr 8 23:09:23 CEST 2011
I forgot about your min_free_kbytes question:
While I would personally recommend 131072 as *a starting point*, this value
does not translate directly to what is actually retained as free RAM. In my
experience, the kernel's behavior is non-linear, non-deterministic, and very
delicate. Usually the kernel will keep much more free RAM than specified
(2-3x), and modifying this value too often under load will cause permanent
behavior problems in the kernel.
Setting it to 10% is a terrible idea under any circumstance I can imagine.
The goal with this setting in the context of a backing-store cache is to
set it high enough that you have 5-15 seconds of read/write I/O throughput
available for bursts. For example, if Varnish is committing 5MB/s to/from
disk, make sure you have 25-75MB of RAM free at a minimum. This might only
translate to a min_free_kbytes of 12000-30000.
I'd strongly suggest modifying the value slowly and carefully, ideally only
once after a reboot via sysctl.conf. But once done, my 1TB -spersistent
Varnish instances became very stable.
On Fri, Apr 8, 2011 at 13:55, Ken Brownfield <kbrownfield at google.com> wrote:
> This means the child process died and restarted (the reason for this should
> appear earlier in the log; perhaps your cli_timeout is too low under a
> heavily loaded system -- try 20s).
> "-sfile" is not persistent storage, so when the child process restarts it
> uses a new, empty storage structure. You should have luck with
> "-spersistent" on the latest Varnish or trunk, at least for child process
> On Fri, Apr 8, 2011 at 01:55, Jean-Francois Laurens <
> jean-francois.laurens at rts.ch> wrote:
>> Hi Ken,
>> Thanks for the hint !
>> You’re affecting here 128Mb, how did you get to this munber ? I read
>> somewhere that this value can be set to 10% of the actual memory size which
>> would be in my case 800Mb, does it make sense for you ?
>> I read aswell that setting this value to high would crash the system
>> Yesterday evening, the system was in heavy load but varnish did not hang !
>> Instead it dropped all its objects ! Then the load went back fine.
>> It seems setting –sfile to 40Gb suits better the memory capability for
>> this server.
>> A question remains though ... Why all the objects were dropped ?
>> Attached is a plot from cacti regarding the number of objects.
>> The only thing I could get form the messages log is this :
>> Apr 7 19:00:29 server-01-39 varnishd: Child (3733) died signal=3
>> Apr 7 19:00:29 server-01-39 varnishd: Child cleanup complete
>> Apr 7 19:00:29 server-01-39 varnishd: child (29359) Started
>> Apr 7 19:00:29 server-01-39 varnishd: Child (29359) said
>> Apr 7 19:00:29 server-01-39 varnishd: Child (29359) said Child
>> Apr 7 19:00:29 server-01-39 varnishd: Child (29359) said managed to
>> mmap 42949672960 bytes of 42949672960
>> How could I get to know what is realy happening that could explain this
>> behaviour ?
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