[rrd-users] buffers flush every midnight

[Maxim Kuleshov]

On Thu, 30 Oct 2008 09:39:21 +0100 (CET)
Tobias Oetiker <tobi at oetiker.ch> wrote:

> 
> if  you have an RRA storing daily values, then this is bound to get
> updated at midnight GMT ...
> 

Yes, I have. Typical rrd created like this:

	DS:ds0:DERIVE:600:0:U
	DS:ds1:DERIVE:600:0:U
	RRA:AVERAGE:0.5:1:600
	RRA:AVERAGE:0.5:6:700
	RRA:AVERAGE:0.5:24:775
	RRA:AVERAGE:0.5:288:797
	RRA:MAX:0.5:1:600
	RRA:MAX:0.5:6:700
	RRA:MAX:0.5:24:775
	RRA:MAX:0.5:288:797


> this will use more memory as more diskblocks go to cache
> and it will cause a lot of disk activity as the data blocks get
> read in for the updates.
> 

You seem to be right... Two-hour values computation is slightly slowed
down too. Not that critical, but noticeably.

One unexplained thing is that 'Buffers' values decreases, but not
'Cached'. As far as I know, in modern kernels 'Buffers' shows amount of
RAM allocated for file-system metadata cache and actual content stored
in 'Cached' memory.