Hi,
I'm using RRDTool to store data series produces by flowscan/JKFlow and I hit
a performance problem updating many files. With 256 Mb RAM caching works OK up
to about 2000 RRDs, but after that # performance fall suddenly. About 180Mb of
RAM are dedicated to file caching, and I imagen that at certain amount of rrd
files the caching system start to drop based on some LRU algorithm and the
windows of caching just run useless behind the secuential update done on rrd
files.
Initially I was using RRDTool 1.0.49 and now I changed to 1.2.11 hoping "MMAP
IO" would help with this. I made sure I compiled it with "--enable-mmap" but
there was no diference in the # of files where performance degrades. I did not
find any detail in how does MMAP works in the web, docs, neither have enough
programming knoledge to understand the code, so I would apreciate if someone
can give me information on:
*The process of updating rrd files: I thought it was just needed to
read/write a few bytes in every file, but it seems it is necesary to load a
considerable part of the file in the cache in order to update it.
*How MMAP IO works and how I use it: I imagen writing the updates of many
files in memory and then sending all the request together to the disk, letting
it to be more efficient. I didn't see any reference in rrdupdate doc on how to
indicate how to use mmap.
One quick solutions seem to be adding RAM, but I just want to do this as
efficient as possible.
Thank in advance,
Alfredo
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