On Mon, Jun 11, 2007 at 12:45:36AM +0200, Tobias Oetiker wrote: >>written daemons. In my rrd data i have often short periods of missing >>data. In result the trend curve is missing over the complete sliding >>window. So i modified the TREND function to ignore NAN-number. I
>Hi Timo, > >NAN safe TREND sounds interesting ... Note that this should happen much, much less frequent (or not at all) with current trunk, since rrdtool-1.2 is excercising the hard-disks way too much, as opposed to the upcoming 1.3 version. Since you seem to observe gaps in your graphs, i assume that you also suffer from very high load-average¹) due to waiting on blocking I/O, which a) renders your machine unuseable for interactive use b) is responsible for the fact that your data-collection and/or RRD updates cannot finish in due time. The new file access method introduced in rrdtool-1.3 has several advantages over the FILE* (filp) based implementation that rrdtool-1.2 uses: a) less copying. The filp-based I/O had to do more than 3 (!) copies per RRD, whereas the mmap-based I/O in rrdtool-1.3 does only 1 copy (in the kernel). This greatly reduces the stress upon the memory-subsystem of your host. b) less buffer-cache pollution. As a consequence of a), we don't pollute the caches like the filp-based file accessors did. c) less seeking The filp-based I/O did several dozend (blocking!) seeks to update the internal positions from where to read/write. In the mmap-based implementation, we do not seek at all, thus greatly reducing the time spent on-disk. We just calculate some integer offsets into the file and use those for our read/write operations. d) less read/write ops While the filp-based file-accessor approach did blocking reads/writes (interleved with a dozend seeks) to read RRDs, then copy this data to a malloc()ed area, eventually updated this now in-memory data only to do a blocking write to propagate the update back to the file, the mmap-based accessors operate directly on the 1 copy we created when opening the RRD file. ¹) where too high of course depends on the number of rrd's you have, but generally, everything above 1.0 which *blocks* will get you into trouble sooner or later. > >if you provide a patch for current trunk I will be glad to include >it for 1.3 ... make sure you patch docs as well. And while you're at it, give 1.3 a whirl and let us know if this makes the immediate need for your patch obsolete. That said, i can see how your proposal is still something very useful for machines that are way too small for the workload they are supposed to handle. cheers, _______________________________________________ rrd-developers mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/rrd-developers
