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March 2020

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Re: Fwd: [mirror] Suboptimal (for mirrors) download pattern by opensuse clients
by Benjamin Zeller 03 Mar '20

03 Mar '20

Hi, Sorry for top posting but I just subscribed to this ML for this conversation. I'm currently working on the libzypp/zypper http/https media backend and have suspected something like that myself. Currently we do not download multiple files at once but download one file in multiple chunks. I have a new downloader implemented that would support multiple downloads in parallel but I suffer from the problem that mirrorbrains forwards me from HTTPS to HTTP if I disable the metalink downloads in favour of downloading full files only, curl errors out in that case. I know we could disable that error but I'm not really sure that this is what we want. With metalink files we get the metalink description over https , which includes all checksums for the several chunks and then can use http connections as well because we can check if we really got what we asked for. Would be interesting to know here if we can configure mirrorbrains to just redirect to HTTPS if that's what the incoming connection is using. Not sure if we could drop Metalinks completely, however it makes the code much more complex supporting it and if it actually does more harm then good we should think about something else. As to the suggestion to use dynamic or bigger chunks: The metalink description file we download at the beginning has the list of chunks included and they are fixed. We probably could try and download multiple chunks in the same request though. Cheers, Benjamin On 3/2/20 3:04 PM, Michael Andres wrote: > > -------- Forwarded Message -------- > Subject: [mirror] Suboptimal (for mirrors) download pattern by opensuse > clients > Date: Fri, 21 Feb 2020 14:36:26 +0100 (CET) > From: Niklas Edmundsson <nikke(a)acc.umu.se> > To: mirror(a)opensuse.org > > > Hi, > > am I the only mirror admin that finds the current behavior of opensuse > clients suboptimal? > > Requests by "ZYpp 17.11.4 (curl 7.60.0) openSUSE-Leap-15.1-x86_64" etc > seem to be done with 256 kb chunk size, always, as an example: > > GET bytes=0-262143 > /mirror/opensuse.org/tumbleweed/repo/oss/x86_64/libqt5-qtwebengine-5.14.1-1.5.x86_64.rpm > GET bytes=262144-524287 > /mirror/opensuse.org/tumbleweed/repo/oss/x86_64/libqt5-qtwebengine-5.14.1-1.5.x86_64.rpm > > That's a silly small size, since TCP won't be able to ramp window sizes > and get good speed before those 256k are done. Also, we get > int($filesize/256k) entries in our logs for each download. > > To make matters worse, the thing seems to do some kind of round robin > between sites, with this pattern being the most ineffective looking from > a mirror admin standpoint: > > GET bytes=2097152-2359295 > /mirror/opensuse.org/tumbleweed/repo/oss/x86_64/libqt5-qtwebengine-5.14.1-1.5.x86_64.rpm > GET bytes=2621440-2883583 > /mirror/opensuse.org/tumbleweed/repo/oss/x86_64/libqt5-qtwebengine-5.14.1-1.5.x86_64.rpm > > Since the OS normally does read-ahead on file system reads, it will > read-ahead after byte 2359295 in preparation for the next read(). In > this case though, that's in vain as the request never comes but the next > data read is instead byte 2621440 and forward... OS read-ahead is most > commonly in the 64kB-1MB range, so it's not unlikely that the entire > 256k gap inbetween is read from disk without being used... > > Downloading files this way is just plain stupid, IMHO. > > I don't know what problem this behavior is supposed so solve, but it's > definitely not beneficial for us as a mirror, and I think it's hurting > your end users as well. > > If you want more bandwidth from us, request larger chunks (or whole > files). The TCP window will grow and you'll get the performance (within > the limits of 10 gigabit networking for one download). > > If you want to spread the load between mirrors, use larger chunks, and > specifically avoid small chunks and striped access. > > In any case, merge requests! If you're going to request a number of > consecutive chunks, do it in one request, preferrably as one range, to > make the most of the tcp connection you've set up. > > My minimum suggestion would be to bump the chunk-size to multiple > megabytes at the minimum, possibly varying depending on download > performance, aiming for each GET taking at least a couple of seconds to > allow for TCP to ramp speed (and reduce the noise in our logs). In > extreme cases we're seeing multiple tens of GET:s each second for some > downloads, I'm guessing the rate throttles due to the RTT latency (ping > time) and not some real bandwidth limit... > > > /Nikke - admin of ftp.acc.umu.se -- Benjamin Zeller <bzeller(a)suse.de> Systems Programmer SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nuremberg, Germany Tel: +49-911-74053-0; Fax: +49-911-7417755; https://www.suse.com/ (HRB 36809, AG Nürnberg) Managing Director: Felix Imendörffer -- To unsubscribe, e-mail: mirror+unsubscribe(a)opensuse.org To contact the owner, email: mirror+owner(a)opensuse.org

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