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  • DNS Resolver Speed Techniques

    - by Rob Olmos
    I recently received a reply to my concerns about some DNS servers being slower than others despite all servers being anycast: In practice, most resolvers won't be impacted by the slower paths to some of the name servers in the set. Most resolvers employ various techniques to provide fast lookups, such as preferring name servers that were previously seen to be faster, sending simultaneous queries to multiple name servers, or pre-fetching queries before the TTL has expired. I was not aware that resolvers used these techniques and I was unsuccessful at searching for more info about this. Are there any names for these techniques? Which resolvers employ which of these techniques?

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  • Diagnose cause of long running requests in IIS 7.0

    - by Shlomi Fruchter
    We are running an ASP.NET web application on IIS 7.0, Windows Server 2008 R2, with SQL Server 2008 R2 for DB. On weekends, when the traffic is high, the request queue length in the IIS servers increase (up to 800 requests) and then drops, every minute or so. I can see that the servers are handling some requests which, according to the 'Current Requests' view in IIS Manager, are long running (thier Time Elapsed value ranges from 20 to 50 seconds). Those requests are not necessarily heavy queries, actually, I can't understand why they are taking so long. Can it be because the client is closing the connection on his side? Thanks, Shlomi

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  • How to start embedded development for developing a handheld game console?

    - by Quakeboy
    I work as a iPhone app developer now, so I know a bit of c, c++ and objective c. Also have fiddled with Java and many other. All of them have been just high level application/games development. My final goal is to make a handheld game console. More like a home made NES/SNES handheld console or even an Atari. I have found out about RaspberryPI and Arduino. But I need more information about how to approach this. 1) How Do I learn to pick the best board/cpu/controller/GPU/LCD screen/LCD controller etc? 2) Will learning to make a NES emulator first help me understand this field? If so are there any tutorials?

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  • Esxi with iSCSI SAN slows down with many multiple VMs running

    - by varesa
    I have a server with ESXi 5 and iSCSI attached network storage(4x1Tb Raid-Z on freenas). Those two machines are connected to each other with Gigabit ethernet, and a procurve switch in between. After a while, if I have many(4-5 or more) vms running, they start to get un-responsive (long delays before anything happens). We are trying to find the reason behind this. Today we looked at esxtop, and found that DAVG of that iSCSI LUN stays at 70-80. I read that +30 is critical! What could be causing those high response-times?

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  • How to have an Arduino wait until it receives data over serial?

    - by SonicDH
    So I've wired up a little robot with a sound shield and some sensors. I'm trying to write a sketch that will let check the sensors. What I'd like for it to do is print out a little menu over serial, wait until the user sends a selection, jump to the function that matches their selection, then (once the function is done) jump back and print the menu again. Here's what I've written, but I'm not a that good of a coder, so it doesn't work. Where am I going wrong? #include <Servo.h> Servo steering; Servo throttle; int pos = 0; int val = 0; void setup(){   Serial.begin(9600);   throttle.write(90);   steering.write(90);   pinMode(A0, INPUT);   pinMode(7, INPUT);   char ch = 0; } void loop(){   Serial.println("Menu");   Serial.println("--------------------");   Serial.println("1. Motion Readout");   Serial.println("2. Distance Readout");   Serial.println("3. SD Directory Listing");   Serial.println("4. Sound Test");   Serial.println("5. Car Test");   Serial.println("--------------------");   Serial.println("Type the number and press enter");   while(char ch = 0){   ch = Serial.read();}   char ch;   switch(ch)   {     case '1':     motion();   }    ch = 0; } //menu over, lets get to work. void motion(){   Serial.println("Haha, it works!"); } I'm pretty sure a While loop is the right thing to do, but I'm probably implementing it wrong. Can anyone shed some light on this?

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  • How to fix "The system is running in low-graphics mode" error?

    - by jokerdino
    Note: This is an attempt to create a canonical question that covers all instances of "low-graphics mode" error that occurs to a user, including but not limited to installation of wrong drivers, incorrect or invalid lightdm greeters, low disk space, incorrect installation of graphics card like ATI and Nvidia, incorrect configuration of xorg.conf file while setting up multiple monitors among others. If you are experiencing the "low-graphics mode" error when trying to login but none of the following answers work for you, please do ask a new question and then update the answers of this canonical question as and when your new question gets answered. When I try to boot into my computer, I am getting this error: The system is running in low-graphics mode Your screen, graphics cards, and input device settings could not be detected correctly. You will need to configure these yourself. How do I fix the failsafe X mode and login into my computer? Answer index: The greeter is invalid

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  • High frequency, kernel bypass vs tuning kernels?

    - by Keith
    I often hear tales about High Frequency shops using network cards which do kernel bypass. However, I also often hear about them using operating systems where they "tune" the kernel. If they are bypassing the kernel, do they need to tune the kernel? Is it a case of they do both because whilst the network packets will bypass the kernel due to the card, there is still all the other stuff going on which tuning the kernel would help? So in other words, they use both approaches, one is just to speed up network activity and the other makes the OS generally more responsive/faster? I ask because a friend of mine who works within this industry once said they don't really bother with kernel tuning anymore-because they use kernel bypass network cards? This didn't make too much sense as I thought you would always want a faster kernel for all the CPU-offloaded calculations.

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  • How much does a IPtables router slow down a connection?

    - by RayQuang
    Hi, I would like to know if introducing a new gateway in my network will slow things down. The question may sound unclear but here is an illustration: Before Installing gateway server Main Router <=> switches <=> servers after installing gateway Server Main Router <=> IPtables router <=> switches <=> servers My question is. How much will this delay incoming outgoing requests / file transfers. thanks, RayQuang

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  • Slow Gmail attachment download over HTTPS

    - by Todd
    It only affects Gmail. I have tested other HTTP, FTP and HTTPS websites and downloading is fine, at the exact same time the problem is affecting a Gmail attachment download. The symptoms include both: High waiting time, before the download starts (on the order of 30 seconds); AND Very slow download transfer speeds (on the order of 1kbps) It's a very strange problem, and I didn't find any recent issues relating to Google Australia. The account works fine at another site with a different ISP, so it's either a computer configuration or ISP - I lean to the latter.

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  • What interface does python use to implement sockets?

    - by user2738698
    When I programmed in python, I believe I interfaced with the transport layer using sockets. If python was programmed by humans, they must have used an interface that was "lower" than sockets, to provide us with the interface to sockets. I assume firewalls, also programmed by humans, use interfaces of lower layers in the same manner, so is there a way to access such lower layers, in terms of programming?

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  • Slow Gmail Attachment Download over HTTPS [closed]

    - by Todd
    It only affects Gmail. I have tested other HTTP, FTP and HTTPS websites and downloading is fine, at the exact same time the problem is affecting a Gmail attachment download. The symptoms include both: High waiting time, before the download starts (in the order of 30 seconds); AND Very slow download transfer speeds ( in the order of 1kbps) It's a very strange problem, and I didn't find any recent issues relating to Google Australia. The account works fine at another site with a different ISP, so it's either a computer configuration or ISP - I lean to the latter.

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  • Best Java 'framework' for LOW-END 3D Graphics?

    - by CodeJustin.com
    I've made my share of 2D games on various platforms but I have never developed a 3D game. I want to make a small "mmorpg". I already made my server in python and it works just fine with my flash 2D game but I decided I want to step it up and try out 3D. I want to make a 3D game for the web browser and I think Java might be a good choice for this. So basically I'm just looking for a straight forward and well documents 'framework' to make LOW-END 3D games. Keep in mind that I will be targeting peoples with very low-end PC's (plus my 3d modeling skills aren't great so I wouldn't mind hiding it somewhat, haha)

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  • How can I get latency info from Android's AudioTrack class?

    - by Ryan
    I've noticed that the C++ classes underlying the AudioTrack and AudioRecord APIs in Android both have a latency() method that is not exposed via JNI. As far as I can see, the latency() method in AudioRecord still does not take into account the hardware latency (they have a TODO comment for that), but the latency() method in AudioTrack does add in the hardware latency. I absolutely need to get this latency value from AudioTrack. Is there any possible way I can do this? I don't care what kind of crazy hack is needed as long as it doesn't require a rooted phone (the resulting code must still be packaged as an app on the market).

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  • Question about mysql indexes on low to medium cardinality columns

    - by Kevin J
    I have a general question about the way that database indexing works, particularly in mysql. Let's say I have a table with a million rows with a column "ClientID" that is distributed relatively equally among 30 values. Thus, this column is very low cardinality (30) relative to the primary key (1 million). Now, I understand that you shouldn't create indexes on low cardinality fields. However, in this case, queries are only ever done with one of the 30 clientIDs. Thus, wouldn't creating an index on ClientID be helpful, as the search space is automatically reduced to 1/30th what it normally would be? Or is my understanding of how the index works flawed? Thanks

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  • Need help with Drupal bulk mail low open rate for legitimate mailing list

    - by Ron Williams
    I've moved from constant contact to Drupal Simplenews/Mimemail/SMTP. Previously the open rate was around 50% for constant contact, but now it's 4-5% for the same list via the mentioned setup. Mail is getting out from the server, but it's having an issue anyway. Here's the setup: -The e-mail list consists of approximately 80,000 addresses which is queued at 10,000 e-mails per cron run (which runs hourly). -The server is a Dual Core2Quad machine with 2GB of RAM. -When mail is being sent, the mail queue will usually go up to ~1000 at the beginning of the hour before reducing to ~250 by the time the next cron occurs. -Newsletter is themed to display custom style for newsletter on send -Newsletter is received by some, but appears to be bounced by many (based on low open rate_ -I've added SPF, domain keys, and a PTR record to the DNS -Server hostname (listed in ptr) is different from hosted domain -Very low spam number via Spamassassin -IP and domain are not blacklisted -Mail goes out via SMTP module on delivery. Any ideas?

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  • How do you determine up/down latency of a web app.

    - by Brodie
    I am trying to work out how to calculate the latency of requests through a web-app (Javascript) to a .net webservice. Currently I am essentially trying to sync both client and server time, which when hitting the webservice I can look at the offset (which would accurately show the 'up' latency. The problem is - when you sync the time's, you have to factor in latency for that also. So currently I am timeing the sync request (round trip) and dividing by 2, in an attempt to get the 'up' latency...and then modify the sync accordingly. This works on the assumption that latency is symmetrical, which it isn't. Does anyone know a procedure that would be able to determine specifically the up/down latency of a JS http request to a .net service? If it needs to involve multiple handshakes thats fine, what ever is as accurate as possible. Thanks!!

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  • Rails - Preventing users from contributing to website when there score is too low - callback / obser

    - by adam
    A User can add a Sentence directly on my website, via twitter or email. To add a sentence they must have a minimum score. If they don't have the minimum score they cant post the sentence and a warning message is either flashed on the website, sent back to them via twitter or email. So I'm wondering how best to code this check. Im thinking a sentence observer. So far my thoughts are in before_create score_sufficient() - score ok = save - score too low = do not save In the case of too low i need to return some flag so that the calling code can then fire off teh relevant warning. What type of flag should I return? False is too ambiguous as that could refer to validation. I could raise an exception but that doesn't sound right or I could return a symbol? Is this even the right approach? What's the best way to code this?

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  • Low memory with 640Kb of live bytes?

    - by Chiodo
    Hello, i've a problem with my application that need to display a lot of images and video. After running ObjectAlloc tool, i see that the live bytes is 640Kb and the overall memory is 31,54Mb when the application crash. In the organizer i get a "low memory" report so i guess the app crashed because low memory but the ObjectAllocation data don't make any sense to me... Any ideas? This is the Organizer crash log: Incident Identifier: CDCAF38C-CFFD-4316-9C4A-5C8E37794B49 CrashReporter Key: 65390aeb97b2b81076576c3e33b025feb5db9202 OS Version: iPhone OS 3.1.3 (7E18) Date: 2010-05-19 10:07:19 +0200 Free pages: 372 Wired pages: 12260 Purgeable pages: 0 Largest process: DTMobileIS Processes Name UUID Count resident pages ATreeTest <1d51c3a5fef8b747c3a1be9405bdd52a 1150 (jettisoned) (active) DTMobileIS <69c3fa96db2f29474d62964aa1a69bfa 3316 notification_pro <8a7725017106a28b545fd13ed58bf98c 68 mediaserverd <3d3800d6acfff050e4d0ed91cbe2467e 464 (jettisoned) syslogd <8eddddc00294d5615afded36ee3f1b62 56 (jettisoned) apsd <32070d91b216d806973c8f1b1d8077a4 173 SpringBoard <324939a437d1cca1fa4af72d9f5d0eba 2475 (jettisoned) (active) accessoryd <8f21c8b376d16e2ccb95ed6d21d8317a 99 (jettisoned) notification_pro <8a7725017106a28b545fd13ed58bf98c 64 ptpd 129 notifyd <591dd4dd804b4b8741f52335ea1fa4ab 64 CommCenter 167 configd <85efd41aceac34ccc0019df76623c7a9 294 fairplayd 91 mDNSResponder 101 lockdownd <80d2bd44c0bcca273d48ce52010f7e65 285 launchd 71 End

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  • C++ code which is slower than its C equivalent?

    - by user997112
    Are there any aspects to the C++ programming language where the code is known to be slower than the equivalent C language? Obviously this would be excluding the OO features like virtual functions and vtable features etc. I am wondering whether, when you are programming in a latency-critical area (and you aren't worried about OO features) whether you could stick with basic C++ or would C be better?

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  • How to implement low pass filter using java

    - by chai
    Hello Everyone, I am trying to implement a low pass filter in Java. My requirement is very simple,I have to eliminate signals beyond a particular frequency (Single dimension). Looks like Butterworth filter would suit my need. Now the important thing is that CPU time should be as low as possible. There would be close to a million sample the filter would have to process and our users don't like waiting too long. Are there any readymade implementation of Butterworth filters which has optimal algorithms for filtering. Regards, Chaitannya

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  • Apache jamming at low load average

    - by Apikot
    Apache seems to stop responding sometimes even though apache processes are still running. After restarting apache, the load average usually shoots up from 1 - 2 to 13 - 15 in a matter of seconds. What would the cause of this be, or how could I find out why apache stops serving? My httpd.conf is: <IfModule mpm_prefork_module> StartServers 8 MinSpareServers 5 MaxSpareServers 20 MaxClients 50 ServerLimit 50 MaxRequestsPerChild 4000 </IfModule> It's running on an EC2 c1.medium (1.7 GB of memory) Thanks

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  • Win 7 running slowly with low CPU usage and memory

    - by guywhoneedsahand
    I have a relatively new (under 2 yrs old) windows 7 machine. It has 9GB of RAM, and an i7 core CPU (930 @ 2.8GHz w/ 8 CPUs). After about 8 months since a clean install, I noticed my computer was running slowly. I figure it was fragmentation etc, and I did a complete wipe & clean reinstall. However, my problems are somehow persisting. The computer is running painfully slowly (but in leaps and bounds - sometimes it will work fine for 3 hrs, then suddenly freeze up just from clicking the start button). The 'freezes' happen randomly - not during any especially intensive computing. I initially thought something might be eating through my CPU and/or Memory, but Task Manager indicates that neither the CPU or Memory spike. In fact, even during serious lag, CPU usage remains at less than 5% and Memory at ~ 1.5GB. It's beyond me why a fresh install on a powerful machine is performing so poorly... and it certainly is frustrating! What could be causing the poor performance, and what can I do to fix it?

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  • High load average, low CPU and IO (Centos 5.7)

    - by Ben
    A Drupal 7 site with CiviCRM, after running smoothly for a year on a 1&1 VPS suddenly became unresponsive. Now pages eventually load, but can take more than a minute. Looking at resource use in Virtuozzo, the load average carries a warning, and has remained above 1. While I understand this isn't particularly high, this is a change from when the site was working. Here is a typical snapshot of top: top - 03:10:32 up 3:21, 1 user, load average: 1.16, 1.22, 1.30 Tasks: 43 total, 1 running, 42 sleeping, 0 stopped, 0 zombie Cpu(s): 0.1%us, 0.1%sy, 0.1%ni, 99.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 2097152k total, 1015112k used, 1082040k free, 0k buffers Swap: 0k total, 0k used, 0k free, 0k cached CPU idle level never seems to go much below 70%. wa is virtually always at 0. There appears to be lots of free memory. And here is some vmstat output, again showign wa at 0, plenty of free memory, and an idle CPU: procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 2 0 0 1100872 0 0 0 0 2783 23672 0 538 1 0 99 0 0 1 0 0 1100872 0 0 0 0 0 16 0 101754 0 0 100 0 0 0 0 0 1100872 0 0 0 0 0 17 0 103133 0 0 100 0 0 0 0 0 1100872 0 0 0 0 0 1 0 102080 0 0 100 0 0 1 0 0 1100872 0 0 0 0 0 6 0 99881 0 0 100 0 0 0 0 0 1100872 0 0 0 0 0 1 0 105187 0 0 100 0 0 I've spoken to 1&1 but they don't have any ideas as to what could be causing the high load average. Instead they suggested an upgrade :) I've looked for processes that might be causing this, examined MySQL showprocesslist, and restarted the container with no result. Does anyone have more troubleshooting suggestions or insights?

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