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• "Failed to create swap space" error during installation

  - by Welsh Heron

  I've been trying to install Ubuntu for the past two days or so, but I've been running into a problem: every time I run the installation program on the LiveCD, I always get the same (or a very similar) error: "Failed to create Swap space The creation of swap space in partition #3 of SCSI5 (0,0,0)(sda) failed." So far, I've run DBAN (Darik's Boot and Nuke) on my HDD once, to make absolutely sure that everything on it had been erased. Then, I simply put in the LiveCD, and let it run the automated install. I get the above error directly after I tell it to automatically partition the HDD (it will work for a second or so, then this will pop up), forcing me back to the screen that lets me choose whether I want to automatically or manually partition the HDD. Well, after failing to install the software manually, I did a little research and learned enough about partitioning Linux to use the 'Manual partitioning' option. I partitioned the HDD as follows (it's a 1TB drive): /home - (the rest)- ext2, / - 20GB - ext2, /boot - 100MB - ext2, /swap - 8GB /EFIboot - 40MB The only difference when I tried this method was that I got THIS message: "Failed to create Swap space The creation of swap space in partition #2 of SCSI5 (0,0,0)(sda) failed." Basically, the only difference was that there was now a '2' instead of a '3'. If I may ask, what exactly am I doing wrong? I've tried looking around the internet (that's basically all I've done for the last two days), but no one seems to have the same problem that I have, and I've tried most of the solutions for similar problems (DBAN, formatting partitions in ext2 format, etc). The only thing I haven't tried is using the terminal to manually partition the HDD...and I actually DID try to do this, but I wasn't able to get past 'su' 's password demand, so I wasn't able to use the terminal. Thank you for your help in advance. ~Welsh

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• SQL Saturday Atlanta: Intro To Performance Tuning

  - by Mike Femenella

  I'm looking forward to speaking in Atlanta on the 24th, will be fun to get back down that way to visit with some friends and present two topics that I really enjoy. First, an introduction to performance tuning. Performance tuning is a very wide and deep topic and we're staying close to the surface. I direct this class for newbie sql users who have less than 2 years of experience. It's all the things I wish someone would have told me in my first 2 years about what to look for when the database was slow...or allegedly slow I should say. We'll cover using profiler to find slow performing queries and how to save the data off to a table as well as a tour of other features. The difference between clustered, non clustered and covering indexes. How to look at and understand an execution plan (at a high level) and finally the difference between a temp table and a table variable and what the implications are of using either one in your code. That pretty much takes up a full hour. Second presentation, Loading Data in Real Time. It's really a presentation about partitioning but with a twist that we used at work recently to solve a need to load some data quickly and put it into production with minimal downtime. We'll cover partition functions, schemes,$partition, merge, sys.partitions and show some examples of building a set of partitioned tables and using the switch statement to move it from one table to another. Finally we'll cover the differences in partitioning between 2005 and 2008. Hope to see you there! And if you read my blog please introduce yourself!

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• Unknown CSS font-family oddity with IE7-10 on Windows Vista, 7, 8

  - by Jeff

  I am seeing the following "oddity" with IE7-10 on Windows Vista, 7, 8: When declaring font-family: serif; I am seeing an old bitmapped serif font that I can't identify (see screenshot below) instead of the expected font Times New Roman. I know it's an old bitmapped font because it displays aliased, without any font smoothing, with IE7-10 on Win Vista-8 (just like Courier on every version of Win). Screenshot: I would like to know (1) can anyone else confirm my research and (2) BONUS: which font is IE displaying? Notes: IE6 and IE7 on Win XP displays Times New Roman, as they should. It doesn't matter if font-family: serif; is declared in an external stylesheet or inline on the element. Quoting the CSS attribute makes no difference. Adding "Unkown Font" to the stack also makes no difference. New Screenshot: The answer from Jukka below is correct. Here is a new screenshot with Batang (not BatangChe) to illustrate. Hope this helps someone.

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• Is Linq having a mind-numbing effect on .NET programmers?

  - by Aaronaught

  A lot of us started seeing this phenomenon with jQuery about a year ago when people started asking how to do absolutely insane things like retrieve the query string with jQuery. The difference between the library (jQuery) and the language (JavaScript) is apparently lost on many programmers, and results in a lot of inappropriate, convoluted code being written where it is not necessary. Maybe it's just my imagination, but I swear I'm starting to see an uptick in the number of questions where people are asking to do similarly insane things with Linq, like find ranges in a sorted array. I can't get over how thoroughly inappropriate the Linq extensions are for solving that problem, but more importantly the fact that the author just assumed that the ideal solution would involve Linq without actually thinking about it (as far as I can tell). It seems that we are repeating history, breeding a new generation of .NET programmers who can't tell the difference between the language (C#/VB.NET) and the library (Linq). What is responsible for this phenomenon? Is it just hype? Magpie tendencies? Has Linq picked up a reputation as a form of magic, where instead of actually writing code you just have to utter the right incantation? I'm hardly satisfied with those explanations but I can't really think of anything else. More importantly, is it really a problem, and if so, what's the best way to help enlighten these people?

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• Why is Samba Access from Windows So Slow?

  - by swalker2001

  I have set up a file server using Ubuntu 12.04 Server. The purpose is to serve several network drives to Windows users that have heretofore been served by numerous NAS drives. I have Samba set up with one share defined so far. I can connect to it fine from my test Windows 7 and Windows XP machines. When I do a directory listing on the share from Windows, it can take up to two minutes to get all the files listed--would have taken about 1.5 seconds when I was using the Buffalo NAS. Sometimes it times out with no response at all. I have used the default smb.conf and simply added the following for the share I have set up so far: [engineering] comment = Ubuntu File Server Share path = /networkdriveshares/engineering browsable = yes guest ok = yes read only = no create mask = 0755 I have tried changing the workgroup setting to the Active Domain name our Windows computer use but didn't notice any difference. The only other change I made to the default smb.conf was adding in the recommended socket settings: SO_RCVBUF=8192 SO_SNDBUF=8192 socket options = TCP_NODELAY Lots of information about slow Samba shares online but I have tried all of the solutions I have found and none have made a lick of difference. If there is no solution, is there a better way to set up a file server to be used by Windows clients?

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• Laptop battery life drastically decreased compared to Windows 7

  - by Aron Rotteveel

  I am running Ubuntu 10.10 on my Dell Studio XPS 1640 and have about one hour of battery life in it, compared to about 2.5 hours running on Windows 7. This is with wireless and bluetooth on, but still, the difference seems incredible. What could be causing such a difference and is there a way to close the gap without losing core functionality? EDIT: here's some output from powertop. This is with bluetooth turned off and Wifi turned on. The output seems pretty normal to me, but as indicated, this is about 1 hour of battery life on a full battery... Wakeups-from-idle per second : 476.2 interval: 10.0s Power usage (ACPI estimate): 2.5W (1.2 hours) Top causes for wakeups: 30.0% (167.2)D chrome 21.0% (117.3) [extra timer interrupt] 13.9% ( 77.4) [kernel scheduler] Load balancing tick 3.4% ( 18.9)D xchat 7.1% ( 39.8) [iwlagn] <interrupt> 5.9% ( 32.9) AptanaStudio3 3.9% ( 21.6)D java 2.7% ( 14.9) [TLB shootdowns] <kernel IPI> 2.5% ( 14.1) docky 1.8% ( 10.0) nautilus 1.6% ( 9.0) thunderbird-bin 1.0% ( 5.5) [ahci] <interrupt> 0.9% ( 5.0) syndaemon 0.8% ( 4.3) [kernel core] hrtimer_start (tick_sched_timer) EDIT: after changing /proc/sys/vm/laptop_mode to 5 (it was set to 0), wakeups seem to have decreased, although usage still seems far too high: Wakeups-from-idle per second : 263.8 interval: 10.0s Power usage (ACPI estimate): 2.6W (0.9 hours) EDIT: I seem to have discovered the main cause: I was using the open source ATI Drivers. I recently installed the official ATI drivers and laptop battery life seems to have doubled since. EDIT: last edit. The previous 'solution' of installing the official ATI drivers turns out to be a non-solution. Although it does increase battery life, my laptop resolution is maxed out at 1200x800 after a reboot. (Please note that this problem does not need answering in this question as it is a seperate case)

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• Shared to Dedicated or Amazon CloudFront to improve performances and keep secured?

  - by user978548

  I have a Wordpress which currently takes about 1.8s to 2.5s for the home page to completely load in my country. The page weight is about 700Ko (static content included). In order to increase performances, I'm considering two solutions: Switching to a dedicated host. Using amazon s3 cloudfront to serve static contents. My current shared hosting have servers in a neighboring country but not exactly in mine, and both amazon and the dedicated hosting have some, so that's already an advantage. So considering all that, I still have three questions remaining: Currently having a low traffic (100 unique visitors/days, but growing) will it make a huge difference between my shared hosting and a dedicated server ? Knowing that I already use a cookie-less domain to deliver static contents (but using a redirection to the same server), would using amazon s3 make a real difference ? Talking about the cons of dedicated vs amazon s3, if I choose for the dedicated server something like Ubuntu server and do daily package updates and have only port 80 open, would it be sufficient in terms of security (in comparison with my current shared hosting which manage everything for me) ?

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• Multiplayer Network Game - Interpolation and Frame Rate

  - by J.C.

  Consider the following scenario: Let's say, for sake of example and simplicity, that you have an authoritative game server that sends state to its clients every 45ms. The clients are interpolating state with an interpolation delay of 100 ms. Finally, the clients are rendering a new frame every 15ms. When state is updated on the client, the client time is set from the incoming state update. Each time a frame renders, we take the render time (client time - interpolation delay) and identify a previous and target state to interpolate from. To calculate the interpolation amount/factor, we take the difference of the render time and previous state time and divide by the difference of the target state and previous state times: var factor = ((renderTime - previousStateTime) / (targetStateTime - previousStateTime)) Problem: In the example above, we are effectively displaying the same interpolated state for 3 frames before we collected the next server update and a new client (render) time is set. The rendering is mostly smooth, but there is a dash of jaggedness to it. Question: Given the example above, I'd like to think that the interpolation amount/factor should increase with each frame render to smooth out the movement. Should this be considered and, if so, what is the best way to achieve this given the information from above?

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• When is it better to offload work to the RDBMS rather than to do it in code?

  - by GeminiDomino

  Okay, I'll cop to it: I'm a better coder than I am at databases, and I'm wondering where thoughts on "best practices" lie on the subject of doing "simple" calculations in the SQL query vs. in the code, such as this MySQL example (I didn't write it, I just have to maintain it!) -- This returns the username, and the users age as of the last event. SELECT u.username as user, IF ((DAY(max(e.date)) - DAY(u.DOB)) &lt; 0 , TRUNCATE(((((YEAR(max(e.date))*12)+MONTH(max(e.date))) -((YEAR(u.DOB)*12)+MONTH(u.DOB)))-1)/12, 0), TRUNCATE((((YEAR(max(e.date))*12)+MONTH(max(e.date))) - ((YEAR(u.DOB)*12)+MONTH(u.DOB)))/12, 0)) AS age FROM users as u JOIN events as e ON u.id = e.uid ... Compared to doing the "heavy" lifting in code: Query: SELECT u.username, u.DOB as dob, e.event_date as edate FROM users as u JOIN events as e ON u.id = e.uid code: function ageAsOfDate($birth, $aod) { //expects dates in mysql Y-m-d format... list($by,$bm,$bd) = explode('-',$birth); list($ay,$am,$ad) = explode('-',$aod); //Insert Calculations here ... return $Dy; //Difference in years } echo "Hey! ". $row['user'] ." was ". ageAsOfDate($row['dob'], $row['edate']) . " when we last saw him."; I'm pretty sure in a simple case like this it wouldn't make much difference (other than the creeping feeling of horror when I have to make changes to queries like the first one), but I think it makes it clearer what I'm looking for. Thanks!

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• Application Scope v's Static - Not Quite the same

  - by Duncan Mills

  An interesting question came up today which, innocent as it sounded, needed a second or two to consider. What's the difference between storing say a Map of reference information as a Static as opposed to storing the same map as an application scoped variable in JSF?  From the perspective of the web application itself there seems to be no functional difference, in both cases, the information is confined to the current JVM and potentially visible to your app code (note that Application Scope is not magically propagated across a cluster, you would need a separate instance on each VM). To my mind the primary consideration here is a matter of leakage. A static will be (potentially) visible to everything running within the same VM (OK this depends on which class-loader was used but let's keep this simple), and this includes your model code and indeed other web applications running in the same container. An Application Scoped object, in JSF terms, is much more ring-fenced and is only visible to the Web app itself, not other web apps running on the same server and not directly to the business model layer if that is running in the same VM. So given that I'm a big fan of coding applications to say what I mean, then using Application Scope appeals because it explicitly states how I expect the data to be used and a provides a more explicit statement about visibility and indeed dependency as I'd generally explicitly inject it where it is needed.  Alternative viewpoints / thoughts are, as ever, welcomed...

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• Impossible to enable bluetooth under Ubuntu

  - by PCh

  I just installed Ubuntu 12.04 (dual boot, kept Windows just in case) on my new Acer Aspire One 756-877. As soon as I installed it I also installed the Broadcom driver, since wifi wasn't working, and that solved it right away. But when I tried Bluetooth, I had a problem that I see is quite recurring: -The hardware is on (and working fine under Windows) -The icon shows up on the menu, giving me the options of turning Bluetooth on or off, and then just "Bluetooth preferences". -I can apparently turn it on that way, which only lights up the icon but makes no difference at all (and doesn't give any other options in the Bluetooth menu) -When I open "Bluetooth preferences" (whether Bluetooth is apparently on or off, it makes no difference), it says it's disabled and will not let me slide the button to enable it. I've rebooted, but nothing happens. -The material is Broadcom and the port (if it's relevant at all) is Port_#0001.Hub_#0003 I tried the following commands suggested in other similar questions, with no result at all: sudo dmesg | grep blue and sudo service bluetooth start and sudo /etc/init.d/bluetooth start Any other clues on what I can do? Thanks for your time!

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• Ubuntu sound volume is 40% lower than in Windows

  - by ncomx

  I have 2x 2.1 speakers connected to the computer where I have Ubuntu 12.04 installed. On the software side I've set all the volume controls to 100% with the alsamixer program. The speakers have their own volume control, maintaining those at the same level, and switching between Ubuntu and Windows (XP and 7), on windows the output volume is at least 40% higher, even when having the windows volume control at 50% (without touching the speakers volume control) it's still much higher than the sound on Ubuntu. Why can this be happening? Are there some alternative sound drivers (other than the default ones) I could test to see if it makes a difference? some info about the card: root:$ cat /proc/asound/cards 0 [PCH ]: HDA-Intel - HDA Intel PCH HDA Intel PCH at 0xfbff4000 irq 55 1 [Generic ]: HDA-Intel - HD-Audio Generic HD-Audio Generic at 0xfbcfc000 irq 56 root:$ lspci | grep -i audio 00:1b.0 Audio device: Intel Corporation 6 Series/C200 Series Chipset Family High Definition Audio Controller (rev 04) 02:00.1 Audio device: Advanced Micro Devices [AMD] nee ATI Cayman/Antilles HDMI Audio [Radeon HD 6900 Series] I think the one i am using is the Intel one, the other seems to be from the vga card which is an ati radeon 6950. Running gstreamer-properties and switching between alsa, oss, ossv4 and pulseaudio doesn't seem to make any difference.

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• Hosting and scaling of a facebook application on cloud?

  - by DhruvPathak

  We would be building a facebook application in django(Python), but still not sure of where to host it economically,and with a good provision to scale in case the app gets viral. Some details about the app: i) Would be HTML based like a website,using django as a framework. ii) 100K is the number of expected pageviews in a day,if the app is viral. iii) The users will not generate any media content,only some database data will be generated by them. It would be great if someone with more experience can guide on following points: A) Hosting on google app engine or Amazon EC2 or some other cloud like RackSpace : Preferable points found in AppEngine were ease of deployment,cost effectiveness and easy scaling. For EC2: Full hold of the virtual machine,Amazon NoSQL and RDMBS database services in case we decide to use them. B) Does backend technology affect monthly cost ? eg. would CPU and memory usage difference of Django over , for example , PHP framework like CodeIgnitor really make remarkable difference in running costs. ( Here is the article that triggered this thought process : http://journal.dedasys.com/2010/01/12/rough-estimates-of-the-dollar-cost-of-scaling-web-platforms-part-i#comments) C) Does something like Heroku , which provides additional services over Amazon EC2, prove to be better than raw cloud management ? It is not that we are trying for premature scaling, we just want to have a good start so that we are ready to handle unpredicted growth and scale.

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• Precise: Evolution laggy due to IMAP -profile or due to some odd Sync -issue?

  - by Izzy

  I'm fighting with Evolution. Basically it's working fine -- but it is very slow to react in certain situations. There is apparently some problem with syncing and IMAP. Helper questios Could be that changing away from Bonobo has to do with slowing-down? There might be some trouble with the new engine and "asynchronous actions". What to do about it? I want to get the previous "working mood" back. How can I speed this thing up? Different scenarios when sending a mail, the composer window hangs there inactive for a couple of seconds, everything grayed out. Though there is a green check mark saying it's sent, I'm not sure a) why it's still blocking everything and b) whether I could simply close it without "breaking"/"losing" anything. In earlier versions, the composer window was closing pretty fast, and one could see the message being stored into the local "outbox" until it was sent, and one could immediately continue with the next task. I prefer that behaviour over the current. switching between modules. Coming from mail and switching to the address book takes a couple of seconds. Same for switching to the calendar. I read about different "possible causes" and tried a few things: I only have 3 local address books, so no networking should be involved here. To make sure, I switched to offline mode and then tried to access the address book. No noticeable difference. I use 3 Google Calendars. Switching to offline mode made a minor difference, but so minor that it also could be "imagination" since one might have expected this in this case according to some reports, disabling the tasks should help. Well, it didn't in my case, as I don't use them regularly (just two local items stored here)

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• Is the way I'm implementing my genetic algorithm right?

  - by Mhjr

  In my graduation project, I am asked to use a genetic algorithm (any variation of it can be chosen) to generate valid timetables. What I did was make a simple program that generates unique sequences representing genes, the sequence is described below: (sorry if it's mathematically incorrect) The only variable in the sequence is the room element, so basically the program takes a tree that goes like this: [Course] -(contains)-> [Units] -(contains)-> [Offerings] -(contains)-> [Instructors] -(contains)-> [Rooms] Each course can have n units (duplicates). Each unit can have n offerings (lectures,lab session, excercises,...). Each offering has only 1 instructor. Each instructor (or the whole lecture composed from the four elements of the sequence) has multiple rooms. When a timetable is initialized, one of these sequences that differ in rooms will be taken into the timetable, so the difference in genes (sequences) of each timetable will be just the rooms random choice and the difference between chromosomes (timetables) will be time placements of these genes (sequences). My question is, before I proceed in implementing what I described, is it valid? Is the representation used here for chromosomes a permutation representation?

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• What is the program "Additional Drivers" (jockey-gtk) talking me about?

  - by Robert Vila

  The program says: "No proprietary drivers are in use on this system" But it doesn't say if it is talking about graphical drivers only or what. Then, it lists two drivers: NVIDIA accelerated graphics driver (version 173). NVIDIA accelerated graphics driver (version current) [recomended] Both have exactly the same description. What is the difference then? When I select the 1st one, it says: "This river is not activated",and there's a button to "activate" it. When I select the 2nd one, it says: "This river is activated but it is not currently in use", and the button is to "remove". So which one is in use? Why or what for should I have activated (enabled) and not in use? If it is in use it is activated? What is the difference between activate and remove? and what is the relationship between installed, activated, in use, enabled and removed, disabled, inactive and not-installed? Why can I activate the inactivated and remove (but not deactivate) the activated that is not in use? All this is very puzzling... What other drivers can I use for an Apple MacBook pro 3,1 and how? I see that there's a nouveau and I heard that there was going to be a new open source even better. > -display > description: VGA compatible controller > product: G84 [GeForce 8600M GT] > vendor: nVidia Corporation

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• Hosting and scaling a Facebook application in the cloud? [migrated]

  - by DhruvPathak

  We would be building a Facebook application in Django (Python), but still not sure of where to host it economically, and with a good provision to scale in case the app gets viral. Some details about the app: Would be HTML based like a website,using django as a framework. 100K is the number of expected pageviews in a day, if the app is viral. The users will not generate any media content, only some database data will be generated by them. It would be great if someone with more experience can guide on following points: A) Hosting on Google app engine or Amazon EC2 or some other cloud like RackSpace : Preferable points found in AppEngine were ease of deployment, cost effectiveness and easy scaling. For EC2: Full hold of the virtual machine,Amazon NoSQL and RDMBS database services in case we decide to use them. B) Does backend technology affect monthly cost? eg. would CPU and memory usage difference of Django over , for example , PHP framework like CodeIgnitor really make remarkable difference in running costs. (Here is the article that triggered this thought process : http://journal.dedasys.com/2010/01/12/rough-estimates-of-the-dollar-cost-of-scaling-web-platforms-part-i#comments) C) Does something like Heroku , which provides additional services over Amazon EC2, prove to be better than raw cloud management? It is not that we are trying for premature scaling, we just want to have a good start so that we are ready to handle unpredicted growth and scale.

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• Is there a PROPRIETARY driver (NVIDIA or ATI) that actually works with 12.10?

  - by DS13

  NOTE: I see many similar topics on this, but I've tried all their suggestions, and nothing has worked. THE MAIN DIFFERENCE SEEMS TO BE: I always get a black screen with a blinking cursor, while others seem to get through the boot-up and see distorted graphics or just their wallpaper. ISSUE: I do a clean install of Ubuntu 12.10. Boots fine with the “nouveau” graphics driver – graphics (even just menus) are very slow, choppy, and distorted. The three other driver options in Ubuntu (official NVIDIA drivers), all result in a variation of the black screen on boot up. There will be NO access to a command line/GUI in anyway what-so-ever (tried every option recommended out there, but the system is unusable at this stage). I can only reinstall, and try different drivers…and I only ever get one shot at it. QUESTIONS: -Does anyone know of a PROPRIETARY driver that will actually work on 12.10 with a NVIDIA or ATI card? -Should I just buy a newer graphics card to put in as a replacement? MORE INFO: This is my second computer, and I’m just trying to get a working install of Ubuntu on it. I don’t want to put much money into it, as I have seen Ubuntu run great on much older/less capable machines. I’ve got a decent'ish Core2Duo Intel processor (2.13Ghz), 2GB of RAM, 320GB hard drive, 32-bit architecture, and there is no other O/S installed. It appears as if the graphics card (NVIDIA Geforce 7350 LE) is holding me back. TRIED SO FAR: -all drivers available in Ubuntu *all fail -manual install of some different NVIDIA drivers *all fail -also tried installing the generic kernel, Nvidia driver doesn't work in 12.10 *no difference -tried installing 12.04 *same results -every method suggested to at least get a command line after switching to a NVIDIA driver *all fail -UPDATE- Re-tried everything above with a new NVIDIA Geforce 210...same results for everything. -UPDATE #2- Re-tried everything above with a new AMD Radeon HD 6450...installed the proprietary driver from Ubuntu's "Software Sources" menu...EVERYTHING NOW WORKS. See "answer" below for summary.

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• Context switches much slower in new linux kernels

  - by Michael Goldshteyn

  We are looking to upgrade the OS on our servers from Ubuntu 10.04 LTS to Ubuntu 12.04 LTS. Unfortunately, it seems that the latency to run a thread that has become runnable has significantly increased from the 2.6 kernel to the 3.2 kernel. In fact the latency numbers we are getting are hard to believe. Let me be more specific about the test. We have a program that has two threads. The first thread gets the current time (in ticks using RDTSC) and then signals a condition variable once a second. The second thread waits on the condition variable and wakes up when it is signaled. It then gets the current time (in ticks using RDTSC). The difference between the time in the second thread and the time in the first thread is computed and displayed on the console. After this the second thread waits on the condition variable once more. So, we get a thread to thread signaling latency measurement once a second as a result. In linux 2.6.32, this latency is somewhere on the order of 2.8-3.5 us, which is reasonable. In linux 3.2.0, this latency is somewhere on the order of 40-100 us. I have excluded any differences in hardware between the two host hosts. They run on identical hardware (dual socket X5687 {Westmere-EP} processors running at 3.6 GHz with hyperthreading, speedstep and all C states turned off). We are changing the affinity to run both threads on physical cores of the same socket (i.e., the first thread is run on Core 0 and the second thread is run on Core 1), so there is no bouncing of threads on cores or bouncing/communication between sockets. The only difference between the two hosts is that one is running Ubuntu 10.04 LTS with kernel 2.6.32-28 (the fast context switch box) and the other is running the latest Ubuntu 12.04 LTS with kernel 3.2.0-23 (the slow context switch box). Have there been any changes in the kernel that could account for this ridiculous slow down in how long it takes for a thread to be scheduled to run?

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• What's the benefit to learn Java programming?

  - by user30139

  I'm from the PHP world. Recently I'm trying to learn about Java. Because simply I'm a bit interested in Android development. Learning about Java gives more control about my cellphone. Say I could fine tune some applications to fit my personal requirements or even make my own ones. Still Java is a new world to me. I guess I'm already too comfortable with weak typed languages such as PHP. Honestly I think application development of no matter which kind wouldn't make too much difference. Because just as web development mostly framework based, what the developer do is to fill the blanks meaning to follow the protocols the given by the framework. Most of the code is still about business logic, that's what application development all about, right? The big difference seems to lie on the programming languages. Comparing to PHP, Java holds a whole package of constraints and practices. At this point, what are the benefits to learn programming in it?

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• More Win 8 Education is Needed

  - by D'Arcy Lussier

  “My mail doesn’t work”. That’s what a colleague running Windows 8 said to me the day after he installed Windows 8 on his work laptop. “When I click my email, nothing comes up.” I took a look and realized what was going on – he was clicking the Windows 8 UI Mail app and assumed that this was somehow connected to his Outlook which was installed as a desktop app. And so highlights a major educational challenge that Windows 8 will encounter – millions of users used to one style of interface now being introduced to a new one that runs side-by-side with their desktop. At work we had an internal tech user group meeting, and we were showing new features of VS.NET 2012 and Windows 8. When we started talking about the difference between Windows 8 UI Apps (AKA Windows Store Apps), people started asking some good questions: - Can we share a codebase between desktop and Windows Store Apps? - What’s the difference between WinRT and .NET? - Why would we create a Windows Store App and not just a Desktop app? Of course, people are looking at this from a traditional desktop point of view and not a tablet platform, which is really the market that Windows Store Apps will shine on. Still, for developers who not only need to educate themselves but also educate their clients, we’re going to need a better understanding of Windows 8 to see it get real traction within the business/enterprise market. D

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• How to synchronize a whole Ubuntu?

  - by Avio

  I think that the time is ripe to have my whole Ubuntu synchronized just as my Dropbox folder is. Given that we are always talking about files and directories, what's the difference between my Documents folder and my /usr system directory? Almost none, except for their location. In fact, I think that there is just one big issue that prevents people to have their beloved installations mirrored wherever they go: symlinks. Dropbox, Google Drive, Ubuntu One, Sugarsync, Skydrive, none of these services support symlinking. This means that if I push a symlink in one of the synced folders, locally the symlink is kept as is, but remotely (in the cloud or on the other synced machines) the symlink is resolved to the actual file that was originally pointed to. This completely disrupts Linux installations, thus these services can't be used for this purpose. So the question is. Does anybody knows a way to achieve this? A whole Ubuntu, always synchronized with a remote running copy, but still locally stored on both disks? My best guess is that I could use NFS. But the main difference between Dropbox and NFS is that NFS is a remote filesystem that always forces to remotely access the files, while Dropbox pushes modifcations to local filesystems (and thus would perform better). I've also heard about NFS caching. Does anybody knows if this solution could approximate Dropbox in this sense? P.s. I know that /boot, /dev, /proc, /run, /tmp and device-specific mountpoints in /mnt and /media will have to be left out the sync mechanism. What I'm interested in is the principle. Can this be done with reasonable performance, having reasonable resources (e.g. ~ 1Mbps upload bandwidth and a public IP address)?

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• Hosting and scaling a Facebook application in the cloud? [closed]

  - by DhruvPathak

  Possible Duplicate: How to find web hosting that meets my requirements? We would be building a Facebook application in Django (Python), but still not sure of where to host it economically, and with a good provision to scale in case the app gets viral. Some details about the app: Would be HTML based like a website,using django as a framework. 100K is the number of expected pageviews in a day, if the app is viral. The users will not generate any media content, only some database data will be generated by them. It would be great if someone with more experience can guide on following points: A) Hosting on Google app engine or Amazon EC2 or some other cloud like RackSpace : Preferable points found in AppEngine were ease of deployment, cost effectiveness and easy scaling. For EC2: Full hold of the virtual machine,Amazon NoSQL and RDMBS database services in case we decide to use them. B) Does backend technology affect monthly cost? eg. would CPU and memory usage difference of Django over , for example , PHP framework like CodeIgnitor really make remarkable difference in running costs. (Here is the article that triggered this thought process : http://journal.dedasys.com/2010/01/12/rough-estimates-of-the-dollar-cost-of-scaling-web-platforms-part-i#comments) C) Does something like Heroku , which provides additional services over Amazon EC2, prove to be better than raw cloud management? It is not that we are trying for premature scaling, we just want to have a good start so that we are ready to handle unpredicted growth and scale.

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• Loading PNGs into OpenGL performance issues - Java & JOGL much slower than C# & Tao.OpenGL

  - by Edward Cresswell

  I am noticing a large performance difference between Java & JOGL and C# & Tao.OpenGL when both loading PNGs from storage into memory, and when loading that BufferedImage (java) or Bitmap (C# - both are PNGs on hard drive) 'into' OpenGL. This difference is quite large, so I assumed I was doing something wrong, however after quite a lot of searching and trying different loading techniques I've been unable to reduce this difference. With Java I get an image loaded in 248ms and loaded into OpenGL in 728ms The same on C# takes 54ms to load the image, and 34ms to load/create texture. The image in question above is a PNG containing transparency, sized 7200x255, used for a 2D animated sprite. I realise the size is really quite ridiculous and am considering cutting up the sprite, however the large difference is still there (and confusing). On the Java side the code looks like this: BufferedImage image = ImageIO.read(new File(fileName)); texture = TextureIO.newTexture(image, false); texture.setTexParameteri(GL.GL_TEXTURE_MIN_FILTER, GL.GL_LINEAR); texture.setTexParameteri(GL.GL_TEXTURE_MAG_FILTER, GL.GL_LINEAR); The C# code uses: Bitmap t = new Bitmap(fileName); t.RotateFlip(RotateFlipType.RotateNoneFlipY); Rectangle r = new Rectangle(0, 0, t.Width, t.Height); BitmapData bd = t.LockBits(r, ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb); Gl.glBindTexture(Gl.GL_TEXTURE_2D, tID); Gl.glTexImage2D(Gl.GL_TEXTURE_2D, 0, Gl.GL_RGBA, t.Width, t.Height, 0, Gl.GL_BGRA, Gl.GL_UNSIGNED_BYTE, bd.Scan0); Gl.glTexParameteri(Gl.GL_TEXTURE_2D, Gl.GL_TEXTURE_MIN_FILTER, Gl.GL_LINEAR); Gl.glTexParameteri(Gl.GL_TEXTURE_2D, Gl.GL_TEXTURE_MAG_FILTER, Gl.GL_LINEAR); t.UnlockBits(bd); t.Dispose(); After quite a lot of testing I can only come to the conclusion that Java/JOGL is just slower here - PNG reading might not be as quick, or that I'm still doing something wrong. Thanks. Edit2: I have found that creating a new BufferedImage with format TYPE_INT_ARGB_PRE decreases OpenGL texture load time by almost half - this includes having to create the new BufferedImage, getting the Graphics2D from it and then rendering the previously loaded image to it. Edit3: Benchmark results for 5 variations. I wrote a small benchmarking tool, the following results come from loading a set of 33 pngs, most are very wide, 5 times. testStart: ImageIO.read(file) -> TextureIO.newTexture(image) result: avg = 10250ms, total = 51251 testStart: ImageIO.read(bis) -> TextureIO.newTexture(image) result: avg = 10029ms, total = 50147 testStart: ImageIO.read(file) -> TextureIO.newTexture(argbImage) result: avg = 5343ms, total = 26717 testStart: ImageIO.read(bis) -> TextureIO.newTexture(argbImage) result: avg = 5534ms, total = 27673 testStart: TextureIO.newTexture(file) result: avg = 10395ms, total = 51979 ImageIO.read(bis) refers to the technique described in James Branigan's answer below. argbImage refers to the technique described in my previous edit: img = ImageIO.read(file); argbImg = new BufferedImage(img.getWidth(), img.getHeight(), TYPE_INT_ARGB_PRE); g = argbImg.createGraphics(); g.drawImage(img, 0, 0, null); texture = TextureIO.newTexture(argbImg, false); Any more methods of loading (either images from file, or images to OpenGL) would be appreciated, I will update these benchmarks.

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• Ball to Ball Collision - Detection and Handling

  - by Simucal

  With the help of the Stack Overflow community I've written a pretty basic-but fun physics simulator. You click and drag the mouse to launch a ball. It will bounce around and eventually stop on the "floor". My next big feature I want to add in is ball to ball collision. The ball's movement is broken up into a x and y speed vector. I have gravity (small reduction of the y vector each step), I have friction (small reduction of both vectors each collision with a wall). The balls honestly move around in a surprisingly realistic way. I guess my question has two parts: What is the best method to detect ball to ball collision? Do I just have an O(n^2) loop that iterates over each ball and checks every other ball to see if it's radius overlaps? What equations do I use to handle the ball to ball collisions? Physics 101 How does it effect the two balls speed x/y vectors? What is the resulting direction the two balls head off in? How do I apply this to each ball? Handling the collision detection of the "walls" and the resulting vector changes were easy but I see more complications with ball-ball collisions. With walls I simply had to take the negative of the appropriate x or y vector and off it would go in the correct direction. With balls I don't think it is that way. Some quick clarifications: for simplicity I'm ok with a perfectly elastic collision for now, also all my balls have the same mass right now, but I might change that in the future. In case anyone is interested in playing with the simulator I have made so far, I've uploaded the source here (EDIT: Check the updated source below). Edit: Resources I have found useful 2d Ball physics with vectors: 2-Dimensional Collisions Without Trigonometry.pdf 2d Ball collision detection example: Adding Collision Detection Success! I have the ball collision detection and response working great! Relevant code: Collision Detection: for (int i = 0; i < ballCount; i++) { for (int j = i + 1; j < ballCount; j++) { if (balls[i].colliding(balls[j])) { balls[i].resolveCollision(balls[j]); } } } This will check for collisions between every ball but skip redundant checks (if you have to check if ball 1 collides with ball 2 then you don't need to check if ball 2 collides with ball 1. Also, it skips checking for collisions with itself). Then, in my ball class I have my colliding() and resolveCollision() methods: public boolean colliding(Ball ball) { float xd = position.getX() - ball.position.getX(); float yd = position.getY() - ball.position.getY(); float sumRadius = getRadius() + ball.getRadius(); float sqrRadius = sumRadius * sumRadius; float distSqr = (xd * xd) + (yd * yd); if (distSqr <= sqrRadius) { return true; } return false; } public void resolveCollision(Ball ball) { // get the mtd Vector2d delta = (position.subtract(ball.position)); float d = delta.getLength(); // minimum translation distance to push balls apart after intersecting Vector2d mtd = delta.multiply(((getRadius() + ball.getRadius())-d)/d); // resolve intersection -- // inverse mass quantities float im1 = 1 / getMass(); float im2 = 1 / ball.getMass(); // push-pull them apart based off their mass position = position.add(mtd.multiply(im1 / (im1 + im2))); ball.position = ball.position.subtract(mtd.multiply(im2 / (im1 + im2))); // impact speed Vector2d v = (this.velocity.subtract(ball.velocity)); float vn = v.dot(mtd.normalize()); // sphere intersecting but moving away from each other already if (vn > 0.0f) return; // collision impulse float i = (-(1.0f + Constants.restitution) * vn) / (im1 + im2); Vector2d impulse = mtd.multiply(i); // change in momentum this.velocity = this.velocity.add(impulse.multiply(im1)); ball.velocity = ball.velocity.subtract(impulse.multiply(im2)); } Source Code: Complete source for ball to ball collider. Binary: Compiled binary in case you just want to try bouncing some balls around. If anyone has some suggestions for how to improve this basic physics simulator let me know! One thing I have yet to add is angular momentum so the balls will roll more realistically. Any other suggestions? Leave a comment!

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