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  • Hyper-V Virtual Machine Networking issues related to Max Ethernet Frame Size

    - by Goatmale
    I fixed an issue today earlier today but i'm interested in learning WHY it worked. We set up a new Hyper-V virtual machine only to discover that HTTP traffic wasn't working. HTTPS, pings, everything else was working fine. After months of prodding around I took a shot in the dark. On the Hyper-V host server, the physical NIC card had an advanced setting of "Max Ethernet Frame Size" set to 1500. After setting this setting to 1514 the issue was fixed. Alternatively, setting this to 1512 did not solve the issue; 1514 is the magic number. My best guess it that when this setting was set to 1500 it was allowing incoming pings because the data payload was a lot smaller of say, HTTP traffic. As far as HTTPS traffic, I read about something called "Path MTU discovery" which i'm going to assume why is HTTPs traffic was getting through fine, albeit slower. Looking at this post, people agree that 1518 is the max total frame size. Why didn't I need to change this to 1518 instead of 1514 bytes? Why is the default frame size 1500 if that's the max size of the Ethernet payload and not the max size.

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  • Reduce power consumption of gaming computer while idle

    - by White Phoenix
    This is my current build: EVGA X58 (first generation) motherboard Intel i7 965 clocked @ 3.3 Ghz 3x DDR3-1600 Corsair RAM at stock timings and voltages Corsair AX750 80 Plus Gold PSU 1 Optical Drive 1 Seagate 7200.10 500 GB drive 2x Western Digital Caviar Black 1 TB drives OCZ Vertex 1 60 GB EVGA GTX 460 oc'd at 800/1600/1850 Antec 1200 case HT-Omega Striker 7.1 Sound Card Windows 7 32-bit Professional (PAE Enabled) I've already seen this post Reduce power use on computer and this post How do I lower power consumption of my computer and while useful, I'm looking for answers specific to my build and OS. I'm pretty sure this build is a energy-intensive build by default, but I want to try to reduce the amount of energy my build uses when I leave it idle (when I go to bed or go out, etc). The first requirement for this machine is that I need to leave it on, so I cannot turn it off while it's being unused. I run it as a file server for personal reasons and I also leave it on in case people leave me messages on various IM services and chat clients (IRC, MSN, Steam, XFire, Pidgin, etc). I'm also unable to replace the parts in my computer with a cheaper "greener" part. What are some ways to minimize the amount of power the machine uses? I'm already using a high efficiency power supply (80 Plus Gold), but I imagine there's other things that can be done in the BIOS and Windows' power settings to reduce power usage while I'm not using the computer. From what I can tell, I can't use Sleep since that'll disable network access (whole reason why I leave the computer on in the first place). I already turn off my monitor when it's not in use. I enabled Intel SpeedStep within the BIOS (I know, I have a 965 and why am I enabling SpeedStep?) Should I bring the graphics card back to stock speeds and lower the clock on the processor even more? Main reason why I'm asking is I think this computer alone is the reason why my power bill is high, so I want to reduce its consumption to as low as possible without having to shut the thing down.

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  • SQL Server 2008 Web VS SQL Server 2008 Enterprise

    - by Jeremy
    I wrote an application a few months ago, and was hosting it out of our offices on a workstation with an Intel Core 2 Quad Q8200 @ 2.33GHz, 8 GB RAM, Windows Server 2008 Enterprise and SQL Server 2008 Enterprise. Both the webserver and database server were run on the same machine. We had a huge influx in traffic, and moved ClubUptime.com, and got 2 of their top teir windows VMs. The Database server runs Windows 2008 R2 Standard and SQL Server 2008 R2 Web on 8 GB ram and an Intel Xeon e5620 @ 2.40GHz. Ever since switching, the database which used to run at around 400MB in RAM now runs at around 4-7GB, and there haven't been any changes to it (other than a couple columns here and there). Our traffic has quadrupled, and our DB is 6 GB on disk, why would SQL server take up 7 GB if the DB is only 6. And why would it be storing the ENTIRE database in memory? Another thing is why growing 4 times in size did the database's memory footprint grow 12 times? Last question: Why does the CPU peg at 100% now where it didn't before? The design is simple, VERY few joins, NO subqueries. I am just at a loss, unless it is the SQL server edition, or the fact that I moved from real hardware to a VM.

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  • Disadvantages of enabling 'Low Fragmentation Heap' LFH on Windows Server 2003?

    - by James Wiseman
    I've been investigating an issue with a production Classic ASP website running on IIS6 which seems indicative of memory fragmentation. One of the suggestions of how to ameliorate this came from Stackoverflow: How can I find why some classic asp pages randomly take a real long time to execute?. It suggested flipping a setting in the site's global.asa file to 'turn on' Low Fragmentation Heap (LFH). The following code (with a registered version of the accompanying DLL) did the trick. Set LFHObj=CreateObject("TURNONLFH.ObjTurnOnLFH") LFHObj.TurnOnLFH() application("TurnOnLFHResult")=CStr(LFHObj.TurnOnLFHResult) (Really the code isn't that important to the question). An author of a linked post reported a seemingly magic resolution to this issue, and, reading around a little more, I discovered that this setting is enabled by default on Windows Server 2008. So, naturally, this left me a little concerned: Why is this setting not enabled by default on 2003, or If it works in 2008 why have Microsoft not issued a patch to enable it by default on 2003? I suspect the answer to the above is the same for both (if there is one). Obviously, we're testing it in a non-production environment, and doing an array of metrics and comparisons to deem if it does help us. But aside from this I'm really just trying to understand if there's any technical reason why we should do this, or if there are any gotchas that we need to be aware of.

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  • Online computer not responding to pings

    - by mastercork889
    I was doing a bit of scanning on my network lately, knew all the hostnames to each computer connected. But whilst pinging one of them ping returned Request timed out.. This is strange as I know the computer is online and that the computer responds correctly to pinging on a different (enterprise) network. Is there something on the computer, my network, or my computer that is bugging with this? - That's just a sub-question, I don't expect this to be the main answer. The real question: Why does this happen? Why does pinging the IP4 address not work? EDIT : Pinging the Hostname used to default to the IP4 address, but now it defaults to the IP6 address. Why does this happen? But now that it pings using IP6, how come it all of a sudden works? > ping -6 THE_COMPUTER Pinging THE_COMPUTER [lengthy IP6 address] with 32 bytes of data: Reply from [lengthy IP6 address]: time=1ms Reply from [lengthy IP6 address]: time=1ms Reply from [lengthy IP6 address]: time=1ms Reply from [lengthy IP6 address]: time=1ms Ping stats: Sent = 4, Recieved = 4, Lost = 0 (0% loss) But when this is done using IP4 it doesn't work. So there are now two questions: How come IP6 works and not IP4? Why does IP4 not work?

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  • SeLinux blocking connection to sshd on Ubuntu 9.10

    - by Barton Chittenden
    When I try to log on to my laptop, which runs Ubuntu 9.10, the server rejects my login attempts. Checking /var/log/auth.log, I see the following: Feb 14 12:41:16 tiger-laptop sshd[6798]: error: ssh_selinux_getctxbyname: Failed to get default SELinux security context for tiger I googled for this, and ran across the following: http://www.spinics.net/lists/fedora-.../msg13049.html Here's the part that I think relates to the problem that I'm having: Quote: What's wrong on my system? Why it's not possible to login even if selinux is in permissive mode? Any suggestions? I'd start by trying to figure out why sshd isn't running in sshd_t (it seems to be running in sysadm_t). Paul. selinux mailing list selinux@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mail...stinfo/selinux Yes, sshd is running in sysadm_t: ps axZ | grep sshd system_u:system_r:sysadm_t 3632 ? Ss 0:00 /usr/sbin/sshd -o PidFile=/var/run/sshd.init.pi ls -Z /usr/sbin/sshd system_ubject_r:sshd_exec_t /usr/sbin/sshd Don't know why it's not sshd_t. I didn't modified something. It's a standard installation of sles11 with the default reference policy from tresys. Maybe this code snippet from policy/modules/services/ssh.te is responsible for that: Allow ssh logins as sysadm_r:sysadm_t gen_tunable(ssh_sysadm_login, true) Any ideas? Do you have boolean init_upstart set to on? if not try setting it to on. I do not believe ssh_sysadm_login boolean works currently but i may be mistaken. -- Yeah, setting init_upstart to on did the trick! THANK A LOT! Do you know why this prevents the user from logging in through ssh even if selinux is set to permissive?? Ok, so the million dollar question is "where do I set 'init_upstart=1'"? It's not clear from context which configuration file needs to be edited, and I'm not at all familiar with SELinux configuration.

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  • Partitioning & Linux

    - by Zac
    Every tutorial on Linux-based partitioning schemes (or, just partitioning in general) will tell you that a PC can have either 4 primary partitions, or 3 primaries and 1 extended. They will all also tell you that Linux (in my case, Ubuntu) can be installed on either. It's also come to my attention that it is not too atypical for FHS directories, such as usr/, tmp/, etc/, home/ or var/ to be mounted separately on other partitions. Several questions I am unable to find the answers to, purely for my own edification: (1) By "PC", are we really talking about common PC disk types, like IDE or SATA? I guess I'm wondering why PC uses are limited to 4 primaries or 3 primaries + 1 extended (2) I'm choking on some basic OS concepts: it is said that a partition can be mounted by a file system or an OS. So I assume this means I can somehow instruct Ubuntu to mount to 1 partition, and then any part of, say, ReiserFS, to be mounted to another partition? How? (3)(a) What about creating swap partitions? Is there too much of a good thing with swap partitioning? If I have 4GB RAM over 320GB disk, what should my swap partition size be, and why? (3)(b) Are swap files the only way to create swap partitions? Wouldn't a Linux partitioning utility allow me to define a partition as being for virtual memory only? (4) Why are partitions limited to being "mounted" by just OSes and file systems? Why couldn't I write a program to take up its own, say, 512 MB partition, and then have it invoked or uses by an OS installed on another partition? Thanks for shedding any light here... not critical that I know this stuff, but it's got me thinking incessantly. And when I think incessantly, I...can't......sleep....

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  • Command prompt cannot find PATH variable

    - by davidXYZ
    Sometimes, my command prompt cannot find the PATH variable. I have this occasional problem at work where when I open command-prompt and run commands like ipconfig or subst, I get an error saying something like 'ipconfig' is not recognized as an internal or external command. When I try this echo %path%, it prints out %path% instead of the PATH value. If I look at my Environment Variables window, the PATH is defined right there but I don't know why CMD can't find it. At this point, I understand why the other commands were not being recognized since their paths are in PATH variable. However, I cannot understand why the PATH variable is not being found. If I restart the computer, everything is back to normal. In a few days, I might have the same experience again. I tried using this answer. It suggested changing a registry value but mine already had the value that was suggested yet it wasn't working. (The restart step at the end would have solved it as usual but that's not the point.) Any suggestions regarding why the PATH variable may become invisible every now and then and how I can prevent it from happening again?

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  • How Expedia Made My New Bride Cry

    - by Lance Robinson
    Tweet this? Email Expedia and ask them to give me and my new wife our honeymoon? When Expedia followed up their failure with our honeymoon trip with a complete and total lack of acknowledgement of any responsibility for the problem and endless loops of explaining the issue over and over again - I swore that they would make it right. When they brought my new bride to tears, I got an immediate and endless supply of motivation. I hope you will help me make them make it right by posting our story on Twitter, Facebook, your blog, on Expedia itself, and when talking to your friends in person about their own travel plans.   If you are considering using them now for an important trip - reconsider. Short summary: We arrived early for a flight - but Expedia had made a mistake with the data they supplied to JetBlue and Emirates, which resulted in us not being able to check in (one leg of our trip was missing)!  At the time of this post, three people (myself, my wife, and an exceptionally patient JetBlue employee named Mary) each spent hours on the phone with Expedia.  I myself spent right at 3 hours (according to iPhone records), Lauren spent an hour and a half or so, and poor Mary was probably on the phone for a good 3.5 hours.  This is after 5 hours total at the airport.  If you add up our phone time, that is nearly 8 hours of phone time over a 5 hour period with little or no help, stall tactics (?), run-around, denial, shifting of blame, and holding. Details below (times are approximate): First, my wife and I were married yesterday - June 18th, the 3 year anniversary of our first date. She is awesome. She is the nicest person I have ever known, a ton of fun, absolutely beautiful in every way. Ok enough mushy - here are the dirty details. 2:30 AM - Early Check-in Attempt - we attempted to check-in for our flight online. Some sort of technology error on website, instructed to checkin at desk. 4:30 AM - Arrive at airport. Try to check-in at kiosk, get the same error. We got to the JetBlue desk at RDU International Airport, where Mary helped us. Mary discovered that the Expedia provided itinerary does not match the Expedia provided tickets. We are informed that when that happens American, JetBlue, and others that use the same software cannot check you in for the flight because. Why? Because the itinerary was missing a leg of our flight! Basically we were not shown in the system as definitely being able to make it home. Mary called Expedia and was put on hold by their automated system. 4:55 AM - Mary, myself, and my brand new bride all waited for about 25 minutes when finally I decided I would make a call myself on my iPhone while Mary was on the airport phone. In their automated system, I chose "make a new reservation", thinking they might answer a little more quickly than "customer service". Not surprisingly I was connected to an Expedia person within 1 minute. They informed me that they would have to forward me to a customer service specialist. I explained to them that we were already on hold for that and had been for nearly half an hour, that we were going on our honeymoon and that our flight would be leaving soon - could they please help us. "Yes, I will help you". I hand the phone to JetBlue Mary who explains the situation 3 or 4 times. Obviously I couldn't hear both ends of the conversation at this point, but the Expedia person explained what the problem was by stating exactly what Mary had just spent 15 minutes explaining. Mary calmly confirms that this is the problem, and asks Expedia to re-issue the itinerary. Expedia tells Mary that they'll have to transfer her to customer service. Mary asks for someone specific so that we get an answer this time, and goes on hold. Mary get's connected, explains the situation, and then Mary's connection gets terminated. 5:10 AM - Mary calls back to the Expedia automated system again, and we wait for about 5 minutes on hold this time before I pick up my iPhone and call Expedia again myself. Again I go to sales, a person picks up the phone in less than a minute. I explain the situation and let them know that we are now very close to missing our flight for our honeymoon, could they please help us. "Yes, I will help you". Again I give the phone to Mary who provides them with a call back number in case we get disconnected again and explains the situation again. More back and forth with Expedia doing nothing but repeating the same questions, Mary answering the questions with the same information she provided in the original explanation, and Expedia simply restating the problem. Mary again asks them to re-issue the itinerary, and explains that doing so will fix the problem. Expedia again repeats the problem instead of fixing it, and Mary's connection gets terminated. 5:20 AM - Mary again calls back to Expedia. My beautiful bride also calls on her own phone. At this point she is struggling to hold back her tears, stumbling through an explanation of all that has happened and that we are about to miss our flight. Please help us. "Yes, I will help". My beautiful bride's connection gets terminated. Ok, maybe this disconnection isn't an accident. We've now been disconnected 3 times on two different phones. 5:45 AM - I walk away and pleadingly beg a person to help me. They "escalate" the issue to "Rosy" (sp?) at Expedia. I go through the whole song and dance again with Rosy, who gives me the same treatment Mary was given. Rosy blames JetBlue for now having the correct data. Meanwhile Mary is on the phone with Emirates Air (the airline for the second leg of our trip), who agrees with JetBlue that Expedia's data isn't up to date. We are informed by two airport employees that issues like this with Expedia are not uncommon, and that the fix is simple. On the phone iwth Rosy, I ask her to re-issue the itinerary because we are about to miss our flight. She again explains the problem to me. At this point, I am standing at the window, pleading with Rosy to help us get to our honeymoon, watching our airplane. Then our airplane leaves without us. 6:03 AM - At this point we have missed our flight. Re-issuing the itinerary is no longer a solution. I ask Rosy to start from the beginning and work us up a new trip. She says that she cannot do that. She says that she needs to talk to JetBlue and Emirates and find out why we cannot check-in for our flight. I remind Rosy that our flight has already left - I just watched it taxi away - it no longer matters why (not to mention the fact that we already knew why, and have known why since 4:30 AM), and have known the solution since 4:30 AM. Rosy, can you please book a new trip? Yes, but it will cost $400. Excuse me? Now you can, but it will cost ME to fix your mistake? Rosy says that she can escalate the situation to her supervisor but that will take 1.5 hours. 6:15 AM - I told Rosy that if they had re-issued the itinerary as JetBlue asked (at 4:30 AM), my new wife and I might be on the airplane now instead of dealing with this on the phone and missing the beginning (and how much more?) of our honeymoon. Rosy said that it was not necessary to re-issue the itinerary. Out of curiosity, i asked Rosy if there was some financial burden on them to re-issue the itinerary. "No", said Rosy. I asked her if it was a large time burden on Expedia to re-issue the itinerary. "No", said Rosy. I directly asked Rosy: Why wouldn't Expedia have re-issued the itinerary when JetBlue asked? No answer. I asked Rosy: If you had re-issued the itinerary at 4:30, isn't it possible that I would be on that flight right now? She actually surprised me by answering "Yes" to that question. So I pointed out that it followed that Expedia was responsible for the fact that we missed out flight, and she immediately went into more about how the problem was with JetBlue - but now it was ALSO an Emirates Air problem as well. I tell Rosy to go ahead and escalate the issue again, and please call me back in that 1.5 hours (which how is about 1 hour and 10 minutes away). 6:30 AM - I start tweeting my frustration with iPhone. It's now pretty much impossible for us to make it to The Maldives by 3pm, which is the time at which we would need to arrive in order to be allowed service to the actual island where we are staying. Expedia has now given me the run-around for 2 hours, caused me to miss my flight, and worst of all caused my amazing new wife Lauren to miss our honeymoon. You think I was mad? No. Furious. Its ok to make mistakes - but to refuse to fix them and to ruin our honeymoon? No, not ok, Expedia. I swore right then that Expedia would make this right. 7:45 AM - JetBlue mary is still talking her tail off to other people in JetBlue and Emirates Air. Mary works it out so that if Expedia simply books a new trip, JetBlue and Emirates will both waive all the fees. Now we just have to convince Expedia to fix their mistake and get us on our way! Around this time Expedia Rosy calls me back! I inform her of the excellent work of JetBlue Mary - that JetBlue and Emirates both will waive the fees so Expedia can fix their mistake and get us going on our way. She says that she sees documentation of this in her system and that she needs to put me on hold "for 1 to 10 minutes" to talk to Emirates Air (why I'm not exactly sure). I say ok. 8:45 AM - After an hour on hold, Rosy comes on the line and asks me to hold more. I ask her to call me back. 9:35 AM - I put down the iPhone Twitter app and picks up the laptop. You think I made some noise with my iPhone? Heh 11:25 AM - Expedia follows me and sends a canned "We're sorry, DM us the details".  If you look at their Twitter feed, 16 out of the most recent 20 tweets are exactly the same canned response.  The other 4?  Ads.  Um - #MultiFAIL? To Expedia:  You now have had (as explained above) 8 hours of 3 different people explaining our situation, you know the email address of our Expedia account, you know my web blog, you know my Twitter address, you know my phone number.  You also know how upset you have made both me and my new bride by treating us with such a ... non caring, scripted, uncooperative, argumentative, and possibly even deceitful manner.  In the wise words of the great Kenan Thompson of SNL: "FIX IT!".  And no, I'm NOT going away until you make this right. Period. 11:45 AM - Expedia corporate office called.  The woman I spoke to was very nice and apologetic.  She listened to me tell the story again, she says she understands the problem and she is going to work to resolve it.  I don't have any details on what exactly that resolution might me, she said she will call me back in 20 minutes.  She found out about the problem via Twitter.  Thank you Twitter, and all of you who helped.  Hopefully social media will win my wife and I our honeymoon, and hopefully Expedia will encourage their customer service teams treat their customers properly. 12:22 PM - Spoke to Fran again from Expedia corporate office.  She has a flight for us tonight.  She is booking it now.  We will arrive at our honeymoon destination of beautiful Veligandu Island Resort only 1 day late.  She cannot confirm today, but she expects that Expedia will pay for the lost honeymoon night.  Thank you everyone for your help.  I will reflect more on this whole situation and confirm its resolution after our flight is 100% confirmed.  For now, I'm going to take a breather and go kiss my wonderful wife! 1:50 PM - Have not yet received the promised phone call.  We did receive an email with a new itinerary for a flight but the booking is not for specific seats, so there is no guarantee that my wife and I will be able to sit together.  With the original booking I carefully selected our seats for every segment of our trip.  I decided to call into the phone number that Fran from the Expedia corporate office gave me.  Its automated voice system identified itself as "Tier 3 Support".  I am currently still on hold with them, I have not gotten through to a human yet. 1:55 PM - Fran from Expedia called me back.  She confirmed us as booked.  She called the airlines to confirm.  Unfortunately, Expedia was unwilling or unable to allow us any type of seat selection.  It is possible that i won't get to sit next to the woman I married less than a day ago on our 40 total hours of flight time (there and back).  In addition, our seats could be the worst seats on the planes, with no reclining seat back or right next to the restroom.  Despite this fact (which in my opinion is huge), the horrible inconvenience, the hours at the airport, and the negative Internet publicity that Expedia is receiving, Expedia declined to offer us any kind of upgrade or to mark us as SFU (suitable for upgrade).  Since they didn't offer - I asked, and was rejected.  I am grateful to finally be heading in the right direction, but not only did Expedia horribly botch this job from the very beginning, they followed that botch job with near zero customer service, followed by a verbally apologetic but otherwise half-hearted resolution.  If this works out favorably for us, great.  If not - I'm not done making noise, Expedia.  You owe us, and I expect you to make it right.  You haven't quite done that yet. Thanks - Thank you to Twitter.  Thanks to all those who sympathize with us and helped us get the attention of Expedia, since three people (one of them an airline employee) using Expedia's normal channels of communication for many hours didn't help.  Thanks especially to my PowerShell and Sharepoint friends, my local friends, and those connectors who encouraged me and spread my story. 5:15 PM - Love Wins - After all this, Lauren and I are exhausted.  We both took a short nap, and when we woke up we talked about the last 24 hours.  It was a big, amazing, story-filled 24 hours.  I said that Expedia won, but Lauren said no.  She pointed out how lucky we are.  We are in love and married.  We have wonderful family and friends.  We are both hard-working successful people who love what they do.  We get to go to an amazing exotic destination for our honeymoon like Veligandu in The Maldives...  That's a lot of good.  Expedia didn't win.  This was (is) a big loss for Expedia.  It is a public blemish for all to see.  But Lauren and I did win, big time.  Expedia may not have made things right - but things are right for us.  Post in progress... I will relay any further comments (or lack of) from Expedia soon, as well as an update on confirmation of their repayment of our lost resort room rates.  I'll also post a picture of us on our honeymoon as soon as I can!

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  • Comments on Comments

    - by Joe Mayo
    I almost tweeted a reply to Capar Kleijne's question about comments on Twitter, but realized that my opinion exceeded 140 characters. The following is based upon my experience with extremes and approaches that I find useful in code comments. There are a couple extremes that I've seen and reasons why people go the distance in each approach. The most common extreme is no comments in the code at all.  A few bad reasons why this happens is because a developer is in a hurry, sloppy, or is interested in job preservation. The unfortunate result is that the code is difficult to understand and hard to maintain. The drawbacks to no comments in code are a primary reason why teachers drill the need for commenting code into our heads.  This viewpoint assumes the lack of comments are bad because the code is bad, but there is another reason for not commenting that is gaining more popularity. I've heard/and read that code should be self documenting. Following this thought pattern, if code is well written with meaningful names, there should not be a reason for comments.  An addendum to this argument is that comments are often neglected and get out-of-date, but the code is what is kept up-to-date. Presumably, if code contained very good naming, it would be easy to maintain.  This is a noble perspective and I like the practice of meaningful naming of identifiers. However, I think it's also an extreme approach that doesn't cover important cases.  i.e. If an identifier is named badly (subjective differences in opinion) or not changed appropriately during maintenance, then the badly named identifier is no more useful than a stale comment. These were the two no-comment extremes, so let's look at the too many comments extreme. On a regular basis, I'll see cases where the code is over-commented; not nearly as often as the no-comment scenarios, but still prevalent.  These are examples of where every single line in the code is commented.  These comments make the code harder to read because they get in the way of the algorithm.  In most cases, the comments parrot what each line of code does.  If a developer understands the language, then most statements are immediately intuitive.  i.e. what use is it to say that I'm assigning foo to bar when it's clear what the code is doing. I think that over-commenting code is a waste of time that slows down initial development and maintenance.  Understandably, the developer's intentions are admirable because they've had it beaten into their heads that they must comment. However, I think it's an extreme and prefer a more moderate approach. I don't think the extremes do justice to code because each can make maintenance harder.  No comments on bad code is obviously a problem, but the other two extremes are subtle and require qualification to address properly. The problem I see with the code-as-documentation approach is that it doesn't lift the developer out of the algorithm to identify dependencies, intentions, and hacks. Any developer can read code and follow an algorithm, but they still need to know where it fits into the big picture of the application. Because of indirections with language features like interfaces, delegates, and virtual members, code can become complex.  Occasionally, it's useful to point out a nuance or reason why a piece of code is there. i.e. If you've building an app that communicates via HTTP, you'll have certain headers to include for the endpoint, and it could be useful to point out why the code for setting those header values is there and how they affect the application. An argument against this could be that you should extract that code into a separate method with a meaningful name to describe the scenario.  My problem with such an approach would be that your code base becomes even more difficult to navigate and work with because you have all of this extra code just to make the code more meaningful. My opinion is that a simple and well-stated comment stating the reasons and intention for the code is more natural and convenient to the initial developer and maintainer.  I just don't agree with the approach of going out of the way to avoid making a comment.  I'm also concerned that some developers would take this approach as an excuse to not comment their bad code. Another area where I like comments is on documentation comments.  Java has it and so does C# and VB.  It's convenient because we can build automated tools that extract these comments.  These extracted comments are often much better than no documentation at all.  The "go read the code" answer always doesn't fulfill the need for a quick summary of an API. To summarize, I think that the extremes of no comments and too many comments are less than desirable approaches. I prefer documentation comments to explain each class and member (API level) and code comments as necessary to supplement well-written code. Joe

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  • SQLCMD Mode: give it one more chance

    - by Maria Zakourdaev
      - Click on me. Choose me. - asked one forgotten feature when some bored DBA was purposelessly wondering through the Management Studio menu at the end of her long and busy working day. - Why would I use you? I have heard of no one who does. What are you for? - perplexedly wondered aged and wise DBA. At least that DBA thought she was aged and wise though each day tried to prove to her that she wasn't. - I know you. You are quite lazy. Why would you do additional clicks to move from window to window? From Tool to tool ? This is irritating, isn't it? I can run windows system commands, sql statements and much more from the same script, from the same query window! - I have all my tools that I‘m used to, I have Management Studio, Cmd, Powershell. They can do anything for me. I don’t need additional tools. - I promise you, you will like me. – the thing continued to whine . - All right, show me. – she gave up. It’s always this way, she thought sadly, - easier to agree than to explain why you don’t want. - Enable me and then think about anything that you always couldn’t do through the management studio and had to use other tools. - Ok. Google for me the list of greatest features of SQL SERVER 2012. - Well... I’m not sure... Think about something else. - Ok, here is something easy for you. I want to check if file folder exists or if file is there. Though, I can easily do this using xp_cmdshell … - This is easy for me. – rejoiced the feature. By the way, having the items of the menu talking to you usually means you should stop working and go home. Or drink coffee. Or both. Well, aged and wise dba wasn’t thinking about the weirdness of the situation at that moment. - After enabling me, – said unfairly forgotten feature (it was thinking of itself in such manner) – after enabling me you can use all command line commands in the same management studio query window by adding two exclamation marks !! at the beginning of the script line to denote that you want to use cmd command: -Just keep in mind that when using this feature, you are actually running the commands ON YOUR computer and not on SQL server that query window is connected to. This is main difference from using xp_cmdshell which is executing commands on sql server itself. Bottomline, use UNC path instead of local path. - Look, there are much more than that. - The SQLCMD feature was getting exited.- You can get IP of your servers, create, rename and drop folders. You can see the contents of any file anywhere and even start different tools from the same query window: Not so aged and wise DBA was getting interested: - I also want to run different scripts on different servers without changing connection of the query window. - Sure, sure! Another great feature that CMDmode is providing us with and giving more power to querying. Use “:” to use additional features, like :connect that allows you to change connection: - Now imagine, you have one script where you have all your changes, like creating staging table on the DWH staging server, adding fact table to DWH itself and updating stored procedures in the server where reporting database is located. - Now, give me more challenges! - Script out a list of stored procedures into the text files. - You can do it easily by using command :out which will write the query results into the specified text file. The output can be the code of the stored procedure or any data. Actually this is the same as changing the query output into the file instead of the grid. - Now, take all of the scripts and run all of them, one by one, on the different server.  - Easily - Come on... I’m sure that you can not... -Why not? Naturally, I can do it using :r commant which is opening a script and executing it. Look, I can also use :setvar command to define an environment variable in SQLCMD mode. Just note that you have to leave the empty string between :r commands, otherwise it’s not working although I have no idea why. - Wow.- She was really impressed. - Ok, I’ll go to try all those… -Wait, wait! I know how to google the SQL SERVER features for you! This example will open chrome explorer with search results for the “SQL server 2012 top features” ( change the path to suit your PC): “Well, this can be probably useful stuff, maybe this feature is really unfairly forgotten”, thought the DBA while going through the dark empty parking lot to her lonely car. “As someone really wise once said: “It is what we think we know that keeps us from learning. Learn, unlearn and relearn”.

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  • Down Tools Week Cometh: Kissing Goodbye to CVs/Resumes and Cover Letters

    - by Bart Read
    I haven't blogged about what I'm doing in my (not so new) temporary role as Red Gate's technical recruiter, mostly because it's been routine, business as usual stuff, and because I've been trying to understand the role by doing it. I think now though the time has come to get a little more radical, so I'm going to tell you why I want to largely eliminate CVs/resumes and cover letters from the application process for some of our technical roles, and why I think that might be a good thing for candidates (and for us). I have a terrible confession to make, or at least it's a terrible confession for a recruiter: I don't really like CV sifting, or reading cover letters, and, unless I've misread the mood around here, neither does anybody else. It's dull, it's time-consuming, and it's somewhat soul destroying because, when all is said and done, you're being paid to be incredibly judgemental about people based on relatively little information. I feel like I've dirtied myself by saying that - I mean, after all, it's a core part of my job - but it sucks, it really does. (And, of course, the truth is I'm still a software engineer at heart, and I'm always looking for ways to do things better.) On the flip side, I've never met anyone who likes writing their CV. It takes hours and hours of faffing around and massaging it into shape, and the whole process is beset by a gnawing anxiety, frustration, and insecurity. All you really want is a chance to demonstrate your skills - not just talk about them - and how do you do that in a CV or cover letter? Often the best candidates will include samples of their work (a portfolio, screenshots, links to websites, product downloads, etc.), but sometimes this isn't possible, or may not be appropriate, or you just don't think you're allowed because of what your school/university careers service has told you (more commonly an issue with grads, obviously). And what are we actually trying to find out about people with all of this? I think the common criteria are actually pretty basic: Smart Gets things done (thanks for these two Joel) Not an a55hole* (sorry, have to get around Simple Talk's swear filter - and thanks to Professor Robert I. Sutton for this one) *Of course, everyone has off days, and I don't honestly think we're too worried about somebody being a bit grumpy every now and again. We can do a bit better than this in the context of the roles I'm talking about: we can be more specific about what "gets things done" means, at least in part. For software engineers and interns, the non-exhaustive meaning of "gets things done" is: Excellent coder For test engineers, the non-exhaustive meaning of "gets things done" is: Good at finding problems in software Competent coder Team player, etc., to me, are covered by "not an a55hole". I don't expect people to be the life and soul of the party, or a wild extrovert - that's not what team player means, and it's not what "not an a55hole" means. Some of our best technical staff are quiet, introverted types, but they're still pleasant to work with. My problem is that I don't think the initial sift really helps us find out whether people are smart and get things done with any great efficacy. It's better than nothing, for sure, but it's not as good as it could be. It's also contentious, and potentially unfair/inequitable - if you want to get an idea of what I mean by this, check out the background information section at the bottom. Before I go any further, let's look at the Red Gate recruitment process for technical staff* as it stands now: (LOTS of) People apply for jobs. All these applications go through a brutal process of manual sifting, which eliminates between 75 and 90% of them, depending upon the role, and the time of year**. Depending upon the role, those who pass the sift will be sent an assessment or telescreened. For the purposes of this blog post I'm only interested in those that are sent some sort of programming assessment, or bug hunt. This means software engineers, test engineers, and software interns, which are the roles for which I receive the most applications. The telescreen tends to be reserved for project or product managers. Those that pass the assessment are invited in for first interview. This interview is mostly about assessing their technical skills***, although we're obviously on the look out for cultural fit red flags as well. If the first interview goes well we'll invite candidates back for a second interview. This is where team/cultural fit is really scoped out. We also use this interview to dive more deeply into certain areas of their skillset, and explore any concerns that may have come out of the first interview (these obviously won't have been serious or obvious enough to cause a rejection at that point, but are things we do need to look into before we'd consider making an offer). We might subsequently invite them in for lunch before we make them an offer. This tends to happen when we're recruiting somebody for a specific team and we'd like them to meet all the people they'll be working with directly. It's not an interview per se, but can prove pivotal if they don't gel with the team. Anyone who's made it this far will receive an offer from us. *We have a slightly quirky definition of "technical staff" as it relates to the technical recruiter role here. It includes software engineers, test engineers, software interns, user experience specialists, technical authors, project managers, product managers, and development managers, but does not include product support or information systems roles. **For example, the quality of graduate applicants overall noticeably drops as the academic year wears on, which is not to say that by now there aren't still stars in there, just that they're fewer and further between. ***Some organisations prefer to assess for team fit first, but I think assessing technical skills is a more effective initial filter - if they're the nicest person in the world, but can't cut a line of code they're not going to work out. Now, as I suggested in the title, Red Gate's Down Tools Week is upon us once again - next week in fact - and I had proposed as a project that we refactor and automate the first stage of marking our programming assessments. Marking assessments, and in fact organising the marking of them, is a somewhat time-consuming process, and we receive many assessment solutions that just don't make the cut, for whatever reason. Whilst I don't think it's possible to fully automate marking, I do think it ought to be possible to run a suite of automated tests over each candidate's solution to see whether or not it behaves correctly and, if it does, move on to a manual stage where we examine the code for structure, decomposition, style, readability, maintainability, etc. Obviously it's possible to use tools to generate potentially helpful metrics for some of these indices as well. This would obviously reduce the marking workload, and would provide candidates with quicker feedback about whether they've been successful - though I do wonder if waiting a tactful interval before sending a (nicely written) rejection might be wise. I duly scrawled out a picture of my ideal process, which looked like this: The problem is, as soon as I'd roughed it out, I realised that fundamentally it wasn't an ideal process at all, which explained the gnawing feeling of cognitive dissonance I'd been wrestling with all week, whilst I'd been trying to find time to do this. Here's what I mean. Automated assessment marking, and the associated infrastructure around that, makes it much easier for us to deal with large numbers of assessments. This means we can be much more permissive about who we send assessments out to or, in other words, we can give more candidates the opportunity to really demonstrate their skills to us. And this leads to a question: why not give everyone the opportunity to demonstrate their skills, to show that they're smart and can get things done? (Two or three of us even discussed this in the down tools week hustings earlier this week.) And isn't this a lot simpler than the alternative we'd been considering? (FYI, this was automated CV/cover letter sifting by some form of textual analysis to ideally eliminate the worst 50% or so of applications based on an analysis of the 20,000 or so historical applications we've received since 2007 - definitely not the basic keyword analysis beloved of recruitment agencies, since this would eliminate hardly anyone who was awful, but definitely would eliminate stellar Oxbridge candidates - #fail - or some nightmarishly complex Google-like system where we profile all our currently employees, only to realise that we're never going to get representative results because we don't have a statistically significant sample size in any given role - also #fail.) No, I think the new way is better. We let people self-select. We make them the masters (or mistresses) of their own destiny. We give applicants the power - we put their fate in their hands - by giving them the chance to demonstrate their skills, which is what they really want anyway, instead of requiring that they spend hours and hours creating a CV and cover letter that I'm going to evaluate for suitability, and make a value judgement about, in approximately 1 minute (give or take). It doesn't matter what university you attended, it doesn't matter if you had a bad year when you took your A-levels - here's your chance to shine, so take it and run with it. (As a side benefit, we cut the number of applications we have to sift by something like two thirds.) WIN! OK, yeah, sounds good, but will it actually work? That's an excellent question. My gut feeling is yes, and I'll justify why below (and hopefully have gone some way towards doing that above as well), but what I'm proposing here is really that we run an experiment for a period of time - probably a couple of months or so - and measure the outcomes we see: How many people apply? (Wouldn't be surprised or alarmed to see this cut by a factor of ten.) How many of them submit a good assessment? (More/less than at present?) How much overhead is there for us in dealing with these assessments compared to now? What are the success and failure rates at each interview stage compared to now? How many people are we hiring at the end of it compared to now? I think it'll work because I hypothesize that, amongst other things: It self-selects for people who really want to work at Red Gate which, at the moment, is something I have to try and assess based on their CV and cover letter - but if you're not that bothered about working here, why would you complete the assessment? Candidates who would submit a shoddy application probably won't feel motivated to do the assessment. Candidates who would demonstrate good attention to detail in their CV/cover letter will demonstrate good attention to detail in the assessment. In general, only the better candidates will complete and submit the assessment. Marking assessments is much less work so we'll be able to deal with any increase that we see (hopefully we will see). There are obviously other questions as well: Is plagiarism going to be a problem? Is there any way we can detect/discourage potential plagiarism? How do we assess candidates' education and experience? What about their ability to communicate in writing? Do we still want them to submit a CV afterwards if they pass assessment? Do we want to offer them the opportunity to tell us a bit about why they'd like the job when they submit their assessment? How does this affect our relationship with recruitment agencies we might use to hire for these roles? So, what's the objective for next week's Down Tools Week? Pretty simple really - we want to implement this process for the Graduate Software Engineer and Software Engineer positions that you can find on our website. I will be joined by a crack team of our best developers (Kevin Boyle, and new Red-Gater, Sam Blackburn), and recruiting hostess with the mostest Laura McQuillen, and hopefully a couple of others as well - if I can successfully twist more arms before Monday.* Hopefully by next Friday our experiment will be up and running, and we may have changed the way Red Gate recruits software engineers for good! Stay tuned and we'll let you know how it goes! *I'm going to play dirty by offering them beer and chocolate during meetings. Some background information: how agonising over the initial CV/cover letter sift helped lead us to bin it off entirely The other day I was agonising about the new university/good degree grade versus poor A-level results issue, and decided to canvas for other opinions to see if there was something I could do that was fairer than my current approach, which is almost always to reject. This generated quite an involved discussion on our Yammer site: I'm sure you can glean a pretty good impression of my own educational prejudices from that discussion as well, although I'm very open to changing my opinion - hopefully you've already figured that out from reading the rest of this post. Hopefully you can also trace a logical path from agonising about sifting to, "Uh, hang on, why on earth are we doing this anyway?!?" Technorati Tags: recruitment,hr,developers,testers,red gate,cv,resume,cover letter,assessment,sea change

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  • Pirates, Treasure Chests and Architectural Mapping

    Pirate 1: Why do pirates create treasure maps? Pirate 2: I do not know.Pirate 1: So they can find their gold. Yes, that was a bad joke, but it does illustrate a point. Pirates are known for drawing treasure maps to their most prized possession. These documents detail the decisions pirates made in order to hide and find their chests of gold. The map allows them to trace the steps they took originally to hide their treasure so that they may return. As software engineers, programmers, and architects we need to treat software implementations much like our treasure chest. Why is software like a treasure chest? It cost money, time,  and resources to develop (Usually) It can make or save money, time, and resources (Hopefully) If we operate under the assumption that software is like a treasure chest then wouldn’t make sense to document the steps, rationale, concerns, and decisions about how it was designed? Pirates are notorious for documenting where they hide their treasure.  Shouldn’t we as creators of software do the same? By documenting our design decisions and rationale behind them will help others be able to understand and maintain implemented systems. This can only be done if the design decisions are correctly mapped to its corresponding implementation. This allows for architectural decisions to be traced from the conceptual model, architectural design and finally to the implementation. Mapping gives software professional a method to trace the reason why specific areas of code were developed verses other options. Just like the pirates we need to able to trace our steps from the start of a project to its implementation,  so that we will understand why specific choices were chosen. The traceability of a software implementation that actually maps back to its originating design decisions is invaluable for ensuring that architectural drifting and erosion does not take place. The drifting and erosion is prevented by allowing others to understand the rational of why an implementation was created in a specific manor or methodology The process of mapping distinct design concerns/decisions to the location of its implemented is called traceability. In this context traceability is defined as method for connecting distinctive software artifacts. This process allows architectural design models and decisions to be directly connected with its physical implementation. The process of mapping architectural design concerns to a software implementation can be very complex. However, most design decision can be placed in  a few generalized categories. Commonly Mapped Design Decisions Design Rationale Components and Connectors Interfaces Behaviors/Properties Design rational is one of the hardest categories to map directly to an implementation. Typically this rational is mapped or document in code via comments. These comments consist of general design decisions and reasoning because they do not directly refer to a specific part of an application. They typically focus more on the higher level concerns. Components and connectors can directly be mapped to architectural concerns. Typically concerns subdivide an application in to distinct functional areas. These functional areas then can map directly back to their originating concerns.Interfaces can be mapped back to design concerns in one of two ways. Interfaces that pertain to specific function definitions can be directly mapped back to its originating concern(s). However, more complicated interfaces require additional analysis to ensure that the proper mappings are created. Depending on the complexity some Behaviors\Properties can be translated directly into a generic implementation structure that is ready for business logic. In addition, some behaviors can be translated directly in to an actual implementation depending on the complexity and architectural tools used. Mapping design concerns to an implementation is a lot of work to maintain, but is doable. In order to ensure that concerns are mapped correctly and that an implementation correctly reflects its design concerns then one of two standard approaches are usually used. All Changes Come From ArchitectureBy forcing all application changes to come through the architectural model prior to implementation then the existing mappings will be used to locate where in the implementation changes need to occur. Allow Changes From Implementation Or Architecture By allowing changes to come from the implementation and/or the architecture then the other area must be kept in sync. This methodology is more complex compared to the previous approach.  One reason to justify the added complexity for an application is due to the fact that this approach tends to detect and prevent architectural drift and erosion. Additionally, this approach is usually maintained via software because of the complexity. Reference:Taylor, R. N., Medvidovic, N., & Dashofy, E. M. (2009). Software architecture: Foundations, theory, and practice Hoboken, NJ: John Wiley & Sons  

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  • Does anyone really understand how HFSC scheduling in Linux/BSD works?

    - by Mecki
    I read the original SIGCOMM '97 PostScript paper about HFSC, it is very technically, but I understand the basic concept. Instead of giving a linear service curve (as with pretty much every other scheduling algorithm), you can specify a convex or concave service curve and thus it is possible to decouple bandwidth and delay. However, even though this paper mentions to kind of scheduling algorithms being used (real-time and link-share), it always only mentions ONE curve per scheduling class (the decoupling is done by specifying this curve, only one curve is needed for that). Now HFSC has been implemented for BSD (OpenBSD, FreeBSD, etc.) using the ALTQ scheduling framework and it has been implemented Linux using the TC scheduling framework (part of iproute2). Both implementations added two additional service curves, that were NOT in the original paper! A real-time service curve and an upper-limit service curve. Again, please note that the original paper mentions two scheduling algorithms (real-time and link-share), but in that paper both work with one single service curve. There never have been two independent service curves for either one as you currently find in BSD and Linux. Even worse, some version of ALTQ seems to add an additional queue priority to HSFC (there is no such thing as priority in the original paper either). I found several BSD HowTo's mentioning this priority setting (even though the man page of the latest ALTQ release knows no such parameter for HSFC, so officially it does not even exist). This all makes the HFSC scheduling even more complex than the algorithm described in the original paper and there are tons of tutorials on the Internet that often contradict each other, one claiming the opposite of the other one. This is probably the main reason why nobody really seems to understand how HFSC scheduling really works. Before I can ask my questions, we need a sample setup of some kind. I'll use a very simple one as seen in the image below: Here are some questions I cannot answer because the tutorials contradict each other: What for do I need a real-time curve at all? Assuming A1, A2, B1, B2 are all 128 kbit/s link-share (no real-time curve for either one), then each of those will get 128 kbit/s if the root has 512 kbit/s to distribute (and A and B are both 256 kbit/s of course), right? Why would I additionally give A1 and B1 a real-time curve with 128 kbit/s? What would this be good for? To give those two a higher priority? According to original paper I can give them a higher priority by using a curve, that's what HFSC is all about after all. By giving both classes a curve of [256kbit/s 20ms 128kbit/s] both have twice the priority than A2 and B2 automatically (still only getting 128 kbit/s on average) Does the real-time bandwidth count towards the link-share bandwidth? E.g. if A1 and B1 both only have 64kbit/s real-time and 64kbit/s link-share bandwidth, does that mean once they are served 64kbit/s via real-time, their link-share requirement is satisfied as well (they might get excess bandwidth, but lets ignore that for a second) or does that mean they get another 64 kbit/s via link-share? So does each class has a bandwidth "requirement" of real-time plus link-share? Or does a class only have a higher requirement than the real-time curve if the link-share curve is higher than the real-time curve (current link-share requirement equals specified link-share requirement minus real-time bandwidth already provided to this class)? Is upper limit curve applied to real-time as well, only to link-share, or maybe to both? Some tutorials say one way, some say the other way. Some even claim upper-limit is the maximum for real-time bandwidth + link-share bandwidth? What is the truth? Assuming A2 and B2 are both 128 kbit/s, does it make any difference if A1 and B1 are 128 kbit/s link-share only, or 64 kbit/s real-time and 128 kbit/s link-share, and if so, what difference? If I use the seperate real-time curve to increase priorities of classes, why would I need "curves" at all? Why is not real-time a flat value and link-share also a flat value? Why are both curves? The need for curves is clear in the original paper, because there is only one attribute of that kind per class. But now, having three attributes (real-time, link-share, and upper-limit) what for do I still need curves on each one? Why would I want the curves shape (not average bandwidth, but their slopes) to be different for real-time and link-share traffic? According to the little documentation available, real-time curve values are totally ignored for inner classes (class A and B), they are only applied to leaf classes (A1, A2, B1, B2). If that is true, why does the ALTQ HFSC sample configuration (search for 3.3 Sample configuration) set real-time curves on inner classes and claims that those set the guaranteed rate of those inner classes? Isn't that completely pointless? (note: pshare sets the link-share curve in ALTQ and grate the real-time curve; you can see this in the paragraph above the sample configuration). Some tutorials say the sum of all real-time curves may not be higher than 80% of the line speed, others say it must not be higher than 70% of the line speed. Which one is right or are they maybe both wrong? One tutorial said you shall forget all the theory. No matter how things really work (schedulers and bandwidth distribution), imagine the three curves according to the following "simplified mind model": real-time is the guaranteed bandwidth that this class will always get. link-share is the bandwidth that this class wants to become fully satisfied, but satisfaction cannot be guaranteed. In case there is excess bandwidth, the class might even get offered more bandwidth than necessary to become satisfied, but it may never use more than upper-limit says. For all this to work, the sum of all real-time bandwidths may not be above xx% of the line speed (see question above, the percentage varies). Question: Is this more or less accurate or a total misunderstanding of HSFC? And if assumption above is really accurate, where is prioritization in that model? E.g. every class might have a real-time bandwidth (guaranteed), a link-share bandwidth (not guaranteed) and an maybe an upper-limit, but still some classes have higher priority needs than other classes. In that case I must still prioritize somehow, even among real-time traffic of those classes. Would I prioritize by the slope of the curves? And if so, which curve? The real-time curve? The link-share curve? The upper-limit curve? All of them? Would I give all of them the same slope or each a different one and how to find out the right slope? I still haven't lost hope that there exists at least a hand full of people in this world that really understood HFSC and are able to answer all these questions accurately. And doing so without contradicting each other in the answers would be really nice ;-)

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  • Does anyone really understand how HFSC scheduling in Linux/BSD works?

    - by Mecki
    I read the original SIGCOMM '97 PostScript paper about HFSC, it is very technically, but I understand the basic concept. Instead of giving a linear service curve (as with pretty much every other scheduling algorithm), you can specify a convex or concave service curve and thus it is possible to decouple bandwidth and delay. However, even though this paper mentions to kind of scheduling algorithms being used (real-time and link-share), it always only mentions ONE curve per scheduling class (the decoupling is done by specifying this curve, only one curve is needed for that). Now HFSC has been implemented for BSD (OpenBSD, FreeBSD, etc.) using the ALTQ scheduling framework and it has been implemented Linux using the TC scheduling framework (part of iproute2). Both implementations added two additional service curves, that were NOT in the original paper! A real-time service curve and an upper-limit service curve. Again, please note that the original paper mentions two scheduling algorithms (real-time and link-share), but in that paper both work with one single service curve. There never have been two independent service curves for either one as you currently find in BSD and Linux. Even worse, some version of ALTQ seems to add an additional queue priority to HSFC (there is no such thing as priority in the original paper either). I found several BSD HowTo's mentioning this priority setting (even though the man page of the latest ALTQ release knows no such parameter for HSFC, so officially it does not even exist). This all makes the HFSC scheduling even more complex than the algorithm described in the original paper and there are tons of tutorials on the Internet that often contradict each other, one claiming the opposite of the other one. This is probably the main reason why nobody really seems to understand how HFSC scheduling really works. Before I can ask my questions, we need a sample setup of some kind. I'll use a very simple one as seen in the image below: Here are some questions I cannot answer because the tutorials contradict each other: What for do I need a real-time curve at all? Assuming A1, A2, B1, B2 are all 128 kbit/s link-share (no real-time curve for either one), then each of those will get 128 kbit/s if the root has 512 kbit/s to distribute (and A and B are both 256 kbit/s of course), right? Why would I additionally give A1 and B1 a real-time curve with 128 kbit/s? What would this be good for? To give those two a higher priority? According to original paper I can give them a higher priority by using a curve, that's what HFSC is all about after all. By giving both classes a curve of [256kbit/s 20ms 128kbit/s] both have twice the priority than A2 and B2 automatically (still only getting 128 kbit/s on average) Does the real-time bandwidth count towards the link-share bandwidth? E.g. if A1 and B1 both only have 64kbit/s real-time and 64kbit/s link-share bandwidth, does that mean once they are served 64kbit/s via real-time, their link-share requirement is satisfied as well (they might get excess bandwidth, but lets ignore that for a second) or does that mean they get another 64 kbit/s via link-share? So does each class has a bandwidth "requirement" of real-time plus link-share? Or does a class only have a higher requirement than the real-time curve if the link-share curve is higher than the real-time curve (current link-share requirement equals specified link-share requirement minus real-time bandwidth already provided to this class)? Is upper limit curve applied to real-time as well, only to link-share, or maybe to both? Some tutorials say one way, some say the other way. Some even claim upper-limit is the maximum for real-time bandwidth + link-share bandwidth? What is the truth? Assuming A2 and B2 are both 128 kbit/s, does it make any difference if A1 and B1 are 128 kbit/s link-share only, or 64 kbit/s real-time and 128 kbit/s link-share, and if so, what difference? If I use the seperate real-time curve to increase priorities of classes, why would I need "curves" at all? Why is not real-time a flat value and link-share also a flat value? Why are both curves? The need for curves is clear in the original paper, because there is only one attribute of that kind per class. But now, having three attributes (real-time, link-share, and upper-limit) what for do I still need curves on each one? Why would I want the curves shape (not average bandwidth, but their slopes) to be different for real-time and link-share traffic? According to the little documentation available, real-time curve values are totally ignored for inner classes (class A and B), they are only applied to leaf classes (A1, A2, B1, B2). If that is true, why does the ALTQ HFSC sample configuration (search for 3.3 Sample configuration) set real-time curves on inner classes and claims that those set the guaranteed rate of those inner classes? Isn't that completely pointless? (note: pshare sets the link-share curve in ALTQ and grate the real-time curve; you can see this in the paragraph above the sample configuration). Some tutorials say the sum of all real-time curves may not be higher than 80% of the line speed, others say it must not be higher than 70% of the line speed. Which one is right or are they maybe both wrong? One tutorial said you shall forget all the theory. No matter how things really work (schedulers and bandwidth distribution), imagine the three curves according to the following "simplified mind model": real-time is the guaranteed bandwidth that this class will always get. link-share is the bandwidth that this class wants to become fully satisfied, but satisfaction cannot be guaranteed. In case there is excess bandwidth, the class might even get offered more bandwidth than necessary to become satisfied, but it may never use more than upper-limit says. For all this to work, the sum of all real-time bandwidths may not be above xx% of the line speed (see question above, the percentage varies). Question: Is this more or less accurate or a total misunderstanding of HSFC? And if assumption above is really accurate, where is prioritization in that model? E.g. every class might have a real-time bandwidth (guaranteed), a link-share bandwidth (not guaranteed) and an maybe an upper-limit, but still some classes have higher priority needs than other classes. In that case I must still prioritize somehow, even among real-time traffic of those classes. Would I prioritize by the slope of the curves? And if so, which curve? The real-time curve? The link-share curve? The upper-limit curve? All of them? Would I give all of them the same slope or each a different one and how to find out the right slope? I still haven't lost hope that there exists at least a hand full of people in this world that really understood HFSC and are able to answer all these questions accurately. And doing so without contradicting each other in the answers would be really nice ;-)

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  • Logs show failed password for invalid user root from <IP Address> port 2924 ssh2

    - by Chris Hanson
    I'm getting a constant flow of these messages in my logs. The port is variable (seemingly between 1024 and 65535). I can simulate it myself by running sftp root@<my ip> I've commented out the sftp subsystem line in my sshd_config. These ports should be closed by provider's firewall. I don't understand: Why sftp would be selecting a random port like that. It seems to be behaving like FTP in passive mode, but I can't make any sense of why that would be. Why it can even hit my server in the first place if these ports are closed.

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  • What is the deal with hard drive technology moving to 4K sectors, vs. 512 bytes? Are 4K sector disk

    - by Chris W. Rea
    I've noticed that some Western Digital hard drives are now sporting 4K sectors, that is, the sectors are larger: 4096 bytes vs. the actual de facto standard of 512 bytes. So: What's the big deal with 4K sectors? Is it marketing hype, or a real advantage? Why should somebody building a new PC care, or not, about 4K sectors? Why is this transition taking place now? Why didn't it happen sooner? Are there things to look out for when buying a 4K sector hard drive? e.g. incompatibility? Anything else we should know about 4K sectors?

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  • Unable to click on tabs in Firefox unless I press Command-Q

    - by Philip
    Why does clicking on tabs in Firefox sometimes fail until I hit cmd-Q, and then why does that not quit but instead make clicking on the tabs work, and how do I stop that behavior? I'm running Firefox 3.5.5 on Mac OS X 10.5 and this has been happening for a while (with previous versions of FF as well). I can't forcibly reproduce the behavior, but every now and then (few days?) I just can't click on tabs or on the x's to close the tabs. I can still ctrl-tab between tabs, though. But if I press cmd-Q, instead of quitting, Firefox seems to seize for a second and then I can click on tabs and click to close them just fine. No clue why this is happening or how to stop it. And I do have tons of extensions installed, so it's plausible one of them is the problem..... Thanks.

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  • Apache denying requests with VirtualHosts

    - by Ross
    This is the error I get in my log: Permission denied: /home/ross/.htaccess pcfg_openfile: unable to check htaccess file, ensure it is readable My VirtualHost is pretty simple: <VirtualHost 127.0.0.1> ServerName jotter.localhost DocumentRoot /home/ross/www/jotter/public DirectoryIndex index.php index.html <Directory /home/ross/www/jotter/public> AllowOverride all Order allow,deny allow from all </Directory> CustomLog /home/ross/www/jotter/logs/access.log combined ErrorLog /home/ross/www/jotter/logs/error.log LogLevel warn </VirtualHost> Any ideas why this is happening? I can't see why Apache is looking for a .htaccess there and don't know why this should stop the request. Thanks.

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  • Disable Offline Files (mobsync.exe) on Windows 7 Home

    - by Synetech
    This morning I was watching the CPU graph of a Windows 7 Home laptop and noticed that every few seconds, the CPU would spike several percent. I watched the processes and determined that it was mobsync.exe (Offline Files) that was the culprit. I tried the usual steps that Googling turns up, and clicking the Manage Offline Files link to bring up the Offline Files dialog to click Disable Synch does not work because the dialog will not display. This makes sense since everything I have read indicates that Offline Files is not even included/supported in the Home version, so I am at a loss as to why it is running at all, let alone why it is sucking up CPU cycles. (My best guess is that it was started when they pressed Win+X to access the Mobility Center.) Of course I can just kill mobsync, but it could always just come back. How/why would mobsync be running on a Home version and how can it be disabled (of course the Group Policy editor is not available on a Home version).

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  • UTF-8 bit representation

    - by Yanick Rochon
    I'm learning about UTF-8 standards and this is what I'm learning : Definition and bytes used UTF-8 binary representation Meaning 0xxxxxxx 1 byte for 1 à 7 bits chars 110xxxxx 10xxxxxx 2 bytes for 8 à 11 bits chars 1110xxxx 10xxxxxx 10xxxxxx 3 bytes for 12 à 16 bits chars 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx 4 bytes for 17 à 21 bits chars And I'm wondering, why 2 bytes UTF-8 code is not 10xxxxxx instead, thus gaining 1 bit all the way up to 22 bits with a 4 bytes UTF-8 code? The way it is right now, 64 possible values are lost (from 1000000 to 10111111). I'm not trying to argue the standards, but I'm wondering why this is so? ** EDIT ** Even, why isn't it UTF-8 binary representation Meaning 0xxxxxxx 1 byte for 1 à 7 bits chars 110xxxxx xxxxxxxx 2 bytes for 8 à 13 bits chars 1110xxxx xxxxxxxx xxxxxxxx 3 bytes for 14 à 20 bits chars 11110xxx xxxxxxxx xxxxxxxx xxxxxxxx 4 bytes for 21 à 27 bits chars ...? Thanks!

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  • routing weirdness - traceroute 'vanishes' en route

    - by The Journeyman geek
    I'm attempting to set up one of my boxes as a server (again), but i'm having some odd connection issues- the box itself connects fine to the internet, but trying to connect to my external ip address seems to result in the trace getting 'lost' partway. http://pastebin.com/HCQAGbvn - this is a traceroute from another system that's connected to another ISP - starhub is my own one, while i have another system that i have access to on singtel. I'm wondering if my ISP is messing around with routing, or is something very odd going on. As you note, the traceroute dosen't reach me, but if it helps, i use a dd-wrt router. edit: Facepalmishly, turning the firewall on my router on and off fixed it. I don't get why it dropped off at different ip addresses each time, or why the router set it self to block.. everything, or why it affected the ipv6 tunnel as well.

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  • File/folder Write/Delete wise, is my server secure?

    - by acidzombie24
    I wanted to know if someone got access to my server by using a nonroot account, how much damage can he do? After i su someuser I used this command to find all files and folders that are writeable. find / -writable >> list.txt Here is the result. Its most /dev/something and /proc/something and these /var/lock /var/run/mysqld/mysqld.sock /var/tmp /var/lib/php5 Is my system secure? /var/tmp makes sense but i am unsure why this user has write access to those folders. Should i change them? stat /var/lib/php5 gives me 1733 which is odd. Why write access? why no read? is this some kind of weird use of a temp file?

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  • How to explain DRM cannot work?

    - by jerryjvl
    I am looking for the shortest comprehensive way to explain to people that are trying to use DRM as a technology to prevent users from using their data in some fashion deemed undesirable, why their solution cannot work by definition. Ideally I'd like something that: Covers why technically it is impossible to have people access local data, but only in such-and-such a way Imparts an understanding of why this is, to avoid follow-on "But what if" rebuttals Is intuitive enough and short enough that even a politician (j/k) could grasp it When faced with this situation I try to be clear and concise, but I usually end up failing at least on one of these points. I'd really like to have a 'stock' answer that I can use in the future.

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  • Disabled annotation tools in Skim

    - by Kit
    Here's a portion of the toolbar in Skim In the Add Note section, why are the following tools disabled (dimmed)? Add New Highlight (A in the yellow box) Add New Underline (red line under A) Add New Strike Out (A struck out by red line) However, in the Tool Mode section, there is a drop down button (shown as active in the screenshot). To illustrate, I can select and use the Add New Underline tool, as well as the other tools I mentioned above, using the drop down button. But those tools are dimmed out in the Add Note section. Why? I have observed that the drop down button is just a duplicate of the Add Note section. Why not just enable all the buttons in the Add Note section and save the user from making an extra click just to bring down a list of tools? Is this because of some property of the presently open PDF, or what?

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