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  • ZFS for Database Log Files

    - by user12620111
    I've been troubled by drop outs in CPU usage in my application server, characterized by the CPUs suddenly going from close to 90% CPU busy to almost completely CPU idle for a few seconds. Here is an example of a drop out as shown by a snippet of vmstat data taken while the application server is under a heavy workload. # vmstat 1  kthr      memory            page            disk          faults      cpu  r b w   swap  free  re  mf pi po fr de sr s3 s4 s5 s6   in   sy   cs us sy id  1 0 0 130160176 116381952 0 16 0 0 0 0  0  0  0  0  0 207377 117715 203884 70 21 9  12 0 0 130160160 116381936 0 25 0 0 0 0 0  0  0  0  0 200413 117162 197250 70 20 9  11 0 0 130160176 116381920 0 16 0 0 0 0 0  0  1  0  0 203150 119365 200249 72 21 7  8 0 0 130160176 116377808 0 19 0 0 0 0  0  0  0  0  0 169826 96144 165194 56 17 27  0 0 0 130160176 116377800 0 16 0 0 0 0  0  0  0  0  1 10245 9376 9164 2  1 97  0 0 0 130160176 116377792 0 16 0 0 0 0  0  0  0  0  2 15742 12401 14784 4 1 95  0 0 0 130160176 116377776 2 16 0 0 0 0  0  0  1  0  0 19972 17703 19612 6 2 92  14 0 0 130160176 116377696 0 16 0 0 0 0 0  0  0  0  0 202794 116793 199807 71 21 8  9 0 0 130160160 116373584 0 30 0 0 0 0  0  0 18  0  0 203123 117857 198825 69 20 11 This behavior occurred consistently while the application server was processing synthetic transactions: HTTP requests from JMeter running on an external machine. I explored many theories trying to explain the drop outs, including: Unexpected JMeter behavior Network contention Java Garbage Collection Application Server thread pool problems Connection pool problems Database transaction processing Database I/O contention Graphing the CPU %idle led to a breakthrough: Several of the drop outs were 30 seconds apart. With that insight, I went digging through the data again and looking for other outliers that were 30 seconds apart. In the database server statistics, I found spikes in the iostat "asvc_t" (average response time of disk transactions, in milliseconds) for the disk drive that was being used for the database log files. Here is an example:                     extended device statistics     r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device     0.0 2053.6    0.0 8234.3  0.0  0.2    0.0    0.1   0  24 c3t60080E5...F4F6d0s0     0.0 2162.2    0.0 8652.8  0.0  0.3    0.0    0.1   0  28 c3t60080E5...F4F6d0s0     0.0 1102.5    0.0 10012.8  0.0  4.5    0.0    4.1   0  69 c3t60080E5...F4F6d0s0     0.0   74.0    0.0 7920.6  0.0 10.0    0.0  135.1   0 100 c3t60080E5...F4F6d0s0     0.0  568.7    0.0 6674.0  0.0  6.4    0.0   11.2   0  90 c3t60080E5...F4F6d0s0     0.0 1358.0    0.0 5456.0  0.0  0.6    0.0    0.4   0  55 c3t60080E5...F4F6d0s0     0.0 1314.3    0.0 5285.2  0.0  0.7    0.0    0.5   0  70 c3t60080E5...F4F6d0s0 Here is a little more information about my database configuration: The database and application server were running on two different SPARC servers. Storage for the database was on a storage array connected via 8 gigabit Fibre Channel Data storage and log file were on different physical disk drives Reliable low latency I/O is provided by battery backed NVRAM Highly available: Two Fibre Channel links accessed via MPxIO Two Mirrored cache controllers The log file physical disks were mirrored in the storage device Database log files on a ZFS Filesystem with cutting-edge technologies, such as copy-on-write and end-to-end checksumming Why would I be getting service time spikes in my high-end storage? First, I wanted to verify that the database log disk service time spikes aligned with the application server CPU drop outs, and they did: At first, I guessed that the disk service time spikes might be related to flushing the write through cache on the storage device, but I was unable to validate that theory. After searching the WWW for a while, I decided to try using a separate log device: # zpool add ZFS-db-41 log c3t60080E500017D55C000015C150A9F8A7d0 The ZFS log device is configured in a similar manner as described above: two physical disks mirrored in the storage array. This change to the database storage configuration eliminated the application server CPU drop outs: Here is the zpool configuration: # zpool status ZFS-db-41   pool: ZFS-db-41  state: ONLINE  scan: none requested config:         NAME                                     STATE         ZFS-db-41                                ONLINE           c3t60080E5...F4F6d0  ONLINE         logs           c3t60080E5...F8A7d0  ONLINE Now, the I/O spikes look like this:                     extended device statistics                  r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device     0.0 1053.5    0.0 4234.1  0.0  0.8    0.0    0.7   0  75 c3t60080E5...F8A7d0s0                     extended device statistics                  r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device     0.0 1131.8    0.0 4555.3  0.0  0.8    0.0    0.7   0  76 c3t60080E5...F8A7d0s0                     extended device statistics                  r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device     0.0 1167.6    0.0 4682.2  0.0  0.7    0.0    0.6   0  74 c3t60080E5...F8A7d0s0     0.0  162.2    0.0 19153.9  0.0  0.7    0.0    4.2   0  12 c3t60080E5...F4F6d0s0                     extended device statistics                  r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device     0.0 1247.2    0.0 4992.6  0.0  0.7    0.0    0.6   0  71 c3t60080E5...F8A7d0s0     0.0   41.0    0.0   70.0  0.0  0.1    0.0    1.6   0   2 c3t60080E5...F4F6d0s0                     extended device statistics                  r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device     0.0 1241.3    0.0 4989.3  0.0  0.8    0.0    0.6   0  75 c3t60080E5...F8A7d0s0                     extended device statistics                  r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device     0.0 1193.2    0.0 4772.9  0.0  0.7    0.0    0.6   0  71 c3t60080E5...F8A7d0s0 We can see the steady flow of 4k writes to the ZIL device from O_SYNC database log file writes. The spikes are from flushing the transaction group. Like almost all problems that I run into, once I thoroughly understand the problem, I find that other people have documented similar experiences. Thanks to all of you who have documented alternative approaches. Saved for another day: now that the problem is obvious, I should try "zfs:zfs_immediate_write_sz" as recommended in the ZFS Evil Tuning Guide. References: The ZFS Intent Log Solaris ZFS, Synchronous Writes and the ZIL Explained ZFS Evil Tuning Guide: Cache Flushes ZFS Evil Tuning Guide: Tuning ZFS for Database Performance

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  • Automatically adding CD box art so that I can put it on my iPod.

    - by Seamus
    I know it's possible to automatically find CD covers for albums, because rhythmbox is doing it on the fly. (When I listen to stuff, it finds the CD cover online...) What I want is to get this information onto my ipod. As it stands pretty much all my songs have the default blank CD cover... I use gtkpod to transfer music to it. This needs to be an automatic process, because I have a large music library and I'm lazy and it's not exactly an important thing... I rip CDs I buy with the basic CD extractor, so all the files are in a Artist/Album/song.mp3 structure. (Yes I know, mp3 is evil, but iPod doesn't like .ogg so whatever)

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  • How do I pitch ASP.NET over PHP to a potential client?

    - by roman m
    I work at a Microsoft shop doing mainly web development. We had a client who asked us to review (improve) the data model for his web app, but said that he wants to develop his app in PHP (he knows "a guy" who can do it). When I asked him why he wants to go with PHP, he gave me the standard set of arguments from the 90's: Microsoft is evil, and PHP is free Writing an ASP.NET app is more expensive (software-wise) Why would Facebook use PHP if it was a bad idea? [classic] He had a few more comments about the costs associated with going .NET. The truth is that "Microsoft is expensive" does not hold water any longer, with their "Express" suite, you can develop an ASP.NET app without paying anything for software. When it comes to hosting, you can save a few bucks with PHP over .NET, but that's a small fraction of the projected development costs (we quoted 10-15k). Going back to my question, what arguments would I give to a client in favor of ASP.NET over PHP? [please provide sources for quantitative claims]

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  • Are there jobs which are oriented towards optimisation programming or assembly

    - by jokoon
    3D engine programmers have to care a little about execution speed, but what about the programmers at ATI and nVidia ? How much do they need to optimize their driver applications ? Are there jobs out there who only purpose is execution speed and optimisation, or jobs for people to program only in assembly ? Please, no flame war about "premature optimisation is the root of all evil", I just want to know if such jobs exists, maybe in security ? In kernel programming ? Where ? Not at all ?

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  • How To Deliberately Hide Bugs In Code (for use in a Novel I'm writing) [closed]

    - by Dennis Murphy
    I'm writing a novel in which an evil programmer wants to include subtle errors in his code that are likely to go unnoticed by his supervisor during a code review and unlikely to be caught by a compiler, yet cause damage at possibly random times when the program is executed by an end-user. I only need a couple of examples, which may be exotic but which have to be easily explainable to non-technical readers. Procedural or object-oriented examples would be equally helpful. (It's been a VERY long time since I've written any code.) Thanks for your help.

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  • Why can't I get into my repositories?

    - by ken1943
    Upgraded from 10.04 to 10.10 by mistake and am having problems with some of my programs. They either don't work or they disappear from view on the screen. The Repositories menu item in Synaptic Packages Manager is a case in point. The computer does nothing when I choose this item. I am locked out of unless I edit /etc/apt/sources.list. The rest of the application seems to work, however. Update Manager just flashes on screen then disappears without doing, as does Printing. How do I downgrade from a higher to a lower level repository? I need to downgrade from 10.10 to 10.04. Each time Ubuntu upgrades to 10.10 evil things happen and the operating system really gets messed up. I really do not want to have to erase and install my operating system all over again if I can help it.

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  • Google Maps keeps displaying in Spanish

    - by Ken Hortsch
    Originally posted on: http://geekswithblogs.net/BlueProbe/archive/2013/11/12/154610.aspxIn Chrome I use Google Maps as a search provider.  That way I can just type maps for the URL address, hit a couple of tab keys, and enter the maps address and have the page rendered with my map.  Now periodically maps were displaying in Spanish with a "click here to translate to English” option.  Huh?  My language settings on the browser and within Google settings all were English.  Turns out I had set my Chrome search provider string to include a language query parm=es.  Why would I do that?  Evil twin perhaps.

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  • where does the discrepancy between \# in PS1 and n in !n come from?

    - by Cbhihe
    Something has been gnawing at me for a while now and I can't seem to find a relevant answer either in man pages or using your 'Don't be evil' search engine. My .bashrc has the following: shopt -s histappend HISTSIZE=100 HISTFILESIZE=0 # 200 previous value Putting HISTFILESIZE to 0 allows me to start with a clean history slate with each new term window. I find it practical in conjunction with using a prompt that contains \#, because when visualizing a previous command before recalling it with !n or !-p, one can just do: $ history | more to see its relevant "n" value In my case, usually the result of: $ \history | tail -1 | awk '{print $1}' # (I know this is an overkill, don't flame me) equals the expanded value of # in PS1 minus 1, which is how I like it to be at all times. But then, sometimes not. At times the expanded value of # sort of "runs away". It's incremented in such a a manner that it becomes than $(( $(\history | tail -1 | awk '{print $1}')+1 )) Any pointers, anyone?

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  • How do I create a fire sphere (fireball) in opengl? (opengl Visual C++)

    - by gn66
    I'm making an evil Pacman in OpenGL and I need to make my spheres look like a fireballs, does anyone know how I do that? And what material colour should I use? Also, is there a colour palette to change the colour of my materials? This is how I create a sphere: GLfloat mat_ambient[] = { 0.25, 0.25, 0.25, 1.0 }; GLfloat mat_diffuse[] = { 0.4, 0.4, 0.4, 1.0 }; GLfloat mat_specular[] = { 0.774597, 0.774597, 0.774597, 1.0 }; GLfloat mat_shine = 0.6; glMaterialfv (GL_FRONT, GL_AMBIENT, mat_ambient); glMaterialfv (GL_FRONT, GL_DIFFUSE, mat_diffuse); glMaterialfv (GL_FRONT, GL_SPECULAR, mat_specular); glMaterialf (GL_FRONT, GL_SHININESS, mat_shine * 128); glPushMatrix(); glTranslatef(x,y,0); glutSolidSphere(size, 20, 10); glFlush(); glPopMatrix();

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  • SQL Why is prefixing column names considered bad practice?

    - by P.Brian.Mackey
    According to a popular SO post is it considered a bad practice to prefix table names. At my company every column is prefixed by a table name. This is difficult for me to read. I'm not sure the reason, but this naming is actually the company standard. I can't stand the naming convention, but I have no documentation to back up my reasoning. All I know is that reading AdventureWorks is much simpler. In this our company DB you will see a table, Person and it might have column name: Person_First_Name or maybe even Person_Person_First_Name (don't ask me why you see person 2x) Why is it considered a bad practice to pre-fix column names? Are underscores considered evil in SQL as well? Note: I own Pro SQL Server 2008 - Relation Database design and implementation. References to that book are welcome.

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  • Is a function plotter a legitimate use of eval() in JavaScript?

    - by moose
    From PHP development I know that eval is evil and I've recently read What constitutes “Proper use” of the javascript Eval feature? and Don't be eval. The only proper use of eval I've read is Ajax. I'm currently developing a visualization tool that lets users see how polynomials can interpolate functions: Example Code on GitHub I use eval for evaluation of arbitrary functions. Is this a legitimate use of eval? How could I get rid of eval? I want the user to be able to execute any function of the following forms: a x^i with a,i in R sin, cos, tan b^x with b in R any combination that you can get by adding (e.g. x^2 + x^3 + sin(x)), multiplying (e.g. sin(x)*x^2) or inserting (e.g. sin(x^2))

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  • Layering Design Pattern in Java clean code style

    - by zeraDev
    As a Java developer, I am developing trying to use the clean code rules. But in my team we are facing a concrete problem: We have a business layer offering a service called "createObject", this service makes a lot of operation which can result to problem. E.g: parentObjectDontExist, objectAlreadyExist, dontHaveAuthorizationToCreate, operationFailed... and we want the UI using this service to display different information messages depending which error occurred. In old java dev, we should have create all signed exception type and throw it in createObject. As Clean code says, it is forbidden to use Exception for business logic AND signed exceptions are evil... Why not...But i don't know how to solved this problem and i don't want to use return code. How do you do? Thanks for youre experience return.

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  • How do I know if I've gone too far with processing things in a game?

    - by ThePlan
    A common programming quote I see every day is: Premature optimization is the root of all evil! I admit I'm one of those guys that like to do premature optimization in a pretty obssessive manner but that's probably because I'm not aware how powerful modern processors are. I can think of lots of sollutions for a problem, but all of them are tough on the memory side, and I keep thinking "This will hurt me more in the future when I'll have to re-do it because it's bad performance-wise." How do you know when the code you are thinking of is going too far and is not a case of premature optimization? How much can your game handle at a time before performance becomes a problem?

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  • Why is casting Derived** to Base*const* forbidden ?

    - by smerlin
    After reading this question, i saw the answer by Naveen containing a link to this page, which basically says, that casting from Derived** to Base** is forbidden since could change a pointer to an pointer to a Derived1 object point to a pointer to a Derived2 object (like: *derived1PtrPtr=derived2Ptr). OK, i understand this is evil ... But when casting Derived** to Base*const* this is not even possible, so whats the reason that this is not allowed anyway ?

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  • Casting of interfaces

    - by Srinivas Reddy Thatiparthy
    interfaces provide a useful abstraction capability. One can have a class Foo implement some interfaces, say A, B, and C. Some client code may get a reference of type A, others one of type B, etc. each actually the same Foo object but the interface exposing only a narrow subset of the functionality. Of course, evil client code can try to cast the A reference to Foo, then access the other functionality.How to prevent this?

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  • Flex 4 IntelliJ IDEA wrapper html crashes browser

    - by user347641
    I'm building an Flex 4 application using IntelliJ IDEA generated sample Flex application. I replace the mxml with the following code from the book Hello Flex 4. It simply crashes the browser when I run it. I tried it on both FF and Chrome. Any clues? [Bindable] public var _bread:Number = Number.NaN; ]]></fx:Script> <fx:Declarations> <s:RadioButtonGroup id="moralityRBG"/> <s:RadioButtonGroup id="restaurantRBG" selectedValue="{_theory.length % 2 == 0 ? 'smoking' : 'non'}"/> </fx:Declarations> <s:Panel width="100%" height="100%" title="Simple Components!"> <s:layout> <s:HorizontalLayout paddingLeft="5" paddingTop="5"/> </s:layout> <s:VGroup> <s:TextArea id="textArea" width="200" height="50" text="@{_theory}"/> <s:TextInput id="textInput" width="200" text="@{_theory}"/> <s:HSlider id="hSlider" minimum="0" maximum="11" liveDragging="true" width="200" value="@{_bread}"/> <s:VSlider id="vSlider" minimum="0" maximum="11" liveDragging="true" height="50" value="@{_bread}"/> <s:Button label="{_theory}" width="200" color="{alarmTB.selected ? 0xFF0000 : 0}" click="_bread = Math.min(_theory.length, 11)"/> <s:CheckBox id="checkBox" selected="{_bread % 2 == 0}" label="even?"/> </s:VGroup> <s:VGroup> <s:RadioButton label="Good" value="good" group="{moralityRBG}"/> <s:RadioButton label="Evil" value="evil" group="{moralityRBG}"/> <s:RadioButton label="Beyond" value="beyond" group="{moralityRBG}"/> <s:RadioButton label="Smoking" value="smoking" group="{restaurantRBG}"/> <s:RadioButton label="Non-Smoking" value="non" group="{restaurantRBG}"/> <s:ToggleButton id="alarmTB" label="ALARM!"/> <s:NumericStepper id="numericStepper" value="@{_bread}" minimum="0" maximum="11" stepSize="1"/> <s:Spinner id="spinner" value="@{_bread}" minimum="0" maximum="11" stepSize="1"/> </s:VGroup> </s:Panel>

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  • Validation framework for .NET Compact Framework 3.5.

    - by Michal Drozdowicz
    Do you know of a fast and simple entity validation framework that could be used in a Compact Framework project? I've done some experiments with FluentValidation (using db4o System.Linq.Expressions, but it's rather slow) and EViL (but it seems a bit half-baked). Can you suggest any other or maybe point me to some resources on how to design such a framework so that it's both easy to use and performant?

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  • what browser is document.layers sniffing?

    - by mkoryak
    I am looking at some JS code from the 20th century, and they are using document.layers in code that is trying to get the current key code. What browser are they sniffing for? i am about to replace the code with something like this: var fn = function(event){ event = event || window.event; var code = event.charCode || event.keyCode; } but i am afraid of breaking something arcane and releasing the evil

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  • Big O, how do you calculate/approximate it?

    - by Sven
    Most people with a degree in CS will certainly know what Big O stands for. It helps us to measure how (in)efficient an algorithm really is and if you know in what category the problem you are trying to solve lays in you can figure out if it is still possible to squeeze out that little extra performance.* But I'm curious, how do you calculate or approximate the complexity of your algorithms? *: but as they say, don't overdo it, premature optimization is the root of all evil, and optimization without a justified cause should deserve that name as well.

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  • Is unobtrusive RJS files in Rails 3 considered a good idea?

    - by midas06
    I'm working on implementing javascript functionality in my rails 3 app. Now that rjs is supposedly unobtrusive (I honestly don't know a lot about rjs), is it still "evil"? It seems to me the downside may be a lack of testability, but partial page updates via rjs seem to be easier than jumping through the rails hurdles to make ajax requests via jquery. Thoughts? Examples?

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  • What are the DB smells?

    - by Jonas Byström
    We all know 'code smells', but what are the fundamental 'database smells'? I'm a DB n00b, but I'll give an example of something that I find fishy. It seems to me like when I have to join 6-8 tables together to optimize our loading that we have a DB smell? Or would that be a pretty 'normal' database layout? (Sure, early optimization is the root of all evil, but this seems to me like early pessimisation, not to mention the cumbersomeness?)

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  • Providing raw MP3/AAC data to Flex/Flash from a custom container

    - by Joonas Trussmann
    Having had a quick look at the Flex docs I can't seem to find any reference to providing audio content to be played from a custom (possibly encrypted - don't worry, it's not that evil) container format. Is this possible and if so, could someone point me in the right direction. Or if that's not possible, some way to hook into the disk/network (disk is much more important in this case) I/O of the sound playing mechanism to provide a supported container in memory from a custom wrapper.

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  • golang closure variable scope

    - by waaadim
    I'm reading 'CreateSpace An Introduction to Programming in Go 2012' and on page 86 I found this evil magic func makeEvenGenerator() func() uint { i := uint(0) return func() (ret uint) { ret = i i += 2 return } } // here's how it's called nextEven := makeEvenGenerator() fmt.Println(nextEven()) fmt.Println(nextEven()) fmt.Println(nextEven()) 1) Why is i not resetting ? 2) is nextEven() returning and uint or is Println so smart that it can work with everything ?

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