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• LASTDATE dates arguments and upcoming events #dax #tabular #powerpivot

  - by Marco Russo (SQLBI)

  Recently I had to write a DAX formula containing a LASTDATE within the logical condition of a FILTER: I found that its behavior was not the one I expected and I further investigated. At the end, I wrote my findings in this article on SQLBI, which can be applied to any Time Intelligence function with a <dates> argument.The key point is that when you write LASTDATE( table[column] )in reality you obtain something like LASTDATE( CALCULATETABLE( VALUES( table[column] ) ) )which converts an existing row context into a filter context.Thus, if you have something like FILTER( table, table[column] = LASTDATE( table[column] ) the FILTER will return all the rows of table, whereas you probably want to use FILTER( table, table[column] = LASTDATE( VALUES( table[column] ) ) )so that the existing filter context before executing FILTER is used to get the result from VALUES( table[column] ), avoiding the automatic expansion that would include a CALCULATETABLE that would hide the existing filter context.If after reading the article you want to get more insights, read the Jeffrey Wang's post here.In these days I'm speaking at SQLRally Nordic 2012 in Copenhagen and I will be in Cologne (Germany) next week for a SSAS Tabular Workshop, whereas Alberto will teach the same workshop in Amsterdam one week later. Both workshops still have seats available and the Amsterdam's one is still in early bird discount until October 3rd!Then, in November I expect to meet many blog readers at PASS Summit 2012 in Seattle and I hope to find the time to write other article on interesting things on Tabular and PowerPivot. Stay tuned!

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• Is there a resource that explains the benefits of layered programming?

  - by P.Brian.Mackey

  Some developers I know favor what I would call a procedural programming style. I recognize that procedural programming has its uses, albeit not in the business application world of .NET programming. So let's say we have a winform application with a buttonclick event. The buttonclick handles everything from the UI configuration to the database call and data manipulation. So you end up with a method that is 100's of lines of code long. Outside the fact that this code can't be considered test-able for various reasons, this style of programming is fragile to change. I can talk bout OO, Anti-patterns, etc. The problem is that any distinct topic I can dream up requires a great deal of explanation to understand the potential benefits. Outside of finding a new job (lots of businesses program this way), how can I teach these kinds of developers how to write better code? Obviously we can't sit around a round table and discuss pro's and con's all day due to time constraints and real work that has to be done. Although, training and intense training is the only thing I can think of to fix these problems. Not to say I write perfect code, I most certainly do not. I do believe there are certain best practices that should be followed as a rule E.G. OO in the context of .NET. The most common excuse I hear is "we can't write code fast enough if we do it like that".

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• Access Officejet Pro L7590 memory card reader

  - by luri

  I can't manage to access my printer's memory card reader in Nautilus. I can just access it with hp-unload. Here's a sample output from this command: lubuntu@L-X6:~$ hp-unload hp:/net/Officejet_Pro_L7500?zc=HP065193 HP Linux Imaging and Printing System (ver. 3.10.6) Photo Card Access Utility ver. 3.3 Copyright (c) 2001-9 Hewlett-Packard Development Company, LP This software comes with ABSOLUTELY NO WARRANTY. This is free software, and you are welcome to distribute it under certain conditions. See COPYING file for more details. Using device: hp:/net/Officejet_Pro_L7500?zc=HP065193 |error: Photo card write failed (Card may be write protected) / Photocard on device hp:/net/Officejet_Pro_L7500?zc=HP065193 mounted DO NOT REMOVE PHOTO CARD UNTIL YOU EXIT THIS PROGRAM warning: Photo card is write protected. Type 'help' for a list of commands. Type 'exit' to quit. pcard: / > ls \ Name Size Type dcim/ directory eos_digi.tal 0 B unknown/unknown 1 files, 0 B pcard: / > cd dcim |pcard: /dcim > ls | Name Size Type . directory .. directory 100eos5d/ directory 267canon/ directory 270canon/ directory 271canon/ directory 272canon/ directory 0 files, 0 B pcard: /dcim > cd 272canon -pcard: /dcim/272canon > ls \ Name Size Type . directory .. directory _mg_7201.jpg 3.1 MB image/jpeg ...........(some more files)................. _mg_7281.jpg 2.5 MB image/jpeg _mg_7282.jpg 2.5 MB image/jpeg 82 files, 241.6 MB (253377883) How can I acess it from nautilus or mount it as a filesystem? Note that this is similar to this other question: Can't get HP Officejet 6500 card reader to work. but actually there seemed to be no supported device here, while in my case I manage to access the memory card from hp-unload.

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• What does your Lisp workflow look like?

  - by Duncan Bayne

  I'm learning Lisp at the moment, coming from a language progression that is Locomotive BASIC - Z80 Assembler - Pascal - C - Perl - C# - Ruby. My approach is to simultaneously: write a simple web-scraper using SBCL, QuickLisp, closure-html, and drakma watch the SICP lectures I think this is working well; I'm developing good 'Lisp goggles', in that I can now read Lisp reasonably easily. I'm also getting a feel for how the Lisp ecosystem works, e.g. Quicklisp for dependencies. What I'm really missing, though, is a sense of how a seasoned Lisper actually works. When I'm coding for .NET, I have Visual Studio set up with ReSharper and VisualSVN. I write tests, I implement, I refactor, I commit. Then when I'm done enough of that to complete a story, I write some AUATs. Then I kick off a Release build on TeamCity to push the new functionality out to the customer for testing & hopefully approval. If it's an app that needs an installer, I use either WiX or InnoSetup, obviously building the installer through the CI system. So, my question is: as an experienced Lisper, what does your workflow look like? Do you work mostly in the REPL, or in the editor? How do you do unit tests? Continuous integration? Packaging & deployment? When you sit down at your desk, steaming mug of coffee to one side and a framed photo of John McCarthy to the other, what is it that you do? Currently, I feel like I am getting to grips with Lisp coding, but not Lisp development ...

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• Javascript: Machine Constants Applicable?

  - by DavidB2013

  I write numerical routines for students of science and engineering (although they are freely available for use by anybody else as well) and am wondering how to properly use machine constants in a JavaScript program, or if they are even applicable. For example, say I am writing a program in C++ that numerically computes the roots of the following equation: exp(-0.7x) + sin(3x) - 1.2x + 0.3546 = 0 A root-finding routine should be able to compute roots to within the machine epsilon. In C++, this value is specified by the language: DBL_EPSILON. C++ also specifies the smallest and largest values that can be held by a float or double variable. However, how does this convert to JavaScript? Since a Javascript program runs in a web browser, and I don't know what kind of computer will run the program, and JavaScript does not have corresponding predefined values for these quantities, how can I implement my own version of these constants so that my programs compute results to as much accuracy as allowed on the computer running the web browser? My first draft is to simply copy over the literal constants from C++: FLT_MIN: 1.17549435082229e-038 FLT_MAX: 3.40282346638529e+038 DBL_EPSILON: 2.2204460492503131e-16 I am also willing to write small code blocks that could compute these values for each machine on which the program is run. That way, a supercomputer might compute results to a higher accuracy than an old, low-level, PC. BUT, I don't know if such a routine would actually reach the computer, in which case, I would be wasting my time. Anybody here know how to compute and use (in Javascript) values that correspond to machine constants in a compiled language? Is it worth my time to write small programs in Javascript that compute DBL_EPSILON, FLT_MIN, FLT_MIN, etc. for use in numerical routines? Or am I better off simply assigning literal constants that come straight from C++ on a standard Windows PC?

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• SCO UNIX problem: "Cannot create /var/adm/utmp or /var/adm/utmpx"

  - by Maktouch

  Hey everyone, I have an old server that doesn't boot. I don't know the version of unix installed, but I see SCO UNIX. It stops with that error: UX:init: ERROR: Cannot create /var/adm/utmp or /var/adm/utmpx UX:init: ERROR: failed write of utmpx entry: " " UX:init: ERROR: failed write of utmpx entry: " " UX:init: INFO: SINGLE USER MODE After that message, it just stops. I cannot write or press anything. Even CTRL + ALT + DEL does not work. I cannot get into the system. I have tried booting with a DamnSmallLinux LiveCD but it does not recognize the file system on HDA. Is there a way to either log in as root or bypass this error? Thanks.

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• What does your Lisp workflow look like?

  - by Duncan Bayne

  I'm learning Lisp at the moment, coming from a language progression that is Locomotive BASIC - Z80 Assembler - Pascal - C - Perl - C# - Ruby. My approach is to simultaneously: write a simple web-scraper using SBCL, QuickLisp, closure-html, and drakma watch the SICP lectures I think this is working well; I'm developing good 'Lisp goggles', in that I can now read Lisp reasonably easily. I'm also getting a feel for how the Lisp ecosystem works, e.g. Quicklisp for dependencies. What I'm really missing, though, is a sense of how a seasoned Lisper actually works. When I'm coding for .NET, I have Visual Studio set up with ReSharper and VisualSVN. I write tests, I implement, I refactor, I commit. Then when I'm done enough of that to complete a story, I write some AUATs. Then I kick off a Release build on TeamCity to push the new functionality out to the customer for testing & hopefully approval. If it's an app that needs an installer, I use either WiX or InnoSetup, obviously building the installer through the CI system. So, my question is: as an experienced Lisper, what does your workflow look like? Do you work mostly in the REPL, or in the editor? How do you do unit tests? Continuous integration? Packaging & deployment? When you sit down at your desk, steaming mug of coffee to one side and a framed photo of John McCarthy to the other, what is it that you do? Currently, I feel like I am getting to grips with Lisp coding, but not Lisp development ...

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• Samba permissions on a Debian server with Fedora client

  - by norova

  I have a Debian server sharing files via Samba. I can access the files via Windows with no problems whatsoever, but when I try to mount the share on a Fedora client using the same credentials I am unable to write to any files. I have proper read access, but no write permissions. Here are the settings for the share from my smb.conf: [lampp] path = /opt/lampp writable = yes browsable = yes I have to assume that it is an issue on the Fedora side of things because accessing the share from Windows works fine. I have also tried mounting via SSHFS with no luck; it also will allow me to read files but not write. However, in Windows, using a program called WebDrive I am able to access the files (essentially via SSHFS) with no issues whatsoever. I have tried setting up NFS but not much luck there either; I'd rather just stick with Samba if possible. Any suggestions?

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• How to present a stable data model in a public API that allows internal data structures to be changed without breaking the public view of the data?

  - by Max Palmer

  I am in the process of developing an application that allows users to write C# scripts. These scripts allow users to call selected methods and to access and manipulate data in a document. This works well, however, in the development version, scripts access the document's (internal) data structures directly. This means that if we were to change the internal data model/structure, there is a good chance that someone's script will no longer compile. We obviously want to prevent this breaking change from happening, but still want to allow the user to write sensible C# code (whilst not restricting how we develop our internal data model as a result). We therefore need to decouple our scripting API and its data structures from our internal methods and data structures. We've a few ideas as to how we might allow the user to access a what is effectively a stable public version of the document's internal data*, but I wanted to throw the question out there to someone who might have some real experience of this problem. NB our internal document's data structure is quite complex and it could be quite difficult to wrap. We know we want to expose as little as possible in our public API, especially as once it's out there, it's out there for good. Can anyone help? How do scripting languages / APIs decouple their public API and data structures from their internal data structures? Is there no real alternative to having to write a complex interaction layer? If we need to do this, what's a good approach or pattern for wrapping complex data structures that include nested objects, including collections? I've looked at the API facade pattern, which looks like it's trying to address these kinds of issues, but are there alternatives? *One idea is to build a data facade that is kept stable across versions of our application. The facade exposes a set of facade data objects that are used in the script code. These maintain backwards compatibility and wrap access to our internal document's data model.

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• Why is testing MVC Views frowned upon?

  - by Peter Bernier

  I'm currently setting the groundwork for an ASP.Net MVC application and I'm looking into what sort of unit-tests I should be prepared to write. I've seen in multiple places people essentially saying 'don't bother testing your views, there's no logic and it's trivial and will be covered by an integration test'. I don't understand how this has become the accepted wisdom. Integration tests serve an entirely different purpose than unit tests. If I break something, I don't want to know a half-hour later when my integration tests break, I want to know immediately. Sample Scenario : Lets say we're dealing with a standard CRUD app with a Customer entity. The customer has a name and an address. At each level of testing, I want to verify that the Customer retrieval logic gets both the name and the address properly. To unit-test the repository, I write an integration test to hit the database. To unit-test the business rules, I mock out the repository, feed the business rules appropriate data, and verify my expected results are returned. What I'd like to do : To unit-test the UI, I mock out the business rules, setup my expected customer instance, render the view, and verify that the view contains the appropriate values for the instance I specified. What I'm stuck doing : To unit-test the repository, I write an integration test, setup an appropriate login, create the required data in the database, open a browser, navigate to the customer, and verify the resulting page contains the appropriate values for the instance I specified. I realize that there is overlap between the two scenarios discussed above, but the key difference it time and effort required to setup and execute the tests. If I (or another dev) removes the address field from the view, I don't want to wait for the integration test to discover this. I want is discovered and flagged in a unit-test that gets multiple times daily. I get the feeling that I'm just not grasping some key concept. Can someone explain why wanting immediate test feedback on the validity of an MVC view is a bad thing? (or if not bad, then not the expected way to get said feedback)

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• Where is it permissible to add logging code in a MVC model?

  - by BDotA

  Working on a C# WinForms program that is written in a MVC ( actually Model-View-Presenter) style and I want to add a few lines of code that is responsible for logging some events. Where should I write two or three lines of code that I need? Should I write it in the Presenter section? To get an idea, here is some lines of sample code that already exists in the Save() metohd in Company.MyApplication.Presenter.MyPresenter.cs class: he has written codes lie the following in this part of presenter: private void Save(Helper.SaveStatusEnum status) { if (notification.CheckLocks(orderIdCollection)) { using (new HourglassController()) { controller.FireActiveCellLeaving(); ViewDocumentedValues(); int result = saveController.Save(status); if (result == Helper.SAVE_SUCCESSFUL) { // IS IT OK TO WRITE MY COUPLE LINES OF CODE IN HERE??????????? model.Dirty = false; if ((model.CurrentStatus == Helper.OrderStatusEnum.Complete) || (model.CurrentStatus == Helper.OrderStatusEnum.Corrected)) { controller.EnableDisableSheet(false); } CheckApplicationState(); SheetHelper.ClearUnsavedDataRowImage(view.ActiveSheet); } else { MessageBox.Show("An unexpected error occuring trying to save."); } } } }

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• What permissions / ownership to set on PHP Sessions Folder when running FastCGI / PHP-FPM (as user "nobody")?

  - by Professor Frink

  I'm having trouble getting a number of scripts running because PHP-FPM can't write to my session folder: "2009/10/01 23:54:07 [error] 17830#0: *24 FastCGI sent in stderr: "PHP Warning: Unknown: open(/var/lib/php/session/sess_cskfq4godj4ka2a637i5lq41o5, O_RDWR) failed: Permission denied (13) in Unknown on line 0 PHP Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/lib/php/session) in Unknown on line 0" while reading upstream" Obviously this is a permission issue; my session folder's owner/group is the webserver's user, NGINX. PHP-FPM runs as nobody though, and hence adding it to the nginx group is not so trivial. A temporary solution is to set the permissions of /var/lib/php/session to 777 - I have a feeling that's not the "best practice" though. What is the best practice when you need to assign a daemon write access to a folder, but it is running as nobody ?

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• Apache server doesn't create directory or file under www-data user [duplicate]

  - by Harkonnen

  This question already has an answer here: What permissions should my website files/folders have on a Linux webserver? 4 answers very newbie to Apache here I installed Apache 2.4 on my Arch server where I installed newznab (a newsgroups indexer). I have noticed that all files newznab needs to create are created under my login user, and not apache default user (www-data). I read here that it's bad security practice to allow www-data to write files. I agree. But as an apache newbie, I would like to know where (in the httpd.conf I suppose ?) the user allowed to write files can be configured, because I want another account to be allowed to write files instead of my main account.

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• ASMLib

  - by wcoekaer

  Oracle ASMlib on Linux has been a topic of discussion a number of times since it was released way back when in 2004. There is a lot of confusion around it and certainly a lot of misinformation out there for no good reason. Let me try to give a bit of history around Oracle ASMLib. Oracle ASMLib was introduced at the time Oracle released Oracle Database 10g R1. 10gR1 introduced a very cool important new features called Oracle ASM (Automatic Storage Management). A very simplistic description would be that this is a very sophisticated volume manager for Oracle data. Give your devices directly to the ASM instance and we manage the storage for you, clustered, highly available, redundant, performance, etc, etc... We recommend using Oracle ASM for all database deployments, single instance or clustered (RAC). The ASM instance manages the storage and every Oracle server process opens and operates on the storage devices like it would open and operate on regular datafiles or raw devices. So by default since 10gR1 up to today, we do not interact differently with ASM managed block devices than we did before with a datafile being mapped to a raw device. All of this is without ASMLib, so ignore that one for now. Standard Oracle on any platform that we support (Linux, Windows, Solaris, AIX, ...) does it the exact same way. You start an ASM instance, it handles storage management, all the database instances use and open that storage and read/write from/to it. There are no extra pieces of software needed, including on Linux. ASM is fully functional and selfcontained without any other components. In order for the admin to provide a raw device to ASM or to the database, it has to have persistent device naming. If you booted up a server where a raw disk was named /dev/sdf and you give it to ASM (or even just creating a tablespace without asm on that device with datafile '/dev/sdf') and next time you boot up and that device is now /dev/sdg, you end up with an error. Just like you can't just change datafile names, you can't change device filenames without telling the database, or ASM. persistent device naming on Linux, especially back in those days ways to say it bluntly, a nightmare. In fact there were a number of issues (dating back to 2004) : Linux async IO wasn't pretty persistent device naming including permissions (had to be owned by oracle and the dba group) was very, very difficult to manage system resource usage in terms of open file descriptors So given the above, we tried to find a way to make this easier on the admins, in many ways, similar to why we started working on OCFS a few years earlier - how can we make life easier for the admins on Linux. A feature of Oracle ASM is the ability for third parties to write an extension using what's called ASMLib. It is possible for any third party OS or storage vendor to write a library using a specific Oracle defined interface that gets used by the ASM instance and by the database instance when available. This interface offered 2 components : Define an IO interface - allow any IO to the devices to go through ASMLib Define device discovery - implement an external way of discovering, labeling devices to provide to ASM and the Oracle database instance This is similar to a library that a number of companies have implemented over many years called libODM (Oracle Disk Manager). ODM was specified many years before we introduced ASM and allowed third party vendors to implement their own IO routines so that the database would use this library if installed and make use of the library open/read/write/close,.. routines instead of the standard OS interfaces. PolyServe back in the day used this to optimize their storage solution, Veritas used (and I believe still uses) this for their filesystem. It basically allowed, in particular, filesystem vendors to write libraries that could optimize access to their storage or filesystem.. so ASMLib was not something new, it was basically based on the same model. You have libodm for just database access, you have libasm for asm/database access. Since this library interface existed, we decided to do a reference implementation on Linux. We wrote an ASMLib for Linux that could be used on any Linux platform and other vendors could see how this worked and potentially implement their own solution. As I mentioned earlier, ASMLib and ODMLib are libraries for third party extensions. ASMLib for Linux, since it was a reference implementation implemented both interfaces, the storage discovery part and the IO part. There are 2 components : Oracle ASMLib - the userspace library with config tools (a shared object and some scripts) oracleasm.ko - a kernel module that implements the asm device for /dev/oracleasm/* The userspace library is a binary-only module since it links with and contains Oracle header files but is generic, we only have one asm library for the various Linux platforms. This library is opened by Oracle ASM and by Oracle database processes and this library interacts with the OS through the asm device (/dev/asm). It can install on Oracle Linux, on SuSE SLES, on Red Hat RHEL,.. The library itself doesn't actually care much about the OS version, the kernel module and device cares. The support tools are simple scripts that allow the admin to label devices and scan for disks and devices. This way you can say create an ASM disk label foo on, currently /dev/sdf... So if /dev/sdf disappears and next time is /dev/sdg, we just scan for the label foo and we discover it as /dev/sdg and life goes on without any worry. Also, when the database needs access to the device, we don't have to worry about file permissions or anything it will be taken care of. So it's a convenience thing. The kernel module oracleasm.ko is a Linux kernel module/device driver. It implements a device /dev/oracleasm/* and any and all IO goes through ASMLib - /dev/oracleasm. This kernel module is obviously a very specific Oracle related device driver but it was released under the GPL v2 so anyone could easily build it for their Linux distribution kernels. Advantages for using ASMLib : A good async IO interface for the database, the entire IO interface is based on an optimal ASYNC model for performance A single file descriptor per Oracle process, not one per device or datafile per process reducing # of open filehandles overhead Device scanning and labeling built-in so you do not have to worry about messing with udev or devlabel, permissions or the likes which can be very complex and error prone. Just like with OCFS and OCFS2, each kernel version (major or minor) has to get a new version of the device drivers. We started out building the oracleasm kernel module rpms for many distributions, SLES (in fact in the early days still even for this thing called United Linux) and RHEL. The driver didn't make sense to get pushed into upstream Linux because it's unique and specific to the Oracle database. As it takes a huge effort in terms of build infrastructure and QA and release management to build kernel modules for every architecture, every linux distribution and every major and minor version we worked with the vendors to get them to add this tiny kernel module to their infrastructure. (60k source code file). The folks at SuSE understood this was good for them and their customers and us and added it to SLES. So every build coming from SuSE for SLES contains the oracleasm.ko module. We weren't as successful with other vendors so for quite some time we continued to build it for RHEL and of course as we introduced Oracle Linux end of 2006 also for Oracle Linux. With Oracle Linux it became easy for us because we just added the code to our build system and as we churned out Oracle Linux kernels whether it was for a public release or for customers that needed a one off fix where they also used asmlib, we didn't have to do any extra work it was just all nicely integrated. With the introduction of Oracle Linux's Unbreakable Enterprise Kernel and our interest in being able to exploit ASMLib more, we started working on a very exciting project called Data Integrity. Oracle (Martin Petersen in particular) worked for many years with the T10 standards committee and storage vendors and implemented Linux kernel support for DIF/DIX, data protection in the Linux kernel, note to those that wonder, yes it's all in mainline Linux and under the GPL. This basically gave us all the features in the Linux kernel to checksum a data block, send it to the storage adapter, which can then validate that block and checksum in firmware before it sends it over the wire to the storage array, which can then do another checksum and to the actual DISK which does a final validation before writing the block to the physical media. So what was missing was the ability for a userspace application (read: Oracle RDBMS) to write a block which then has a checksum and validation all the way down to the disk. application to disk. Because we have ASMLib we had an entry into the Linux kernel and Martin added support in ASMLib (kernel driver + userspace) for this functionality. Now, this is all based on relatively current Linux kernels, the oracleasm kernel module depends on the main kernel to have support for it so we can make use of it. Thanks to UEK and us having the ability to ship a more modern, current version of the Linux kernel we were able to introduce this feature into ASMLib for Linux from Oracle. This combined with the fact that we build the asm kernel module when we build every single UEK kernel allowed us to continue improving ASMLib and provide it to our customers. So today, we (Oracle) provide Oracle ASMLib for Oracle Linux and in particular on the Unbreakable Enterprise Kernel. We did the build/testing/delivery of ASMLib for RHEL until RHEL5 but since RHEL6 decided that it was too much effort for us to also maintain all the build and test environments for RHEL and we did not have the ability to use the latest kernel features to introduce the Data Integrity features and we didn't want to end up with multiple versions of asmlib as maintained by us. SuSE SLES still builds and comes with the oracleasm module and they do all the work and RHAT it certainly welcome to do the same. They don't have to rebuild the userspace library, it's really about the kernel module. And finally to re-iterate a few important things : Oracle ASM does not in any way require ASMLib to function completely. ASMlib is a small set of extensions, in particular to make device management easier but there are no extra features exposed through Oracle ASM with ASMLib enabled or disabled. Often customers confuse ASMLib with ASM. again, ASM exists on every Oracle supported OS and on every supported Linux OS, SLES, RHEL, OL withoutASMLib Oracle ASMLib userspace is available for OTN and the kernel module is shipped along with OL/UEK for every build and by SuSE for SLES for every of their builds ASMLib kernel module was built by us for RHEL4 and RHEL5 but we do not build it for RHEL6, nor for the OL6 RHCK kernel. Only for UEK ASMLib for Linux is/was a reference implementation for any third party vendor to be able to offer, if they want to, their own version for their own OS or storage ASMLib as provided by Oracle for Linux continues to be enhanced and evolve and for the kernel module we use UEK as the base OS kernel hope this helps.

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• RPi and Java Embedded GPIO: Java code to blink more LEDs

  - by hinkmond

  Now, it's time to blink the other GPIO ports with the other LEDs connected to them. This is easy using Java Embedded, since the Java programming language is powerful and flexible. Embedded developers are not used to this, since the C programming language is more popular but less easy to develop in. We just need to use a dynamic Java String array to map to the pinouts of the GPIO port names from the previous diagram posted. This way we can address each "channel" with an index into that String array. static String[] GpioChannels = { "0", "1", "4", "17", "21", "22", "10", "9" }; With this new dynamic array, we can streamline the main() of this Java program to activate all the ports. /** * @param args the command line arguments */ public static void main(String[] args) { FileWriter[] commandChannels; try { /*** Init GPIO port for output ***/ // Open file handles to GPIO port unexport and export controls FileWriter unexportFile = new FileWriter("/sys/class/gpio/unexport"); FileWriter exportFile = new FileWriter("/sys/class/gpio/export"); for (String gpioChannel : GpioChannels) { System.out.println(gpioChannel); // Reset the port unexportFile.write(gpioChannel); unexportFile.flush(); // Set the port for use exportFile.write(gpioChannel); exportFile.flush(); // Open file handle to port input/output control FileWriter directionFile = new FileWriter("/sys/class/gpio/gpio" + gpioChannel + "/direction"); // Set port for output directionFile.write(GPIO_OUT); directionFile.flush(); } And, then simply add array code to where we blink the LED to make it blink all the LEDS on and off at once. /*** Send commands to GPIO port ***/ commandChannels = new FileWriter[GpioChannels.length]; for (int channum=0; channum It's easier than falling off a log... or at least easier than C programming. Hinkmond

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• WEB based HPC cluster node management

  - by Skuja

  Hello, i am working on my school diploma thesis. The main goal is to create web based application where logged users could see free and busy nodes, turn them on and off, see what process they are running etc. Figured out that i could do something like this - write some cron daemon that would run every 30seconds or so, and it could run ping utility for each node to find out if it is on or off, then write results to some file. Then from my web app (i will write in PHP) i could read the info. Will it be a good solution? How would you suggest me to do it? And finally, is there any existing solutions (it may not be a definetly ewb based) for managment of cluster nodes?

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• Is "White-Board-Coding" inappropriate during interviews?

  - by Eoin Campbell

  This is a somewhat subjective quesiton but I'd love to hear feedback/opinions from either interviewers/interviewees on the topic. We split our technical part into 4 parts. Write Code, Read & Analyse Code, Design Session & Code on the white board. For the last part what we ask interviewees to do is write a small code snippet (4-5 lines) on the whiteboard and explain as they go through it. Let me be clear the purpose is not to catch people out. We're not looking for perfect syntax. Hell it can even be pseudo-code. but the point is to give them a very simple problem and see if their brain can communicate the solution to us. By simple problems I mean "Reverse a string", "FizzBuzz" etc... EDIT Just with regards the comment about Pseudo-Code. We always ask for an explicit language first. We;re a .NET C# house. we've only said "pseudo-code" where someone has been blanking/really struggling with the code. My question is "Is it innappropriate / unreasonable to expect a programmer to write a code snippet on a whiteboard during an interview ?"

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• SELinux adding new allowed samba type to access httpd_sys_content_t?

  - by Josh

  allow samba_share_t httpd_sys_content_t {read execute getattr setattr write}; allow smbd_t httpd_sys_content_t {read execute getattr setattr write}; I am taking a stab in the dark with resources I've looked at, at various places that the above policies are what I want. I basically want to allow Samba to write to my web docs without giving it free access to the operating system. I read a post by a NSA rep saying the best way was defining a new type and allowing both samba and httpd access. Setting the content to public content (public_content_rw_t) does not work without making use of some unrestrictive booleans. To state this in short, how do I allow samba to access a new type?

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• How to Generate a Create Table DDL Script Along With Its Related Tables

  - by Compudicted

  Have you ever wondered when creating table diagrams in SQL Server Management Studio (SSMS) how slickly you can add related tables to it by just right-clicking on the interesting table name? Have you also ever needed to script those related tables including the master one? And you discovered you have dozens of related tables? Or may be no SSMS at your disposal? That was me one day. Well, creativity to the rescue! I Binged and Googled around until I found more or less what I wanted, but it was all involving T-SQL, yeah, a long and convoluted CROSS APPLYs, then I saw a PowerShell solution that I quickly adopted to my needs (I am not referencing any particular author because it was a mashup): 1: ########################################################################################################### 2: # Created by: Arthur Zubarev on Oct 14, 2012 # 3: # Synopsys: Generate file containing the root table CREATE (DDL) script along with all its related tables # 4: ########################################################################################################### 5:   6: [System.Reflection.Assembly]::LoadWithPartialName('Microsoft.SqlServer.SMO') | out-null 7:   8: $RootTableName = "TableName" # The table name, no schema name needed 9:   10: $srv = new-Object Microsoft.SqlServer.Management.Smo.Server("TargetSQLServerName") 11: $conContext = $srv.ConnectionContext 12: $conContext.LoginSecure = $True 13: # In case the integrated security is not used uncomment below 14: #$conContext.Login = "sa" 15: #$conContext.Password = "sapassword" 16: $db = New-Object Microsoft.SqlServer.Management.Smo.Database 17: $db = $srv.Databases.Item("TargetDatabase") 18:   19: $scrp = New-Object Microsoft.SqlServer.Management.Smo.Scripter($srv) 20: $scrp.Options.NoFileGroup = $True 21: $scrp.Options.AppendToFile = $False 22: $scrp.Options.ClusteredIndexes = $False 23: $scrp.Options.DriAll = $False 24: $scrp.Options.ScriptDrops = $False 25: $scrp.Options.IncludeHeaders = $True 26: $scrp.Options.ToFileOnly = $True 27: $scrp.Options.Indexes = $False 28: $scrp.Options.WithDependencies = $True 29: $scrp.Options.FileName = 'C:\TEMP\TargetFileName.SQL' 30:   31: $smoObjects = New-Object Microsoft.SqlServer.Management.Smo.UrnCollection 32: Foreach ($tb in $db.Tables) 33: { 34: Write-Host -foregroundcolor yellow "Table name being processed" $tb.Name 35: 36: If ($tb.IsSystemObject -eq $FALSE -and $tb.Name -eq $RootTableName) # feel free to customize the selection condition 37: { 38: Write-Host -foregroundcolor magenta $tb.Name "table and its related tables added to be scripted." 39: $smoObjects.Add($tb.Urn) 40: } 41: } 42:   43: # The actual act of scripting 44: $sc = $scrp.Script($smoObjects) 45:   46: Write-host -foregroundcolor green $RootTableName "and its related tables have been scripted to the target file." Enjoy!

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• Managing arbitrary user permissions under PureFTPd

  - by Sebastián Grignoli

  I need to provide an FTP service that needs to be web-managed in the simplest way possible. My customer wants to create folders and users, and give them read only or read/write access arbitrarily. For example: The folder 'Documents' should be read only for several users, writable for internal users, and invisible for the rest. The folder 'Pictures' should be read only for journalists, writable for associates, and invisible for the rest. The folder 'Media' should be read only, writable or invisible for arbitrary users specified on the admin. There could be a large number of users and folders. I can't find a good way to accomplish that. I thought that I could give each user a home folder and put symlinks for the folders he has read access to, and make the user part of the folder's group when he has write access too, but now I think that this wouldn't work, because with PureFTPd (or ProFTPd) I can only specify the virtual user's mapping to a system user, and only one GUID for each virtual user. My approach requires that I could specify several GUIDs for each user (one by each folder he has write access to). I need to start programming this admin and I still don't know wich approach would work, if any. ¿Any ideas?

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• Vantec NexStar NAS Encloser - Writing large files

  - by peter

  Hi, I have one of these 'Vantec NexStar LX - NST-475LX-BK' drive enclosures. It is a NAS drive. When I write a file to the device using eSata, or a SMB share I cannot write files over 2GB. I think this is because the drive is formatted with FAT32. But when I access the device using FTP it doesn't matter. I can write files of any size. E.g. I wrote one on there last night which was 30GB. Does this make any sense? Why? I guess the most important thing for me is data integrity.

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• UDF Partition reported full when it is not

  - by Capt.Nemo

  I was using these instructions to setup an external hard disk with udf. I have been able to setup a multi-partition system using those instructions, but I seem to have hit a wall, where the partition is reported as full while writing to the disk. Every other tool available to me reports it as free. Relevant lshw output Here's a screenshot showing the disk: Both the output of df and the file manager (caja) report the disk as free. Filesystem Size Used Avail Use% Mounted on /dev/sda9 9.0G 7.6G 910M 90% / udev 974M 12K 974M 1% /dev /dev/sda1 50G 47G 295M 100% /media/Data /dev/sda6 49G 41G 5.9G 88% /home /dev/sda2 155G 127G 29G 82% /media/Entertainment /dev/sda8 14G 13G 516M 96% /media/Stuff /dev/sdb2 120G 1.9G 112G 2% /media/3c887659-5676-4946-875b-b797be508ce7 /dev/sdb3 11G 2.6G 7.7G 25% /media/108b0a1d-fd1a-4f38-b1c6-4ad1a20e34a3 /dev/sdb1 802G 34G 768G 5% /media/disk I seem to have hit a wall near the 35GB mark. Despite being shown as 35gb/860gb used everywhere, the following happens on a write attempt: [2017][/media/Dory]$ echo D>>echo bash: echo: write error: No space left on device Writing byte by byte, the maximum I can take it to is 34719248K. The most weird part is that on mounting it Windows, Windows can write to the disk easily, and the writes are being read fine back in Ubuntu. However, the used-bytes remains at 34719248K in Ubuntu (It goes higher on Windows, however).

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• Standards & compliances for secure web application development?

  - by MarkusK

  I am working with developers right now that write code the way they want and when i tell them to do it other way they respond that its just matter of preference how to do it and they have their way and i have mine. I am not talking about the formatting of code, but rather of way site is organized in classes and the way the utilize them. and the way they create functions and process forms etc. Their coding does not match my standards, but again they argue that its matter of preference and as long as goal achieved the can be different way's to do it. I agree but their way is proven to have bugs and we spend a lot of time going back and forth with them to fix all problems security or functionality, yet they still write same code no matter how many times i asked them to stop doing certain things. Now i am ready to dismiss them but friend of mine told me that he has same exact problem with freelance developers he work with. So i don't want to trade one bad apple for another. Question is is there some world wide (or at least europe and usa) accepted standard or compliance on how write secure web based applications. What application architecture should be for maintainable application. Is there are some general standard that can be used for any language ruby php or java govern security and functionality and quality of code? Or at least for PHP and MySQL i use for my website. So i can make them follow this strict standard and stop making excuses.

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• Empty interface to combine multiple interfaces

  - by user1109519

  Suppose you have two interfaces: interface Readable { public void read(); } interface Writable { public void write(); } In some cases the implementing objects can only support one of these but in a lot of cases the implementations will support both interfaces. The people who use the interfaces will have to do something like: // can't write to it without explicit casting Readable myObject = new MyObject(); // can't read from it without explicit casting Writable myObject = new MyObject(); // tight coupling to actual implementation MyObject myObject = new MyObject(); None of these options is terribly convenient, even more so when considering that you want this as a method parameter. One solution would be to declare a wrapping interface: interface TheWholeShabam extends Readable, Writable {} But this has one specific problem: all implementations that support both Readable and Writable have to implement TheWholeShabam if they want to be compatible with people using the interface. Even though it offers nothing apart from the guaranteed presence of both interfaces. Is there a clean solution to this problem or should I go for the wrapper interface? UPDATE It is in fact often necessary to have an object that is both readable and writable so simply seperating the concerns in the arguments is not always a clean solution. UPDATE2 (extracted as answer so it's easier to comment on) UPDATE3 Please beware that the primary usecase for this is not streams (although they too must be supported). Streams make a very specific distinction between input and output and there is a clear separation of responsibilities. Rather, think of something like a bytebuffer where you need one object you can write to and read from, one object that has a very specific state attached to it. These objects exist because they are very useful for some things like asynchronous I/O, encodings,...

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• Fast Data - Big Data's achilles heel

  - by thegreeneman

  At OOW 2013 in Mark Hurd and Thomas Kurian's keynote, they discussed Oracle's Fast Data software solution stack and discussed a number of customers deploying Oracle's Big Data / Fast Data solutions and in particular Oracle's NoSQL Database.  Since that time, there have been a large number of request seeking clarification on how the Fast Data software stack works together to deliver on the promise of real-time Big Data solutions.   Fast Data is a software solution stack that deals with one aspect of Big Data, high velocity.   The software in the Fast Data solution stack involves 3 key pieces and their integration:  Oracle Event Processing, Oracle Coherence, Oracle NoSQL Database.   All three of these technologies address a high throughput, low latency data management requirement.   Oracle Event Processing enables continuous query to filter the Big Data fire hose, enable intelligent chained events to real-time service invocation and augments the data stream to provide Big Data enrichment. Extended SQL syntax allows the definition of sliding windows of time to allow SQL statements to look for triggers on events like breach of weighted moving average on a real-time data stream.    Oracle Coherence is a distributed, grid caching solution which is used to provide very low latency access to cached data when the data is too big to fit into a single process, so it is spread around in a grid architecture to provide memory latency speed access.  It also has some special capabilities to deploy remote behavioral execution for "near data" processing.   The Oracle NoSQL Database is designed to ingest simple key-value data at a controlled throughput rate while providing data redundancy in a cluster to facilitate highly concurrent low latency reads.  For example, when large sensor networks are generating data that need to be captured while analysts are simultaneously extracting the data using range based queries for upstream analytics.  Another example might be storing cookies from user web sessions for ultra low latency user profile management, also leveraging that data using holistic MapReduce operations with your Hadoop cluster to do segmented site analysis.  Understand how NoSQL plays a critical role in Big Data capture and enrichment while simultaneously providing a low latency and scalable data management infrastructure thru clustered, always on, parallel processing in a shared nothing architecture. Learn how easily a NoSQL cluster can be deployed to provide essential services in industry specific Fast Data solutions. See these technologies work together in a demonstration highlighting the salient features of these Fast Data enabling technologies in a location based personalization service. The question then becomes how do these things work together to deliver an end to end Fast Data solution.  The answer is that while different applications will exhibit unique requirements that may drive the need for one or the other of these technologies, often when it comes to Big Data you may need to use them together.   You may have the need for the memory latencies of the Coherence cache, but just have too much data to cache, so you use a combination of Coherence and Oracle NoSQL to handle extreme speed cache overflow and retrieval.   Here is a great reference to how these two technologies are integrated and work together.  Coherence & Oracle NoSQL Database.   On the stream processing side, it is similar as with the Coherence case.  As your sliding windows get larger, holding all the data in the stream can become difficult and out of band data may need to be offloaded into persistent storage.  OEP needs an extreme speed database like Oracle NoSQL Database to help it continue to perform for the real time loop while dealing with persistent spill in the data stream.  Here is a great resource to learn more about how OEP and Oracle NoSQL Database are integrated and work together.  OEP & Oracle NoSQL Database.

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