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  • Version hash to solve Event Sourcing problems

    - by SystematicFrank
    The basic examples I have seen about Event Sourcing do not deal with out of order events, clock offsets in different systems and late events from system partitions. I am wondering if more polished Event Sourcing implementations rely on a version stamp of modified objects? For example, assuming that the system is rendering the entity Client with version id ABCD1234. If the user modifies the entity, the system will create an event with the modified fields AND the version id reference to which version it applies. Later the event responder would detect out of order events and merge them.

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  • Is it a waste of time to free resources before I exit a process?

    - by Martin
    Let's consider a fictional program that builds a linked list in the heap, and at the end of the program there is a loop that frees all the nodes, and then exits. For this case let's say the linked list is just 500K of memory, and no special space managing is required. Is that a wast of time, because the OS will do that anyway? Will there be a different behavior later? Is that different according to the OS version? I'm mainly interested in UNIX based systems, but any information will be appreciated. I had today my first lesson in OS course and I'm wondering about that now.

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  • How difficult is it to change from Embedded programming to a high level programming [on hold]

    - by anudeep shetty
    I have a background in Computer Science. I worked on Embedded programming on Linux file systems, after I finished my Bachelor's degree, for over a year. After that I pursued my masters where most of my course choices involved working on web, java and databases. Now I have an offer to work with a company that is offering a job to work on the OS level. The company is pretty good but I am feeling that my Masters has gone to waste. I wanted to know is it common that a Computer Science major works on low-level coding and is there a possibility that I can work in this company for some years and then move onto an opportunity where I can work on high-level coding? Also is working on low-level programming a safe choice in terms of job opportunities?

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  • What are best practices for testing programs with stochastic behavior?

    - by John Doucette
    Doing R&D work, I often find myself writing programs that have some large degree of randomness in their behavior. For example, when I work in Genetic Programming, I often write programs that generate and execute arbitrary random source code. A problem with testing such code is that bugs are often intermittent and can be very hard to reproduce. This goes beyond just setting a random seed to the same value and starting execution over. For instance, code might read a message from the kernal ring buffer, and then make conditional jumps on the message contents. Naturally, the ring buffer's state will have changed when one later attempts to reproduce the issue. Even though this behavior is a feature it can trigger other code in unexpected ways, and thus often reveals bugs that unit tests (or human testers) don't find. Are there established best practices for testing systems of this sort? If so, some references would be very helpful. If not, any other suggestions are welcome!

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  • How to organize my site's file system properly?

    - by Wolfpack'08
    Doing some reading on Stack Overflow, I've found a lot of information suggesting that proper organization of a file system is crucial to a well-written web app. One of the key pieces of evidence is high-frequency references to "separation of concerns" in questions related to keeping programs organized. Now, I've found some information on organizing file systems (Filesystem Hierarchy Standard) from 2004. It raises only two concerns: first, the standard's a bit dated, so I believe it may be possible to do better given the changes in technology over the past 8 years; second, and most important, my application is very small compared to an entire Linux distro. I think that the file system should be organized very differently because of that. Here's what I'm looking at, currently: /scripts, /databases, /www -> /dev, /production -> login, router, admin pages, /sites -> content types, static pages /modules, /includes, /css, /media -> /module-specific-media

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  • What are steps in making an operating system in C ? [duplicate]

    - by ps06756
    This question already has an answer here: Compiler/OS Design - Where to start [closed] 3 answers I am trying to make an my own OS. This is for educational purpose only, so that I get to understand the internals as well as get a good idea of low level programming. I have some prior application development experience in C#/python/C++/C. I am a noob in assembly language(very less experience and knowledge). I understand that in writing an operating system,we can't go without assembly language. Currently, I have just printed a string in assembly language in the boot sector using qemu and BIOS interrupts. What I want is that, can someone specifically point out the steps that I need to follow to make my operating systems run C programs. So that, I can start writing my OS in C. Any other piece of advice to help a newbie, regarding the same is also welcome. Although, I have looked into many os development related tutorials/websites, I can't seem to find this information anywhere.

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  • Windows 7 disk backup and clone for deployment to multiple systems

    - by gregmac
    I'm in the process of deploying some new PCs (there's only 8), all identical hardware. What I'd like to do is install Windows 7 (64bit), join to domain etc, install a bunch of other software, and then clone that drive to multiple other machines. I'd also like to be able to use it as a backup image, so the machine can be restored back to that image at some future date. I understand this involves at least sysprep, but I am confused after reading some tutorials that talk about using Windows Automated Installation Kit, or hacks with the registry and custom-build batch files. This process seems overly complex to me: I did something similar 10+ years ago, and and don't remember it being this bad. Surely things have improved in a decade? There's also some products that involve having network servers running deployment software, network boot, etc etc.. this is way more than I want to set up. My systems are all identical hardware. Is there a simplified way to clone PCs? Preferably (since I'm a lazy developer, and not an IT admin) I'd like to find some off-the-shelf product that I can run after I get the machine setup, that will spit out a bootable DVD I can run on all the other systems, which will boot up, ask for a computer name, join it to the domain, and that's it. Does such as product exist?

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  • Recommendation on remote access setup for accessing customer systems

    - by gregmac
    I'm looking for a product recommendation (open or commercial) that will allow remote access to customer sites for tech support purposes. We need to be able to gain access to help troubleshoot problems on servers. Currently end up using anything from RDP on public IP, to various VPNs that clients happen to have, to webex-type sessions that require lots of interaction from both sides to get things working. This often means a problem that could take 10 minutes to solve takes an extra 30+ minutes messing around trying to get a connection up. There are multiple customer sites, which should NOT have access to each other. At each site, there is anywhere from 1 to 8 servers (Windows 2003 or 2008) that need to be accessed. Support connection to machines even if they're behind a firewall/router with no public IP Be able to selectively allow/deny access from customer site. Customer site should not be able to connect outbound to anywhere else (our systems, or other customer sites) Support multiple users from our end If not a VPN connection (where RDP could be used over top), should support: Remote desktop access, including copy/paste File transfers Preferably would have some way to list all remote systems, showing online/offline. Anyone have any suggestions?

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  • java distributed cache for low latency, high availability

    - by Shahbaz
    I've never used distributed caches/DHTs like memcached, jboss cache, ehcache, etc. I'm wondering which, if any, is appropriate for my use. First, I'm not doing web applications (as most of these project seem to be geared towards web apps). I write servers (Order Management Systems actually) for financial trading firms. The servers themselves are not too complicated. They need to receive information (market data, orders, executions, etc.) rout them to their destination while possibly transforming some of these messages. I am looking at these products to solve the following problems: * Safe repository of the state of the server. I'd rather build the logic of my application as a bunch of transformers (similar to Apache Camel) and store the state in a 'safe' place * This repository should be distributed: in case one of these data stores crashes, one or two more should be up and I should be able to switch to them seamlessly * This repository should be fast. Single digits milliseconds count here, in other words, systems which consume/process this data are automated systems, not humans clicking on links. This system needs to have high-throughput and low latency. By sending my data outside the process, I am necessarily slowing performance, but I am trying to balance absolute raw speed and absolute protection of data. * This repository should be safe. Similar to the point about several on-line backups, this system needs to write data to disk (potentially more than one disk). I'd really like to stop writing my own 'transaction servers.' Am I correct to be looking into projects such as jboss cache, ehcache, etc.? Thanks

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  • How much system and business analysis should a programmer be reasonably expected to do?

    - by Rahul
    In most places I have worked for, there were no formal System or Business Analysts and the programmers were expected to perform both the roles. One had to understand all the subsystems and their interdependencies inside out. Further, one was also supposed to have a thorough knowledge of the business logic of the applications and interact directly with the users to gather requirements, answer their queries etc. In my current job, for ex, I spend about 70% time doing system analysis and only 30% time programming. I consider myself a good programmer but struggle with developing a good understanding of the business rules of a complex application. Often, this creates a handicap because while I can write efficient algorithms and thread-safe code, I lose out to guys who may be average programmers but have a much better understanding of the business processes. So I want to know - How much business and systems knowledge should a programmer have ? - How does one go about getting this knowledge in an immensely complex software system (e.g. trading applications) with several interdependent business processes but poorly documented business rules.

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  • Examples of limitations in IT due to different bit length by design

    - by Alaudo
    I am teaching the course "Introduction in Programming" for the first-year students and would like to find interesting examples where the datatype size in bits, chosen by design, led to certain known restrictions or important values. Here are some examples: Due to the fact that the Bell teleprinter used 7-bit-code (later accepted as ASCII) until now have we often to encode attachments in electronic messages to contain only 7 bit data. Classical limitation of 32-bit address space leads to the 4Gb maximal RAM size available for 32-bit systems and 4Gb maximal file size in FAT32. Do you know some other interesting examples how the choice of the data type (and especially its binary length) influenced the modern IT world. Added after some discussion in comments: I am not going to teach how to overcome limitations. I just want them to know that 1 byte can hold the values from -127..0..+127 o 0..255, 2 bytes cover the range 0..65535 etc by proving examples they know from other sources, like the above-mentioned base64 encoding etc. We are just learning the basic datatypes and I am trying to find a good reference for "how large" these types are.

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  • Moving From IT to Embedded software Developing

    - by Ameer Adel
    i worked for two years at a channel station, managing various Types of tasks, varying from printers installation, software solution, down to managing and maintaining server automation, to be honest, i always been enthusiastic about programming, i studied at some affordable college and finished my IT path successfully, my graduation project was in C# ADO.NET couple of years ago. Obviously it was so much of a beginner spaghetti code than a well furnished code. I also had the chance; after leaving the IT career, to study about some ASP.NET MVC and web apps development. I have rookie level of coding skills due to the poor level of education i endured, and sufficient resources. Currently i m working as a trainee in a newly opened embedded software development company, that is being said, i am, as i sound, have a little idea about the algorithms included, as i was reading for the past couple of days, embedded system development requires more strict coding skills, including memory management, CPU optimization according to its architect, and couple of other tricks regarding the display, and power management if mobile.. etc. My question is, What type of Algorithms am i supposed to use in such cases, as i mentioned before, i am really enthusiastic about learning programming skills and algorithms related to embedded systems and programming languages, including C/C++, Java, C#, and some EC++ if still operational.

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  • What Computing/Programming Qualifications should I aspire for

    - by indevel
    I am a computing science post graduate in my first job from after my degree. During my 12 month review my boss posed the question "What can we do for you in terms of progressing your career?". This got me thinking, after university I hadn't really thought about what other qualifications were available. So this is my question, what courses/qualifications should I be looking to do. Which are highly regarded and which would be really useful to complete. I've searched Google it but all I see is a jumble of courses with no idea of the credibility of each. Any help is much appreciated. I'm traditionally a systems architect, but with this job I've turned to more embedded work so Id like to edge towards electronics, embedded programming, real time OS to help with my work also it would be more likely to be accepted if it was related to my job. Finally UK based courses/ qualifications are a must as travel is probably out of the question. Help me grow as a programmer.

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  • Hazelcast Distributed Executor Service KeyOwner

    - by János Veres
    I have problem understanding the concept of Hazelcast Distributed Execution. It is said to be able to perform the execution on the owner instance of a specific key. From Documentation: <T> Future<T> submitToKeyOwner(Callable<T> task, Object key) Submits task to owner of the specified key and returns a Future representing that task. Parameters: task - task key - key Returns: a Future representing pending completion of the task I believe that I'm not alone to have a cluster built with multiple maps which might actually use the same key for different purposes, holding different objects (e.g. something along the following setup): IMap<String, ObjectTypeA> firstMap = HazelcastInstance.getMap("firstMap"); IMap<String, ObjectTypeA_AppendixClass> secondMap = HazelcastInstance.getMap("secondMap"); To me it seems quite confusing what documentation says about the owner of a key. My real frustration is that I don't know WHICH - in which map - key does it refer to? The documentation also gives a "demo" of this approach: import com.hazelcast.core.Member; import com.hazelcast.core.Hazelcast; import com.hazelcast.core.IExecutorService; import java.util.concurrent.Callable; import java.util.concurrent.Future; import java.util.Set; import com.hazelcast.config.Config; public void echoOnTheMemberOwningTheKey(String input, Object key) throws Exception { Callable<String> task = new Echo(input); HazelcastInstance hz = Hazelcast.newHazelcastInstance(); IExecutorService executorService = hz.getExecutorService("default"); Future<String> future = executorService.submitToKeyOwner(task, key); String echoResult = future.get(); } Here's a link to the documentation site: Hazelcast MultiHTML Documentation 3.0 - Distributed Execution Did any of you guys figure out in the past what key does it want?

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  • Performance Testing through distributed jmeter instances and bamboo

    - by user1617754
    I´m working on performance test for several services running in an Amazon network. Our architecture is: Continuous Integration server running in our facilities (Bamboo); A Jmeter server instance in the same network than the services to test; A Jmeter client connected to the JMeter server (ssh tunnels) in our facilities. I want to start the execution of tests from bamboo, and see the different results on it too. Bamboo with <---------> Jmeter server <--------> WebService Jmeter client on Amazon on Amazon Has anybody tried something like this?

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  • Reverse proxy setup for distributed storage

    - by vise
    I have 4 file servers that I want to access under a single mount point from another server. This server has a web application that should serve content from the mounted point. I think I can achieve this with glusterfs. Considering that the file servers have fairly powerful hardware, I want to install a webserver on each of them and serve those files via a reverse proxy. Any thoughts on how I may be able to do so?

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  • One-way forest trust between geographically distributed forests using Server 2008 R2

    - by bwerks
    Hi all, I'm planning out a joinder between two domains, as would take place with contracting companies. Forests A and B exist in distant sites, and there is to be a one-way forest trust so that domain users in Forest A can be authenticated on machines in Forest B. In order to facilitate this, each forest's domain controller must be able to contact each other in order to set up & confirm the trust, but my question is what underlying networking magic must take place beneath it. So far the prevailing approach has been to maintain a VPN connection between the two sites, but the technet documentation seems to indicate that DNS forwarding may be the way to go. Is this the case? Furthermore, if DNS will suffice, does that mean that there must be a server running DNS on boundary servers in each domain so that they can be reached from across the internet? How must they be configured? Thanks!

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  • Backup hardware and strategy on distributed Windows Server 2008 network

    - by CesarGon
    This question is a follow up to this. We have a Windows Server 2008 R2 domain over a network that spans two different buildings, linked by a 100-Mbps point-to-point line. Over 60 users work in the organisation. We are planning to use DFS folders and DFS replication for file serving across the organisation. The estimated data volume is over 2 TB, and will grow at approximately 20% annually. The idea is to set up a DFS file server in each building and use DFS so that all the contents stay replicated over the 100-Mbps link. We are now considering backup hardware and strategies. We are Dell customers and, after browsing the online Dell catalogue, I can see a number of backup hardware options. My main doubts are the following: Would you go for a tape library, disk backup, or are there other options worth considering? Would you perform batch backups (i.e. nightly) or would you use continuous backup (i.e. while users are working)? Would you use a dedicated backup server to which the tape library (or any other backup device) is attached, or is there any other alternative way of doing things? My experience with backup hardware and overall setup is limited, so I appreciate any good piece of advice that you may have. Thanks.

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  • Cache coherence literature for big (>=16CPU) systems

    - by osgx
    Hello What books and articles can you recommend to learn basis of cache coherence problems in big SMP systems (which are NUMA and ccNUMA really) with =16 cpu sockets? Something like SGI Altix architecture analysis may be interesting. What protocols (MOESI, smth else) can scale up well?

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  • faking NAT with a VMware distributed switch across multiple hosts

    - by romant
    I need to construct a NAT for certain machines within the network. Wish to do this with dvSwitch - as it seems the logical way of attacking the problem as in this scenario there's just under 30 hosts. In order for the NAT'ed VM's to have access to the 'real' network. I am providing a 'router' VM, which will have access to the WAN/outside network, and also act as the DHCP server for the NAT'ed machines. Problem Space When the machines connected to the NAT interface and the router are on the same host, then they get an IP from the router VM, and work perfectly (routed outside). Unfortunately machines on other Hosts that are connected to the dvSwitch do not get an IP and further tcpdump shows no network data getting through across the hosts within the dvSwitch. Has anyone achieved a NAT solution using a dvSwitch before that they could share?! Thank you. EDIT: Including the diagram.

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  • One EC2 source with distributed varnish machines

    - by Elad Lachmi
    I have a web site hosted in an EC2 instance (2008 r2 + iis7.5 + sql server). I put one linux box running RHEL with varnish. After some configuration trail and error, I found a configuration that works. Now I want to duplicate the varnish boxes to other availability zones, but continue to pull the pages from the original windows box. It is my understanding that I can put the varnish boxes in different zones and pull from the windows box via it's external IP. But what do I need to do in order for each user to receive content from the box physically closest to them? Is this even possible? Thank you!

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