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  • Generics vs inheritance (when no collection classes are involved)

    - by Ram
    This is an extension of this questionand probably might even be a duplicate of some other question(If so, please forgive me). I see from MSDN that generics are usually used with collections The most common use for generic classes is with collections like linked lists, hash tables, stacks, queues, trees and so on where operations such as adding and removing items from the collection are performed in much the same way regardless of the type of data being stored. The examples I have seen also validate the above statement. Can someone give a valid use of generics in a real-life scenario which does not involve any collections ? Pedantically, I was thinking about making an example which does not involve collections public class Animal<T> { public void Speak() { Console.WriteLine("I am an Animal and my type is " + typeof(T).ToString()); } public void Eat() { //Eat food } } public class Dog { public void WhoAmI() { Console.WriteLine(this.GetType().ToString()); } } and "An Animal of type Dog" will be Animal<Dog> magic = new Animal<Dog>(); It is entirely possible to have Dog getting inherited from Animal (Assuming a non-generic version of Animal)Dog:Animal Therefore Dog is an Animal Another example I was thinking was a BankAccount. It can be BankAccount<Checking>,BankAccount<Savings>. This can very well be Checking:BankAccount and Savings:BankAccount. Are there any best practices to determine if we should go with generics or with inheritance ?

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  • rabbitmq-erlang-client, using rebar friendly pkg, works on dev env fails on rebar release

    - by lfurrea
    I am successfully using the rebar-friendly package of rabbitmq-erlang-client for a simple Hello World rebarized and OTP "compliant" app and things work fine on the dev environment. I am able to fire up an erl console and do my application:start(helloworld). and connect to the broker, open up a channel and communicate to queues. However, then I proceed to do rebar generate and it builds up the release just fine, but when I try to fire up from the self contained release package then things suddenly explode. I know rebar releases are known to be an obscure art, but I would like to know what are my options as far as deployment for an app using the rabbitmq-erlang-client. Below you will find the output of the console on the crash: =INFO REPORT==== 18-Dec-2012::16:41:35 === application: session_record exited: {{{badmatch, {error, {'EXIT', {undef, [{amqp_connection_sup,start_link, [{amqp_params_network,<<"guest">>,<<"guest">>,<<"/">>, "127.0.0.1",5672,0,0,0,infinity,none, [#Fun<amqp_auth_mechanisms.plain.3>, #Fun<amqp_auth_mechanisms.amqplain.3>], [],[]}], []}, {supervisor2,do_start_child_i,3, [{file,"src/supervisor2.erl"},{line,391}]}, {supervisor2,handle_call,3, [{file,"src/supervisor2.erl"},{line,413}]}, {gen_server,handle_msg,5, [{file,"gen_server.erl"},{line,588}]}, {proc_lib,init_p_do_apply,3, [{file,"proc_lib.erl"},{line,227}]}]}}}}, [{amqp_connection,start,1, [{file,"src/amqp_connection.erl"},{line,164}]}, {hello_qp,start_link,0,[{file,"src/hello_qp.erl"},{line,10}]}, {session_record_sup,init,1, [{file,"src/session_record_sup.erl"},{line,55}]}, {supervisor_bridge,init,1, [{file,"supervisor_bridge.erl"},{line,79}]}, {gen_server,init_it,6,[{file,"gen_server.erl"},{line,304}]}, {proc_lib,init_p_do_apply,3, [{file,"proc_lib.erl"},{line,227}]}]}, {session_record_app,start,[normal,[]]}} type: permanent

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  • How do I make custom functions chain-able with jQuery's?

    - by sergio
    I need a "callfront" or "precall" (the opposite of "callback" ¿?) to add in MANY places before an animation occurs in an existing plugin, To be used like e.g. $(some_unpredictable_obj).preFunct().animate(… The problem is, as I said they are MANY places, and all of them are different animations, on different objects. I can TELL where all of them occur, but I don't want to add over and over the same code. I actually have to add both a function before and after those animations, but I think I can use the callback for all of them. In a perfect world, I'd like to replace every animate(property, duration) by preFunct().animate(property,duration).postFunct() preFunct and postFunct don't need parameters, since they are always the same action, on the same object. This could be an amazing addition to "jQuery" (an easy way to jQuerize custom functions to be added to the normal chain (without messing with queues) I found this example but it will act on the applied element, and I don't want that because, as I said above, all the original animations to be added to are on different elements. I also found jQuery.timing, but it looks cooler the chain-able function :) Thanks.

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  • Social Media Java Design Problem

    - by jboyd
    I need to put something together quickly that will take blog posts and place them on social media sites, the requirements are as follows: Blog Entries are independent records that already exist, they have a published date and a modified date, the blog entry application cannot be changed, at least not substantially A new blog entry, or update needs to be sent to social media sites I currently do not need to update or delete social media communications if the blog entry is edited, or deleted, though I may need to later My design problems here are as follows: how do I know the status of each update how can I figure out what blog entry updates and postings have already been sent out? how can I quickly poll the blog entry table for postings that haven't yet been sent out? Avoiding looking at each Entry record from the DB as an object and asking if it's been sent already. That would be too slow. I cannot hook into any Blog Entry update code, my only option would be to create a trigger that an update queues something to be processed I'm looking for general guiding principles here, the biggest problem I'm having is coming up with any reasonable way to figure out if a blog entry should be sent to our social media sites in the first place

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  • How can I run an appear effect and a fade effect in scriptaculous? I need them to run in tandam so t

    - by LeeRM
    Hi, Ive been fiddling with this for hours and hours and just cant get it right. First off my sites are already using Prototytpe and Scriptaculous, and to change would take a long time. Basically I am after achieving a slideshow effect similar to jQuery Cycle plugin. I have written most of it but cant get over this hurdle: I need the user to be able to press a control button which will skip the slide to which ever one they have picked. My problem is that if a fade / appear effect is running, then it causes an overlap. I am using queues and they are in their own scope. The problem as I see it is that the fade effect on one slide and the appear effect on the next slide are separate functions. Which means that if the user clicks the control button to move to another slide whilst the animation is inbetween fade & appear, then the next cycle will slot itself in the queue between those 2 effects. The default is to append to the end of the existing queue, which should be fine. But if the appear hasnt been added when a new fade is instantiated, then the queue messes up. I can make it so nothing happens if animation is in effect but thats not the effect I am after. I want to be able to click a slide and whatever is happening to effectively stop and the next slide appear. This is an example of what I am after: http://www.zendesk.com/ Im sorry if that doesnt make sense. Its a tough one to explain. Thanks Lee

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  • Where are possible locations of queueing/buffering delays in Linux multicast?

    - by Matt
    We make heavy use of multicasting messaging across many Linux servers on a LAN. We are seeing a lot of delays. We basically send an enormous number of small packages. We are more concerned with latency than throughput. The machines are all modern, multi-core (at least four, generally eight, 16 if you count hyperthreading) machines, always with a load of 2.0 or less, usually with a load less than 1.0. The networking hardware is also under 50% capacity. The delays we see look like queueing delays: the packets will quickly start increasing in latency, until it looks like they jam up, then return back to normal. The messaging structure is basically this: in the "sending thread", pull messages from a queue, add a timestamp (using gettimeofday()), then call send(). The receiving program receives the message, timestamps the receive time, and pushes it in a queue. In a separate thread, the queue is processed, analyzing the difference between sending and receiving timestamps. (Note that our internal queues are not part of the problem, since the timestamps are added outside of our internal queuing.) We don't really know where to start looking for an answer to this problem. We're not familiar with Linux internals. Our suspicion is that the kernel is queuing or buffering the packets, either on the send side or the receive side (or both). But we don't know how to track this down and trace it. For what it's worth, we're using CentOS 4.x (RHEL kernel 2.6.9).

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  • Why does my Perl TCP server script hang with many TCP connections?

    - by viraptor
    I've got a strange issue with a server accepting TCP connections. Even though there are normally some processes waiting, at some volume of connections it hangs. Long version: The server is written in Perl and binds a $srv socket with the reuse flag and listen == 5. Afterwards, it forks into 10 processes with a loop of $clt=$srv->accept(); do_processing($clt); $clt->shutdown(2); The client written in C is also very simple - it sends some lines, then receives all lines available and does a shutdown(sockfd, 2); There's nothing async going on and at the end both send and receive queues are empty (as reported by netstat). Connections last only ~20ms. All clients behave the same way, are the same implementation, etc. Now let's say I'm accepting X connections from client 1 and another X from client 2. Processes still report that they're idle all the time. If I add another X connections from client 3, suddenly the server processes start hanging just after accepting. The first blocking thing they do after accept(); is while (<$clt>) ... - but they don't get any data (on the first try already). Suddenly all 10 processes are in this state and do not stop waiting. On strace, the server processes seem to hang on read(), which makes sense. There are loads of connections in TIME_WAIT state belonging to that server (~100 when the problem starts to manifest), but this might be a red herring. What could be happening here?

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  • Fastest reliable way for Clojure (Java) and Ruby apps to communicate

    - by jkndrkn
    Hi There, We have cloud-hosted (RackSpace cloud) Ruby and Java apps that will interact as follows: Ruby app sends a request to Java app. Request consists of map structure containing strings, integers, other maps, and lists (analogous to JSON). Java app analyzes data and sends reply to Ruby App. We are interested in evaluating both messaging formats (JSON, Buffer Protocols, Thrift, etc.) as well as message transmission channels/techniques (sockets, message queues, RPC, REST, SOAP, etc.) Our criteria: Short round-trip time. Low round-trip-time standard deviation. (We understand that garbage collection pauses and network usage spikes can affect this value). High availability. Scalability (we may want to have multiple instances of Ruby and Java app exchanging point-to-point messages in the future). Ease of debugging and profiling. Good documentation and community support. Bonus points for Clojure support. What combination of message format and transmission method would you recommend? Why? I've gathered here some materials we have already collected for review: Comparison of various java serialization options Comparison of Thrift and Protocol Buffers (old) Comparison of various data interchange formats Comparison of Thrift and Protocol Buffers Fallacies of Protocol Buffers RPC features Discussion of RPC in the context of AMQP (Message-Queueing) Comparison of RPC and message-passing in distributed systems (pdf) Criticism of RPC from perspective of message-passing fan Overview of Avro from Ruby programmer perspective

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  • Communicating with a running python daemon

    - by hanksims
    I wrote a small Python application that runs as a daemon. It utilizes threading and queues. I'm looking for general approaches to altering this application so that I can communicate with it while it's running. Mostly I'd like to be able to monitor its health. In a nutshell, I'd like to be able to do something like this: python application.py start # launches the daemon Later, I'd like to be able to come along and do something like: python application.py check_queue_size # return info from the daemonized process To be clear, I don't have any problem implementing the Django-inspired syntax. What I don't have any idea how to do is to send signals to the daemonized process (start), or how to write the daemon to handle and respond to such signals. Like I said above, I'm looking for general approaches. The only one I can see right now is telling the daemon constantly log everything that might be needed to a file, but I hope there's a less messy way to go about it. UPDATE: Wow, a lot of great answers. Thanks so much. I think I'll look at both Pyro and the web.py/Werkzeug approaches, since Twisted is a little more than I want to bite off at this point. The next conceptual challenge, I suppose, is how to go about talking to my worker threads without hanging them up. Thanks again.

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  • Celery Received unregistered task of type (run example)

    - by Echeg
    I'm trying to run example from Celery documentation. I run: celeryd --loglevel=INFO /usr/local/lib/python2.7/dist-packages/celery/loaders/default.py:64: NotConfigured: No 'celeryconfig' module found! Please make sure it exists and is available to Python. "is available to Python." % (configname, ))) [2012-03-19 04:26:34,899: WARNING/MainProcess] -------------- celery@ubuntu v2.5.1 ---- **** ----- --- * *** * -- [Configuration] -- * - **** --- . broker: amqp://guest@localhost:5672// - ** ---------- . loader: celery.loaders.default.Loader - ** ---------- . logfile: [stderr]@INFO - ** ---------- . concurrency: 4 - ** ---------- . events: OFF - *** --- * --- . beat: OFF -- ******* ---- --- ***** ----- [Queues] -------------- . celery: exchange:celery (direct) binding:celery tasks.py: # -*- coding: utf-8 -*- from celery.task import task @task def add(x, y): return x + y run_task.py: # -*- coding: utf-8 -*- from tasks import add result = add.delay(4, 4) print (result) print (result.ready()) print (result.get()) In same folder celeryconfig.py: CELERY_IMPORTS = ("tasks", ) CELERY_RESULT_BACKEND = "amqp" BROKER_URL = "amqp://guest:guest@localhost:5672//" CELERY_TASK_RESULT_EXPIRES = 300 When I run "run_task.py": on python console eb503f77-b5fc-44e2-ac0b-91ce6ddbf153 False errors on celeryd server [2012-03-19 04:34:14,913: ERROR/MainProcess] Received unregistered task of type 'tasks.add'. The message has been ignored and discarded. Did you remember to import the module containing this task? Or maybe you are using relative imports? Please see http://bit.ly/gLye1c for more information. The full contents of the message body was: {'retries': 0, 'task': 'tasks.add', 'utc': False, 'args': (4, 4), 'expires': None, 'eta': None, 'kwargs': {}, 'id': '841bc21f-8124-436b-92f1-e3b62cafdfe7'} Traceback (most recent call last): File "/usr/local/lib/python2.7/dist-packages/celery/worker/consumer.py", line 444, in receive_message self.strategies[name](message, body, message.ack_log_error) KeyError: 'tasks.add' Please explain what's the problem.

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  • Does the Java Memory Model (JSR-133) imply that entering a monitor flushes the CPU data cache(s)?

    - by Durandal
    There is something that bugs me with the Java memory model (if i even understand everything correctly). If there are two threads A and B, there are no guarantees that B will ever see a value written by A, unless both A and B synchronize on the same monitor. For any system architecture that guarantees cache coherency between threads, there is no problem. But if the architecture does not support cache coherency in hardware, this essentially means that whenever a thread enters a monitor, all memory changes made before must be commited to main memory, and the cache must be invalidated. And it needs to be the entire data cache, not just a few lines, since the monitor has no information which variables in memory it guards. But that would surely impact performance of any application that needs to synchronize frequently (especially things like job queues with short running jobs). So can Java work reasonably well on architectures without hardware cache-coherency? If not, why doesn't the memory model make stronger guarantees about visibility? Wouldn't it be more efficient if the language would require information what is guarded by a monitor? As i see it the memory model gives us the worst of both worlds, the absolute need to synchronize, even if cache coherency is guaranteed in hardware, and on the other hand bad performance on incoherent architectures (full cache flushes). So shouldn't it be more strict (require information what is guarded by a monitor) or more lose and restrict potential platforms to cache-coherent architectures? As it is now, it doesn't make too much sense to me. Can somebody clear up why this specific memory model was choosen? EDIT: My use of strict and lose was a bad choice in retrospect. I used "strict" for the case where less guarantees are made and "lose" for the opposite. To avoid confusion, its probably better to speak in terms of stronger or weaker guarantees.

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  • DB optimization to use it as a queue

    - by anony
    We have a table called worktable which has some columns(key(primary key), ptime, aname, status, content) we have something called producer which puts in rows in this table and we have consumer which does an order-by on the key column and fetches the first row which has status as 'pending'. The consumer does some processing on this row: 1. updates status to "processing" 2. does some processing using content 3. deletes the row we are facing contention issues when we try to run multiple consumers(probably due to the order-by which does a full table scan)... using Advanced queues would be our next step but before we go there we want to check what is the max throughput we can achieve with multiple consumers and producer on the table. What are the optimizations we can do to get the best numbers possible? Can we do an in-memory processing where a consumer fetches 1000 rows at a time processes and deletes? will that improve? What are other possibilities? partitioning of table? parallelization? Index organized tables?...

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  • How can I avoid garbage collection delays in Java games? (Best Practices)

    - by Brian
    I'm performance tuning interactive games in Java for the Android platform. Once in a while there is a hiccup in drawing and interaction for garbage collection. Usually it's less than one tenth of a second, but sometimes it can be as large as 200ms on very slow devices. I am using the ddms profiler (part of the Android SDK) to search out where my memory allocations come from and excise them from my inner drawing and logic loops. The worst offender had been short loops done like, for(GameObject gob : interactiveObjects) gob.onDraw(canvas); where every single time the loop was executed there was an iterator allocated. I'm using arrays (ArrayList) for my objects now. If I ever want trees or hashes in an inner loop I know that I need to be careful or even reimplement them instead of using the Java Collections framework since I can't afford the extra garbage collection. That may come up when I'm looking at priority queues. I also have trouble where I want to display scores and progress using Canvas.drawText. This is bad, canvas.drawText("Your score is: " + Score.points, x, y, paint); because Strings, char arrays and StringBuffers will be allocated all over to make it work. If you have a few text display items and run the frame 60 times a second that begins to add up and will increase your garbage collection hiccups. I think the best choice here is to keep char[] arrays and decode your int or double manually into it and concatenate strings onto the beginning and end. I'd like to hear if there's something cleaner. I know there must be others out there dealing with this. How do you handle it and what are the pitfalls and best practices you've discovered to run interactively on Java or Android? These gc issues are enough to make me miss manual memory management, but not very much.

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  • Using NServiceBus behind a custom web service

    - by Michael Stephenson
    In this post I'd like to talk about an architecture scenario we had recently and how we were able to utilise NServiceBus to help us address this problem. Scenario Cognos is a reporting system used by one of my clients. A while back we developed a web service façade to allow line of business applications to be able to access reports from Cognos to support their various functions. The service was intended to provide access to reports which were quick running reports or pre-generated reports which could be accessed real-time on demand. One of the key aims of the web service was to provide a simple generic interface to allow applications to get any report without needing to worry about the complex .net SDK for Cognos. The web service also supported multi-hop kerberos delegation so that report data could be accesses under the context of the end user. This service was working well for a period of time. The Problem The problem we encountered was that reports were now also required to be available to batch processes. The original design was optimised for low latency so users would enjoy a positive experience, however when the batch processes started to request 250+ concurrent reports over an extended period of time you can begin to imagine the sorts of problems that come into play. The key problems this new scenario caused are: Users may be affected and the latency of on demand reports was significantly slower The Cognos infrastructure was not scaled sufficiently to be able to cope with these long peaks of load From a cost perspective it just isn't feasible to scale the Cognos infrastructure to be able to handle the load when it is only for a couple of hour window each night. We really needed to introduce a second pattern for accessing this service which would support high through-put scenarios. We also had little control over the batch process in terms of being able to throttle its load. We could however make some changes to the way it accessed the reports. The Approach My idea was to introduce a throttling mechanism between the Web Service Façade and Cognos. This would allow the batch processes to push reports requests hard at the web service which we were confident the web service can handle. The web service would then queue these requests and process them behind the scenes and make a call back to the batch application to provide the report once it had been accessed. In terms of technology we had some limitations because we were not able to use WCF or IIS7 where the MSMQ-Activated WCF services could have helped, but we did have MSMQ as an option and I thought NServiceBus could do just the job to help us here. The flow of how this would work was as follows: The batch applications would send a request for a report to the web service The web service uses NServiceBus to send the message to a Queue The NServiceBus Generic Host is running as a windows service with a message handler which subscribes to these messages The message handler gets the message, accesses the report from Cognos The message handler calls back to the original batch application, this is decoupled because the calling application provides a call back url The report gets into the batch application and is processed as normal This approach looks something like the below diagram: The key points are an application wanting to take advantage of the batch driven reports needs to do the following: Implement our call back contract Make a call to the service providing a call back url Provide a correlation ID so it knows how to tie each response back to its request What does NServiceBus offer in this solution So this scenario is not the typical messaging service bus type of solution people implement with NServiceBus, but it did offer the following: Simplified interaction with MSMQ Offered the ability to configure the number of processes working through the queue so we could find a balance between load on Cognos versus the applications end to end processing time NServiceBus offers retries and a way to manage failed messages NServiceBus offers a high availability setup The simple thing is that NServiceBus gave us the platform to build the solution on. We just implemented a message handler which functionally processed a message and we could rely on NServiceBus to do all of the hard work around managing the queues and all of the lower level things that would have took ages to write to any kind of robust level. Conclusion With this approach we were able to deal with a fairly significant performance issue with out too much rework. Hopefully this write up gives people some insight into ideas on how to leverage the excellent NServiceBus framework to help solve integration and high through-put scenarios.

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  • Big Data: Size isn’t everything

    - by Simon Elliston Ball
    Big Data has a big problem; it’s the word “Big”. These days, a quick Google search will uncover terabytes of negative opinion about the futility of relying on huge volumes of data to produce magical, meaningful insight. There are also many clichéd but correct assertions about the difficulties of correlation versus causation, in massive data sets. In reading some of these pieces, I begin to understand how climatologists must feel when people complain ironically about “global warming” during snowfall. Big Data has a name problem. There is a lot more to it than size. Shape, Speed, and…err…Veracity are also key elements (now I understand why Gartner and the gang went with V’s instead of S’s). The need to handle data of different shapes (Variety) is not new. Data developers have always had to mold strange-shaped data into our reporting systems, integrating with semi-structured sources, and even straying into full-text searching. However, what we lacked was an easy way to add semi-structured and unstructured data to our arsenal. New “Big Data” tools such as MongoDB, and other NoSQL (Not Only SQL) databases, or a graph database like Neo4J, fill this gap. Still, to many, they simply introduce noise to the clean signal that is their sensibly normalized data structures. What about speed (Velocity)? It’s not just high frequency trading that generates data faster than a single system can handle. Many other applications need to make trade-offs that traditional databases won’t, in order to cope with high data insert speeds, or to extract quickly the required information from data streams. Unfortunately, many people equate Big Data with the Hadoop platform, whose batch driven queries and job processing queues have little to do with “velocity”. StreamInsight, Esper and Tibco BusinessEvents are examples of Big Data tools designed to handle high-velocity data streams. Again, the name doesn’t do the discipline of Big Data any favors. Ultimately, though, does analyzing fast moving data produce insights as useful as the ones we get through a more considered approach, enabled by traditional BI? Finally, we have Veracity and Value. In many ways, these additions to the classic Volume, Velocity and Variety trio acknowledge the criticism that without high-quality data and genuinely valuable outputs then data, big or otherwise, is worthless. As a discipline, Big Data has recognized this, and data quality and cleaning tools are starting to appear to support it. Rather than simply decrying the irrelevance of Volume, we need as a profession to focus how to improve Veracity and Value. Perhaps we should just declare the ‘Big’ silent, embrace these new data tools and help develop better practices for their use, just as we did the good old RDBMS? What does Big Data mean to you? Which V gives your business the most pain, or the most value? Do you see these new tools as a useful addition to the BI toolbox, or are they just enabling a dangerous trend to find ghosts in the noise?

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  • How Exactly Is One Linux OS “Based On” Another Linux OS?

    - by Jason Fitzpatrick
    When reviewing different flavors of Linux, you’ll frequently come across phrases like “Ubuntu is based on Debian” but what exactly does that mean? Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites. The Question SuperUser reader PLPiper is trying to get a handle on how Linux variants work: I’ve been looking through quite a number of Linux distros recently to get an idea of what’s around, and one phrase that keeps coming up is that “[this OS] is based on [another OS]“. For example: Fedora is based on Red Hat Ubuntu is based on Debian Linux Mint is based on Ubuntu For someone coming from a Mac environment I understand how “OS X is based on Darwin”, however when I look at Linux Distros, I find myself asking “Aren’t they all based on Linux..?” In this context, what exactly does it mean for one Linux OS to be based on another Linux OS? So, what exactly does it mean when we talk about one version of Linux being based off another version? The Answer SuperUser contributor kostix offers a solid overview of the whole system: Linux is a kernel — a (complex) piece of software which works with the hardware and exports a certain Application Programming Interface (API), and binary conventions on how to precisely use it (Application Binary Interface, ABI) available to the “user-space” applications. Debian, RedHat and others are operating systems — complete software environments which consist of the kernel and a set of user-space programs which make the computer useful as they perform sensible tasks (sending/receiving mail, allowing you to browse the Internet, driving a robot etc). Now each such OS, while providing mostly the same software (there are not so many free mail server programs or Internet browsers or desktop environments, for example) differ in approaches to do this and also in their stated goals and release cycles. Quite typically these OSes are called “distributions”. This is, IMO, a somewhat wrong term stemming from the fact you’re technically able to build all the required software by hand and install it on a target machine, so these OSes distribute the packaged software so you either don’t need to build it (Debian, RedHat) or they facilitate such building (Gentoo). They also usually provide an installer which helps to install the OS onto a target machine. Making and supporting an OS is a very complicated task requiring a complex and intricate infrastructure (upload queues, build servers, a bug tracker, and archive servers, mailing list software etc etc etc) and staff. This obviously raises a high barrier for creating a new, from-scratch OS. For instance, Debian provides ca. 37k packages for some five hardware architectures — go figure how much work is put into supporting this stuff. Still, if someone thinks they need to create a new OS for whatever reason, it may be a good idea to use an existing foundation to build on. And this is exactly where OSes based on other OSes come into existence. For instance, Ubuntu builds upon Debian by just importing most packages from it and repackaging only a small subset of them, plus packaging their own, providing their own artwork, default settings, documentation etc. Note that there are variations to this “based on” thing. For instance, Debian fosters the creation of “pure blends” of itself: distributions which use Debian rather directly, and just add a bunch of packages and other stuff only useful for rather small groups of users such as those working in education or medicine or music industry etc. Another twist is that not all these OSes are based on Linux. For instance, Debian also provide FreeBSD and Hurd kernels. They have quite tiny user groups but anyway. Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.     

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  • SQLAuthority News – Book Signing Event – SQLPASS 2011 Event Log

    - by pinaldave
    I have been dreaming of writing book for really long time, and I finally got the chance – in fact, two chances!  I recently wrote two books: SQL Programming Joes 2 Pros: Programming and Development for Microsoft SQL Server 2008 [Amazon] | [Flipkart] | [Kindle] and SQL Wait Stats Joes 2 Pros: SQL Performance Tuning Techniques Using Wait Statistics, Types & Queues [Amazon] | [Flipkart] | [Kindle].  I had a lot of fun writing these two books, even though sometimes I had to sacrifice some family time and time for other personal development to write the books. The good side of writing book is that when the efforts put in writing books are recognize by books readers and kind organizations like expressor studio. Book Signing Event Book writing is a complex process.  Even after you spend months, maybe years, writing the material you still have to go through the editing and fact checking processes.  And, once the book is out there, there is no way to take back all the copies to change mistakes or add something you forgot.  Most of the time it is a one-way street. Book Signing Event Just like every author, I had a dream that after the books were written, they would be loved by people and gain acceptance by an audience. My first book, SQL Programming Joes 2 Pros: Programming and Development for Microsoft SQL Server 2008, is extremely popular because it helps lots of people learn various fundamental topics. My second book covers beginning to learn SQL Server Wait Stats, which is a relatively new subject. This book has had very good acceptance in the community. Book Signing Event Helping my community is my primary focus, so I was happy to see this year’s SQLPASS tag line: ‘This is a Community.‘ At the event, the expressor studio guys came up with a very novel idea. They had previously used my books and they had found them very useful. They got 100 copies of the book and decided to give it away to community folks. They invited me and my co-author Rick Morelan to hold a book signing event. We did a book signing on Thursday between 1 pm and 2 pm. Book Signing Event This event was one of the best events for me. This was my first book signing event outside of India. I reached the book signing location around 20 minutes before the scheduled time and what I saw was a big line for the book signing event. I felt very honored looking at the crowd and all the people around the event location. I felt very humbled when I saw some of my very close friends standing in the line to get my signature. It was really heartwarming to see so many enthusiasts waiting for more than an hour to get my signature. While standing in line I had the chance to have a conversation with every single person who showed up for the signature. I made sure that I repeated every single name and wrote it in every book with my signature. There is saying that if we write a name once we will remember it forever. I want to remember all of you who saw me at the book signing. Your comments were wonderful, your feedback was amazing and you were all very supportive. Book Signing Event I have made a note of every conversation I had with all of you when I was signing the books. Once again, I just want to express my thanks for coming to my book signing event. The whole experience was very humbling. On the top of it, I want to thank the expressor studio people who made it possible, who organized the whole signing event. I am so thankful to them for facilitating the whole experience, which is going to be hard to beat by any future experience. My books Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL PASS, SQL Query, SQL Server, SQL Tips and Tricks, SQLAuthority Author Visit, SQLAuthority News, T SQL, Technology

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  • career in Mobile sw/Application Development [closed]

    - by pramod
    i m planning to do a course on Wireless & mobile computing.The syllabus are given below.Please check & let me know whether its worth to do.How is the job prospects after that.I m a fresher & from electronic Engg.The modules are- *Wireless and Mobile Computing (WiMC) – Modules* C, C++ Programming and Data Structures 100 Hours C Revision C, C++ programming tools on linux(Vi editor, gdb etc.) OOP concepts Programming constructs Functions Access Specifiers Classes and Objects Overloading Inheritance Polymorphism Templates Data Structures in C++ Arrays, stacks, Queues, Linked Lists( Singly, Doubly, Circular) Trees, Threaded trees, AVL Trees Graphs, Sorting (bubble, Quick, Heap , Merge) System Development Methodology 18 Hours Software life cycle and various life cycle models Project Management Software: A Process Various Phases in s/w Development Risk Analysis and Management Software Quality Assurance Introduction to Coding Standards Software Project Management Testing Strategies and Tactics Project Management and Introduction to Risk Management Java Programming 110 Hours Data Types, Operators and Language Constructs Classes and Objects, Inner Classes and Inheritance Inheritance Interface and Package Exceptions Threads Java.lang Java.util Java.awt Java.io Java.applet Java.swing XML, XSL, DTD Java n/w programming Introduction to servlet Mobile and Wireless Technologies 30 Hours Basics of Wireless Technologies Cellular Communication: Single cell systems, multi-cell systems, frequency reuse, analog cellular systems, digital cellular systems GSM standard: Mobile Station, BTS, BSC, MSC, SMS sever, call processing and protocols CDMA standard: spread spectrum technologies, 2.5G and 3G Systems: HSCSD, GPRS, W-CDMA/UMTS,3GPP and international roaming, Multimedia services CDMA based cellular mobile communication systems Wireless Personal Area Networks: Bluetooth, IEEE 802.11a/b/g standards Mobile Handset Device Interfacing: Data Cables, IrDA, Bluetooth, Touch- Screen Interfacing Wireless Security, Telemetry Java Wireless Programming and Applications Development(J2ME) 100 Hours J2ME Architecture The CLDC and the KVM Tools and Development Process Classification of CLDC Target Devices CLDC Collections API CLDC Streams Model MIDlets MIDlet Lifecycle MIDP Programming MIDP Event Architecture High-Level Event Handling Low-Level Event Handling The CLDC Streams Model The CLDC Networking Package The MIDP Implementation Introduction to WAP, WML Script and XHTML Introduction to Multimedia Messaging Services (MMS) Symbian Programming 60 Hours Symbian OS basics Symbian OS services Symbian OS organization GUI approaches ROM building Debugging Hardware abstraction Base porting Symbian OS reference design porting File systems Overview of Symbian OS Development – DevKits, CustKits and SDKs CodeWarrior Tool Application & UI Development Client Server Framework ECOM STDLIB in Symbian iPhone Programming 80 Hours Introducing iPhone core specifications Understanding iPhone input and output Designing web pages for the iPhone Capturing iPhone events Introducing the webkit CSS transforms transitions and animations Using iUI for web apps Using Canvas for web apps Building web apps with Dashcode Writing Dashcode programs Debugging iPhone web pages SDK programming for web developers An introduction to object-oriented programming Introducing the iPhone OS Using Xcode and Interface builder Programming with the SDK Toolkit OS Concepts & Linux Programming 60 Hours Operating System Concepts What is an OS? Processes Scheduling & Synchronization Memory management Virtual Memory and Paging Linux Architecture Programming in Linux Linux Shell Programming Writing Device Drivers Configuring and Building GNU Cross-tool chain Configuring and Compiling Linux Virtual File System Porting Linux on Target Hardware WinCE.NET and Database Technology 80 Hours Execution Process in .NET Environment Language Interoperability Assemblies Need of C# Operators Namespaces & Assemblies Arrays Preprocessors Delegates and Events Boxing and Unboxing Regular Expression Collections Multithreading Programming Memory Management Exceptions Handling Win Forms Working with database ASP .NET Server Controls and client-side scripts ASP .NET Web Server Controls Validation Controls Principles of database management Need of RDBMS etc Client/Server Computing RDBMS Technologies Codd’s Rules Data Models Normalization Techniques ER Diagrams Data Flow Diagrams Database recovery & backup SQL Android Application 80 Hours Introduction of android Why develop for android Android SDK features Creating android activities Fundamental android UI design Intents, adapters, dialogs Android Technique for saving data Data base in Androids Maps, Geocoding, Location based services Toast, using alarms, Instant messaging Using blue tooth Using Telephony Introducing sensor manager Managing network and wi-fi connection Advanced androids development Linux kernel security Implement AIDL Interface. Project 120 Hours

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  • DAC pack up all your troubles

    - by Tony Davis
    Visual Studio 2010, or perhaps its apparently-forthcoming sister, "SQL Studio", is being geared up to become the natural way for developers to create databases. Central to this drive is the introduction of 'data-tier application components', or DACs. Applications are developed as normal but when it comes to deployment, instead of supplying the DBA with a bunch of scripts to create the required database objects, the developer creates a single DAC Package ("DAC Pack"); a zipped XML file containing all the database objects needed by the application, along with versioning information, policies for deployment, and so on. It's an intriguing prospect. Developers can work on their development database using their existing tools and source control, and then package up the changes into a single DACPAC for deployment and management. DBAs get an "application level view" of how their instances are being used and the ability to collectively, rather than individually, manage the objects. The DBA needing to manage a large number of relatively small databases can use "DAC snapshots" to get a quick overview of what has changed across all the databases they manage. The reason that DAC packs haven't caused more excitement is that they can only be pushed to SQL Server 2008 R2, and they must be developed or inspected using Visual Studio 2010. Furthermore, what we see right now in VS2010 is more of a 'work-in-progress' or 'vision of the future', with serious shortcomings and restrictions that render it unsuitable for anything but small 'non-critical' departmental databases. The first problem is that DAC packs support a limited set of schema objects (corresponding closely to the features available on 'Azure'). This means that Service Broker queues, CLR Objects, and perhaps most critically security (permissions, certificates etc.), are off-limits. Applications that require these objects will need to add them via a post-deployment TSQL script, rather defeating the whole idea. More worrying still is the process for altering a database with a DAC pack. The grand 'collective' philosophy, whereby a single XML file can be used for deploying and managing builds and changes, extends, unfortunately, to database upgrades. Any change to a database object will result in the creation of a new database, copying the data from the old version, nuking the previous one, and then renaming the new one. Simple eh? The problem is that even something as trivial as adding a comment to a stored procedure in a 5GB database will require the server to find at least twice as much space, as well sufficient elbow-room in the transaction log for copying the largest table. Of course, you'll need to take the database offline for the full course of the deployment, which is likely to take a long time if there is a lot of data. This upgrade/rename process breaks the log chain, makes any subsequent full restore operation highly complicated, and will also break log shipping. As with any grand vision, the devil is always in the detail. It's hard to fathom why Microsoft hasn't used a SQL Compare-style approach to the upgrade process, altering a database with a change script, and this will surely be adopted in the near future. Something had to be in place for VS2010, but right now DAC packs only make sense for Azure. For this, they're cute, but hardly compelling. Nevertheless, DBAs would do well to get familiar with VS 2010 and DAC packs. Like it or not, they're both coming. Cheers, Tony.

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  • Why do I need two Instances in Windows Azure?

    - by BuckWoody
    Windows Azure as a Platform as a Service (PaaS) means that there are various components you can use in it to solve a problem: Compute “Roles” - Computers running an OS and optionally IIS - you can have more than one "Instance" of a given Role Storage - Blobs, Tables and Queues for Storage Other Services - Things like the Service Bus, Azure Connection Services, SQL Azure and Caching It’s important to understand that some of these services are Stateless and others maintain State. Stateless means (at least in this case) that a system might disappear from one physical location and appear elsewhere. You can think of this as a cashier at the front of a store. If you’re in line, a cashier might take his break, and another person might replace him. As long as the order proceeds, you as the customer aren’t really affected except for the few seconds it takes to change them out. The cashier function in this example is stateless. The Compute Role Instances in Windows Azure are Stateless. To upgrade hardware, because of a fault or many other reasons, a Compute Role's Instance might stop on one physical server, and another will pick it up. This is done through the controlling fabric that Windows Azure uses to manage the systems. It’s important to note that storage in Azure does maintain State. Your data will not simply disappear - it is maintained - in fact, it’s maintained three times in a single datacenter and all those copies are replicated to another for safety. Going back to our example, storage is similar to the cash register itself. Even though a cashier leaves, the record of your payment is maintained. So if a Compute Role Instance can disappear and re-appear, the things running on that first Instance would stop working. If you wrote your code in a Stateless way, then another Role Instance simply re-starts that transaction and keeps working, just like the other cashier in the example. But if you only have one Instance of a Role, then when the Role Instance is re-started, or when you need to upgrade your own code, you can face downtime, since there’s only one. That means you should deploy at least two of each Role Instance not only for scale to handle load, but so that the first “cashier” has someone to replace them when they disappear. It’s not just a good idea - to gain the Service Level Agreement (SLA) for our uptime in Azure it’s a requirement. We point this out right in the Management Portal when you deploy the application: (Click to enlarge) When you deploy a Role Instance you can also set the “Upgrade Domain”. Placing Roles on separate Upgrade Domains means that you have a continuous service whenever you upgrade (more on upgrades in another post) - the process looks like this for two Roles. This example covers the scenario for upgrade, so you have four roles total - One Web and one Worker running the "older" code, and one of each running the new code. In all those Roles you want at least two instances, and this example shows that you're covered for High Availability and upgrade paths: The take-away is this - always plan for forward-facing Roles to have at least two copies. For Worker Roles that do background processing, there are ways to architect around this number, but it does affect the SLA if you have only one.

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  • Build 2012, the first post

    - by Dennis Vroegop
    Yes, I was one of the lucky few who made it to Build. Build, formerly known as the Professional Developers Conference (or PDC) is the place to be if you are a developer on the Microsoft platform. Since I take my job seriously I took out some time on my busy schedule, sighed at the thought of not seeing my family for another week and signed up for it. Now, before I talk about the amazing Surface devices (yes, this posting is written on one of them), the great Lumia 920 we all got, the long deserved love for touch, NUI and other things I have been talking about for years, I need to do some ranting. So if you are anxious to read about the technical goodies you’ll have to wait until the next post. Still here? Good. When I signed up for the Build conference during my holidays this summer it was pretty obvious that demand would be high. Therefor I made sure I was on time. But even though I registered only 7 minutes after the initial opening time the Early Bird discount for the first 500 attendees was already sold out. I later learned that registration actually started 5 minutes before the scheduled time but even though it is still impressive how fast things went. The whole event sold out in 57 minutes Or so they say… A lot of people got put on the waiting list. There was room for about 1500 attendees and I heard that at least 1000 people were on that waiting list, including a lot of people I know. Strangely, all of them got tickets assigned after 2 weeks. Here at the conference I heard from a guy from Nokia that they had shipped 2500 Lumia 920 phones. That number matches the rumors that the organization added 1000 extra tickets. This, of course is no problem. I am not an elitist and I think large crowds have a special atmosphere that I quite like. But…. The Microsoft Campus is not equipped for that sheer volume of visitors. That was painfully obvious during on-site registration where people had to stand in line for over 2 hours. The conference is spread out over 2 buildings, divided by a 15 minute busride (yes, the campus is that big). I have seen queues of over 200 people waiting for the bus and when that arrived it had a capacity of 16. I can assure you: that doesn’t fit. This of course means that travelling from one site to the other might take about 30 minutes. So you arrive at the session room just in time, only to find out it’s full. Since you can’ get into that session you try to find another one but now you’re even more late so you have no chance at all of entering. The doors are closed and you’re told: “Well, you can watch the live stream online”. Mmmm… So I spend thousands of dollars, a week away from home, family and work to be told I can also watch the sessions online? Are you fricking kidding me? I could go on but I won’t. You get the idea. It’s jus badly organized, something I am not really used to in my 20 years of experience at Microsoft events. Yes, I am disappointed. I hope a lot of people here in Redmond will also fill in the evals and that the organization next year will do a better job. Really, Build deserves better. </rantmode>

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  • It happens only at Devoxx ...

    - by arungupta
    After attending several Java conferences world wide, this was my very first time at Devoxx. Here are some items I found that happens only at Devoxx ... Pioneers of theater-style seating - This not only provides comfortable seating for each attendee but the screens are very clearly visible to everybody in the room. Intellectual level of attendees is very high - Read more explanation on the Java EE 6 lab blog. In short, a lab, 1/3 of the content delivered at Devoxx 2011, could not be completed at other developer days in more than 1/3 the time. Snack box for lunches - Even though this suits well to the healthy lifestyle of multiple-snacks-during-a-day style but leaves attendees hungry sooner in the day. The longer breaks before the next snack in the evening does not help at all. Fortunately, Azure cupcakes and Android ice creams turned out to be handy. I finally carried my own apple :-) Wrist band instead of lanyard - The good part about this is that once tied to your hand then you are less likely to forget in your room. But OTOH you are a pretty much a branded conference attendee all through out the city. It was cost effective as it costed 20c as opposed to 1 euro for the lanyard. Live streaming from theater #8 (the biggest room) on parleys.com All talks recorded and released on parleys.com over next year. This allows attendees to not to miss any session and watch replay at their own leisure. Stephan promised to start sharing the sessions by mid December this year. No need to pre-register for a session - This is true for most of the conferences but bigger rooms (+ overflow room for key sessions) provide sufficient space for all those who want to attend the session. And of course all sessions are available on parleys.com anyway! Community votes on whiteboard - Devoxx attendees gets a chance to vote on topics ranging from their favorite non-Java language, operating system, or love from Oracle. Captured pictures at the end of Day 2 are shown below. Movie on the last but one night - This year it was The Adventures of Tintin and was lots of fun. Fries with mayo - This is a typical Belgian thing. Guys going in ladies room to avoid the long queues ... wow! Tweet wall everywhere and I mean literally everywhere, in rooms, hallways, front desk, and other places. The tweet picking algorithm was not very clear as I never saw my tweet appear on the wall ;-) You can also watch it at wall.devoxx.com. Cozy speaker dinner with great food and wine List of parallel and upcoming sessions displayed on the screen - This makes the information more explicit with the attendees. REST API with multiple mobile clients - This API is also used by some other conferences as well. And there always is iphone.devoxx.com. Steering committee members were recognized multiple times. The committee members were clearly identifiable wearing red hoodies. The wireless SSID was intuitive "Devoxx" but hidden to avoid some crap from Microsoft Windows. All of 9000 addresses were used up most of the times with each attendee having multiple devices. A 1 GB fibre optic cable was stretched to Metropolis to support the required network bandwidth. Stephan is already planning to upgrade the equipment and have a better infrastructure next year. Free water, soda, juice in a cooler Kinect connected to TV screens so that attendees can use their hands to browse through the list of sesssions. #devoxxblog, #devoxxwomen, #devoxxfrance, #devoxxgreat, #devoxxsuggestions And Devoxx attendees are called Devoxxians ... how cool is that ? :-) What other things do you think happen only at Devoxx ? And now the pictures from the community whiteboard: And a more complete album (including bigger pics of community votes) is available below:

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  • Head in the Clouds

    - by Tony Davis
    We're just past the second anniversary of the launch of Windows Azure. A couple of years' experience with Azure in the industry has provided some obvious success stories, but has deflated some of the initial marketing hyperbole. As a general principle, Azure seems to work well in providing a Service-Oriented Architecture for services in enterprises that suffer wide fluctuations in demand. Instead of being obliged to provide hardware sufficient for the occasional peaks in demand, one can hire capacity only when it is needed, and the cost of hosting an application is no longer a capital cost. It enables companies to avoid having to scale out hardware for peak periods only to see it underused for the rest of the time. A customer-facing application such as a concert ticketing system, which suffers high demand in short, predictable bursts of activity, is a great example of an application that would work well in Azure. However, moving existing applications to Azure isn't something to be done on impulse. Unless your application is .NET-based, and consists of 'stateless' components that communicate via queues, you are probably in for a lot of redevelopment work. It makes most sense for IT departments who are already deep in this .NET mindset, and who also want 'grown-up' methods of staging, testing, and deployment. Azure fits well with this culture and offers, as a bonus, good Visual Studio integration. The most-commonly stated barrier to porting these applications to Azure is the problem of reconciling the use of the cloud with legislation for data privacy and security. Putting databases in the cloud is a sticky issue for many and impossible for some due to compliance and security issues, the need for direct control over data, and so on. In the face of feedback from the early adopters of Azure, Microsoft has broadened the architectural choices to cater for a wide range of requirements. As well as SQL Azure Database (SAD) and Azure storage, the unstructured 'BLOB and Entity-Attribute-Value' NoSQL storage alternative (which equates more closely with folders and files than a database), Windows Azure offers a wide range of storage options including use of services such as oData: developers who are programming for Windows Azure can simply choose the one most appropriate for their needs. Secondly, and crucially, the Windows Azure architecture allows you the freedom to produce hybrid applications, where only those parts that need cloud-based hosting are deployed to Azure, whereas those parts that must unavoidably be hosted in a corporate datacenter can stay there. By using a hybrid architecture, it will seldom, if ever, be necessary to move an entire application to the cloud, along with personal and financial data. For example that we could port to Azure only put those parts of our ticketing application that capture and process tickets orders. Once an order is captured, the financial side can be processed in our own data center. In short, Windows Azure seems to be a very effective way of providing services that are subject to wide but predictable fluctuations in demand. Have you come to the same conclusions, or do you think I've got it wrong? If you've had experience with Azure, would you recommend it? It would be great to hear from you. Cheers, Tony.

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  • Django + gunicorn + virtualenv + Supervisord issue

    - by Florian Le Goff
    Dear all, I have a strange issue with my virtualenv + gunicorn setup, only when gunicorn is launched via supervisord. I do realize that it may very well be an issue with my supervisord and I would appreciate any feedback on a better place to ask for help... In a nutshell : when I run gunicorn from my user shell, inside my virtualenv, everything is working flawlessly. I'm able to access all the views of my Django project. When gunicorn is launched by supervisord at the system startup, everything is OK. But, if I have to kill the gunicorn_django processes, or if I perform a supervisord restart, once that gunicorn_django has relaunched, every request is answered with a weird Traceback : (...) File "/home/hc/prod/venv/lib/python2.6/site-packages/Django-1.2.5-py2.6.egg/django/db/__init__.py", line 77, in connection = connections[DEFAULT_DB_ALIAS] File "/home/hc/prod/venv/lib/python2.6/site-packages/Django-1.2.5-py2.6.egg/django/db/utils.py", line 92, in __getitem__ backend = load_backend(db['ENGINE']) File "/home/hc/prod/venv/lib/python2.6/site-packages/Django-1.2.5-py2.6.egg/django/db/utils.py", line 50, in load_backend raise ImproperlyConfigured(error_msg) TemplateSyntaxError: Caught ImproperlyConfigured while rendering: 'django.db.backends.postgresql_psycopg2' isn't an available database backend. Try using django.db.backends.XXX, where XXX is one of: 'dummy', 'mysql', 'oracle', 'postgresql', 'postgresql_psycopg2', 'sqlite3' Error was: cannot import name utils Full stack available here : http://pastebin.com/BJ5tNQ2N I'm running... Ubuntu/maverick (up-to-date) Python = 2.6.6 virtualenv = 1.5.1 gunicorn = 0.12.0 Django = 1.2.5 psycopg2 = '2.4-beta2 (dt dec pq3 ext)' gunicorn configuration : backlog = 2048 bind = "127.0.0.1:8000" pidfile = "/tmp/gunicorn-hc.pid" daemon = True debug = True workers = 3 logfile = "/home/hc/prod/log/gunicorn.log" loglevel = "info" supervisord configuration : [program:gunicorn] directory=/home/hc/prod/hc command=/home/hc/prod/venv/bin/gunicorn_django -c /home/hc/prod/hc/gunicorn.conf.py user=hc umask=022 autostart=True autorestart=True redirect_stderr=True Any advice ? I've been stuck on this one for quite a while. It seems like some weird memory limit, as I'm not enforcing anything special : $ ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 20 file size (blocks, -f) unlimited pending signals (-i) 16382 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 8192 cpu time (seconds, -t) unlimited max user processes (-u) unlimited virtual memory (kbytes, -v) unlimited file locks (-x) unlimited Thank you.

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  • gunicorn + django + nginx unix://socket failed (11: Resource temporarily unavailable)

    - by user1068118
    Running very high volume traffic on these servers configured with django, gunicorn, supervisor and nginx. But a lot of times I tend to see 502 errors. So I checked the nginx logs to see what error and this is what is recorded: [error] 2388#0: *208027 connect() to unix:/tmp/gunicorn-ourapp.socket failed (11: Resource temporarily unavailable) while connecting to upstream Can anyone help debug what might be causing this to happen? This is our nginx configuration: sendfile on; tcp_nopush on; tcp_nodelay off; listen 80 default_server; server_name imp.ourapp.com; access_log /mnt/ebs/nginx-log/ourapp-access.log; error_log /mnt/ebs/nginx-log/ourapp-error.log; charset utf-8; keepalive_timeout 60; client_max_body_size 8m; gzip_types text/plain text/xml text/css application/javascript application/x-javascript application/json; location / { proxy_pass http://unix:/tmp/gunicorn-ourapp.socket; proxy_pass_request_headers on; proxy_read_timeout 600s; proxy_connect_timeout 600s; proxy_redirect http://localhost/ http://imp.ourapp.com/; #proxy_set_header Host $host; #proxy_set_header X-Real-IP $remote_addr; #proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; #proxy_set_header X-Forwarded-Proto $my_scheme; #proxy_set_header X-Forwarded-Ssl $my_ssl; } We have configure Django to run in Gunicorn as a generic WSGI application. Supervisord is used to launch the gunicorn workers: home/user/virtenv/bin/python2.7 /home/user/virtenv/bin/gunicorn --config /home/user/shared/etc/gunicorn.conf.py daggr.wsgi:application This is what the gunicorn.conf.py looks like: import multiprocessing bind = 'unix:/tmp/gunicorn-ourapp.socket' workers = multiprocessing.cpu_count() * 3 + 1 timeout = 600 graceful_timeout = 40 Does anyone know where I can start digging to see what might be causing the problem? This is what my ulimit -a output looks like on the server: core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 59481 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 50000 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 8192 cpu time (seconds, -t) unlimited max user processes (-u) 1024 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited

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