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• When is BIG, big enough for a database?

  - by David ???

  I'm developing a Java application that has performance at its core. I have a list of some 40,000 "final" objects, i.e., I have an initialization input data of 40,000 vectors. This data is unchanged throughout the program's run. I am always preforming lookups against a single ID property to retrieve the proper vectors. Currently I am using a HashMap over a sub-sample of a 1,000 vectors, but I'm not sure it will scale to production. When is BIG, actually big enough for a use of DB? One more thing, an SQLite DB is a viable option as no concurrency is involved, so I guess the "threshold" for db use, is perhaps lower.

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• Updating a database periodically with Java

  - by MSR

  I would like to perform updates to a MySQL database using two separate classes (that do different things) -- one doing so every 10 seconds, and the second every minute. I have a few gaps in my Java knowledge and I'm wondering what the best way to achieve it is. Importantly, if connectivity to the database is lost, I need reconnection attempts to occur indefinitely, and I'm guessing the use of Prepared Statements will make queries more efficient. Should the connection to the database be left open all the time or closed between the updates being run? Maybe I also need to think about clearing objects/resources out of memory if the class instances are going to be run indefinitely.

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• Delphi Memory Management

  - by nomad311

  I haven't been able to find the answers to a couple of my Delphi memory management questions. I could test different scenarios (which I did to find out what breaks the FreeAndNil method), but its takes too long and its hard! But seriously, I would also like to know how you all (Delphi developers) handle these memory management issues. My Questions (Feel free to pose your own I'm sure the answers to them will help me too): Does FreeAndNil work for COM objects? My thoughts are I don't need it, but if all I need to do is set it to nil than why not stay consistent in my finally block and use FreeAndNil for everything? Whats the proper way to clean up static arrays (myArr : Array[0..5] of TObject). I can't FreeAndNil it, so is it good enough to just set it to nil (do I need to do that after I've FreeAnNil'd each object?)? Thanks Guys!

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• Websphere/Oracle 11 - much more Heap Usage than with Oracle 10

  - by swalkner

  Hi all, while testing our application with Oracle 11 (previously, we had Oracle 10), we saw that our server uses much more heap space. It seems as it has something to do with T4CConnection; there are 500 objects of T4CConnection allocated. Someone told me, that Oracle 11 is using SoftReferences to keep the connection pool; but we don't need that. Is that correct? Could that be the problem for the increased heap space? If yes - how can we avoid connection pooling? Thanks a lot!!

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• In-memory data structure that supports boolean querying

  - by sanity

  I need to store data in memory where I map one or more key strings to an object, as follows: "green", "blue" -> object1 "red", "yellow" -> object2 I need to be able to efficiently receive a list of objects, where the strings match some boolean criteria, such as: ("red" OR "green") AND NOT "blue" I'm working in Java, so the ideal solution would be an off-the-shelf Java library. I am, however, willing to implement something from scratch if necessary. Anyone have any ideas? I'd rather avoid the overhead of an in-memory database if possible, I'm hoping for something comparable in speed to a HashMap (or at least the same order of magnitude).

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• Iterating through a range of dates in Python

  - by ShawnMilo

  This is working fine, but I'm looking for any feedback on how to do it better. Right now I think it's better than nested loops, but it starts to get Perl-one-linerish when you have a generator in a list comprehension. Any suggestions are welcome. day_count = (end_date - start_date).days + 1 for single_date in [d for d in (start_date + timedelta(n) for n in range(day_count)) if d <= end_date]: print strftime("%Y-%m-%d", single_date.timetuple()) Notes: I'm not actually using this to print; that's just for demo purposes. The variables start_date and end_date are datetime.date objects, because I don't need the timestamps (they're going to be used to generate a report). I checked the StackOverflow questions which were similar before posting this, but none were exactly the same. Sample Output (for a start date of 2009-05-30 and an end date of 2009-06-09): 2009-05-30 2009-05-31 2009-06-01 2009-06-02 2009-06-03 2009-06-04 2009-06-05 2009-06-06 2009-06-07 2009-06-08 2009-06-09

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• Adapting Map Iterators Using STL/Boost/Lambdas

  - by John Dibling

  Consider the following non-working code: typedef map<int, unsigned> mymap; mymap m; for( int i = 1; i < 5; ++i ) m[i] = i; // 'remove' all elements from map where .second < 3 remove(m.begin(), m.end(), bind2nd(less<int>(), 3)); I'm trying to remove elements from this map where .second < 3. This obviously isn't written correctly. How do I write this correctly using: Standard STL function objects & techniques Boost.Bind C++0x Lambdas I know I'm not eraseing the elements. Don't worry about that; I'm just simplifying the problem to solve.

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• Choose between multiple options with defined probability

  - by Sijin

  I have a scenario where I need to show a different page to a user for the same url based on a probability distribution, so for e.g. for 3 pages the distribution might be page 1 - 30% of all users page 2 - 50% of all users page 3 - 20% of all users When deciding what page to load for a given user, what technique can I use to ensure that the overall distribution matches the above? I am thinking I need a way to choose an object at "random" from a set X { x1, x2....xn } except that instead of all objects being equally likely the probability of an object being selected is defined beforehand.

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• Prevent initial array from sorting

  - by George

  I have an array where the order of the objects is important for when I finally output the array in a document. However, I'm also sorting the array in a function to find the highest value. The problem is that I after I run the function to find the highest value, I can't get the original sort order of the array back. // html document var data = [75,300,150,500,200]; createGraph(data); // js document function createGraph(data) { var maxRange = getDataRange(data); // simpleEncode() = google encoding function for graph var dataSet = simpleEncode(data,maxRange); } function getDataRange(dataArray) { var num = dataArray.sort(sortNumber); return num[0]; } I've also tried setting data to dataA and dataB and using dataB in the getDataRange function and dataA in the simpleEncode function. Either way, data always end up being sorted from highest to lowest.

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• Count The Amount Of Data In An Array Including SOME Null

  - by Josephine

  I'm coding in java and I need to create a function that returns the number of Data objects that are currently in an ArrayList. At the moment I have this: int count = 0; for (int i = 0; i < data.length; i++) { if (data[i] != null) { count ++; } } return count; But the problem is that an array list that includes null data is acceptable, and I have to count their null data towards this counter. How do I include the null data that's in the middle of this array, and not the null data that's not supposed to be counted for? For example, I have some tester code that adds (8),null,null,(23),(25) to the array, and this function should return 5 when the initial array size is 10. Thank you so much

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• How to change the value of progressbar in C#?

  - by shekhar

  Hi, I want to add an progress bar into my C# based application. I would like to know what is the good way of updating its value at particular events? My problem is, I have single function in UI which does all the processing.This function in turn calls many more functions, creates objects, updates database, etc. (basically performs all the work) and returns values in an output file. I have access to that function only. So in this how to update the progressbar's value at the end of each step? What is the best practice for this kind of situation? What is the good way to keep UI logic and business logic seperate? I want to avoid writting progressbar related code in my library code. Please suggest some solution. Thanks and Regards,

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• How to find selected node in Tree?

  - by badgirl

  Hello. I have dynamic tree (moreover nodes can have children). Every node has some action. When I right click on some node, it offers me some actions. One action, for example createChildNode creates child node, which in turn creates MyObject2. MyObject2 must be created with assistance of MyOject1, which was created in parent node(that one where I right click for actions ). How to get that object from selected node? That objects in nodes are putted to lookups.singleton(MyObjectX)

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• I want to make my own Malloc

  - by Unknown

  I want to make my own malloc/free so I can make a precise copying allocator. Any gurus have any tips and suggestions? I have a few questions for now: Should I just malloc large chunks of memory, and then distribute from that so I don't have to call the system calls? How are copying collectors usually done? I would imagine that this part is a bit complicated to do efficiently. My naive implementation would just malloc a block the size of the remaining objects which would require 2x the space.

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• Json.Net CustomSerialization

  - by BonyT

  I am serializing a collection of objects that contains a dictionary called dynamic properties. The default Json emitted looks like this: [{"dynamicProperties":{"WatchId":7771,"Issues":0,"WatchType":"x","Location":"Equinix Source","Name":"PI_5570_5580"}}, {"dynamicProperties":{"WatchId":7769,"Issues":0,"WatchType":"x","Location":"Equinix Source","Name":"PI_5570_5574"}}, {"dynamicProperties":{"WatchId":7767,"Issues":0,"WatchType":"x","Location":"Equinix Source","Name":"PI_5570_5572"}}, {"dynamicProperties":{"WatchId":7765,"Issues":0,"WatchType":"y","Location":"Equinix Source","Name":"highlight_SM"}}, {"dynamicProperties":{"WatchId":8432,"Issues":0,"WatchType":"y","Location":"Test Devices","Name":"Cisco1700PI"}}] I'd like to produce Json that looks like this: [{"WatchId":7771,"Issues":0,"WatchType":"x","Location":"Equinix Source","Name":"PI_5570_5580"}, {"WatchId":7769,"Issues":0,"WatchType":"x","Location":"Equinix Source","Name":"PI_5570_5574"}, {"WatchId":7767,"Issues":0,"WatchType":"x","Location":"Equinix Source","Name":"PI_5570_5572"}, {"WatchId":7765,"Issues":0,"WatchType":"y","Location":"Equinix Source","Name":"highlight_SM"}, {"WatchId":8432,"Issues":0,"WatchType":"y","Location":"Test Devices","Name":"Cisco1700PI"}] From reading the Json.Net documentation it looks like I could build a CustomContractResolver for my class, but I cannot find any details on how to go about this... Can anyone shed any light on the direction I should be looking in?

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• will destroyed() be emitted if the constructor of a class derived from QObject throws?

  - by PorkyBrain

  Ive seen Qt GUI syntax like the following all over the place: myDialog::myDialog(QWidget *parent, Qt::WFlags flags):QDialog(parent, flags) { QPushButton *button = new QPushButton("&Download", this); QVBoxLayout *layout = new QVBoxLayout(this); //something that can throw here layout ->addWidget(button ); setLayout(layout); } I've always wondered if this can leak in the event of an exception because the "this" I'm giving as a parent to button and layout is not fully constructed so it might not destroy its children. I tried it out in MSVC2010 Qt4.8.3 and it looks like as soon as the base QObject class is fully created (which is done first of course) it is ok to pass "this" to other objects in the constructor, they will destroyed correctly. I haven't found the spot in the Qt docs guaranteeing this though, can someone point me to it so I have assurance that this will not change in the future?

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• what's the right way to do polymorphism with protocol buffers?

  - by user364003

  I'm trying to long-term serialize a bunch of objects related by a strong class hierarchy in java, and I'd like to use protocol buffers to do it due to their simplicity, performance, and ease of upgrade. However, they don't provide much support for polymorphism. Right now, the way I'm handling it is by having a "one message to rule them all" solution that has a required string uri field that allows me to instantiate the correct type via reflection, then a bunch of optional fields for all the other possible classes I could serialize, only one of which will be used (based on the value of the uri field). Is there a better way to handle polymorphism, or is this as good as I'm going to get?

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• Can't get a List(Of <my class>) from a Dictionary in .NET?

  - by magsto

  I have a Dictionary with key of type UInteger and the value is List(Of Session) where the (Public) class Session contains a couple of variables and a constructor (Public Sub New(...)). Some of the variables in my Session class is: Private count As Integer Private StartDate As Date Private Values As List(Of Integer) and a couple of methods like: Friend Sub Counter(ByVal c as Integer) count += c End Sub There is no problem to add values to the Dictionary: Dim Sessions As New List(Of Session) Dim dict As New Dictionary(Of Integer, Sessions) then some code to fill up a couple of Session objects in Sessions (not shown here) and then: dict.Add(17, Sessions) 'No problem Sessions.Clear() Sessions = dict(17) 'This doesn't return anything! The Sessions object is empty even if the code doesn't returned any error. Is my class Session to compex to be stored in a Dictionary?

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• Game network physics collision

  - by Jonas Byström

  How to simulating two client-controlled vehicles colliding (sensibly) in a typical client/server setup for a network game? I did read this eminent blog post on how to do distributed network physics in general (without traditional client prediction), but this question is specifically on how to handle collisions of owned objects. Example Say client A is 20 ms ahead of server, client B 300 ms ahead of server (counting both latency and maximum jitter). This means that when the two vehicles collide, both clients will see the other as 320 ms behind - in the opposite direction of the velocity of the other vehicle. Head-to-head on a Swedish highway means a difference of 16 meters/17.5 yards! What not to try It is virtually impossible to extrapolate the positions, since I also have very complex vehicles with joints and bodies all over, which in turn have linear and angular positions, velocities and accelerations, not to mention states from user input.

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• Declare variables that depend on unknown type in template functions.

  - by rem

  Suppose I'm writing a template function foo that has type parameter T. It gets an object of type T that must have method bar(). And inside foo I want to create a vector of objects of type returned by bar. In GNU C++ I can write something like that: template<typename T> void foo(T x) { std::vector<__typeof(x.bar())> v; v.push_back(x.bar()); v.push_back(x.bar()); v.push_back(x.bar()); std::cout << v.size() << std::endl; } How to do the same thing in Microsoft Visual C++? Is there some way to write this code that works in both GNU C++ and Visual C++?

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• How to use .DefaultListCellRenderer

  - by loddn

  First, i'm new at Java-programming and my native lang is not english, but still i hope to get some help from you all. What I try to do is a simple java-interface with a jComboBox and a jList. I want to poplate to jComboBox with Object-names and when the user select one of the names get the object-id which i will use to populate the jList. It's probably simple but i have bin stuck with this problem all day. private void loadComboBox() { biz.Object object = new biz.Object(); try { ArrayList<biz.Object> arrayOfObjects= object.getAllObjects();// ArrayList of objects for (biz.Object o:arrayOfObjects) { if (o != null) cbm.addElement(o); //`toString-method } cb.setModel(cbm); //JComboBox

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• A generic list of generics

  - by SnOrfus

  I'm trying to store a list of generic objects in a generic list, but I'm having difficulty declaring it. My object looks like: public class Field<T> { public string Name { get; set; } public string Description { get; set; } public T Value { get; set; } /* ... */ } I'd like to create a list of these. My problem is that each object in the list can have a separate type, so that the populated list could contain something like this: { Field<DateTime>, Field<int>, Field<double>, Field<DateTime> } So how do I declare that? List<Field<?>> (I'd like to stay as typesafe as possible, so I don't want to use an ArrayList).

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• Django store regular expression in DB which then gets evaluated on page

  - by John

  Hi, I want to store a number of url patterns in my django model which a user can provide parameters to which will create a url. For example I might store these 3 urls in my db where %s is the variable parameter provided by the user: www.thisissomewebsite.com?param=%s www.anotherurl/%s/ www.lastexample.co.uk?param1=%s&fixedparam=2 As you can see from these examples the parameter can appear anywhere in the string and not in a fixed position. I have 2 models, one holds the urls and one holds the variables: class URLPatterns(models.Model): pattern = models.CharField(max_length=255) class URLVariables(models.Model): pattern = models.ForeignKey(URLPatterns) param = models.CharField(max_length=255) What would be the best way to generate these urls by replacing the %s with the variable in the database. would it just be a simple replace on the string e.g: urlvariable = URLVariable.objects.get(pk=1) pattern = url.pattern url = pattern.replace("%s", urlvariable.param) or is there a better way? Thanks

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• Can I overwrite an Object that has been Locked() in C#?

  - by makerofthings7

  I have a few objects that I'd like to send to the server, but I want to make sure that this is the only thread that moving the data from Stage to Upload. Is the following code valid in a multithreaded environment? List<CounterInternal> UploadToServer = new List<CounterInternal>(); List<CounterInternal> StagingQueue = new List<CounterInternal>(); lock (this.UploadToServer) lock (this.StagingQueue) { if (UploadToServer.Count == 0) { UploadToServer = StagingQueue.DoDeepCopyExtensionMethod(); // is the following line valid given that I have a Lock() on it? StagingQueue = new List<CounterInternal>(); } } }

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• EntityFramework 4.0: can you return different types depending on data in the database?

  - by user200341

  I have a Media table in the database. I also have an IMedia interface. I have two different media types that implements the same interface: 1) AudioMedia 2) PictureMedia What I wonder here, is if I can use EntityFramework (I'm using an EDMX file but I have my models in a separate library, with automatic code generation turned off), and depending on the data in the database, select what type to get (AutioMedia or PictureMedia). Since they are both implementing the same interface (could be changed to an abstract class if needed I suppose), I'm thinking that somewhere along the way you could specify what class it should be. I should perhaps point out that I have a class that inherits from ObjectContext to access the objects. Perhaps there is something that that can be done?

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• Program output to file in Java (and reading it again)

  - by Cohagen

  I have a large main method in an IO class which creates objects from four different classes in my program (which all use one another to some extent). My main method takes all info in using a scanner, from the console window, and uses this info to call the constructors and methods in the other classes. As this is my first full program in Java I have been focussed on making the main method work via the console, without properly considering file input and output. I cannot see an easy way of making that work now. Ideally what I require is some way of writing everything I input to the console while running the main method to a file, in a format that can be read again and inputed back through the main method? I have refrained from posting the main method as it is 250+ lines long, but will post any relevant parts of it if required. Any help appreciated

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