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• How do I ensure data consistency in this concurrent situation?

  - by MalcomTucker

  The problem is this: I have multiple competing threads (100+) that need to access one database table Each thread will pass a String name - where that name exists in the table, the database should return the id for the row, where the name doesn't already exist, the name should be inserted and the id returned. There can only ever be one instance of name in the database - ie. name must be unique How do I ensure that thread one doesn't insert name1 at the same time as thread two also tries to insert name1? In other words, how do I guarantee the uniqueness of name in a concurrent environment? This also needs to be as efficient as possible - this has the potential to be a serious bottleneck. I am using MySQL and Java. Thanks

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• Is it a good idea to apply some basic macros to simplify code in a large project?

  - by DoctorT

  I've been working on a foundational c++ library for some time now, and there are a variety of ideas I've had that could really simplify the code writing and managing process. One of these is the concept of introducing some macros to help simplify statements that appear very often, but are a bit more complicated than should be necessary. For example, I've come up with this basic macro to simplify the most common type of for loop: #define loop(v,n) for(unsigned long v=0; v<n; ++v) This would enable you to replace those clunky for loops you see so much of: for (int i = 0, i < max_things; i++) With something much easier to write, and even slightly more efficient: loop (i, max_things) Is it a good idea to use conventions like this? Are there any problems you might run into with different types of compilers? Would it just be too confusing for someone unfamiliar with the macro(s)?

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• Hibernate Query - Get latest versions by timestamp?

  - by Slim

  I have a database that is being used as a sort of version control system. That is, instead of ever updating any rows, I add a new row with the same information. Each row also contains a version column that is a date timestamp, so the only difference is the new row will have a more recent timestamp. What I'm having trouble with is writing an efficient hibernate query to return the latest version of these rows. For the sake of example, these are rows in a table called Product, the timestamped column is version. There are multiple versions of multiple products in the table. So there may be multiple versions (rows) of ProductA, multiple versions of ProductB, etc. And I would like to grab the latest version of each. Can I do this in just a single hibernate query? session.createQuery("select product from Product product where...?"); Or would this require some intermediate steps?

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• Ruby on Rails: Best way to save search queries in a database

  - by Adam Templeton

  For a RoR app I'm helping develop, I need to save all search queries in a database so I can analyze them later. My plan right now is to create a Result model and table, and just save each search query's text in that table, along with a user's ID, the time, etc. However, the app has about 15,000 users, so I'm afraid the single table approach won't be super efficient when it comes time to parse that data. (The database is setup via MySQL, if that factors in at all.) Am I just being paranoid? Is there a Ruby gem that handles this sort of thing, or a better approach I could take? Any input would be appreciated.

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• Is there any declare for toggle() that if its open do this, closed to that?

  - by Dejan.S

  Im doing some jquery stuff with toggle(), I'm doing different actions depending on if the current div is closing or showing, i know i can easy check if a div hasClass() or is(':visible') for what i want to do, but I'm thinking maybe there is somehow that i can reduce the amount of code or just do it more efficient? like declare the toggle() with two functions that this is for when its showing and this is for when its closing, is this possible? hope you get what i mean? like this, or check a jsfiddle $('#click_me').on('click', function() { $('#contain').toogle('blind', 300, function (){ alert('open'); }, function (){ alert('close'); }); });

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• Algorithm to Group All the Cycles Together

  - by Ngu Soon Hui

  I have a lot of cycles ( indicated by numeric values, for example, 1-2-3-4 corresponds to a cycle, with 4 edges, edge 1 is {1:2}, edge 2 is {2:3}, edge 3 is {3,4}, edge 4 is {4,1}, and so on). A cycle is said to be connected to another cycle if they share one and only one edge. For example, let's say I have two cycles 1-2-3-4 and 5-6-7-8, then there are two cycle groups because these two cycles are not connecting to each other. If I have two cycles 1-2-3-4 and 3-4-5-6, then I have only one cycle group because these two cycles share the same edge. What is the most efficient way to find all the cycle groups?

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• Is select() Ok to implemnet single socket read/write timeout ?

  - by chmike

  I have an application processing network communication with blocking calls. Each thread manages a single connection. I've added a timeout on the read and write operation by using select prior to read or write on the socket. Select is known to be inefficient when dealing with large number of sockets. But is it ok, in term of performance to use it with a single socket or are there more efficient methods to add timeout support on single sockets calls ? The benefit of select is to be portable.

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• Building a custom iterator.

  - by Isai

  I am making this class which is a custom Map based off a hash map. I have an add method where if you add an object the object will be the key, and its value will be 1 if the object is not currently in the list. However if you add object that is currently in the list its value will be bumped up by 1. So if I added 10 strings which were all the same, the key would be that string and the value will be 10. I understand in practice when I iterate through the map, there is actually only one object to iterate, however, I am trying to create a inner class that will define an iterator that will iterate the same object however many times its value is. I can do this by simply using for loops to construct an appropriate ArrayList and just create an iterator for that, but that is too inefficient. Is there an easy or more efficient way of doing this?

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• C# remove duplicates from List<List<int>>

  - by marseilles84

  I'm having trouble coming up with the most efficient algorithm to remove duplicates from List<List<int>>, for example (I know this looks like a list of int[], but just doing it that way for visual purposes: my_list[0]= {1, 2, 3}; my_list[1]= {1, 2, 3}; my_list[2]= {9, 10, 11}; my_list[3]= {1, 2, 3}; So the output would just be new_list[0]= {1, 2, 3}; new_list[1]= {9, 10, 11}; Let me know if you have any ideas. I would really appreciate it.

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• C#. Struct design. Why 16 byte is recommended size?

  - by maxima120

  I read Cwalina book (recommendations on development and design of .NET apps). He says that good designed struct has to be less than 16 bytes in size (for performance purpose). My questions is - why exactly is this? And (more important) can I have larger struct with same efficiency if I run my .NET 3.5 (soon to be .NET 4.0) 64-bit application on i7 under Win7 x64 (is this limitation CPU / OS based)? Just to stress again - I need as efficient struct as it is possible. I try to keep it in stack all the time, the application is heavily multi-threaded and runs on sub-millisecond intervals, the current size of the struct is 64 byte.

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• Generating Fibonacci series in F#

  - by photo_tom

  I'm just starting to learn F# using VS2010 and below is my first attempt at generating the Fibonacci series. What I'm trying to do is to build a list of all numbers less than 400. let fabList = let l = [1;2;] let mutable a = 1 let mutable b = 2 while l.Tail < 400 do let c = a + b l.Add(c) let a = b let b = c My first problem is that on the last statement, I'm getting an error message "Incomplete structured construct at or before this point in expression" on the last line. I don't understand what I'm doing wrong here. While this seems to be an obvious way to build the list in a fairly efficient way (from a c++/C# programmer), from what little I know of f#, this doesn't seem to feel to be the right way to do the program. Am I correct in this feeling?

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• Appengine backreferences - need composite index?

  - by davezor

  I have a query that is very recently starting to throw: "The built-in indices are not efficient enough for this query and your data. Please add a composite index for this query." I checked the line on which this exception is being thrown, and the problem query is this one: count = self.vote_set.filter("direction =", 1).count() This is literally a one-filter operation using appengine's built-in backreferences. I have no idea how to optimize this query...anyone have any suggestions? I tried to add this index: - kind: Vote properties: - name: direction direction: desc - kind: Vote properties: - name: direction And I got a message (obviously) saying this was an unnecessary index. Thanks for your help in advance.

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• Query with multiple IN-statements but without the cartesian product

  - by Janne

  How could I make this kind of query e.g. in MySQL SELECT * FROM Table t WHERE t.a IN (1,2,3) AND t.b IN (4,5,6) AND t.c IN (7,8,9) ... so that the result would contain only the three rows: t.a|t.b|t.c ---+---+--- 1 | 4 | 7 2 | 5 | 8 3 | 6 | 9 The above query of course returns all the combinations of the values in the IN clauses but I would like to get just the ones where the first elements of each tuple match, second elements of each tuple match and so on. Is there any efficient way to do this? By the way is there some common term for this kind of query or concept? I'm having hard time coming up with the question's title because I can't put this into words..

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• Explanation of NSMutableURLRequest : setHTTPMethod

  - by kkmoslehpour

  I am new to objective c programming. I am currently trying to insert data into mysql database. I have read a couple links on this and could not find the exact answer I am looking for. Here is what I am trying to do: I have my app that user inputs a name in a text field and once the press the add button, it makes a connection to my php file and my php file does the rest of the work (using POST method) and adds the name to the mysql dataase. I have seen a lot of people use NSMutableURLRequest : setHTTPMethod :POST`` in their code (in my case my php file does that and I don't haveNSMutableURLRequest` included in my code and it works perfectly fine.) My questions are: Are there any benefits of including NSMutableURLRequest in your code when you can just call your php code to take care of the POST for you? What does NSMutableURLRequest exactly do and which way is more efficient?

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• Retrieving a single Guid in CRM 4.0

  - by user1746560

  I'm new to CRM (version 4.0) and i'm trying to return a 'yearid' guide based on a given year (which is also stored in the entity).So far i've got: public static Guid GetYearID(string yearName) { ICrmService service = CrmServiceFactory.GetCrmService(); // Create the query object. QueryExpression query = new QueryExpression("year"); ColumnSet columns = new ColumnSet(); columns.AddColumn("yearid"); query.ColumnSet = columns; FilterExpression filter = new FilterExpression(); filter.FilterOperator = LogicalOperator.And; filter.AddCondition(new ConditionExpression { AttributeName = "yearName", Operator = ConditionOperator.Equal, Values = new object[] { yearName} }); query.Criteria = filter; } But my questions are: A) What code do in addition to this to actually store the Guid? B) Is using a QueryExpression the most efficient way to do this?

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• Override onDraw to change how the drawing occurs (Android)

  - by Casebash

  I want to change how my UI elements display, so I am overriding onDraw. The following code allows me to change a View to be drawn using PorterDuff.Mode.DARKEN. Unfortunately, this method involves creating a bitmap the size of the entire screen, then drawing to it then drawing this large bitmap the main screen again, for each UI element. This isn't at all efficient. Is it possible to achieve this in a more effecient way? @Override protected void onDraw(Canvas canvas) { //TODO: Reduce the burden from multiple drawing Bitmap bitmap=Bitmap.createBitmap(canvas.getWidth(), canvas.getHeight(), Config.ARGB_8888); Log.e("tmp",canvas.getClipBounds().toString()); Canvas offscreen=new Canvas(bitmap); super.onDraw(offscreen); //Then draw onscreen Paint p=new Paint(); p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DARKEN)); canvas.drawBitmap(bitmap, 0, 0, p); }

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• Awk or Sed: File Annotation

  - by lukmac

  Hallo, my SO friend, my question is: Specification: annotate the fields of FILE_2 to the corresponding position of FILE_1. A field is marked, and hence identified, by a delimiter pair. I did this job in python before I knew awk and sed, with a couple hundred lines of code. Now I want to see how powerful and efficient awk and sed can be. Show me some masterpiece of awk or sed, please! The delimiter pairs can be configured in FILE_3, but let's assume the first delimiter in a pair is 'Marker (number i) start', the other one is 'Marker (number i) done' Example: |-----------------FILE_1------------------| text text text text blabla Marker_1_start Marker_1_done any text in between blabla Marker_2_start Marker_2_done text text |-----------------FILE_2------------------| Marker_1_start 11 1111 Marker_1_done Marker_2_start 2222 22 Marker_2_done Expected Output: |-----------------FILE_Out------------------| text text text text blabla Marker_1_start 11 1111 Marker_1_done any text in between blabla Marker_2_start 2222 22 Marker_2_done text text

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• linq to sql update data

  - by pranay

  can i update my employee record as given in below function or i have to make query of employee collection first and than i update data public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); db.App3_EMPLOYEEs.Attach(employee); db.SubmitChanges(); return employee.PKEY; } or i have to do this public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); App3_EMPLOYEE emp = db.App3_EMPLOYEEs.Single(e => e.PKEY == employee.PKEY); db.App3_EMPLOYEEs.Attach(employee,emp); db.SubmitChanges(); return employee.PKEY; } But i dont want to use second option is there any efficient way to update data

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• How to save an order (permutation) in an sql db

  - by Bendlas

  I have a tree structure in an sql table like so: CREATE TABLE containers ( container_id serial NOT NULL PRIMARY KEY, parent integer REFERENCES containers (container_id)) Now i want to define an ordering between nodes with the same parent. I Have thought of adding a node_index column, to ORDER BY, but that seem suboptimal, since that involves modifying the index of a lot of nodes when modifying the stucture. That could include adding, removing, reordering or moving nodes from some subtree to another. Is there a sql datatype for an ordered sequence, or an efficient way to emulate one? Doesn't need to be fully standard sql, I just need a solution for mssql and hopefully postgresql EDIT To make it clear, the ordering is arbitrary. Actually, the user will be able to drag'n'drop tree nodes in the GUI

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• Help with algorithm to determine phrase occurrence in string in PHP

  - by Will M.

  I have an array of phrases (max 2 words) like $words = array('barack obama', 'chicago', 'united states'); and then I have a string like: $sentence = "Barack Obama is from Chicago. Barack Obama's favorite food it pizza."; I want to find/create an efficient algorithm that would return the number of occurrences of the words in the array $words in the string $sentence. In this case it would be: 'barack obama' => 2 'chicago' => 0 How can I built this?

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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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• execute javascsript for loop alternately forward and backward

  - by Stiff Mittens

  What I'm trying to do is iterate through an array in chunks, alternating the direction of iteration from chunk to chunk. Confused? So am I. For example, if I want to loop thru an array with 25 elements, but I want to do it in this order: 0, 1, 2, 3, 4, 9, 8, 7, 6, 5, 10, 11, 12, 13, 14, 19, 18, 17, 16, 15, 20, 21, 22, 23, 24, what would be the most efficient way of doing this? I'm looking for something scalable because the array I'm working with now is actually 225 elements and I want to traverse it in 15 element chunks, but that may change at some point. So far, the only method I've figured out that actually works is to hard-wire the iteration order into a second array and then iterate through that in the normal way to get the indices for the original array. But that sucks. Any help would be greatly appreciated.

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• Who owes who money optimisation problem

  - by Francis

  Say you have n people, each who owe each other money. In general it should be possible to reduce the amount of transactions that need to take place. i.e. if X owes Y £4 and Y owes X £8, then Y only needs to pay X £4 (1 transaction instead of 2). This becomes harder when X owes Y, but Y owes Z who owes X as well. I can see that you can easily calculate one particular cycle. It helps for me when I think of it as a fully connected graph, with the nodes being the amount each person owes. Problem seems to be NP-complete, but what kind of optimisation algorithm could I make, nevertheless, to reduce the total amount of transactions? Doesn't have to be that efficient, as N is quite small for me.

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• PHP cURL: get headers only from post

  - by Stewart

  There ought to be a way of sending a post request and getting back just the headers. $ch = curl_init('http://www.stackoverflow.com/'); curl_setopt($ch, CURLOPT_HEADER, true); curl_setopt($ch, CURLOPT_POST, true); curl_setopt($ch, CURLOPT_NOBODY, true); doesn't work, because all setting CURLOPT_NOBODY does is to change the request method to HEAD, thereby overriding CURLOPT_POST. I could just leave the last of these lines out and only process the headers, but is there a more efficient way? It's also odd that there doesn't seem to be a way in cURL to truncate the received content to a specified length as there is with file_get_contents.

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• Q about AbstractApplicationContext.getBeansOfType() and getBean()

  - by Paul Reiners

  We have the following legacy 2.0.7 Spring code: final Map<String, MyClass> secondaryFactories = (Map<String, MyClass>) context.getBeansOfType(MyClass.class, false, true); return (MyClass) context.getBean("myClass"); where context is an instance of org.springframework.context.support.AbstractApplicationContext Note that we ignore the return value of getBeansOfType(). This works just fine, but the problem is that the call to getBeansOfType() is time-consuming. However, even though we ignore the return value of this call, if we try to eliminate this call, then the instance of MyClass returned by getBean() is not fully initialized. (So, apparently, the call to getBeansOfType() is having some sort of side-effects that we need.) We suspect that the call to getBeansOfType() is overkill and we could do something more lightweight so that the instance of MyClass obtained by the call to getBean() would be fully initialized (but it's not null and no exception is thrown). So, is there a more efficient way of doing this?

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