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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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• 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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• ColdFusion Timeout Error

  - by Jason

  I have a scheduled task that runs once a day that builds an XML file that I pass off to another group. Recently the amount of data has greatly increased and is now causing the task to time out (I think). I have tried to optimize my script as much as possible but with no luck. It times out long before an hour and I don't get any kind of ColdFusion error. Instead I get a "This page cannot be found" after it runs. Could this be a timeout someplace other than Coldfusion? Is there a more efficient way to build this XML file? select PersonID, FirstName, LastName from People select d.DepartmentID, DepartmentName, pd.PersonID from Department d inner join PersonDepartment pd on d.DepartmentID = pd.DepartmentID select PaperID, PaperTitle, PaperDescription, pp.PersonID from Paper p inner join PersonPaper pp on p.PaperID = pp.PaperID select DepartmentID, DepartmentName from getDepartments where PersonID = #getPeople.PersonID# select PaperID, PaperDescription from getpapers where PersonID = #getPeople.PersonID# #getPeople.PersonID# #getPeople.Firstname# #getPeople.LastName# #getPersonDepartments.DepartmentID# #getPersonDepartments.DepartmentName# #getPersonPapers.PaperID# #getPersonPapers.PaperDescription# Done!

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• How can I detect common substrings in a list of strings

  - by danio

  Given a set of strings, for example: EFgreen EFgrey EntireS1 EntireS2 J27RedP1 J27GreenP1 J27RedP2 J27GreenP2 JournalP1Black JournalP1Blue JournalP1Green JournalP1Red JournalP2Black JournalP2Blue JournalP2Green I want to be able to detect that these are three sets of files: EntireS[1,2] J27[Red,Green]P[1,2] JournalP[1,2][Red,Green,Blue] Are there any known ways of approaching this problem - any published papers I can read on this? The approach I am considering is for each string look at all other strings and find the common characters and where differing characters are, trying to find sets of strings that have the most in common, but I fear that this is not very efficient and may give false positives. Note that this is not the same as 'How do I detect groups of common strings in filenames' because that assumes that a string will always have a series of digits following it. [Edited 15/09/09 to add more sample strings]

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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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• More intelligent Context Menus in Visual Studio 2008 Database Projects

  - by Mike C.

  I'm using a SQL Server 2008 Database Project, and I'm finding it's very cumbersome to add certain items. For example, if I right click on Tables = Keys and navigate to the Add item, I'd expect to see the different kinds of keys that I can add. Instead, I see the stock items that don't apply, and I'm forced to navigate the Add New Item screen to find Primary Key. Is there a way to make this more efficient? I have Resharper; can I leverage templates somehow (kind of a noob with these). Thanks!

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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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• Is this the best way to get the size of a Paper via CUPS?

  - by Lawrence Johnston

  I've got a CUPS job control file. I need to get the actual dimensions of the print that was made. This is the way I've figure out to do it: Get the paper name using the media attribute. (e.g. Letter) Get the printer uri from the printer-uri attribute. (e.g. ipp://localhost/printers/MyPrinter) Get the printer name by passing the printer uri to the IPP_GET_PRINTER_ATTRIBUTES operation and getting the printer-name attribute. (e.g. MyPrinter) Get the path to the PPD passing the printer name to the the cupsGetPPD method. Open the PPD passing the path to the PPD to the ppdOpenFile method. Get the paper size by passing the PPD and paper name to the ppdPageSize method. This will work, but it seems a bit roundabout. Is there a more efficient way of getting what I need?

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• Find all numbers that appear in each of a set of lists

  - by Ankur

  I have several ArrayLists of Integer objects, stored in a HashMap. I want to get a list (ArrayList) of all the numbers (Integer objects) that appear in each list. My thinking so far is: Iterate through each ArrayList and put all the values into a HashSet This will give us a "listing" of all the values in the lists, but only once Iterate through the HashSet 2.1 With each iteration perform ArrayList.contains() 2.2 If none of the ArrayLists return false for the operation add the number to a "master list" which contains all the final values. If you can come up with something faster or more efficient, funny thing is as I wrote this I came up with a reasonably good solution. But I'll still post it just in case it is useful for someone else. But of course if you have a better way please do let me know.

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• How to find and update the next record in a linking table

  - by someoneinomaha

  I have a classifieds system I'm working on. People are able to add photos to a classified, but I only display one when displaying the list of classifieds. To do that, I have a linking table between classifieds and photos that has a "is_main" boolean field. When someone deletes one of their classified photos, I want to: 1) See if there is more than that photo tied to the classified. 2) If there is, update the next photo and set that "is_main" field to TRUE. Just trying to find out the most efficient way to do 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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