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• Help with MySQL database structure - user notification system

  - by Simon

  Hi, I'd like to send global notifications to my users (1000+ users) and allow them to close the notification box once they have read the message. Basically I may send one notification per week globally ie/ each user get the same message and they are not personal in nature. What is the best way to achieve this? Create 2 tables: **tb_messages** message_id massage_title message_content **tb_read_messages** user_id message_id is-read That way i can just show each user the current notifications that are not read? select * from tb_read_messages WHERE user_id = $user_id AND is-read = no OR is there a more efficient way? Thanks!!!

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• Finding group maxes in SQL join result

  - by Gene

  Two SQL tables. One contestant has many entries: Contestants Entries Id Name Id Contestant_Id Score -- ---- -- ------------- ----- 1 Fred 1 3 100 2 Mary 2 3 22 3 Irving 3 1 888 4 Grizelda 4 4 123 5 1 19 6 3 50 Low score wins. Need to retrieve current best scores of all contestants ordered by score: Best Entries Report Name Entry_Id Score ---- -------- ----- Fred 5 19 Irving 2 22 Grizelda 4 123 I can certainly get this done with many queries. My question is whether there's a way to get the result with one, efficient SQL query. I can almost see how to do it with GROUP BY, but not quite. In case it's relevant, the environment is Rails ActiveRecord and PostgreSQL.

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• how to play an encrypted file in Android.

  - by user306517

  I need to be able to play an encrypted file in Android. The file is AAC. The only way I can see to do this is either: decrypt the file to internal private storage and point the player at that file to play, or decrypt & decode the file to pcm and feed it to an AudioTrack. 1 isn't great because it takes a long time to do that. 2 isn't great either because I don't know how I can take advantage of the HW decoder to do this. Any ideas? tia.

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• python dictionary with constant value-type

  - by s.kap

  hi there, I bumped into a case where I need a big (=huge) python dictionary, which turned to be quite memory-consuming. However, since all of the values are of a single type (long) - as well as the keys, I figured I can use python (or numpy, doesn't really matter) array for the values ; and wrap the needed interface (in: x ; out: d[x]) with an object which actually uses these arrays for the keys and values storage. I can use a index-conversion object (input -- index, of 1..n, where n is the different-values counter), and return array[index]. I can elaborate on some techniques of how to implement such an indexing-methods with reasonable memory requirement, it works and even pretty good. However, I wonder if there is such a data-structure-object already exists (in python, or wrapped to python from C/++), in any package (I checked collections, and some Google searches). Any comment will be welcome, thanks.

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• Can I serialize a BitArray to XML?

  - by SimonNet

  Hello I have a business class which I need to serialize to xml. It has a BitArray property. I have decorated it with [XmlAttribute] but the serialization is failing with To be XML serializable, types which inherit from ICollection must have an implementation of Add(System.Boolean) at all levels of their inheritance hierarchy. System.Collections.BitArray does not implement Add(System.Boolean). I am not sure whether its possible to serialize to xml? If not what would be an efficient means of serializing the BitArray Thanks for looking

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• How do I create a point system in a Rails/Twitter app that assigns points to users and non-authentic

  - by codyvbrown

  I'm building a question and answer application on top of twitter and I'm hitting some snags because I'm inevitably dealing with two classes of users: authenticated and non-authenticated. The site enable users to give points to other users, who may or may not be authenticated, and I want to create a site-wide point system where the application stores and displays this information on their profile. I want to save this point data to the user because that would be faster and more efficient but non-authenticated users aren't in our system, we only have the twitter handle. So instead we display the points in our system like this: @points = point.all( :select => "tag, count(*) AS count", # Return tag and count :group => 'tag', # Group by the tag :order => "2 desc", :conditions => {:twitter_handle => params[:username]}) Is there a better way to do this? Is there a better way to associate data with non-authenticated users?

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• Obtain patterns in one file from another using ack or awk or better way than grep?

  - by Rock

  Is there a way to obtain patterns in one file (a list of patterns) from another file using ack as the -f option in grep? I see there is an -f option in ack but it's different with the -f in grep. Perhaps an example will give you a better idea. Suppose I have file1: file1: a c e And file2: file2: a 1 b 2 c 3 d 4 e 5 And I want to obtain all the patterns in file1 from file2 to give: a 1 c 3 e 5 Can ack do this? Otherwise, is there a better way to handle the job (such like awk or using hash) because I have millions of records in both files and really need an efficient way to complete? Thanks!

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• Sql Server XML-type column duplicate entry detection

  - by aaaa bbbb

  In Sql Server I am using an XML type column to store a message. I do not want to store duplicate messages. I only will have a few messages per user. I am currently querying the table for these messages, converting the XML to string in my C# code. I then compare the strings with what I am about to insert. Unfortunately, Sql Server pretty-prints the data in the XML typed fields. What you store into the database is not necessarily exactly the same string as what you get back out later. It is functionally equivalent, but may have white space removed, etc. Is there an efficient way to compare an XML string that I am considering inserting with those that are already in the database? As an aside, if I detect a duplicate I need to delete the older message then insert the replacement.

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• How to search for closest value in a lookup table?

  - by CSharperWithJava

  I have a simple one dimmensional array of integer values that represent a physical set of part values I have to work with. I then calculate and ideal value mathematically. How could I write an efficient search algorithm that will find the smallest abosulte difference from my ideal value in the array? The array is predetermined and constant, so it can be sorted however I need. Example Lookup array: 100, 152, 256, 282, 300 Searching for an ideal value of 125 would find 100 in the array, whereas 127 would find 152. The actual lookup array will be about 250 items long and never change.

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• Error with global variable in php not extending to included php file

  - by phileaton

  I have an html file that calls has a php section in the header like so: $page = basename($_SERVER['PHP_SELF']); Now further down in the html file I have a included footer like so: <?php include("footer.php"); ?> In this script I am referencing the $page variable, but it doesn't find it. I tried echoing the variable and nothing happened. When I place the basename() code in the footer.php file though, it handled it fine. I'd like to be efficient with the coding, so how can I get the footer.php file to get that $page variable? Is there a better way to do this than including the $page variable twice?

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• Differentiate A Section/Portion of 3D object From Other Parts

  - by Ramshad

  I am trying to write a WPF windows application that dynamically creates a 3 D object for an existing 3D Image. The senerio is as follows. Mark the points randomly on the existing 3D Image. Create a 3D object based on the points already marked. Check the below Sample Screenshots. Screenshot 1 and Screenshot 2 I am successfully able to load the 3D file to the WPF form. And was able to perform the rotation using TrackballDecorator 3D Tools library. I have just read this related post. however i didn't get it exactly :) So,can you suggest some efficient methods to achieve it.

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• What technology to use for a RIA

  - by user297159

  I have to develop a online business software solution (similar to ERP) for a company to manage the information exchange for internal use and with external partners. It should be online. What technology should I use, I have checked framewroks like: Flex, Silverlight, Google/GWT, sencha (ExtJS), jQuery, DoJo, Telereik, Infrajistics and others similar. But they seam to be very low level programming. May be this is advantage for other projects, where you need more flexibility, but this project is stright forward. I need something more focused on business software (tables, forms, processes) where and eventually more efficient with less coding, or something I can save time. Is force.com an option? But I can not install this on the customer's servers... Do you have any ideas for me for a web based framework focused on business applications?

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• How to hash and check for equality of objects with circular references

  - by mfya

  I have a cyclic graph-like structure that is represented by Node objects. A Node is either a scalar value (leaf) or a list of n=1 Nodes (inner node). Because of the possible circular references, I cannot simply use a recursive HashCode() function, that combines the HashCode() of all child nodes: It would end up in an infinite recursion. While the HashCode() part seems at least to be doable by flagging and ignoring already visited nodes, I'm having some troubles to think of a working and efficient algorithm for Equals(). To my surprise I did not find any useful information about this, but I'm sure many smart people have thought about good ways to solve these problems...right? Example (python): A = [ 1, 2, None ]; A[2] = A B = [ 1, 2, None ]; B[2] = B A is equal to B, because it represents exactly the same graph. BTW. This question is not targeted to any specific language, but implementing hashCode() and equals() for the described Node object in Java would be a good practical example.

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• Speed-up of readonly MyISAM table

  - by Ozzy

  We have a large MyISAM table that is used to archive old data. This archiving is performed every month, and except from these occasions data is never written to the table. Is there anyway to "tell" MySQL that this table is read-only, so that MySQL might optimize the performance of reads from this table? I've looked at the MEMORY storage engine, but the problem is that this table is so large that it would take a large portion of the servers memory, which I don't want. Hope my question is clear enough, I'm a novice when it comes to db administration so any input or suggestions are welcome.

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• Determining the order of a list of numbers (possibly without sorting)

  - by Victor Liu

  I have an array of unique integers (e.g. val[i]), in arbitrary order, and I would like to populate another array (ord[i]) with the the sorted indexes of the integers. In other words, val[ord[i]] is in sorted order for increasing i. Right now, I just fill in ord with 0, ..., N, then sort it based on the value array, but I am wondering if we can be more efficient about it since ord is not populated to begin with. This is more of a question out of curiousity; I don't really care about the extra overhead from having to prepopulate a list and then sort it (it's small, I use insertion sort). This may be a silly question with an obvious answer, but I couldn't find anything online.

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• Enumerating combinations in a distributed manner

  - by Reyzooti

  I have a problem where I must analyse 500C5 combinations (255244687600) of something. Distributing it over a 10 node cluster where each cluster processes roughly 10^6 combinations per second means the job will be complete in about 7hours. The problem I have is distributing the 255244687600 combinations over the 10 nodes. I'd like to present each node with 25524468760, however the algorithms I'm using can only produce the combinations sequentially, I'd like to be able to pass the set of elements and a range of combination indicies eg: [0-10^7) or [10^7,2.0 10^7) etc and have the nodes themselves figure out the combinations. The algorithms I'm using at the moment are from the following: http://home.roadrunner.com/~hinnant/combinations.html A logical question I've considered using a master node, that enumerates each of the combinations and sends work to each of the nodes, however the overhead incurred in iterating the combinations from a single node and communicating back and forth work is enormous, and will subsequently lead to the master node becoming the bottleneck. Are there any good combination iterating algorithms geared up for efficient/optimal distributed enumeration?

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• How to write custom SQLite functions in Javascript inside a Webkit browser?

  - by Jay Godse

  I have just learned how to use the SQLite database for local storage in a Webkit web browser (e.g. Google Chrome or Apple Safari) using the Javascript API. For example the "Sticky Notes" application. However, I know that SQLite has a function called sqlite_create_function() that lets you add custom functions to your instance of SQLite on the fly which can then be used inside SQL queries. This function is described at sqlite.org. I also know that you can call an equivalent of this API in Ruby as described here. QUESTION: Can anybody show me how to do this in Javascript - i.e. write a custom function in Javascript that can be bound into the SQLite database at run time to be called by the SQLite engine, and all inside a Webkit browser?

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• How can I speed up line by line reading of an ASCII file? (C++)

  - by Jon

  Here's a bit of code that is a considerable bottleneck after doing some measuring: //----------------------------------------------------------------------------- // Construct dictionary hash set from dictionary file //----------------------------------------------------------------------------- void constructDictionary(unordered_set<string> &dict) { ifstream wordListFile; wordListFile.open("dictionary.txt"); string word; while( wordListFile >> word ) { if( !word.empty() ) { dict.insert(word); } } wordListFile.close(); } I'm reading in ~200,000 words and this takes about 240 ms on my machine. Is the use of ifstream here efficient? Can I do better? I'm reading about mmap() implementations but I'm not understanding them 100%. The input file is simply text strings with *nix line terminations.

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• Function chaining depending on boolean result

  - by Markive

  This is just an efficiency question really.. I'm interested to know if there is a more efficient or logical way that people use to handle this sort of scenario. In my asp.net application I am running a script to generate a new project my code at the top level looks like this: Dim ok As Boolean = True ok = createFolderStructure() If ok Then ok = createMDB() If ok Then ok = createProjectConfig() If ok Then ok = updateCompanyConfig() I create a boolean and each function returns a boolean result, the next function in this chain will only run if the previous one was successful. I do this because an asp.net application will continue to run through the page life cycle unless there is an unhandled exception and I don't want my whole application to be screwed up if something in the chain goes wrong (there is a lot of copying and deleting of files etc.. in this example). I was just wondering how other people handle this scenario? the vb.net single line if statement is quite succinct but I'm wondering if there is a better way?

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• sharpziplib - can you add a file without it copying the entire zip first?

  - by schmoopy

  Im trying to add an existing file to a .zip file using sharpziplib - problem is, the zip file is 1GB in size. When i try to add 1 small file (400k) sharpziplib creates a copy/temp of the orig zip file before adding the new file - this poses a problem when the amount of free disk space is less than 2x the zip file you are trying to update. for example: 1GB zip myfile.zip 1GB zip myfile.zip.tmp.293 ZipFile zf = new ZipFile(path); zf.BeginUpdate(); zf.Add(file); // Adding a 400k file here causes a 1GB temp file to be created zf.EndUpdate(); zf.Close(); Is there a more efficient way to do this? Thanks :-)

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• How can I implement "real time" messaging on Google AppEngine?

  - by Freed

  I'm creating a web application on Google AppEngine where I want the user to be notified a quickly as possible after certain events occour. The problem is similar to say a chat server in that I need something happening on one connection (someone is writing a message in a chat room) to propagate to a number of other connections (other people in that chat room gets the message). To get speedy updates from the server to the client I'm planning on using long polling with XmlHttpRequest, hoping that AppEngine won't interfere other than possibly restriing the timeout. The real problem however is efficient notification between connections on AppEngine. Is there any support for this type of cross connection notification on AppEngine that does not involve busy-waiting? The only tools I can think of to do this at all is either using the data storage (slow) or memcache (unreliable), and none of them would let me avoid busy-waiting. Note: I know about XMPP support on AppEngine. It's related, but I want a browser based solution, sending messages to the users by XMPP is not an option.

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• Fastest way to sort files

  - by Werner

  Hi, I have a huge text file with lines like: -568.563626 159 33 -1109.660591 -1231.295129 4.381508 -541.181308 159 28 -1019.279615 -1059.115975 4.632301 -535.370812 155 29 -1033.071786 -1152.907805 4.420473 -533.547101 157 28 -1046.218277 -1063.389677 4.423696 What I want is to sort the file, depending on the 5th column, so I would get -568.563626 159 33 -1109.660591 -1231.295129 4.381508 -535.370812 155 29 -1033.071786 -1152.907805 4.420473 -533.547101 157 28 -1046.218277 -1063.389677 4.423696 -541.181308 159 28 -1019.279615 -1059.115975 4.632301 For this I use: for i in file.txt ; do sort -k5n $i ; done I wonder if this is the fastest or more efficient way Thanks

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• Database Design Question: GUID + Natural Numbers

  - by Alan

  For a database I'm building, I've decided to use natural numbers as the primary key. I'm aware of the advantages that GUID's allow, but looking at the data, the bulk of row's data were GUID keys. I want to generate XML records from the database data, and one problem with natural numbers is that I don't want to expose my database key's to the outside world, and allow users to guess "keys." I believe GUID's solve this problem. So, I think the solution is to generate a sparse, unique iD derived from the natural ID (hopefully it would be 2-way), or just add an extra column in the database and store a guid (or some other multibyte id) The derived value is nicer because there is no storage penalty, but it would be easier to reverse and guess compared to a GUID. I'm (buy) curious as to what others on SO have done, and what insights they have.

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• Is select() Ok to implement 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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• apache commons http client efficiency

  - by wo_shi_ni_ba_ba

  I use apache commons http client to send data via post every second, is there a way to make the following code more efficient? I know http is stateless, but is there anything I can do to improve since the base url is always the same in this case(only the parameter value change. private void sendData(String s){ try { HttpClient client = getHttpClient(); HttpPost method = new HttpPost("http://192.168.1.100:8080/myapp"); System.err.println("send to server "+s); List formparams = new ArrayList(); formparams.add(new BasicNameValuePair("packet", s)); UrlEncodedFormEntity entity = new UrlEncodedFormEntity(formparams, "UTF-8"); method.setEntity(entity); HttpResponse resp=client.execute(method); String res = EntityUtils.toString(resp.getEntity()); System.out.println(res); } catch (Exception e) { e.printStackTrace(); } } private HttpClient getHttpClient() { if(httpClient==null){ httpClient = new DefaultHttpClient(); } return httpClient; }

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