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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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• 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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• 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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• Removing unused selectors in a CSS stylesheet?

  - by Legend

  I've been developing a web app for a few weeks now and ended up with about a 1000 lines. I am sure not all the selectors are being used and am trying to clean it up. At the same time, I don't want to do it manually for obvious reasons. Is there a safe and an efficient way to remove unused selectors? For this, am I supposed to navigate the entire website to let it know which selectors are not being used? (I use javascript to add some selectors so these might not show up until a particular usecase is seen)

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• Treating a fat webservice in .net 3.5 c#

  - by Chris M

  I'm dealing with an obese 3rd party webservice that returns about 3mb of data for a simple search results, about 50% of the data in that response is junk. Would it make sense then to remap this data to my own result object and ditch the response so I'm storing 1-2 mb in memory for filtering and sorting rather than using the web-responses own object and using 2-4 or am I missing a point? So far I've been accessing the webservice from a separate project and using a new class to provide the interaction and to handle the persistence so my project looks like this |- Web (mvc2 proj) |- DAL (database/storage fluent-nhibernate) |- SVCGateway (interaction layer + webservice related models) |- Services -------------- |- Tests |- Specs I'm trying to make the application behave fast and I also need to store the result set temporarily in case a customer goes to view the product and wants to go back to the results. (Service returns only 500 of possible 14K results). So basically I'm looking for confirmation that I'm doing the right thing in pushing the results into my own objects or if I'm breaking some rule or even if there's a better way of handling it. Thanks

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• mysql does not utilize my cpu and ram enough?

  - by vick

  Hello Everyone! I am importing a 2.5gb csv file to a mysql table. My storage engine is innodb. Here is the script: use xxx; DROP TABLE IF EXISTS `xxx`.`xxx`; CREATE TABLE `xxx`.`xxx` ( `xxx_id` int(10) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(128) NOT NULL, `yy` varchar(128) NOT NULL, `yyy` varchar(64) NOT NULL, `yyyy` varchar(2) NOT NULL, `yyyyy` varchar(10) NOT NULL, `url` varchar(64) NOT NULL, `p` varchar(10) NOT NULL, `pp` varchar(10) NOT NULL, `category` varchar(256) NOT NULL, `flag` varchar(4) NOT NULL, PRIMARY KEY (`xxx_id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; set autocommit = 0; load data local infile '/home/xxx/raw.csv' into table company fields terminated by ',' optionally enclosed by '"' lines terminated by '\r\n' ( name, yy, yyy, yyyy, yyyyy, url, p, pp, category, flag ); commit; Why does my PC (core i7 920 with 6gb ram) only consume 9% cpu power and 60% ram when running these queries?

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• What is the best way to find the digit at n position in a decimal number?

  - by Elijah

  Background I'm working on a symmetric rounding class and I find that I'm stuck with regards to how to best find the number at position x that I will be rounding. I'm sure there is an efficient mathematical way to find the single digit and return it without having to resort to string parsing. Problem Suppose, I have the following (C#) psuedo-code: var position = 3; var value = 102.43587m; // I want this no ? (that is 5) protected static int FindNDigit(decimal value, int position) { // This snippet is what I am searching for } Also, it is worth noting that if my value is a whole number, I will need to return a zero for the result of FindNDigit. Does anyone have any hints on how I should approach this problem? Is this something that is blaringly obvious that I'm missing?

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• What data structure would be the least painful DataTable replacement?

  - by MatthewMartin

  I'm storing a lot of sorted ~10 row 2 column/key value pairs in ASP.NET cache-- they're the data for dropdownlists. Right now they are all DataTables, which isn't very space efficient (the rule of thumb is 10x increase in size when data is strored in a dataset). Old Code DataTable table = dataAccess.GetDataTable(); dropDownList.DataSource = table; Hoped for new Code Unknown data = dataAccess.GetSomethingMoreSpaceEfficient(); dropDownList.DataSource = data; What pre-existing datastructures are similar enough to DataTable that would minimize code breakage and reduce the serialized size when stored in ASP.NET cache?

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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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• IE 8 prompts user on "slow" jQuery script

  - by Jason

  I have a form with over 100 list items that I must reorder on submit. The following code works to reorder my list without any apparent problems in Firefox; however, IE prompts with the message "A script on this page is causing Internet Explorer to run slowly. If it continues to run, your computer may become unresponsive. Do you want to abort the script?" If the user clicks 'No', the script will work as expected. var listitems = $(form).find('li').get(); listitems.sort(function(a, b) { var compA = $(a).attr('id'); var compB = $(b).attr('id'); return (compA - compB); }); Any ideas on how to make this more efficient?

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• How can I persist a large Perl object for re-use between runs?

  - by Alnitak

  I've got a large XML file, which takes over 40 seconds to parse with XML::Simple. I'd like to be able to cache the resulting parsed object so that on the next run I can just retrieve the parsed object and not reparse the whole file. I've looked at using Data::Dumper but the documentation is a bit lacking on how to store and retrieve its output from disk files. Other classes I've looked at (e.g. Cache::Cache appear designed for storage of many small objects, not a single large one. Can anyone recommend a module designed for this? EDIT. The XML file is ftp://ftp.rfc-editor.org/in-notes/rfc-index.xml On my Mac Pro benchmark figures for reading the entire file with XML::Simple vs Storable are: s/iter test1 test2 test1 47.8 -- -100% test2 0.148 32185% --

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• (NOT) NULL for NVARCHAR columns

  - by Anders Abel

  Allowing NULL values on a column is normally done to allow the absense of a value to be represented. When using NVARCHAR there is aldready a possibility to have an empty string, without setting the column to NULL. In most cases I cannot see a semantical difference between an NVARCHAR with an empty string and a NULL value for such a column. Setting the column as NOT NULL saves me from having to deal with the possibility of NULL values in the code and it feels better to not have to different representations of "no value" (NULL or an empty string). Will I run into any other problems by setting my NVARCHAR columns to NOT NULL. Performance? Storage size? Anything I've overlooked on the usage of the values in the client code?

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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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• Facebook user_id as MongoDB BSON ObjectId?

  - by MattDiPasquale

  I'm rebuilding Lovers on Facebook with Sinatra & Redis. I like Redis because it doesn't have the long (12-byte) BSON ObjectIds and I am storing sets of Facebook user_ids for each user. The sets are requests_sent, requests_received, & relationships, and they all contain Facebook user ids. I'm thinking of switching to MongoDB because I want to use it's geospatial indexing. If I do, I'd want to use the FB user ids as the _id field because I want the sets to be small and I want the JSON responses to be small. But, is the BSON ObjectId better (more efficient for MongoDB) to use than just an integer (fb user_id)?

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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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• Sync offline JQuery Mobile form

  - by Dimas

  My name is Dimas and I work as a developer in a hospital. I've developed a web form with JQuery Mobile which is accessed from an Android tablet. It sends data (text and FILES) to the server (PHP) and it's saved in a MySQL database. This tablets are used by doctors that are visiting the patients in their homes. Some of these patients live in remote areas with very bad Internet connection, so I'm thinking on use HTML5 Offline feature to solve these situations. I started reading about it but I'm newbie with this technology. I've some questions: Do you think this is the best/easiest solution? If I could save the form data in a local sqlite storage when the tablet is offline, how I could synchronize it with the data in MySQL server when the tablet become online? Thanks

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• Best place to store large amounts of session data

  - by audiopleb

  I'm building an application that needs to store and re-use large amounts of data per session. So for example, the user selects a large list of list items (say 2000 or significantly more) which have a numeric value as their key then they save that selection and go off to another page, do something else and then come back to the original page and need to load their selections into that page. What is the quickest and most efficient way of storing and reusing that data? In a text file saved with the session id? In a temp db table? In the session data itself (db sessions so size isn't a limit) using a serialised string or using gzcompress or gzencode? Any advice or insight would be great! Thank you!!!!

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• e-commerce product data/metadata schemas

  - by Shreko

  Trying to figure out how is product data/metadata schema designed. For example, how does an e-commerce site enter a product spec. Does it copy and paste from mfg spec sheet, enters it in their own fields or something else? Here is an example, looking at the D3000 Nikon DSLR Manufacturer: http://nikon.ca/en/Product.aspx?m=17300&disp=Specs futureshop.ca: www.futureshop.ca/en-CA/product/nikon-nikon-d3000-10-2mp-dslr-camera-with-18-55mm-lens-kit-d3000/10128435.aspx?path=865c2348a1542e848982c9dbd9253483en02 memoryexpress.com: www.memoryexpress.com/Products/PID-MX25539%28ME%29.aspx They are all slightly different in order or in parent/child field? What's storage is used for this type of info rdbms or xml?

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• Joining two tables (through a link), one which may yield multiple rows, together into one result.

  - by Eikern

  Lets say I've got a table listing car brands or models: Cars: Id | Brand ----------- 1 | BMW 2 | Audi 3 | Volvo And I've also got another table which links features. Link: Id | carid | featureid ----------------------- 1 | 1 | 1 2 | 1 | 2 3 | 2 | 2 4 | 3 | 1 5 | 3 | 2 6 | 3 | 3 And I've got the table listing the features. Features: Id | Feature ----------- 1 | A/C 2 | 4WD 3 | Heated seats I want to list these results on my front page like this: BMW A/C 4WD Audi 4WD Volvo A/C 4WD Heated seats What's the best/most efficient way of doing this (using PHP and MySQL)?

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• Database design for a Fantasy league

  - by Samidh T

  Here's the basic schema for my database Table user{ userid numeber primary key, count number } Table player{ pid number primary key, } Table user-player{ userid number primary key foreign key(user), pid number primary key foreign key(player) } Table temp{ pid number primary key, points number } Here's what I intend to do... After every match the temp table is updated which holds the id of players that played the last match and the points they earned. Next run a procedure that will match the pid from temp table with every uid of user-player table having the same pid. add the points from temp table to the count of user table for every matching uid. empty temp table. My questions is considering 200 players and 10000 users,Will this method be efficient? I am going to be using mysql for this.

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• Injecting a dependancy into a base class

  - by Jamie Dixon

  Hey everyone, I'm on a roll today with questions. I'm starting out with Dependency Injection and am having some trouble injecting a dependency into a base class. I have a BaseController controller which my other controllers inherit from. Inside of this base controller I do a number of checks such as determining if the user has the right privileges to view the current page, checking for the existence of some session variables etc. I have a dependency inside of this base controller that I'd like to inject using Ninject however when I set this up as I would for my other dependencies I'm told by the compiler that: Error 1 'MyProject.Controllers.BaseController' does not contain a constructor that takes 0 argument This makes sense but I'm just not sure how to inject this dependency. Should I be using this pattern of using a base controller at all or should I be doing this in a more efficient/correct way?

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• 2 Select or 1 Join query ?

  - by xRobot

  I have 2 tables: book ( id, title, age ) ---- 100 milions of rows author ( id, book_id, name, born ) ---- 10 millions of rows Now, supposing I have a generic id of a book. I need to print this page: Title: mybook authors: Tom, Graham, Luis, Clarke, George So... what is the best way to do this ? 1) Simple join like this: Select book.title, author.name From book, author WHERE ( author.book_id = book.id ) AND ( book.id = 342 ) 2) For avoid the join, I could make 2 simple query: Select title FROM book WHERE id = 342 Select name FROM author WHERE book_id = 342 What is the most efficient way ?

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• Copy an array backwards? Array.Copy?

  - by daniel

  I have a List<T> that I want to be able to copy to an array backwards, meaning start from List.Count and copy maybe 5 items starting at the end of the list and working its way backwards. I could do this with a simple reverse for loop; however there is probably a faster/more efficient way of doing this so I thought I should ask. Can I use Array.Copy somehow? Originally I was using a Queue as that pops it off in the correct order I need, but I now need to pop off multiple items at once into an array and I thought a list would be faster.

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• Logging NHibernate SQL queries

  - by GuestMVCAsync

  Is there a way to access the full SQL query, including the values, inside my code? I am able to log SQL queries using log4net: <logger name="NHibernate.SQL" additivity="false"> <level value="ALL"/> <appender-ref ref="NHibernateSQLFileLog"/> </logger> However, I would like to find a way to log SQL queries from the code also. This way I will log the specific SQL query that causes an exception in my try/catch statement. Right now I have to data-mine the SQLFileLog to find the query that caused the exception when an exception occurs and it is not efficient.

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• When to use Hibernate?

  - by Ramo

  Hi All, I was asked in an interview this question so I answered with the following: -Better Performance: - Efficient queries. - 1st and 2nd level caching. - Good caching gives better scalability. - Good Database Portability: - Changing the DB is as easy as changing the dialect configuration. - Increased Developer Productivity: - Think only in object terms not in query language terms. But I also feel that systems fall in one of the below categories, and Hibernate may not be suited for all these cases, I'm interested in your thoughts about this, do you agree with me? please let me know when would use HB in the following case and why. Write Only Systems: Read Only Systems: Write Mostly Systems: Read Mostly Systems: Regards Ramo

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