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• Emulating a transaction-safe SEQUENCE in MySQL

  - by Michael Pliskin

  We're using MySQL with InnoDB storage engine and transactions a lot, and we've run into a problem: we need a nice way to emulate Oracle's SEQUENCEs in MySQL. The requirements are: - concurrency support - transaction safety - max performance (meaning minimizing locks and deadlocks) We don't care if some of the values won't be used, i.e. gaps in sequence are ok. There is an easy way to archieve that by creating a separate InnoDB table with a counter, however this means it will take part in transaction and will introduce locks and waiting. I am thinking to try a MyISAM table with manual locks, any other ideas or best practices?

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• Object equality in context of hibernate / webapp

  - by bert

  How do you handle object equality for java objects managed by hibernate? In the 'hibernate in action' book they say that one should favor business keys over surrogate keys. Most of the time, i do not have a business key. Think of addresses mapped to a person. The addresses are keeped in a Set and displayed in a Wicket RefreshingView (with a ReuseIfEquals strategy). I could either use the surrogate id or use all fields in the equals() and hashCode() functions. The problem is that those fields change during the lifetime ob the object. Either because the user entered some data or the id changes due to JPA merge() being called inside the OSIV (Open Session in View) filter. My understanding of the equals() and hashCode() contract is that those should not change during the lifetime of an object. What i have tried so far: equals() based on hashCode() which uses the database id (or super.hashCode() if id is null). Problem: new addresses start with an null id but get an id when attached to a person and this person gets merged() (re-attached) in the osiv-filter. lazy compute the hashcode when hashCode() is first called and make that hashcode @Transitional. Does not work, as merge() returns a new object and the hashcode does not get copied over. What i would need is an ID that gets assigned during object creation I think. What would be my options here? I don't want to introduce some additional persistent property. Is there a way to explicitly tell JPA to assign an ID to an object? Regards

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• c arrays: setting size dynamically?

  - by user336994

  Hello, I am new to C programming. I am trying to set the size of the array using a variable but I am getting an error: Storage size of 'array' isn't constant !! 01 int bound = bound*4; 02 static GLubyte vertsArray[bound]; I have noticed that when I replace bounds (within the brackets on line 02) with the number say '20', the program would run with no problems. But I am trying to set the size of the array dynamically ... Any ideas why I am getting this error ? thanks much,

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• Breaking the SQL Compact 8K Limit?

  - by David Veeneman

  I am creating a desktop application that stores rich text documents to a SQL Compact database. Documents are converted to a byte array and stored as a Binary column, and I am running into SQL Compact's 8K limit for Binary field length. Is there a simple way to get around the 8K limit? I can come up with lots of complicated ways to do it, such as parsing into 8K chunks for storage and reassembling on fetch. But before I get into something that complex, I would like to make sure I can't solve the problem more simply, such as by changing data type. If there is no simple way of getting around the 8K limit, is thare a best practice for storing documents greater than 8K? Thanks for your help.

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• Choosing a Portal / CMS software for developing multi brand websites?

  - by hbagchi

  We are in the early stage of overhauling a multi-brand website built using a custom developed java mvc framework to enable web 2.0 features. Built-in features we are looking at are: i18n, sso, content search and indexing, personalization, mashup support, ajax support, rich media content storage and management support, friendly to search engine optimizations, bookmarkable URLs, support for social networking sites, support for page composition and decoration using templates. A combination of these features are supported by many portal and cms software. Any insights will be very helpful in using a portal/cms combination to address this requirements! This is a follow-up on this post focusing on the portal/cms angle

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• Store data in file system rather than SQL or Oracle database.

  - by nunu

  Hi All, As I am working on Employee Management system, I have two table (for example) in database as given below. EmployeeMaster (DB table structure) EmployeeID (PK) | EmployeeName | City MonthMaster (DB table structure) Month | Year | EmployeeID (FK) | PrenentDays | BasicSalary Now my question is, I want to store data in file system rather than storing data in SQL or ORACLE. I want my data in file system storage for Insert, Edit and Delete opration with keeping relation with objects too. I am a C# developer, Could anybody have thoughts or idea on it. (To store data in file system with keeping relations between them) Thanks in advance. Any ideas on it?

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• Free and Simple Hosting Solution with DB Support?

  - by darren

  Hi everyone I have compiled an sqlite database that I would like to make public. I want to provide a very simple webpage that has a few form elements which are used to query the database. Does anybody know of a free hosting solution that would provide me with free web and database functionality? I am familiar with Google App Engine and that would work but I don't want to spend time using their custom storage scheme. I'm looking for something free that I can put together very quickly. Thanks for any suggestions.

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• svn working copy spanning 2 physical drives?

  - by ronenosity

  I have a large repository hosted on dreamhost that I backup daily on a remote machine using a windows scheduled task which updates the working copy located on an external USB 300GB drive connected to the remote machine. The 300GB drive is nearly full with only 26GB of free space remaining. Recently I added a second USB external 1TB drive to increase storage capacity. I would like to ask: what is the best way to use the new 1TB drive? Is it possible to span the working copy across both drives (ex: somehow create a 1.3 TB drive)? If I copied the working copy from the 300GB to the 1TB would svn continue form do I need to retarget the update working copy script to the new 1TB drive and start downloading everything again (least desired option) thanks

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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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• Does Exchange have ability to run hidden mailboxes?

  - by MadBoy

  Hello, Title of my question may sound a little bit odd but I was thinking if Exchange 2010 or 2007 or any program that would work in conjunction with Exchange has ability to create this structure: Users having their normal mailboxes connected and using them as everyone would in Outlook 2003/2007/2010. Users having additional mailboxes (from old Exchange 2003) attached but hidden on demand of Administrator. For example administrator could easy disable them just like they never been attached making them invisible to users and everyone else. Would be good if such mailboxes could be easily removed out of system (lets say on external drive) by simple step not manual job for 100 mailboxes. Users without ability to copy/move their mails to outside storage (like a local .pst file)? Do you guys have any suggestions on this? I was thinking maybe using public folders but this seems like overkill and not really suited for this. And please don't ask me why I need this type of security (it's not something I requested).

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• STL member variable initalization issue with windows API

  - by Django

  I am creating a windows app that uses a vector of stings as a member variable. For some reason, I can compile but when it tries to get at any of the vectors members is crashes. the error is 0xC0000005: Access violation reading location 0xcdcdcdd9. in the member function of the vector class. this is the size() function where it breaks. size_type capacity() const { // return current length of allocated storage return (this->_Myend - this->_Myfirst); } I am using visual studios 2010. thank you Django

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• Creating a "mountable" File System, where to start?

  - by Mike Curry

  A friend and I are thinking about creating a simple file system for learning purposes. We're going to write it in C/C++, and try to get it to a mountable state from within linux. We've both been coding or over 16 years (32 combined), so I suppose its just a matter of finding some documentation, and a ton of learning. My question is, where could I find out more information? (Documentation for creating a file system, requirements of mounting a file system in linux, etc) Where do we start? Edit: I should also mention, this would not be a boot-able file system, just a file system used for storage, though I am not too sure if that matters or not.

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• How to maintain a persistant network-connection between two applications over a network?

  - by John

  I was recently approached by my management with an interesting problem - where I am pretty sure I am telling my bosses the correct information but I really want to make sure I am telling them the correct stuff. I am being asked to develop some software that has this function: An application at one location is constantly processing real-time data every second and only generates data if the underlying data has changed in any way. On the event that the data has changed send the results to another box over a network Maintains a persistent connection between the both machines, altering the remote box if for some reason the network connection went down From what I understand, I imagine that I need to do some reading on doing some sort of TCP/IP socket-level stuff. That way if the connection is dropped the remote location will be aware that the data it has received may be stale. However management seems to be very convinced that this can be accomplished using SOAP. I was under the impression that SOAP is more or less a way for a client to initiate a procedure from a server and get some results via the HTTP protocol. Am I wrong in assuming this? I haven't been able to find much information on how SOAP might be able to solve a problem like this. I feel like a lot of people around my office are using SOAP as a buzzword and that has generated a bit of confusion over what SOAP actually is - and is capable of. Any thoughts on how to accomplish this task would be appreciated!

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• With the attachment_fu rails plugin, is there any way to delete files uploaded to Amazon S3?

  - by Eric Nguyen

  Let's say I'm using attachment_fu to attach profile pics to user profiles in a system, with Amazon S3 used as the actual file storage. When users upload new profile pics, I'd like to replace the attached file with the new one. I can do this within my database (i.e. the file metadata) easily, but attachment_fu doesn't seem to provide methods for deleting the files from S3. Am I missing something, or am I approaching this the wrong way? Many thanks!

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• Rails diff model config in dev or prod environment

  - by Denis

  Hi, I've a model which use paperclip, in dev env I want to store files on the file system. In production I want to store them on my s3 account. How to configure my model to reflet this difference? Here is my model class Photo < ActiveRecord::Base has_attached_file :photo, :styles => { :medium => "200x200>", :thumb => "100x100>" }, :storage => :s3, :s3_credentials => "#{Rails.root}/config/s3.yml", :path => "/:style/:filename" end

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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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• Getting the Video file Stored on DVR by the IP Camera in BlackBerry

  - by sHaH..

  HI all.. i need help of you guys.. Well i am making an application which will display the live video from the IP camera and display it on my screen. well my friends now the help i required is that many camera also save their videos onto the DVR.. now how can i access the DVR and get the video stored onto that storage medi.. i need some helping material or guide from you all.. since m new in black berry... Thnks a bunch in advance.. i m waiting for ur +ve responce..

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• Android and PHP - Do I need to use sessions?

  - by jtnire

  I have created an Android App that communicates with a PHP web server. They both send JSON to each other. My App is almost finished, however there is one thing left to do: authentication. Since the user's username and password will be stored in Android SharedPreferences, is there any need to use PHP sessions, given that the user won't need to enter the username/password at every request? Since I can just send the username and password in the HTTP POST header for every request, and that I will be using SSL, is this sufficient? I guess I could add an extra field in the header called 'random' that just adds a random value, just to use as a salt so that the encrypted SSL payload will be different everytime. The reason why I don't want to use sessions is that my Android App would either have to handle cookies, or managed the storage of the session ID. If there are some serious cons to using my method above, then I'm more than happy to use sessions, however all advice is appreciated. Thanks

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• Any strategies for assessing the trade-off between CPU loss and memory gain from compression of data

  - by indiehacker

  Are very large TextProperties a burden? Should they be compressed? Say I have a information stored in 2 attributes of type TextProperty in my datastore entities. The strings are always the same length of 65,000 characters and have lots of repeating integers, a sample appearing as follows: entity.pixel_idx = 0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,5,5,5,5,5,5,5,5,5,5,5,5....etc. entity.pixel_color = 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,1,1,1,1,1,1,1,1,1,1,1,1,...etc. So these above could also be represented using much less storage memory by compressing say using only each integer and the length of its series ( '0,8' for '0,0,0,0,0,0,0,0') but then its takes time and CPU to compress and decompress? Any general ideas? Are there some tricks for testing different attempts to the problem?

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• Memcache error: Failed reading line from stream (0) Array

  - by daviddripps

  I get some variation of the following error when our server gets put under any significant load. I've Googled for hours about it and tried everything (including upgrading to the latest versions and clean installs). I've read all the posts about it here on SA, but can't figure it out. A lot of people are having the same problem, but no one seems to have a definitive answer. Any help would be greatly appreciated. Thanks in advance. Fatal error: Uncaught exception 'Zend_Session_Exception' with message 'Zend_Session::start() - /var/www/trunk/library/Zend/Cache/Backend/Memcached.php(Line:180): Error #8 Memcache::get() [memcache.get]: Server localhost (tcp 11211) failed with: Failed reading line from stream (0) Array We have a copy of our production environment for testing and everything works great until we start load-testing. I think the biggest object stored is about 170KB, but it will probably be about 500KB when all is said and done (well below the 1MB limit). Just FYI: Memcache gets hit about 10-20 times per page load. Here's the memcached settings: PORT="11211" USER="memcached" MAXCONN="1024" CACHESIZE="64" OPTIONS="" I'm running Memcache 1.4.5 with version 2.2.6 of the PHP-memcache module. PHP is version 5.2.6. memcache details from php -i: memcache memcache support = enabled Active persistent connections = 0 Version = 2.2.6 Revision = $Revision: 303962 $ Directive = Local Value = Master Value memcache.allow_failover = 1 = 1 memcache.chunk_size = 8192 = 8192 memcache.default_port = 11211 = 11211 memcache.default_timeout_ms = 1000 = 1000 memcache.hash_function = crc32 = crc32 memcache.hash_strategy = standard = standard memcache.max_failover_attempts = 20 = 20 Thanks everyone

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• How do I choose a database?

  - by liamzebedee

  I need a comparison table of some sort for database varieties (MySQL, SQLite etc.). I can't find one. My use case is, I am implementing storage of objects in a distributed hash table. I need a database solution that is: Fast for sorting Simplistic (no users, preferably no additional structures like multiple tables etc.) Concurrent (if possible) Multi-platform File based (not stored in memory primarily) Centralized I will be programming in Go. As I understand, I believe I need what is called a Document Orientated Database, because I am storing objects, identified by keys. EDIT: While I am implementing a DHT, I will also be storing metadata about the objects, such as access counts etc. It would also be preferable to have TLL (time to live)

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• iPhone App with Web Service Access

  - by blake

  I have been asked to write a compliment website/service for an iPhone app. The app creates images. The author wants these images to be uploaded onto the server, into their personal storage area. These images need to be able to be pulled down to the iPhone later for editing. The user will be able to use the website as well to see these images. I have yet to decide (or understand) what the best way of implementing this would be. And with no experience with iPhone development I have no idea what it can actually handle.

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• Sorting 1 million 8-digit numbers in 1MB of RAM

  - by Favourite Chigozie Onwuemene

  I have a computer with 1M of RAM and no other local storage. I must use it to accept 1 million 8-digit decimal numbers over a TCP connection, sort them, and then send the sorted list out over another TCP connection. The list of numbers may contain duplicates, which I must not discard. The code will be placed in ROM, so I need not subtract the size of my code from the 1M. I already have code to drive the ethernet port and handle TCP/IP connections, and it requires 2k for its state data, including a 1k buffer via which the code will read and write data. Is there a solution to this problem?

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• Best way to run multiple queries per second on database, performance wise?

  - by Michael Joell

  I am currently using Java to insert and update data multiple times per second. Never having used databases with Java, I am not sure what is required, and how to get the best performance. I currently have a method for each type of query I need to do (for example, update a row in a database). I also have a method to create the database connection. Below is my simplified code. public static void addOneForUserInChannel(String channel, String username) throws SQLException { Connection dbConnection = null; PreparedStatement ps = null; String updateSQL = "UPDATE " + channel + "_count SET messages = messages + 1 WHERE username = ?"; try { dbConnection = getDBConnection(); ps = dbConnection.prepareStatement(updateSQL); ps.setString(1, username); ps.executeUpdate(); } catch(SQLException e) { System.out.println(e.getMessage()); } finally { if(ps != null) { ps.close(); } if(dbConnection != null) { dbConnection.close(); } } } And my DB connection private static Connection getDBConnection() { Connection dbConnection = null; try { Class.forName(DB_DRIVER); } catch (ClassNotFoundException e) { System.out.println(e.getMessage()); } try { dbConnection = DriverManager.getConnection(DB_CONNECTION, DB_USER,DB_PASSWORD); return dbConnection; } catch (SQLException e) { System.out.println(e.getMessage()); } return dbConnection; } This seems to be working fine for now, with about 1-2 queries per second, but I am worried that once I expand and it is running many more, I might have some issues. My questions: Is there a way to have a persistent database connection throughout the entire run time of the process? If so, should I do this? Are there any other optimizations that I should do to help with performance? Thanks

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• JS: Storing dynamic variables across pages?

  - by user2467599

  I've been looking into local storage options and plugins like Persist.js, sessvars.js, and even sisyphus.js - but I am unsure if any are the best fit (though I'm fairly certain I need to use one). Page one is a form with input fields for data like names, phones, and email. I have a button that replicates a wrapper div (and it's inputs) as long as more inputs are needed. When the form is filled the user hits submit which takes them to a 'confirmation' type php page. I need to the give the user an 'edit' button on page 2 that takes them back to page 1 and leaves all the info alone. For the most part everything returns fine, but if the user had hit the 'replicate' button before submission, and then hits edit afterwards, all the inputs that were dynamically generated return empty and the div no longer exists. Someone suggested that my variables are not persistent (when the replicate button is hit, input with an id="name1" becomes "name2" and so on) so that's when I found out about the plugins mentioned before. Is there a way that I can implement one of those plugins (or any other method) so that when the user returns to page one the div and it's input values remain unchanged? And if I'm on the right track are there any examples?

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