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• Designing a table to store EXIF data

  - by rafale

  I'm looking to get the best performance out of querying a table containing EXIF data. The queries in question will only search the EXIF data for the specified strings and return the row index on a match. With that said, would it better to store the EXIF data in a table with separate columns for each of the tags, or would storing all of the tags in a single column as one long delimited string suit me just as well? There are around 115 EXIF tags I'll be storing, and each record would be around 1500 to 2000 chars in length if concatenated into a single string.

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• Optimising (My)SQL Query

  - by Simon

  I usually use ORM instead of SQL and I am slightly out of touch on the different JOINs... SELECT `order_invoice`.*, `client`.*, `order_product`.*, SUM(product.cost) as net FROM `order_invoice` LEFT JOIN `client` ON order_invoice.client_id = client.client_id LEFT JOIN `order_product` ON order_invoice.invoice_id = order_product.invoice_id LEFT JOIN `product` ON order_product.product_id = product.product_id WHERE (order_invoice.date_created >= '2009-01-01') AND (order_invoice.date_created <= '2009-02-01') GROUP BY `order_invoice`.`invoice_id` The tables/ columns are logically names... it's an shop type application... the query works... it's just very very slow... I use the Zend Framework and would usually use Zend_Db_Table_Row::find(Parent|Dependent)Row(set)('TableClass') but I have to make lots of joins and I thought it'll improve performance by doing it all in one query instead of hundreds... Can I improve the above query by using more appropriate JOINs or a different implementation? Many thanks.

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• entity framework and dirty reads

  - by bryanjonker

  I have Entity Framework (.NET 4.0) going against SQL Server 2008. The database is (theoretically) getting updated during business hours -- delete, then insert, all through a transaction. Practically, it's not going to happen that often. But, I need to make sure I can always read data in the database. The application I'm writing will never do any types of writes to the data -- read-only. If I do a dirty read, I can always access the data; the worst that happens is I get old data (which is acceptable). However, can I tell Entity Framework to always use dirty reads? Are there performance or data integrity issues I need to worry about if I set up EF this way? Or should I take a step back and see about rewriting the process that's doing the delete/insert process?

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• Multivalue Mysql Inserts using HibernateTemplate

  - by Langali

  I am using Spring HibernateTemplate and need to insert hundreds of records into a mysql database every second. Not sure what is the most performant way of doing it, but I am trying to see how the multi value mysql inserts do using hibernate. String query = "insert into user(age, name, birth_date) values(24, 'Joe', '2010-05-19 14:33:14'), (25, 'Joe1', '2010-05-19 14:33:14')" getHibernateTemplate().execute(new HibernateCallback(){ public Object doInHibernate(Session session) throws HibernateException, SQLException { return session.createSQLQuery(query).executeUpdate(); } }); But I get this error: 'could not execute native bulk manipulation query.' Please check your query ..... Any idea of I can use a multi value mysql insert using Hibernate? or is my query incorrect? Any other ways that I can improve the performance? I did try the saveOrUpdateAll() method, and that wasn't good enough!

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• Interview Question: .Any() vs if (.Length > 0) for testing if a collection has elements

  - by Chris

  In a recent interview I was asked what the difference between .Any() and .Length > 0 was and why I would use either when testing to see if a collection had elements. This threw me a little as it seems a little obvious but feel I may be missing something. I suggested that you use .Length when you simply need to know that a collection has elements and .Any() when you wish to filter the results. Presumably .Any() takes a performance hit too as it has to do a loop / query internally.

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• Implementing Tagging using Core Data on the iPhone

  - by Jonathan Penn

  I have an application that uses CoreData and I'm trying to figure out the best way to implement tagging and filtering by tag. For my purposes, if I was doing this in raw SQLite I would only need three tables, tags, item_tags and of course my items table. Then filtering would be as simple as joining between the three tables where only items are related to the given tags. Quite straightforward. But, is there a way to do this in CoreData and utilizing NSFetchedResultsController? It doesn't seem that NSPredicate give you the ability to filter through joins. NSPredicate's aren't full SQL anyway so I'm probably barking up the wrong tree there. I'm trying to avoid reimplementing my app using SQLite without CoreData since I'm enjoying the performance CoreData gives me in other areas. Yes, I did consider (and built a test implementation) diving into the raw SQLite that CoreData generates, but that's not future proof and I want to avoid that, too. Has anyone else tried to tackle tagging/filtering with CoreData in a UITableView with NSFetchedResultsController

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• Managing Data Prefetching and Dependencies with .NET Typed Datasets

  - by Derek Morrison

  I'm using .NET typed datasets on a project, and I often get into situations where I prefetch data from several tables into a dataset and then pass that dataset to several methods for processing. It seems cleaner to let each method decide exactly which data it needs and then load the data itself. However, several of the methods work with the same data, and I want the performance benefit of loading data in the beginning only once. My problem is that I don't know of a good way or pattern to use for managing dependencies (I want to be sure I load all the data that I'm going to need for each class/method that will use the dataset). Currently, I just end up looking through the code for the various classes that will use the dataset to make sure I'm loading everything appropriately. What are good approaches or patterns to use in this situation? Am I doing something fundamentally wrong? Although I'm using typed datasets, this seems like it would be a common situation where prefetching data is used. Thanks!

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• Conceptually, how does replay work in a game?

  - by SnOrfus

  I was kind of curious as to how replay might be implemented in a game. Initially, I thought that there would be just a command list of every player/ai action that was taken in the game, and it then 're-plays' the game and lets the engine render as usual. However, I have looked at replays in FPS/RTS games, and upon careful inspection even things like the particles and graphical/audible glitches are consistent (and those glitches are generally *in*consistent). So How does this happen. In fixed camera angle games I though it might just write every frame of the whole scene to a stream that gets stored and then just replays the stream back, but that doesn't seem like enough for games that allow you to pause and move the camera around. You'd have to store the locations of everything in the scene at all points in time (No?). So for things like particles, that's a lot of data to push which seems like a significant draw on the game's performance whilst playing.

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• Detecting and reloading updated application parameters at runtime

  - by VeeKayBee

  I am working on an ASP.NET web application(using .NET 4.5 and C#).The application deals with lot of units (for measuring like KG,Litre,KM etc). So based on the selected unit we have to implement some allowed range.This values can be configured without much effort. We identified two solutions for this Keeping a configuration xml. Suppose the values in xml, does it requires an iisreset or any other thing which can take the site down for some time, if we are changing the xml file to change some validation. Keeping in Db, then use SQL dependency caching. So an update to DB can reflect the caching values.SO i believe if we change the values, it will update the cache. How much complex is this and does it effect the performance ? It will be great helpful, if we have some other method to achieve this. Thanks in advance.

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• CakePHP repeats same queries

  - by Rytis

  I have a model structure: Category hasMany Product hasMany Stockitem belongsTo Warehouse, Manufacturer. I fetch data with this code, using containable to be able to filter deeper in the associated models: $this->Category->find('all', array( 'conditions' => array('Category.id' => $category_id), 'contain' => array( 'Product' => array( 'Stockitem' => array( 'conditions' => array('Stockitem.warehouse_id' => $warehouse_id), 'Warehouse', 'Manufacturer', ) ) ), ) ); Data structure is returned just fine, however, I get multiple repeating queries like, sometimes hundreds of such queries in a row, based on dataset. SELECT `Warehouse`.`id`, `Warehouse`.`title` FROM `beta_warehouses` AS `Warehouse` WHERE `Warehouse`.`id` = 2 Basically, when building data structure Cake is fetching data from mysql over and over again, for each row. We have datasets of several thousand rows, and I have a feeling that it's going to impact performance. Is it possible to make it cache results and not repeat same queries?

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• When does it make sense to use a map?

  - by kiwicptn

  I am trying to round up cases when it makes sense to use a map (set of key-value entries). So far I have two categories (see below). Assuming more exist, what are they? Please limit each answer to one unique category and put up an example. Property values (like a bean) age -> 30 sex -> male loc -> calgary Presence, with O(1) performance peter -> 1 john -> 1 paul -> 1

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• GetHashCode Method reliability in Silverlight/WP7.1

  - by abhinav

  I am attempting to hash and keep(the hash) an object of type IEnumerable<anotherobject> which has about a 1000 entries. I'll be generating another such object, but this time I'd like to check for any changes in the values of the entries using the hash codes of the two objects. Basically, I was wondering if GetHashCode() is apt for this, both from a performance perspective and reliability perspective (getting different values for different object values and same values for same object values, always). If I have to override it, what would be a good way to do so, does it always depend on the type of anotherobject and what Equals means when comparing two anotherobjects? Is there a generic way to do it? This concern is because my object can be quite big.

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• Is there any significant benefit to reading string directly from control instead of moving it into a

  - by Kevin

  sqlInsertFrame.Parameters.AddWithValue("@UserName", txtUserName.txt); Given the code above...if I don't have any need to move the textbox data into a string variable, is it best to read the data directly from the control? In terms of performance, it would seem smartest to not create any unnecessary variables which use up memory if its not needed. Or is this a situation where its technically true but doesn't yield any real world results due to the size of the data in question. Forgive me, I know this is a very basic question.

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• PostgreSQL: How to index all foreign keys?

  - by biggusjimmus

  I am working with a large PostgreSQL database, and I are trying to tune it to get more performance. Our queries and updates seem to be doing a lot of lookups using foreign keys. What I would like is a relatively simple way to add Indexes to all of our foreign keys without having to go through every table (~140) and doing it manually. In researching this, I've come to find that there is no way to have Postgres do this for you automatically (like MySQL does), but I would be happy to hear otherwise there, too.

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• iPhone. How to intercept system dialogs?

  - by Sjakelien

  My app offers the user the opportunity to put an event in his native calendar. For that, I refer to an online webcal:// URL. Since the underlying .ics file is quite big (containing quite a few events), it sometimes (also depending on the network performance)takes a while before the "Do you want to subscribe"-dialog sequence kicks in. I would like to give the user some feedback in the mean time, like a spinner, or a changing graphic, for him to know that something is going to happen. Question: how does my app know, that the "Do you want to subscribe"-dialog has been shown, and that the user has chosen either a Cancel of OK button in that dialog, so I can stop the spinner?

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• Is there an additional runtime cost for using named parameters?

  - by Jurily

  Consider the following struct: public struct vip { string email; string name; int category; public vip(string email, int category, string name = "") { this.email = email; this.name = name; this.category = category; } } Is there a performance difference between the following two calls? var e = new vip(email: "foo", name: "bar", category: 32); var e = new vip("foo", 32, "bar"); Is there a difference if there are no optional parameters defined?

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• Does Python Django support custom SQL and denormalized databases with no Foreign Key relationships?

  - by Jay

  I've just started learning Python Django and have a lot of experience building high traffic websites using PHP and MySQL. What worries me so far is Python's overly optimistic approach that you will never need to write custom SQL and that it automatically creates all these Foreign Key relationships in your database. The one thing I've learned in the last few years of building Chess.com is that its impossible to NOT write custom SQL when you're dealing with something like MySQL that frequently needs to be told what indexes it should use (or avoid), and that Foreign Keys are a death sentence. Percona's strongest recommendation was for us to remove all FKs for optimal performance. Is there a way in Django to do this in the models file? create relationships without creating actual DB FKs? Or is there a way to start at the database level, design/create my database, and then have Django reverse engineer the models file?

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• storing huge amount of records into classic asp cache object is SLOW

  - by aspm

  we have some nasty legacy asp that is performing like a dog and i narrowed it down to because we are trying to store 15K+ records into the application cache object. but that's not the killer. before it stores it, it converts the ADO stream to XML then stores it. this conversion of the huge record set to XML spikes the CPU and causes all kinds of havoc on users when it's happening. and unfortunately we do this XML conversion to read the cache a lot, causing site wide performance problems. i don't have the resources to convert everything to .net. so that's out. but i need to obviously use caching, but int his case the caching is hurting instead of helping. is there a more effecient way to store this data instead of doing this xml conversion to/from every time we read/update the cache?

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• Android add image to button

  - by Christiaan de Jong

  I want to add an image to a Button (no imagebutton, as the particular button can either contain text or an image; plus the imagebutton has the same problem), while still retaining the original android-style button. So adding android:background in the XML doesn't cut it, as that will remove the android default button with rounded corners etc. (android.R.drawable.btn_default) Is this in any way possible? I think one way is to make a 9patch image for the button pressed (one for up and one for down) and onTouch Action_DOWN make a layered background drawable and put that onto the button, and doing the same thing but with another 9patch for onTouch Action_UP, but I think that will decrease the performance of the application substantially, as that will require quite a lot of resource reading and layer merging for all the button clicks (and for my application, that will be quite a lot). Is what I state above correct?

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• How to I count key collisions when using boost::unordered_map?

  - by Nikhil

  I have a data structure with 15 unsigned longs, I have defined a hash function using hash_combine as follows: friend std::size_t hash_value(const TUPLE15& given) { std::size_t seed = 0; boost::hash_combine(seed, val1); boost::hash_combine(seed, val2); ... return seed; } I insert a large number of values into a boost::unordered_map but the performance is not good enough. Probably, I could do better with an alternative hashing function. To confirm this, I need to check how many collisions I am getting. How do I do this?

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• [Symfony] Admin generator and i18n

  - by David

  I have read lots of questions about i18n, but I haven't found any about performance. I have a simple backend app listing the contents of an ads table. These ads have a category, that is translated in some languages (it's defined as i18n in the Doctrine schema). So, when I add a "table_method" in my generator.yml to include de Category table, it reduces the number of queries, but there are yet some of them referencing i18n translation tables. So, if I add the category Translation table to the query, it reduces even more the queries BUT it increases the processing time considerably. Why this time penalty? Just because of the translation table? And why isn't the filter using this method to avoid so many translation queries as well? I mean, if I want to filter by category, it is making one query per category to include the translation table. Why??

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• Reducing template bloat with inheritance

  - by benoitj

  Does anyone have experience reducing template code bloat using inheritance? i hesitate rewriting our containers this way: class vectorBase { public: int size(); void clear(); int m_size; void *m_rawData; //.... }; template< typename T > class vector : public vectorBase { void push_back( const T& ); //... }; I should keep maximum performance while reducing compile time I'm also wondering why stl implementations do not uses this approach Thanks for your feedbacks

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• asynchronous calls in asp.net

  - by lockedscope

  in this sample, two threads created; a worker thread created by BeginInvoke and an I/O completion thread created by SendAsync method. but another author in his UnsafeQueueNativeOverlapped example, don't recommend this. i want to use SendAsync or ...Async in an asp.net page and i want to use PageAsyncTask. however, its BeginEventHandler requires AsyncResult to be returned which SendAsync does not return. afaik, event based async pattern is the most recommended way so how could we call SendAsync or any ...Async methods without creating two threads and hurting the performance?

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• how to pass in a reference to a string in javascript?

  - by ijjo

  maybe a closure is my solution? not exactly sure how to pull it off though. the code is set up like so: var globalVar = ''; var globalVar2 = ''; function func() { if (condition) func2(globalVar) else func2(globalVar2) } in func2() i cache some HTML in a main container into the appropriate global variable that i pass to it. basically i have a main container that holds different pages depending on what tab they choose. for performance i want to cache the page into global vars so i need to know what tab is active to figure out which global var to assign the html to.

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• Tracing or Logging Resource Governor classification function behavior in Sql Server 2008

  - by nganju

  I'm trying to use the Resource Governor in SQL Server 2008 but I find it hard to debug the classification function and figure out what the input variables will have, i.e. does SUSER_NAME() contain the domain name? What does the APP_NAME() string look like? It's also hard to verify that it's working correctly. What group did the function return? The only way I can see this is to fire up the performance monitor and watch unblinkingly for little blips in the right CPU counter. Is there some way I can either run it in Debug mode, where I can set a breakpoint and step through and look at variable values, or can I at least do the old-school method of writing trace statements to a file so I can see what's going on? Thanks...

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