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• Flashback Data Archives: Ein gutes Gedächtnis für DBA und Entwickler

  - by Heinz-Wilhelm Fabry (DBA Community)

  Daten werden gespeichert und zum Teil lange aufbewahrt. Mitunter werden Daten nach ihrer ersten Speicherung geändert, vielleicht sogar mehrfach. Je nach gesetzlicher oder betrieblicher Vorgabe müssen die Veränderungen sogar nachverfolgbar sein. Damit sind zugleich Mechanismen gefordert, die sicherstellen, dass die Folge der Versionen lückenlos ist. Und implizit bedeutet das zusätzlich, dass die Versionen auch vor Löschen und Verändern geschützt sein müssen. Das Versionieren kann über die Anwendung, mit der die Daten auch erfasst werden, erfolgen, über Trigger oder über besondere Werkzeuge. Jede dieser Lösungen hat ihre eigenen Schwächen. Zusätzlich steht die Frage nach dem Schutz vor unerlaubtem Löschen oder Ändern versionierter Daten im Raum. Flashback Data Archives lösen diese Frage, denn sie bieten nicht nur einen wirksamen Mechanismus zum Versionieren von Datensätzen, sondern sie schützen diese Versionen auch vor Veränderung und löschen sie schließlich sogar automatisch nach Ablauf ihrer Aufbewahrungsfrist.Ursprünglich wurden die Archive als eigenständige Option zur Enterprise Edition der Oracle Database 11g unter dem Namen Total Recall eingeführt. Ende Juni 2012 verloren die Flashback Data Archives ihren Status als eigenständige Option. Weil die Archive aber grundsätzlich komprimiert wurden, hat Oracle sie stattdessen zu einem Feature der Advanced Compression Option der Enterprise Edition (ACO) gemacht. Seit der Version 11.2.0.4 der Datenbank ist das Komprimieren aber für die Archive nicht mehr zwangsläufig, sondern optional. Damit gibt es lizenzrechtlich erneut eine Änderung: Wer die Kompression verwendet, der muss nach wie vor ACO lizensieren. Wer die Flashback Data Archives dagegen ohne Kompression verwendet - also zum Beispiel Entwickler -, dem stehen sie ab 11.2.0.4 aufwärts im Lieferumfang aller Editionen der Datenbank zur Verfügung. Diese Änderung ist in den Handbüchern zur Lizensierung der Versionen 11.2 und 12.1 der Datenbank dokumentiert. Im Rahmen der DBA Community ist bereits über die Flashback Data Archives berichtet worden. Der hier vorliegende Artikel ersetzt alle vorangegangenen Beiträge zum Thema.

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• Compressing 2D level data

  - by Lucius

  So, I'm developing a 2D, tile based game and a map maker thingy - all in Java. The problem is that recently I've been having some memory issues when about 4 maps are loaded. Each one of these maps are composed of 128x128 tiles and have 4 layers (for details and stuff). I already spent a good amount of time searching for solutions and the best thing I found was run-length enconding (RLE). It seems easy enough to use with static data, but is there a way to use it with data that is constantly changing, without a big drop in performance? In my maps, supposing I'm compressing the columns, I would have 128 rows, each with some amount of data (hopefully less than it would be without RLE). Whenever I change a tile, that whole row would have to be checked and I'm affraid that would slow down too much the production (and I'm in a somewhat tight schedule). Well, worst case scenario I work on each map individually, and save them using RLE, but it would be really nice if I could avoind that. EDIT: What I'm currently using to store the data for the tiles is a 2D array of HashMaps that use the layer as key and store the id of the tile in that position - like this: private HashMap< Integer, Integer [][]

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• Non use of persisted data – Part deux

  - by Dave Ballantyne

  In my last blog I showed how persisted data may not be used if you have used the base data on an include on an index. That wasn't the only problem ive had that showed the same symptom.  Using the same code as before,  I was executing similar to the below : select BillToAddressID,SOD.SalesOrderDetailID,SOH.CleanedGuid from sales.salesorderheader SOH join Sales.SalesOrderDetail SOD on SOH.SalesOrderID = SOD.SalesOrderID But,  due to a distribution error in statistics i found it necessary to use a table hint.  In this case, I wanted to force a loop join select BillToAddressID,SOD.SalesOrderDetailID,SOH.CleanedGuid from sales.salesorderheader SOH inner loop join Sales.SalesOrderDetail SOD on SOH.SalesOrderID = SOD.SalesOrderID   But, being the diligent  TSQL developer that I am ,looking at the execution plan I noticed that the ‘compute scalar’ operator was again calling the function.  Again,  profiler is a more graphic way to view this…..   All very odd,  just because ive forced a join , that has NOTHING, to do with my persisted data then something is causing the data to be re-evaluated. Not sure if there is any easy fix you can do to the TSQL here, but again its a lesson learned (or rather reinforced) examine the execution plan of every query you write to ensure that it is operating as you thought it would.

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• NHibernate Session Load vs Get when using Table per Hierarchy. Always use ISession.Get&lt;T&gt; for TPH to work.

  - by Rohit Gupta

  Originally posted on: http://geekswithblogs.net/rgupta/archive/2014/06/01/nhibernate-session-load-vs-get-when-using-table-per-hierarchy.aspxNHibernate ISession has two methods on it : Load and Get. Load allows the entity to be loaded lazily, meaning the actual call to the database is made only when properties on the entity being loaded is first accessed. Additionally, if the entity has already been loaded into NHibernate Cache, then the entity is loaded directly from the cache instead of querying the underlying database. ISession.Get<T> instead makes the call to the database, every time it is invoked. With this background, it is obvious that we would prefer ISession.Load<T> over ISession.Get<T> most of the times for performance reasons to avoid making the expensive call to the database. let us consider the impact of using ISession.Load<T> when we are using the Table per Hierarchy implementation of NHibernate. Thus we have base class/ table Animal, there is a derived class named Snake with the Discriminator column being Type which in this case is “Snake”. If we load This Snake entity using the Repository for Animal, we would have a entity loaded, as shown below: public T GetByKey(object key, bool lazy = false) { if (lazy) return CurrentSession.Load<T>(key); return CurrentSession.Get<T>(key); } var tRepo = new NHibernateReadWriteRepository<TPHAnimal>(); var animal = tRepo.GetByKey(new Guid("602DAB56-D1BD-4ECC-B4BB-1C14BF87F47B"), true); var snake = animal as Snake; snake is null As you can see that the animal entity retrieved from the database cannot be cast to Snake even though the entity is actually a snake. The reason being ISession.Load prevents the entity to be cast to Snake and will throw the following exception: System.InvalidCastException :  Message=Unable to cast object of type 'TPHAnimalProxy' to type 'NHibernateChecker.Model.Snake'. Thus we can see that if we lazy load the entity using ISession.Load<TPHAnimal> then we get a TPHAnimalProxy and not a snake. =============================================================== However if do not lazy load the same cast works perfectly fine, this is since we are loading the entity from database and the entity being loaded is not a proxy. Thus the following code does not throw any exceptions, infact the snake variable is not null: var tRepo = new NHibernateReadWriteRepository<TPHAnimal>(); var animal = tRepo.GetByKey(new Guid("602DAB56-D1BD-4ECC-B4BB-1C14BF87F47B"), false); var snake = animal as Snake; if (snake == null) { var snake22 = (Snake) animal; }

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• Displaying a Grid of Data in ASP.NET MVC

  One of the most common tasks we face as a web developers is displaying data in a grid. In its simplest incarnation, a grid merely displays information about a set of records - the orders placed by a particular customer, perhaps; however, most grids offer features like sorting, paging, and filtering to present the data in a more useful and readable manner. In ASP.NET WebForms the GridView control offers a quick and easy way to display a set of records in a grid, and offers features like sorting, paging, editing, and deleting with just a little extra work. On page load, the GridView automatically renders as an HTML <table> element, freeing you from having to write any markup and letting you focus instead on retrieving and binding the data to display to the GridView. In an ASP.NET MVC application, however, developers are on the hook for generating the markup rendered by each view. This task can be a bit daunting for developers new to ASP.NET MVC, especially those who have a background in WebForms. This is the first in a series of articles that explore how to display grids in an ASP.NET MVC application. This installment starts with a walk through of creating the ASP.NET MVC application and data access code used throughout this series. Next, it shows how to display a set of records in a simple grid. Future installments examine how to create richer grids that include sorting, paging, filtering, and client-side enhancements. We'll also look at pre-built grid solutions, like the Grid component in the MvcContrib project and JavaScript-based grids like jqGrid. But first things first - let's create an ASP.NET MVC application and see how to display database records in a web page. Read on to learn more! Read More >

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• Generate a Word document from list data

  - by PeterBrunone

  This came up on a discussion list lately, so I threw together some code to meet the need.  In short, a colleague needed to take the results of an InfoPath form survey and give them to the user in Word format.  The form data was already in a list item, so it was a simple matter of using the SharePoint API to get the list item, formatting the data appropriately, and using response headers to make the client machine treat the response as MS Word content.  The following rudimentary code can be run in an ASPX (or an assembly) in the 12 hive.  When you link to the page, send the list name and item ID in the querystring and use them to grab the appropriate data. // Clear the current response headers and set them up to look like a word doc.HttpContext.Current.Response.Clear();HttpContext.Current.Response.Charset ="";HttpContext.Current.Response.ContentType ="application/msword";string strFileName = "ThatWordFileYouWanted"+ ".doc";HttpContext.Current.Response.AddHeader("Content-Disposition", "inline;filename=" + strFileName);// Using the current site, get the List by name and then the Item by ID (from the URL).string myListName = HttpContext.Current.Request.Querystring["listName"];int myID = Convert.ToInt32(HttpContext.Current.Request.Querystring["itemID"]);SPSite oSite = SPContext.Current.Site;SPWeb oWeb = oSite.OpenWeb();SPList oList = oWeb.Lists["MyListName"];SPListItem oListItem = oList.Items.GetItemById(myID);// Build a string with the data -- format it with HTML if you like. StringBuilder strHTMLContent = newStringBuilder();// *// Here's where you pull individual fields out of the list item.// *// Once everything is ready, spit it out to the client machine.HttpContext.Current.Response.Write(strHTMLContent);HttpContext.Current.Response.End();HttpContext.Current.Response.Flush();

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• PASS Summit Preconference and Sessions

  - by Davide Mauri

  I’m very pleased to announce that I’ll be delivering a Pre-Conference at PASS Summit 2012. I’ll speak about Business Intelligence again (as I did in 2010) but this time I’ll focus only on Data Warehouse, since it’s big topic even alone. I’ll discuss not only what is a Data Warehouse, how it can be modeled and built, but also how it’s development can be approached using and Agile approach, bringing the experience I gathered in this field. Building the Agile Data Warehouse with SQL Server 2012 http://www.sqlpass.org/summit/2012/Sessions/SessionDetails.aspx?sid=2821 I’m sure you’ll like it, especially if you’re starting to create a BI Solution and you’re wondering what is a Data Warehouse, if it is still useful nowadays that everyone talks about Self-Service BI and In-Memory databases, and what’s the correct path to follow in order to have a successful project up and running. Beside this Preconference, I’ll also deliver a regular session, this time related to database administration, monitoring and tuning: DMVs: Power in Your Hands http://www.sqlpass.org/summit/2012/Sessions/SessionDetails.aspx?sid=3204 Here we’ll dive into the most useful DMVs, so that you’ll see how that can help in everyday management in order to discover, understand and optimze you SQL Server installation, from the server itself to the single query. See you there!!!!!

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• Keeping a domain model consistent with actual data

  - by fstuijt

  Recently domain driven design got my attention, and while thinking about how this approach could help us I came across the following problem. In DDD the common approach is to retrieve entities (or better, aggregate roots) from a repository which acts as a in-memory collection of these entities. After these entities have been retrieved, they can be updated or deleted by the user, however after retrieval they are essentially disconnected from the data source and one must actively inform the repository to update the data source and make is consistent again with our in-memory representation. What is the DDD approach to retrieving entities that should remain connected to the data source? For example, in our situation we retrieve a series of sensors that have a specific measurement during retrieval. Over time, these measurement values may change and our business logic in the domain model should respond to these changes properly. E.g., domain events may be raised if a sensor value exceeds a predefined threshold. However, using the repository approach, these sensor values are just snapshots, and are disconnected from the data source. Does any of you have an idea on how to solve this following the DDD approach?

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• PASS Summit Preconference and Sessions

  - by Davide Mauri

  I’m very pleased to announce that I’ll be delivering a Pre-Conference at PASS Summit 2012. I’ll speak about Business Intelligence again (as I did in 2010) but this time I’ll focus only on Data Warehouse, since it’s big topic even alone. I’ll discuss not only what is a Data Warehouse, how it can be modeled and built, but also how it’s development can be approached using and Agile approach, bringing the experience I gathered in this field. Building the Agile Data Warehouse with SQL Server 2012 http://www.sqlpass.org/summit/2012/Sessions/SessionDetails.aspx?sid=2821 I’m sure you’ll like it, especially if you’re starting to create a BI Solution and you’re wondering what is a Data Warehouse, if it is still useful nowadays that everyone talks about Self-Service BI and In-Memory databases, and what’s the correct path to follow in order to have a successful project up and running. Beside this Preconference, I’ll also deliver a regular session, this time related to database administration, monitoring and tuning: DMVs: Power in Your Hands http://www.sqlpass.org/summit/2012/Sessions/SessionDetails.aspx?sid=3204 Here we’ll dive into the most useful DMVs, so that you’ll see how that can help in everyday management in order to discover, understand and optimze you SQL Server installation, from the server itself to the single query. See you there!!!!!

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• MongoDB: Replicate data in documents vs. “join”

  - by JavierCane

  Disclaimer: This is a question derived from this one. What do you think about the following example of use case? I have a table containing orders. These orders has a lot of related information needed by my current queries (think about the products; the buyer information; the region, country and state of the sale point; and so on) In order to think with a de-normalized approach, I don't have to put identifiers of these related items in my main orders collection. Instead, I have to repeat all the information for each order (ie: I will repeat the buyer's name, surname, etc. for each of its orders). Assuming the previous premise, I'm committing to maintain all the data related to an order without a lot of updates (because if I modify the buyer's name, I'll have to iterate through all orders updating the ones made by the same buyer, and as MongoDB blocks at a document level on updates, I would be blocking the entire order at the update moment). I'll have to replicate all the products' related data? (ie: category, maker and optional attributes like color, size…) What if a new feature is requested and I've to make a lot of queries with the products "as the entry point of the query"? (ie: reports showing the products' sales performance grouping by region, country, or whatever) Is it fair enough to apply the $unwind operation to my orders original collection? (What about the performance?) I should have to do another collection with these queries in mind and replicate again all the products' information (and their orders)? Wouldn't be better to store a product_id in the original orders collection in order to be more tolerable to requirements change? (What about emulating JOINs?) The optimal approach would be a mixed solution with a RDBMS system like MySQL in order to retrieve the complete data? I mean: store products, users, and location identifiers in the orders collection and have queries in MySQL like getAllUsersDataByIds in which I would perform a SELECT * FROM users WHERE user_id IN ( :identifiers_retrieved_from_the_mongodb_query )

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• Why No android.content.SyncAdapter meta-data registering sync-adapter?

  - by mobibob

  I am following the SampleSyncAdapter and upon startup, it appears that my SyncAdapter is not configured correctly. It reports an error trying to load its meta-data. How can I isolate the problem? You can see the other accounts in the system that register correctly. Logcat: 12-21 17:10:50.667 W/PackageManager( 121): Unable to load service info ResolveInfo{4605dcd0 com.myapp.syncadapter.MySyncAdapter p=0 o=0 m=0x108000} 12-21 17:10:50.667 W/PackageManager( 121): org.xmlpull.v1.XmlPullParserException: No android.content.SyncAdapter meta-data 12-21 17:10:50.667 W/PackageManager( 121): at android.content.pm.RegisteredServicesCache.parseServiceInfo(RegisteredServicesCache.java:391) 12-21 17:10:50.667 W/PackageManager( 121): at android.content.pm.RegisteredServicesCache.generateServicesMap(RegisteredServicesCache.java:260) 12-21 17:10:50.667 W/PackageManager( 121): at android.content.pm.RegisteredServicesCache$1.onReceive(RegisteredServicesCache.java:110) 12-21 17:10:50.667 W/PackageManager( 121): at android.app.ActivityThread$PackageInfo$ReceiverDispatcher$Args.run(ActivityThread.java:892) 12-21 17:10:50.667 W/PackageManager( 121): at android.os.Handler.handleCallback(Handler.java:587) 12-21 17:10:50.667 W/PackageManager( 121): at android.os.Handler.dispatchMessage(Handler.java:92) 12-21 17:10:50.667 W/PackageManager( 121): at android.os.Looper.loop(Looper.java:123) 12-21 17:10:50.667 W/PackageManager( 121): at com.android.server.ServerThread.run(SystemServer.java:570) 12-21 17:10:50.747 D/Sources ( 294): Creating external source for type=com.skype.contacts.sync, packageName=com.skype.raider 12-21 17:10:50.747 D/Sources ( 294): Creating external source for type=com.twitter.android.auth.login, packageName=com.twitter.android 12-21 17:10:50.747 D/Sources ( 294): Creating external source for type=com.example.android.samplesync, packageName=com.example.android.samplesync 12-21 17:10:50.747 W/PackageManager( 121): Unable to load service info ResolveInfo{460504b0 com.myapp.syncadapter.MySyncAdapter p=0 o=0 m=0x108000} 12-21 17:10:50.747 W/PackageManager( 121): org.xmlpull.v1.XmlPullParserException: No android.content.SyncAdapter meta-data 12-21 17:10:50.747 W/PackageManager( 121): at android.content.pm.RegisteredServicesCache.parseServiceInfo(RegisteredServicesCache.java:391) 12-21 17:10:50.747 W/PackageManager( 121): at android.content.pm.RegisteredServicesCache.generateServicesMap(RegisteredServicesCache.java:260) 12-21 17:10:50.747 W/PackageManager( 121): at android.content.pm.RegisteredServicesCache$1.onReceive(RegisteredServicesCache.java:110) 12-21 17:10:50.747 W/PackageManager( 121): at android.app.ActivityThread$PackageInfo$ReceiverDispatcher$Args.run(ActivityThread.java:892) 12-21 17:10:50.747 W/PackageManager( 121): at android.os.Handler.handleCallback(Handler.java:587) 12-21 17:10:50.747 W/PackageManager( 121): at android.os.Handler.dispatchMessage(Handler.java:92) 12-21 17:10:50.747 W/PackageManager( 121): at android.os.Looper.loop(Looper.java:123) 12-21 17:10:50.747 W/PackageManager( 121): at com.android.server.ServerThread.run(SystemServer.java:570)

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• GTK+ (GTKSharp) poor performance in Windows

  - by nubela

  Hi, In my Mono (C#) project that is meant to be cross-platform, I am using the GTK for the UI. However one thing I noticed is, on my netbook in Archlinux, the performance is really speedy, so events such as mouse hover, and redrawing of widgets, etc, are really fast. Compared to windows (7) on dual core CPUs, the performance is really really weak. Which perplexes me. Am I doing something wrong that is warranting this difference in performance between OSes? What are some ways I can do to optimize GTK on Windows? Its really bad to take around 0.5 secs for a hover event to kick in whereas its almost immediate on a weak(er) netbook with Linux. My code is here for the GUI layer: http://code.google.com/p/subsynct/source/browse/branches/dev/subsync#subsync/GUI Thanks!

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• Why better isolation level means better performance in SQL Server

  - by Oleg Zhylin

  When measuring performance on my query I came up with a dependency between isolation level and elapsed time that was surprising to me READUNCOMMITTED - 409024 READCOMMITTED - 368021 REPEATABLEREAD - 358019 SERIALIZABLE - 348019 Left column is table hint, and the right column is elapsed time in microseconds (sys.dm_exec_query_stats.total_elapsed_time). Why better isolation level gives better performance? This is a development machine and no concurrency whatsoever happens. I would expect READUNCOMMITTED to be the fasted due to less locking overhead. Update: I did measure this with DBCC DROPCLEANBUFFERS DBCC FREEPROCCACHE issued and Profiler confirms there're no cache hits happening. Update2: The query in question is an OLAP one and we need to run it as fast as possible. Closing the production server from outside world to get the computation done is not out of question if this gives performance benefits.

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• Dynamically add new HTML elements on page load after getting JSON data from Web API

  - by Luis D Urraca

  I'm building an hybrid Android App using Phonegap/Apache Cordova. My app should get data from my web api. I'm using JSON to serve the data to the APP. So i got a the following code: function init() { document.addEventListener('deviceready', onDeviceReady, false); var url = "http://23.21.128.153:3000/regions.json";var jsonresults; $.getJSON(url,function(data){ jsonresults = data; $.each(jsonresults, function(i,v){ $('#main-content').append('<li>'+jsonresults[i].name+'</li>'); }); }); } and also on the body of the html i have a div called main-content. Everythings works fine in the Eclipse browser, but on the Android Emulator is not working. Not sure if there's another way to pull data from Web API using JSON and dinamically create HMTL elements after getting the data. https://gist.github.com/2956660

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• IN statement performance in PostgreSQL (and in general)

  - by Vasil

  I know this has probably been asked before, but I can't find it with SO's search. Lets say i've TABLE1 and TABLE2, who should I expect the performance of a query such as this: SELECT * FROM TABLE1 WHERE id IN SUBQUERY_ON_TABLE2; as the number of rows in TABLE1 and TABLE2 grow and id is a primary key on TABLE1. Yes, I know using IN is such a n00b mistake, but TABLE2 has a generic relation (django generic relation) to multiple other tables so I can't think of another way to filter the data. At what (aproximate) ammount of rows in TABLE1 and TABLE2 should I expect to notice performance issues because of this? Will performance degrade linearly, exponentially etc. depending on the number of rows?

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• Performance hit from C++ style casts?

  - by Trevor Boyd Smith

  I am new to C++ style casts and I am worried that using C++ style casts will ruin the performance of my application because I have a real-time-critical deadline in my interrupt-service-routine. I heard that some casts will even throw exceptions! I would like to use the C++ style casts because it would make my code more "robust". However, if there is any performance hit then I will probably not use C++ style casts and will instead spend more time testing the code that uses C-style casts. Has anyone done any rigorous testing/profiling to compare the performance of C++ style casts to C style casts? What were your results? What conclusions did you draw?

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• using jquery to load data from mysql database

  - by Ieyasu Sawada

  I'm currently using jquery's ajax feature or whatever they call it. To load data from mysql database. Its working fine, but one of the built in features of this one is to load all the data which is on the database when you press on backspace and there's no character left on the text box. Here's my query: SELECT * FROM prod_table WHERE QTYHAND>0 AND PRODUCT LIKE '$prod%' OR P_DESC LIKE '$desc%' OR CATEGORY LIKE '$cat%' As you can see I only want to load the products which has greater than 0 quantity on hand. I'm using this code to communicate to the php file which has the query on it: $('#inp').keyup(function(){ var inpval=$('#inp').val(); $.ajax({ type: 'POST', data: ({p : inpval}), url: 'querys.php', success: function(data) { $('.result').html(data); } }); }); Is it possible to also filter the data that it outputs so that when I press on backspace and there's no character left. The only products that's going to display are those with greater than 0 quantity?

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• How can data not stored in a DB be accessed from any activity in Android?

  - by jul

  hi, I'm passing data to a ListView to display some restaurant names. Now when clicking on an item I'd like to start another activity to display more restaurant data. I'm not sure about how to do it. Shall I pass all the restaurant data in a bundle through the intent object? Or shall I just pass the restaurant id and get the data in the other activity? In that case, how can I access my restaurantList from the other activity? In any case, how can I get data from the restaurant I clicked on (the view only contains the name)? Any help, pointers welcome! Thanks Jul ListView lv= (ListView)findViewById(R.id.listview); lv.setAdapter( new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,restaurantList.getRestaurantNames())); lv.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View view, int position, long id) { Intent i = new Intent(Atable.this, RestaurantEdit.class); Bundle b = new Bundle(); //b.putInt("id", ? ); startActivityForResult(i, ACTIVITY_EDIT); } }); RestaurantList.java package org.digitalfarm.atable; import java.util.ArrayList; import java.util.List; public class RestaurantList { private List<Restaurant> restaurants = new ArrayList<Restaurant>(); public List<Restaurant> getRestaurants() { return this.restaurants; } public void setRestaurants(List<Restaurant> restaurants) { this.restaurants = restaurants; } public List<String> getRestaurantNames() { List<String> restaurantNames = new ArrayList<String>(); for (int i=0; i<this.restaurants.size(); i++) { restaurantNames.add(this.restaurants.get(i).getName()); } return restaurantNames; } } Restaurant.java package org.digitalfarm.atable; public class Restaurant { private int id; private String name; private float latitude; private float longitude; public int getId() { return this.id; } public void setId(int id) { this.id = id; } public String getName() { return this.name; } public void setName(String name) { this.name = name; } public float getLatitude() { return this.latitude; } public void setLatitude(float latitude) { this.latitude = latitude; } public float getLongitude() { return this.longitude; } public void setLongitude(float longitude) { this.longitude = longitude; } }

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• What are best practices for collecting, maintaining and ensuring accuracy of a huge data set?

  - by Kyle West

  I am posing this question looking for practical advice on how to design a system. Sites like amazon.com and pandora have and maintain huge data sets to run their core business. For example, amazon (and every other major e-commerce site) has millions of products for sale, images of those products, pricing, specifications, etc. etc. etc. Ignoring the data coming in from 3rd party sellers and the user generated content all that "stuff" had to come from somewhere and is maintained by someone. It's also incredibly detailed and accurate. How? How do they do it? Is there just an army of data-entry clerks or have they devised systems to handle the grunt work? My company is in a similar situation. We maintain a huge (10-of-millions of records) catalog of automotive parts and the cars they fit. We've been at it for a while now and have come up with a number of programs and processes to keep our catalog growing and accurate; however, it seems like to grow the catalog to x items we need to grow the team to y. I need to figure some ways to increase the efficiency of the data team and hopefully I can learn from the work of others. Any suggestions are appreciated, more though would be links to content I could spend some serious time reading. THANKS! Kyle

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• Is a red-black tree my ideal data structure?

  - by Hugo van der Sanden

  I have a collection of items (big rationals) that I'll be processing. In each case, processing will consist of removing the smallest item in the collection, doing some work, and then adding 0-2 new items (which will always be larger than the removed item). The collection will be initialised with one item, and work will continue until it is empty. I'm not sure what size the collection is likely to reach, but I'd expect in the range 1M-100M items. I will not need to locate any item other than the smallest. I'm currently planning to use a red-black tree, possibly tweaked to keep a pointer to the smallest item. However I've never used one before, and I'm unsure whether my pattern of use fits its characteristics well. 1) Is there a danger the pattern of deletion from the left + random insertion will affect performance, eg by requiring a significantly higher number of rotations than random deletion would? Or will delete and insert operations still be O(log n) with this pattern of use? 2) Would some other data structure give me better performance, either because of the deletion pattern or taking advantage of the fact I only ever need to find the smallest item? Update: glad I asked, the binary heap is clearly a better solution for this case, and as promised turned out to be very easy to implement. Hugo

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• About Data Objects and DAO Design when using Hibernate

  - by X. Ma

  I'm hesitating between two designs of a database project using Hibernate. Design #1. (1) Create a general data provider interface, including a set of DAO interfaces and general data container classes. It hides the underneath implementation. A data provider implementation could access data in database, or an XML file, or a service, or something else. The user of a data provider does not to know about it. (2) Create a database library with Hibernate. This library implements the data provider interface in (1). The bad thing about Design #1 is that in order to hide the implementation details, I need to create two sets of data container classes. One in the general data provider interface - let's call them DPI-Objects, the other set is used in the database library, exclusively for entity/attribute mapping in Hibernate - let's call them H-Objects. In the DAO implementation, I need to read data from database to create H-Objects (via Hibernate) and then convert H-Objects into DPI-Objects. Design #2. Do not create a general data provider interface. Expose H-Objects directly to components that use the database lib. So the user of the database library needs to be aware of Hibernate. I like design #1 more, but I don't want to create two sets of data container classes. Is that the right way to hide H-Objects and other Hibernate implementation details from the user who uses the database-based data provider? Are there any drawbacks of Design #2? I will not implement other data provider in the new future, so should I just forget about the data provider interface and use Design #2? What do you think about this? Thanks for your time!

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• How do I bind an iTunes style source list to an NSTableView using Core Data?

  - by Austin

  I have an iTunes style interface in my application: Source list (NSOutlineView) on the left that contains different libraries and playlists with an NSTableView on the right side of the interface displaying information for "Presentations". Similar to iTunes, I am showing the same type of information in the table view whether a library or playlist is selected (title, author, date created, etc). I currently have an NSArrayController connected to my NSTableView and was setting the fetch predicate based on what was selected in the source list. This works fine when selecting a library because I can just set the fetch predicate to filter by the "type" field in my Presentation Core Data entity. When I try to adjust the fetch predicate for the playlist however, it doesn't look like there is any way to set the fetch predicate because I've got a table in between Playlists and Presentations to keep up with the order within the Playlist. According to the Apple docs, these type of predicates are not doable with Core Data (it basically doesn't multiple inner joins). Below is the relevant portion of my Data Model. Is my data model setup incorrectly? Should I drop the NSArrayController and handle connecting the NSTableView up by hand? I'm trying to figure out if there is a simple fix, or really a design flaw.

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• Handling missing/incomplete data in R--is there function to mask but not remove NAs?

  - by doug

  As you would expect from a DSL aimed at data analysis, R handles missing/incomplete data very well, for instance: Many R functions have an 'na.rm' flag that you can set to 'T' to remove the NAs: mean( c(5,6,12,87,9,NA,43,67), na.rm=T) But if you want to deal with NAs before the function call, you need to do something like this: to remove each 'NA' from a vector: vx = vx[!is.na(a)] to remove each 'NA' from a vector and replace it w/ a '0': ifelse(is.na(vx), 0, vx) to remove entire each row that contains 'NA' from a data frame: dfx = dfx[complete.cases(dfx),] All of these functions permanently remove 'NA' or rows with an 'NA' in them. Sometimes this isn't quite what you want though--making an 'NA'-excised copy of the data frame might be necessary for the next step in the workflow but in subsequent steps you often want those rows back (e.g., to calculate a column-wise statistic for a column that has missing rows caused by a prior call to 'complete cases' yet that column has no 'NA' values in it). to be as clear as possible about what i'm looking for: python/numpy has a class, 'masked array', with a 'mask' method, which lets you conceal--but not remove--NAs during a function call. Is there an analogous function in R?

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• querying huge database table takes too much of time in mysql

  - by Vijay

  Hi all, I am running sql queries on a mysql db table that has 110Mn+ unique records for whole day. Problem: Whenever I run any query with "where" clause it takes at least 30-40 mins. Since I want to generate most of data on the next day, I need access to whole db table. Could you please guide me to optimize / restructure the deployment model? Site description: mysql Ver 14.12 Distrib 5.0.24, for pc-linux-gnu (i686) using readline 5.0 4 GB RAM, Dual Core dual CPU 3GHz RHEL 3 my.cnf contents : [root@reports root]# cat /etc/my.cnf [mysqld] datadir=/data/mysql/data/ socket=/tmp/mysql.sock sort_buffer_size = 2000000 table_cache = 1024 key_buffer = 128M myisam_sort_buffer_size = 64M # Default to using old password format for compatibility with mysql 3.x # clients (those using the mysqlclient10 compatibility package). old_passwords=1 [mysql.server] user=mysql basedir=/data/mysql/data/ [mysqld_safe] err-log=/data/mysql/data/mysqld.log pid-file=/data/mysql/data/mysqld.pid [root@reports root]# DB table details: CREATE TABLE `RAW_LOG_20100504` ( `DT` date default NULL, `GATEWAY` varchar(15) default NULL, `USER` bigint(12) default NULL, `CACHE` varchar(12) default NULL, `TIMESTAMP` varchar(30) default NULL, `URL` varchar(60) default NULL, `VERSION` varchar(6) default NULL, `PROTOCOL` varchar(6) default NULL, `WEB_STATUS` int(5) default NULL, `BYTES_RETURNED` int(10) default NULL, `RTT` int(5) default NULL, `UA` varchar(100) default NULL, `REQ_SIZE` int(6) default NULL, `CONTENT_TYPE` varchar(50) default NULL, `CUST_TYPE` int(1) default NULL, `DEL_STATUS_DEVICE` int(1) default NULL, `IP` varchar(16) default NULL, `CP_FLAG` int(1) default NULL, `USER_LOCATE` bigint(15) default NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1 MAX_ROWS=200000000; Thanks in advance! Regards,

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• How to write these two queries for a simple data warehouse, using ANSI SQL?

  - by morpheous

  I am writing a simple data warehouse that will allow me to query the table to observe periodic (say weekly) changes in data, as well as changes in the change of the data (e.g. week to week change in the weekly sale amount). For the purposes of simplicity, I will present very simplified (almost trivialized) versions of the tables I am using here. The sales data table is a view and has the following structure: CREATE TABLE sales_data ( sales_time date NOT NULL, sales_amt double NOT NULL ) For the purpose of this question. I have left out other fields you would expect to see - like product_id, sales_person_id etc, etc, as they have no direct relevance to this question. AFAICT, the only fields that will be used in the query are the sales_time and the sales_amt fields (unless I am mistaken). I also have a date dimension table with the following structure: CREATE TABLE date_dimension ( id integer NOT NULL, datestamp date NOT NULL, day_part integer NOT NULL, week_part integer NOT NULL, month_part integer NOT NULL, qtr_part integer NOT NULL, year_part integer NOT NULL, ); which partition dates into reporting ranges. I need to write queries that will allow me to do the following: Return the change in week on week sales_amt for a specified period. For example the change between sales today and sales N days ago - where N is a positive integer (N == 7 in this case). Return the change in change of sales_amt for a specified period. For in (1). we calculated the week on week change. Now we want to know how that change is differs from the (week on week) change calculated last week. I am stuck however at this point, as SQL is my weakest skill. I would be grateful if an SQL master can explain how I can write these queries in a DB agnostic way (i.e. using ANSI SQL).

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