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• Oracle Coherence & Oracle Service Bus: REST API Integration

  - by Nino Guarnacci

  This post aims to highlight one of the features found in Oracle Coherence which allows it to be easily added and integrated inside a wider variety of projects.  The features in question are the REST API exposed by the Coherence nodes, with which you can interact in the wider mode in memory data grid.Oracle Coherence and Oracle Service Bus are natively integrated through a feature found in the Oracle Service Bus, which allows you to use the coherence grid cache during the configuration phase of a business service. This feature allows you to use an intermediate layer of cache to retrieve the answers from previous invocations of the same service, without necessarily having to invoke the real business service again. Directly from the web console of Oracle Service Bus, you can decide the policies of eviction of the objects / answers and define the discriminating parameters that identify their uniqueness.The coherence REST APIs, however, allow you to integrate both products for other necessities enabling realization of new architectures design.  Consider coherence’s node as a simple service which interoperates through the stardard services and in particular REST (with JSON and XML). Thinking of coherence as a company’s shared service, able to have an implementation of a centralized “map and reduce” which you can access  by a huge variety of protocols (transport and envelopes).An amazing step forward for those who still imagine connectors and code. This type of integration does not require writing custom code or complex implementation to be self-supported. The added value is made unique by the incredible value of both products independently, and still more out of their simple and robust integration.As already mentioned this scenario discovers a hidden new door behind the columns of these two products. The door leads to new ideas and perspectives for enterprise architectures that increasingly wink to next-generation applications: simple and dynamic, perhaps towards the mobile and web 2.0.Below, a small and simple demo useful to demonstrate how easily is to integrate these two products using the Coherence REST API. This demo is also intended to imagine new enterprise architectures using this approach.The idea is to create a centralized system of alerting, fed easily from any company’s application, regardless of the technology with which they were built . Then use a representation standard protocol: RSS, using a service exposed by the service bus; So you can browse and search only the alerts that you are interested on, by category, author, title, date, etc etc.. The steps needed to implement this system are very simple and very few. Here they are listed below and described to be easily replicated within your environment. I would remind you that the demo is only meant to demonstrate how easily is to integrate Oracle Coherence and the Oracle Service Bus, and stimulate your imagination to new technological approaches.1) Install the two products: In this demo used (if necessary, consult the installation guides of 2 products)  - Oracle Service Bus ver. 11.1.1.5.0 http://www.oracle.com/technetwork/middleware/service-bus/downloads/index.html - Oracle Coherence ver. 3.7.1 http://www.oracle.com/technetwork/middleware/coherence/downloads/index.html 2) Because you choose to create a centralized alerting system, we need to define a structure type containing some alerting attributes useful to preserve and organize the information of the various alerts sent by the different applications. Here, then it was built a java class named Alert containing the canonical properties of an alarm information:- Title- Description- System- Time- Severity 3) Therefore, we need to create two configuration files for the coherence node, in order to save the Alert objects within the grid, through the rest/http protocol (more than the native API for Java, C + +, C,. Net). Here are the two minimal configuration files for Coherence:coherence-rest-config.xml resty-server-config.xml This minimum configuration allows me to use a distributed cache named "alerts" that can  also be accessed via http - rest on the host "localhost" over port "8080", objects are of type “oracle.cohsb.Alert”. 4) Below  a simple Java class that represents the type of alert messages: 5) At this point we just need to startup our coherence node, able to listen on http protocol to manage the “alerts” cache, which will receive incoming XML or JSON objects of type Alert. Remember to include in the classpath of the coherence node, the Alert java class and the following coherence libraries and configuration files:  At this point, just run the coherence class node “com.tangosol.net.DefaultCacheServer”advising you to set the following parameters:-Dtangosol.coherence.log.level=9 -Dtangosol.coherence.log=stdout -Dtangosol.coherence.cacheconfig=[PATH_TO_THE_FILE]\resty-server-config.xml 6) Let's create a procedure to test our configuration of Coherence and in order to insert some custom alerts in our cache. The technology with which you want to achieve this functionality is fully not considerable: Javascript, Python, Ruby, Scala, C + +, Java.... Because the protocol to communicate with Coherence is simply HTTP / JSON or XML. For this little demo i choose Java: A method to send/put the alert to the cache: A method to query and view the content of the cache: Finally the main method that execute our methods:  No special library added in the classpath for our class (json struct static defined), when it will be executed, it asks some information such as title, description,... in order to compose and send an alert to the cache and then it will perform an inquiry, to the same cache. At this point, a good exercise at this point, may be to create the same procedure using other technologies, such as a simple html page containing some JavaScript code, and then using Python, Ruby, and so on.7) Now we are ready to start configuring the Oracle Service Bus in order to integrate the two products. First integrate the internal alerting system of Oracle Service Bus with our centralized alerting system based on coherence node. This ensures that by monitoring, or directly from within our Proxy Message Flow, we can throw alerts and save them directly into the Coherence node. To do this I choose to use the jms technology, natively present inside the Oracle Weblogic / Service Bus. Access to the Oracle WebLogic Administration console and create and configure a new JMS connection factory and a new jms destination (queue). Now we should create a new resource of type “alert destination” within our Oracle Service Bus project. The new “alert destination” resource should be configured using the newly created connection factory jms and jms destination. Finally, in order to withdraw the message alert enqueued in our JMS destination and send it to our coherence node, we just need to create a new business service and proxy service within our Oracle Service Bus project.Our business service is responsible for sending a message to our REST service Coherence using as a method action: PUT Finally our proxy service have to collect all messages enqueued on the destination, execute an xquery transformation on those messages  in order to translate them into valid XML / alert objects useful to be sent to our coherence service, through the newly created business service. The message flow pipeline containing the xquery transformation: Incredibly,  we just did a basic first integration between the native alerting system of Oracle Service Bus and our centralized alerting system by simply configuring our coherence node without developing anything.It's time to test it out. To do this I create a proxy service able to generate an alert using our "alert destination", whenever the proxy is invoked. After some invocation to our proxy that generates fake alerts, we could open an Internet browser and type the URL  http://localhost: 8080/alerts/  so we could see what has been inserted within the coherence node. 8) We are ready for the final step.  We would create a new message flow, that can be used to search and display the results in standard mode. To do this I choosen the standard representation of RSS, to display a formatted result on a huge variety of devices such as readers for the iPhone and Android. The inquiry may be defined already at the time of the request able to return only feed / items related to our needs. To do this we need to create a new business service, a new proxy service, and finally a new XQuery Transformation to take care of translating the collection of alerts that will be return from our coherence node in a nicely formatted RSS standard document.So we start right from this resource (xquery), which has the task of transforming a collection of alerts / xml returned from the node coherence in a type well-formatted feed RSS 2.0 our new business service that will search the alerts on our coherence node using the Rest API. And finally, our last resource, the proxy service that will be exposed as an RSS / feeds to various mobile devices and traditional web readers, in which we will intercept any search query, and transform the result returned by the business service in an RSS feed 2.0. The message flow with the transformation phase (Alert TO Feed Items): Finally some little tricks to follow during the routing to the business service, - check for any queries present in the url to require a subset of alerts  - the http header "Accept" to help get an answer XML instead of JSON: In our little demo we also static added some coherence parameters to the request:sort=time:desc;start=0;count=100I would like to get from Coherence that the results will be sorted by date, and starting from 1 up to a maximum of 100.Done!!Just incredible, our centralized alerting system is ready. Inheriting all the qualities and capabilities of the two products involved Oracle Coherence & Oracle Service Bus: - RASP (Reliability, Availability, Scalability, Performance)Now try to use your mobile device, or a normal Internet browser by accessing the RSS just published: Some urls you may test: Search for the last 100 alerts : http://localhost:7001/alarmsSearch for alerts that do not have time set to null (time is not null):http://localhost:7001/alarms?q=time+is+not+nullSearch for alerts that the system property is “Web Browser” (system = ‘Web Browser’):http://localhost:7001/alarms?q=system+%3D+%27Web+Browser%27Search for alerts that the system property is “Web Browser” and the severity property is “Fatal” and the title property contain the word “Javascript”  (system = ‘Web Broser’ and severity = ‘Fatal’ and title like ‘%Javascript%’)http://localhost:8080/alerts?q=system+%3D+%27Web+Browser%27+AND+severity+%3D+%27Fatal%27+AND+title+LIKE+%27%25Javascript%25%27 To compose more complex queries about your need I would suggest you to read the chapter in the coherence documentation inherent the Cohl language (Coherence Query Language) http://download.oracle.com/docs/cd/E24290_01/coh.371/e22837/api_cq.htm . Some useful links: - Oracle Coherence REST API Documentation http://download.oracle.com/docs/cd/E24290_01/coh.371/e22839/rest_intro.htm - Oracle Service Bus Documentation http://download.oracle.com/docs/cd/E21764_01/soa.htm#osb - REST explanation from Wikipedia http://en.wikipedia.org/wiki/Representational_state_transfer At this URL could be downloaded the whole materials of this demo http://blogs.oracle.com/slc/resource/cosb/coh-sb-demo.zip Author: Nino Guarnacci.

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• SQL SERVER – Disk Space Monitoring – Detecting Low Disk Space on Server

  - by Pinal Dave

  A very common question I often receive is how to detect if the disk space is running low on SQL Server. There are two different ways to do the same. I personally prefer method 2 as that is very easy to use and I can use it creatively along with database name. Method 1: EXEC MASTER..xp_fixeddrives GO Above query will return us two columns, drive name and MB free. If we want to use this data in our query, we will have to create a temporary table and insert the data from this stored procedure into the temporary table and use it. Method 2: SELECT DISTINCT dovs.logical_volume_name AS LogicalName, dovs.volume_mount_point AS Drive, CONVERT(INT,dovs.available_bytes/1048576.0) AS FreeSpaceInMB FROM sys.master_files mf CROSS APPLY sys.dm_os_volume_stats(mf.database_id, mf.FILE_ID) dovs ORDER BY FreeSpaceInMB ASC GO The above query will give us three columns: drive logical name, drive letter and free space in MB. We can further modify above query to also include database name in the query as well. SELECT DISTINCT DB_NAME(dovs.database_id) DBName, dovs.logical_volume_name AS LogicalName, dovs.volume_mount_point AS Drive, CONVERT(INT,dovs.available_bytes/1048576.0) AS FreeSpaceInMB FROM sys.master_files mf CROSS APPLY sys.dm_os_volume_stats(mf.database_id, mf.FILE_ID) dovs ORDER BY FreeSpaceInMB ASC GO This will give us additional data about which database is placed on which drive. If you see a database name multiple times, it is because your database has multiple files and they are on different drives. You can modify above query one more time to even include the details of actual file location. SELECT DISTINCT DB_NAME(dovs.database_id) DBName, mf.physical_name PhysicalFileLocation, dovs.logical_volume_name AS LogicalName, dovs.volume_mount_point AS Drive, CONVERT(INT,dovs.available_bytes/1048576.0) AS FreeSpaceInMB FROM sys.master_files mf CROSS APPLY sys.dm_os_volume_stats(mf.database_id, mf.FILE_ID) dovs ORDER BY FreeSpaceInMB ASC GO The above query will now additionally include the physical file location as well. As I mentioned earlier, I prefer method 2 as I can creatively use it as per the business need. Let me know which method are you using in your production server. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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• Domino Dump Turns Into Van Gogh Painting [Video]

  - by Jason Fitzpatrick

  We’ve seen a lot of domino projects in our day, but this is the first one we’ve seen that turns into a piece of classic art when it’s done. Courtesy of domino enthusiast FlippyCat: I recreated Vincent van Gogh’s “Starry Night” from just over 7,000 dominos. The second attempt took about 11 hours total to build. The first attempt failed, when I dropped a screw from the camera rig onto it. I was able to improve the swirling clouds better in the second attempt as a result though. I do not know how long the first attempt took, but I did not have any accidents building like I did in the second attempt! Next up, Edvard Munch’s The Scream? How to Use an Xbox 360 Controller On Your Windows PC Download the Official How-To Geek Trivia App for Windows 8 How to Banish Duplicate Photos with VisiPic

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• SQL SERVER – Introduction to PERCENTILE_CONT() – Analytic Functions Introduced in SQL Server 2012

  - by pinaldave

  SQL Server 2012 introduces new analytical function PERCENTILE_CONT(). The book online gives following definition of this function: Computes a specific percentile for sorted values in an entire rowset or within distinct partitions of a rowset in Microsoft SQL Server 2012 Release Candidate 0 (RC 0). For a given percentile value P, PERCENTILE_DISC sorts the values of the expression in the ORDER BY clause and returns the value with the smallest CUME_DIST value (with respect to the same sort specification) that is greater than or equal to P. If you are clear with understanding of the function – no need to read further. If you got lost here is the same in simple words – it is lot like finding median with percentile value. Now let’s have fun following query: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS MedianCont FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO The above query will give us the following result: You can see that I have used PERCENTILE_COUNT(0.5) in query, which is similar to finding median. Let me explain above diagram with little more explanation. The defination of median is as following: In case of Even Number of elements = In ordered list add the two digits from the middle and devide by 2 In case of Odd Numbers of elements = In ordered list select the digits from the middle I hope this example gives clear idea how PERCENTILE_CONT() works. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Using Take and skip keyword to filter records in LINQ

  - by vik20000in

  In LINQ we can use the take keyword to filter out the number of records that we want to retrieve from the query. Let’s say we want to retrieve only the first 5 records for the list or array then we can use the following query     int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };     var first3Numbers = numbers.Take(3); The TAKE keyword can also be easily applied to list of object in the following way. var first3WAOrders = (         from cust in customers         from order in cust.Orders         select cust ) .Take(3); [Note in the query above we are using the order clause so that the data is first ordered based on the orders field and then the first 3 records are taken. In both the above example we have been able to filter out data based on the number of records we want to fetch. But in both the cases we were fetching the records from the very beginning. But there can be some requirements whereby we want to fetch the records after skipping some of the records like in paging. For this purpose LINQ has provided us with the skip method which skips the number of records passed as parameter in the result set. int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var allButFirst4Numbers = numbers.Skip(4); The SKIP keyword can also be easily applied to list of object in the following way. var first3WAOrders = (         from cust in customers         from order in cust.Orders         select cust ).Skip(3);  Vikram

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• F# and ArcObjects

  - by Marko Apfel

  After having a first look on F# its time to ask: Who could i use F# with ArcObjects. So my first steps was to do something with a feature in a F# interactive session. And these are my first code lines: open ESRI.ArcGIS.esriSystem;;open ESRI.ArcGIS.DataSourcesGDB;;open ESRI.ArcGIS.Geodatabase;;let aoInitialize = new AoInitializeClass();;let status = aoInitialize.Initialize(esriLicenseProductCode.esriLicenseProductCodeArcEditor);;let workspacefactory = new SdeWorkspaceFactoryClass();;// Spatial Database Connection, property "Service": sde:sqlserver:okullet connection = "user=sfg;password=gfs;server=OKUL;database=Praxair;version=SDE.DEFAULT";;let workspace = workspacefactory.OpenFromString(connection, 0);;let featureWorkspace = (box workspace) :?> IFeatureWorkspace;;let featureClass = featureWorkspace.OpenFeatureClass("Praxair.SFG.BP_L_ROHR");;let feature = featureClass.GetFeature(100);;printfn "%A" feature.OID;;

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• Class Loading Deadlocks

  - by tomas.nilsson

  Mattis follows up on his previous post with one more expose on Class Loading Deadlocks As I wrote in a previous post, the class loading mechanism in Java is very powerful. There are many advanced techniques you can use, and when used wrongly you can get into all sorts of trouble. But one of the sneakiest deadlocks you can run into when it comes to class loading doesn't require any home made class loaders or anything. All you need is classes depending on each other, and some bad luck. First of all, here are some basic facts about class loading: 1) If a thread needs to use a class that is not yet loaded, it will try to load that class 2) If another thread is already loading the class, the first thread will wait for the other thread to finish the loading 3) During the loading of a class, one thing that happens is that the <clinit method of a class is being run 4) The <clinit method initializes all static fields, and runs any static blocks in the class. Take the following class for example: class Foo { static Bar bar = new Bar(); static { System.out.println("Loading Foo"); } } The first time a thread needs to use the Foo class, the class will be initialized. The <clinit method will run, creating a new Bar object and printing "Loading Foo" But what happens if the Bar object has never been used before either? Well, then we will need to load that class as well, calling the Bar <clinit method as we go. Can you start to see the potential problem here? A hint is in fact #2 above. What if another thread is currently loading class Bar? The thread loading class Foo will have to wait for that thread to finish loading. But what happens if the <clinit method of class Bar tries to initialize a Foo object? That thread will have to wait for the first thread, and there we have the deadlock. Thread one is waiting for thread two to initialize class Bar, thread two is waiting for thread one to initialize class Foo. All that is needed for a class loading deadlock is static cross dependencies between two classes (and a multi threaded environment): class Foo { static Bar b = new Bar(); } class Bar { static Foo f = new Foo(); } If two threads cause these classes to be loaded at exactly the same time, we will have a deadlock. So, how do you avoid this? Well, one way is of course to not have these circular (static) dependencies. On the other hand, it can be very hard to detect these, and sometimes your design may depend on it. What you can do in that case is to make sure that the classes are first loaded single threadedly, for example during an initialization phase of your application. The following program shows this kind of deadlock. To help bad luck on the way, I added a one second sleep in the static block of the classes to trigger the unlucky timing. Notice that if you uncomment the "//Foo f = new Foo();" line in the main method, the class will be loaded single threadedly, and the program will terminate as it should. public class ClassLoadingDeadlock { // Start two threads. The first will instansiate a Foo object, // the second one will instansiate a Bar object. public static void main(String[] arg) { // Uncomment next line to stop the deadlock // Foo f = new Foo(); new Thread(new FooUser()).start(); new Thread(new BarUser()).start(); } } class FooUser implements Runnable { public void run() { System.out.println("FooUser causing class Foo to be loaded"); Foo f = new Foo(); System.out.println("FooUser done"); } } class BarUser implements Runnable { public void run() { System.out.println("BarUser causing class Bar to be loaded"); Bar b = new Bar(); System.out.println("BarUser done"); } } class Foo { static { // We are deadlock prone even without this sleep... // The sleep just makes us more deterministic try { Thread.sleep(1000); } catch(InterruptedException e) {} } static Bar b = new Bar(); } class Bar { static { try { Thread.sleep(1000); } catch(InterruptedException e) {} } static Foo f = new Foo(); }

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• A Look at the GridView's New Sorting Styles in ASP.NET 4.0

  Like every Web control in the ASP.NET toolbox, the GridView includes a variety of style-related properties, including CssClass, Font, ForeColor, BackColor, Width, Height, and so on. The GridView also includes style properties that apply to certain classes of rows in the grid, such as RowStyle, AlternatingRowStyle, HeaderStyle, and PagerStyle. Each of these meta-style properties offer the standard style properties (CssClass, Font, etc.) as subproperties. In ASP.NET 4.0, Microsoft added four new style properties to the GridView control: SortedAscendingHeaderStyle, SortedAscendingCellStyle, SortedDescendingHeaderStyle, and SortedDescendingCellStyle. These four properties are meta-style properties like RowStyle and HeaderStyle, but apply to column of cells rather than a row. These properties only apply when the GridView is sorted - if the grid's data is sorted in ascending order then the SortedAscendingHeaderStyle and SortedAscendingCellStyle properties define the styles for the column the data is sorted by. The SortedDescendingHeaderStyle and SortedDescendingCellStyle properties apply to the sorted column when the results are sorted in descending order. These four new properties make it easier to customize the appearance of the column by which the data is sorted. Using these properties along with a touch of Cascading Style Sheets (CSS) it is possible to add up and down arrows to the sorted column's header to indicate whether the data is sorted in ascending or descending order. Likewise, these properties can be used to shade the sorted column or make its text bold. This article shows how to use these four new properties to style the sorted column. Read on to learn more! Read More >

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• Programming Pearls (2nd Edition) vs More Programming Pearls: Confessions of a Coder [closed]

  - by Geek

  I have been reading very good reviews of the books by Jon Bentley : Programming Pearls (2nd Edition) More Programming Pearls: Confessions of a Coder. I know that these books have been out there for a long time and I feel bad that I haven't read either one . But it is always better late than never . I understand that the second one was written after the first one . So are these two books complementary to each other ? Do the second one assume that the reader has read the first one ? For some one who haven't read either which one would you propose to read up first ?

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• Could Ajax + Caching be seen as cloaking?

  - by Angel

  I have a website where we use a technique to speed up loading times based in a combination of AJAX + caching. Basically, when we have a section in a page with content which is slow to retrieve, we first look if it's cached. If it is, then we serve the content, if it's not, we serve a placeholder and then make an AJAX call in the client to retrieve the content, wich is now cached for subsequent requests. As a consecuence, sometimes you get the entire page content in the first request, and sometimes you get those placeholders, wich get filled inmediatly with the responses of the AJAX request. You can see an example in the results count by category in the right column of this page: http://www.inzoco.com/crits/2-1-3-28-185-0-28079-0-0/listado-piso-en-alquiler-en-madrid-madrid.aspx I'm worried if it could be seen as cloaking by search engines because if you make a request for a page wich content isn't cached and then ask again for the same page, you would get different responses, the first with the placeholders and AJAX requests and the second one with al the content rendered.

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• Denali Paging–Key seek lookups

  - by Dave Ballantyne

  In my previous post “Denali Paging – is it win.win ?” I demonstrated the use of using the Paging functionality within Denali.  On reflection,  I think i may of been a little unfair and should of continued always planned to continue my investigations to the next step. In Pauls article, he uses a combination of ctes to first scan the ordered keys which is then filtered using TOP and rownumber and then uses those keys to seek the data.  So what happens if we replace the scanning portion of the code with the denali paging functionality. Heres the original procedure,  we are going to replace the functionality of the Keys and SelectedKeys ctes : CREATE  PROCEDURE dbo.FetchPageKeySeek         @PageSize   BIGINT,         @PageNumber BIGINT AS BEGIN         -- Key-Seek algorithm         WITH    Keys         AS      (                 -- Step 1 : Number the rows from the non-clustered index                 -- Maximum number of rows = @PageNumber * @PageSize                 SELECT  TOP (@PageNumber * @PageSize)                         rn = ROW_NUMBER() OVER (ORDER BY P1.post_id ASC),                         P1.post_id                 FROM    dbo.Post P1                 ORDER   BY                         P1.post_id ASC                 ),                 SelectedKeys         AS      (                 -- Step 2 : Get the primary keys for the rows on the page we want                 -- Maximum number of rows from this stage = @PageSize                 SELECT  TOP (@PageSize)                         SK.rn,                         SK.post_id                 FROM    Keys SK                 WHERE   SK.rn > ((@PageNumber - 1) * @PageSize)                 ORDER   BY                         SK.post_id ASC                 )         SELECT  -- Step 3 : Retrieve the off-index data                 -- We will only have @PageSize rows by this stage                 SK.rn,                 P2.post_id,                 P2.thread_id,                 P2.member_id,                 P2.create_dt,                 P2.title,                 P2.body         FROM    SelectedKeys SK         JOIN    dbo.Post P2                 ON  P2.post_id = SK.post_id         ORDER   BY                 SK.post_id ASC; END; and here is the replacement procedure using paging: CREATE  PROCEDURE dbo.FetchOffsetPageKeySeek         @PageSize   BIGINT,         @PageNumber BIGINT AS BEGIN         -- Key-Seek algorithm         WITH    SelectedKeys         AS      (                 SELECT  post_id                 FROM    dbo.Post P1                 ORDER   BY post_id ASC                 OFFSET  @PageSize * (@PageNumber-1) ROWS                 FETCH NEXT @PageSize ROWS ONLY                 )         SELECT  P2.post_id,                 P2.thread_id,                 P2.member_id,                 P2.create_dt,                 P2.title,                 P2.body         FROM    SelectedKeys SK         JOIN    dbo.Post P2                 ON  P2.post_id = SK.post_id         ORDER   BY                 SK.post_id ASC; END; Notice how all i have done is replace the functionality with the Keys and SelectedKeys CTEs with the paging functionality. So , what is the comparative performance now ?. Exactly the same amount of IO and memory usage , but its now pretty obvious that in terms of CPU and overall duration we are onto a winner.    

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• Create an Alias Directory inside a Virtual Host

  - by Praveen Kumar

  First, let me say, I asked this question in StackOverflow, and thought I could get more replies here. I checked here, here, here, here, here, and here before asking this question. I guess my search skills are weak. I am using the WampServer version 2.2e. I have a need like, I need a virtual path inside a virtual host. Let me say the two hosts that I have. Primary Virtual Host (Localhost) NameVirtualHost *:80 <VirtualHost *:80> ServerName localhost DocumentRoot "C:/Wamp/www" </VirtualHost> My Apps Virtual Hosts <VirtualHost *:80> ServerName apps.ptrl DocumentRoot "C:/Wamp/vhosts/ptrl/apps" ErrorLog "logs/apps-ptrl-error.log" CustomLog "logs/apps-ptrl-access.log" common <Directory "C:/Wamp/vhosts/ptrl/apps"> allow from all order allow,deny AllowOverride All </Directory> DirectoryIndex index.html index.htm index.php </VirtualHost> My Blog Virtual Host <VirtualHost *:80> ServerName blog.praveen-kumar.ptrl DocumentRoot "C:/Wamp/vhosts/ptrl/praveen-kumar/blog" ErrorLog "logs/praveen-kumar-ptrl-error.log" CustomLog "logs/praveen-kumar-ptrl-access.log" common <Directory "C:/Wamp/vhosts/ptrl/praveen-kumar/blog"> allow from all order allow,deny AllowOverride All </Directory> DirectoryIndex index.html index.htm index.php </VirtualHost> My requirement now is to have http://apps.ptrl/blog/ and http://blog.praveen-kumar.ptrl/ should be the same directory. One thing I thought of is, moving the blog folder inside the apps folder, but it is connected with Git and other stuffs are there, so it is not possible to move the folder. So, I thought of creating an alias to the VirtualHost in this way: <VirtualHost *:80> ServerName apps.ptrl DocumentRoot "C:/Wamp/vhosts/ptrl/apps" ErrorLog "logs/apps-ptrl-error.log" CustomLog "logs/apps-ptrl-access.log" common <Directory "C:/Wamp/vhosts/ptrl/apps"> allow from all order allow,deny AllowOverride All </Directory> DirectoryIndex index.html index.htm index.php # The alias to the blog! Alias /blog "C:/Wamp/vhosts/ptrl/praveen-kumar/blog" <Directory "C:/Wamp/vhosts/ptrl/praveen-kumar/blog"> allow from all order allow,deny AllowOverride All </Directory> </VirtualHost> But when I tried to access http://apps.ptrl/blog, I am getting an Error 403 Forbidden page. Am I doing the right thing? If you need to look at the access log, and error log, they are here: # Access Log 127.0.0.1 - - [14/Oct/2012:09:53:11 +0530] "GET /blog HTTP/1.1" 403 206 127.0.0.1 - - [14/Oct/2012:09:53:11 +0530] "GET /favicon.ico HTTP/1.1" 404 209 127.0.0.1 - - [14/Oct/2012:09:53:53 +0530] "GET / HTTP/1.1" 200 6935 127.0.0.1 - - [14/Oct/2012:09:53:53 +0530] "GET /app/blog/thumb.png HTTP/1.1" 404 216 # Error Log [Sun Oct 14 09:53:11 2012] [error] [client 127.0.0.1] client denied by server configuration: C:/Wamp/vhosts/ptrl/praveen-kumar/blog [Sun Oct 14 09:53:11 2012] [error] [client 127.0.0.1] File does not exist: C:/Wamp/vhosts/ptrl/apps/favicon.ico [Sun Oct 14 09:53:53 2012] [error] [client 127.0.0.1] File does not exist: C:/Wamp/vhosts/ptrl/apps/app/blog, referer: http://apps.ptrl/ Waiting eagerly for some help. I am ready to provide more info, if needed. Update #1: Changed VirtualHosts: <VirtualHost *:80> ServerName apps.ptrl DocumentRoot "C:/Wamp/vhosts/ptrl/apps" ErrorLog "logs/apps-ptrl-error.log" CustomLog "logs/apps-ptrl-access.log" common # The alias to the blog! Alias /blog "C:/Wamp/vhosts/ptrl/praveen-kumar/blog" <Directory "C:/Wamp/vhosts/ptrl/praveen-kumar/blog"> allow from all order allow,deny AllowOverride All </Directory> <Directory "C:/Wamp/vhosts/ptrl/apps"> allow from all order allow,deny AllowOverride All </Directory> DirectoryIndex index.html index.htm index.php </VirtualHost> The issue now: I am able to access the site. The physical links are working now. i.e., I am able to open http://apps.ptrl/blog/index.php but not http://apps.ptrl/blog/view-1.ptf, which gets translated to http://apps.ptrl/blog/index.php?page=view&id=1. Any solutions?

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• www.foobar.com works but foobar.com results in a 'Server not found' error

  - by Homunculus Reticulli

  I have just setup a minimal (hopefully secure? - comments welcome) apache website using the following configuration file: <VirtualHost *:80> ServerName foobar.com ServerAlias www.foobar.com ServerAdmin [email protected] DocumentRoot /path/to/websites/foobar/web DirectoryIndex index.php # CustomLog with format nickname LogFormat "%h %l %u %t \"%r\" %>s %b" common CustomLog "|/usr/bin/cronolog /var/log/apache2/%Y%m.foobar.access.log" common LogLevel notice ErrorLog "|/usr/bin/cronolog /var/log/apache2/%Y%m.foobar.errors.log" <Directory /> AllowOverride None Order Deny,Allow Deny from all </Directory> <Directory /path/to/websites/> Options -Indexes FollowSymLinks MultiViews AllowOverride None Order allow,deny allow from all </Directory> </VirtualHost> I am able to access the website by using www.foobar.com, however when I type foobar.com, I get the error 'Server not found' - why is this? My second question concerns the security implications of the directive: <Directory /path/to/websites/> Options -Indexes FollowSymLinks MultiViews AllowOverride None Order allow,deny allow from all </Directory> in the configuration above. What exactly is it doing, and is it necessary?. From my (admitedly limited) understanding of Apache configuration files, this means that anyone will be able to access (write to?) the /path/to/websites/ folder. Is my understanding correct? - and if yes, how is this not a security risk?

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• Apache disable DNS lookups

  - by odeceixe

  I'm using Debian 4.3.2-1 and Apache 2 on my production server. Watching the logs, I noticed Apache is resolving client's hostnames even with HostnameLookups Off in apache2.conf. I want to avoid these lookups so I'm guessing Apache is making this DNS query because I have mod_authz_host enabled. When I try to unlink this module, I get several modules complaining because they use the Order directive. How is the clean way to go? Should I comment all Order directives like Order allow,deny Deny from all Is this the only way to stop Apache from making DNS requests? I would like to deny access to .htaccess files and some rules like that.

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• Recover that Photo, Picture or File You Deleted Accidentally

  - by The Geek

  Have you ever accidentally deleted a photo on your camera, computer, USB drive, or anywhere else? What you might not know is that you can usually restore those pictures—even from your camera’s memory stick. Windows tries to prevent you from making a big mistake by providing the Recycle Bin, where deleted files hang around for a while—but unfortunately it doesn’t work for external USB drives, USB flash drives, memory sticks, or mapped drives. The great news is that this technique also works if you accidentally deleted the photo… from the camera itself. That’s what happened to me, and prompted writing this article. Restore that File or Photo using Recuva The first piece of software that you’ll want to try is called Recuva, and it’s extremely easy to use—just make sure when you are installing it, that you don’t accidentally install that stupid Yahoo! toolbar that nobody wants. Now that you’ve installed the software, and avoided an awful toolbar installation, launch the Recuva wizard and let’s start through the process of recovering those pictures you shouldn’t have deleted. The first step on the wizard page will let you tell Recuva to only search for a specific type of file, which can save a lot of time while searching, and make it easier to find what you are looking for. Next you’ll need to specify where the file was, which will obviously be up to wherever you deleted it from. Since I deleted mine from my camera’s SD card, that’s where I’m looking for it. The next page will ask you whether you want to do a Deep Scan. My recommendation is to not select this for the first scan, because usually the quick scan can find it. You can always go back and run a deep scan a second time. And now, you’ll see all of the pictures deleted from your drive, memory stick, SD card, or wherever you searched. Looks like what happened in Vegas didn’t stay in Vegas after all… If there are a really large number of results, and you know exactly when the file was created or modified, you can switch to the advanced view, where you can sort by the last modified time. This can help speed up the process quite a bit, so you don’t have to look through quite as many files. At this point, you can right-click on any filename, and choose to Recover it, and then save the files elsewhere on your drive. Awesome! Restore that File or Photo using DiskDigger If you don’t have any luck with Recuva, you can always try out DiskDigger, another excellent piece of software. I’ve tested both of these applications very thoroughly, and found that neither of them will always find the same files, so it’s best to have both of them in your toolkit. Note that DiskDigger doesn’t require installation, making it a really great tool to throw on your PC repair Flash drive. Start off by choosing the drive you want to recover from…   Now you can choose whether to do a deep scan, or a really deep scan. Just like with Recuva, you’ll probably want to select the first one first. I’ve also had much better luck with the regular scan, rather than the “dig deeper” one. If you do choose the “dig deeper” one, you’ll be able to select exactly which types of files you are looking for, though again, you should use the regular scan first. Once you’ve come up with the results, you can click on the items on the left-hand side, and see a preview on the right.  You can select one or more files, and choose to restore them. It’s pretty simple! Download DiskDigger from dmitrybrant.com Download Recuva from piriform.com Good luck recovering your deleted files! And keep in mind, DiskDigger is a totally free donationware software from a single, helpful guy… so if his software helps you recover a photo you never thought you’d see again, you might want to think about throwing him a dollar or two. Similar Articles Productive Geek Tips Stupid Geek Tricks: Undo an Accidental Move or Delete With a Keyboard ShortcutRestore Accidentally Deleted Files with RecuvaCustomize Your Welcome Picture Choices in Windows VistaAutomatically Resize Picture Attachments in Outlook 2007Resize Your Photos with Easy Thumbnails TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips DVDFab 6 Revo Uninstaller Pro Registry Mechanic 9 for Windows PC Tools Internet Security Suite 2010 Icelandic Volcano Webcams Open Multiple Links At One Go NachoFoto Searches Images in Real-time Office 2010 Product Guides Google Maps Place marks – Pizza, Guns or Strip Clubs Monitor Applications With Kiwi

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• "No bootable device - insert boot disk" after restart on Ubuntu 10.04 b1 update

  - by anjanesh

  I was making an update on my Ubuntu 10.04 beta1 64-bit PC when, after reboot I get PXE-E61: Mediaa test failure, check cable PXE-M0F: Exiting Intel Boot Agent. No bootable device - insert boot disk and press any key How did my boot record disappear ? BIOS Boot Boot Menu Type : Normal Boot Device Priority : <CD/DVD-ROM Drive> <Hard Disk Drive> <Floppy Drive> <Ethernet> Hard Driver Order : No Hard Disk Drive CD/DVD ROM Drive Order : <PT-TSSTcorp CDDV> Removable Drive Order : No Removable Drive Boot to Optical Devices : <Enable> Boot to Removable Devices : <Enable> Boot to Network : <Enable> USB Boot : <Enable>

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• XNA Health Bar continually decreasing

  - by Craig

  As per the Health bar tutorial on ... http://www.xnadevelopment.com/tutorials/notsohealthy/NotSoHealthy.shtml I have set up the above, how do I make it decrease by 1 health per second? I want to create a mini survival game, and this is an important factor. Where am i going wrong? I want it to visibly decrease every second. using System; using System.Collections.Generic; using System.Linq; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Audio; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.GamerServices; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Input; using Microsoft.Xna.Framework.Media; namespace Health { /// <summary> /// This is the main type for your game /// </summary> public class Game1 : Microsoft.Xna.Framework.Game { GraphicsDeviceManager graphics; SpriteBatch spriteBatch; Texture2D healthBar; int currentHealth = 100; float seconds; public Game1() { graphics = new GraphicsDeviceManager(this); Content.RootDirectory = "Content"; } /// <summary> /// Allows the game to perform any initialization it needs to before starting to run. /// This is where it can query for any required services and load any non-graphic /// related content. Calling base.Initialize will enumerate through any components /// and initialize them as well. /// </summary> protected override void Initialize() { // TODO: Add your initialization logic here base.Initialize(); } /// <summary> /// LoadContent will be called once per game and is the place to load /// all of your content. /// </summary> protected override void LoadContent() { // Create a new SpriteBatch, which can be used to draw textures. spriteBatch = new SpriteBatch(GraphicsDevice); healthBar = Content.Load<Texture2D>("HealthBar"); // TODO: use this.Content to load your game content here } /// <summary> /// UnloadContent will be called once per game and is the place to unload /// all content. /// </summary> protected override void UnloadContent() { // TODO: Unload any non ContentManager content here } /// <summary> /// Allows the game to run logic such as updating the world, /// checking for collisions, gathering input, and playing audio. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Update(GameTime gameTime) { // Allows the game to exit if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed) this.Exit(); // TODO: Add your update logic here currentHealth = (int)MathHelper.Clamp(currentHealth, 0, 100); seconds += (float)gameTime.ElapsedGameTime.TotalSeconds; if (seconds >= 1) { currentHealth -= 1; } seconds = 0; base.Update(gameTime); } /// <summary> /// This is called when the game should draw itself. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Draw(GameTime gameTime) { GraphicsDevice.Clear(Color.CornflowerBlue); spriteBatch.Begin(); spriteBatch.Draw(healthBar, new Rectangle(this.Window.ClientBounds.Width / 2 - healthBar.Width / 2, 30, healthBar.Width, 44), new Rectangle(0, 45, healthBar.Width, 44), Color.Gray); spriteBatch.Draw(healthBar, new Rectangle(this.Window.ClientBounds.Width / 2 - healthBar.Width / 2, 30, (int)(healthBar.Width * ((double)currentHealth / 100)), 44), new Rectangle(0, 45, healthBar.Width, 44), Color.Red); spriteBatch.Draw(healthBar, new Rectangle(this.Window.ClientBounds.Width / 2 - healthBar.Width / 2, 30, healthBar.Width, 44), new Rectangle(0, 0, healthBar.Width, 44), Color.White); spriteBatch.End(); base.Draw(gameTime); } } } Cheers!

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• C#/.NET Little Wonders: The ConcurrentDictionary

  - by James Michael Hare

  Once again we consider some of the lesser known classes and keywords of C#.  In this series of posts, we will discuss how the concurrent collections have been developed to help alleviate these multi-threading concerns.  Last week’s post began with a general introduction and discussed the ConcurrentStack<T> and ConcurrentQueue<T>.  Today's post discusses the ConcurrentDictionary<T> (originally I had intended to discuss ConcurrentBag this week as well, but ConcurrentDictionary had enough information to create a very full post on its own!).  Finally next week, we shall close with a discussion of the ConcurrentBag<T> and BlockingCollection<T>. For more of the "Little Wonders" posts, see the index here. Recap As you'll recall from the previous post, the original collections were object-based containers that accomplished synchronization through a Synchronized member.  While these were convenient because you didn't have to worry about writing your own synchronization logic, they were a bit too finely grained and if you needed to perform multiple operations under one lock, the automatic synchronization didn't buy much. With the advent of .NET 2.0, the original collections were succeeded by the generic collections which are fully type-safe, but eschew automatic synchronization.  This cuts both ways in that you have a lot more control as a developer over when and how fine-grained you want to synchronize, but on the other hand if you just want simple synchronization it creates more work. With .NET 4.0, we get the best of both worlds in generic collections.  A new breed of collections was born called the concurrent collections in the System.Collections.Concurrent namespace.  These amazing collections are fine-tuned to have best overall performance for situations requiring concurrent access.  They are not meant to replace the generic collections, but to simply be an alternative to creating your own locking mechanisms. Among those concurrent collections were the ConcurrentStack<T> and ConcurrentQueue<T> which provide classic LIFO and FIFO collections with a concurrent twist.  As we saw, some of the traditional methods that required calls to be made in a certain order (like checking for not IsEmpty before calling Pop()) were replaced in favor of an umbrella operation that combined both under one lock (like TryPop()). Now, let's take a look at the next in our series of concurrent collections!For some excellent information on the performance of the concurrent collections and how they perform compared to a traditional brute-force locking strategy, see this wonderful whitepaper by the Microsoft Parallel Computing Platform team here. ConcurrentDictionary – the fully thread-safe dictionary The ConcurrentDictionary<TKey,TValue> is the thread-safe counterpart to the generic Dictionary<TKey, TValue> collection.  Obviously, both are designed for quick – O(1) – lookups of data based on a key.  If you think of algorithms where you need lightning fast lookups of data and don’t care whether the data is maintained in any particular ordering or not, the unsorted dictionaries are generally the best way to go. Note: as a side note, there are sorted implementations of IDictionary, namely SortedDictionary and SortedList which are stored as an ordered tree and a ordered list respectively.  While these are not as fast as the non-sorted dictionaries – they are O(log2 n) – they are a great combination of both speed and ordering -- and still greatly outperform a linear search. Now, once again keep in mind that if all you need to do is load a collection once and then allow multi-threaded reading you do not need any locking.  Examples of this tend to be situations where you load a lookup or translation table once at program start, then keep it in memory for read-only reference.  In such cases locking is completely non-productive. However, most of the time when we need a concurrent dictionary we are interleaving both reads and updates.  This is where the ConcurrentDictionary really shines!  It achieves its thread-safety with no common lock to improve efficiency.  It actually uses a series of locks to provide concurrent updates, and has lockless reads!  This means that the ConcurrentDictionary gets even more efficient the higher the ratio of reads-to-writes you have. ConcurrentDictionary and Dictionary differences For the most part, the ConcurrentDictionary<TKey,TValue> behaves like it’s Dictionary<TKey,TValue> counterpart with a few differences.  Some notable examples of which are: Add() does not exist in the concurrent dictionary. This means you must use TryAdd(), AddOrUpdate(), or GetOrAdd().  It also means that you can’t use a collection initializer with the concurrent dictionary. TryAdd() replaced Add() to attempt atomic, safe adds. Because Add() only succeeds if the item doesn’t already exist, we need an atomic operation to check if the item exists, and if not add it while still under an atomic lock. TryUpdate() was added to attempt atomic, safe updates. If we want to update an item, we must make sure it exists first and that the original value is what we expected it to be.  If all these are true, we can update the item under one atomic step. TryRemove() was added to attempt atomic, safe removes. To safely attempt to remove a value we need to see if the key exists first, this checks for existence and removes under an atomic lock. AddOrUpdate() was added to attempt an thread-safe “upsert”. There are many times where you want to insert into a dictionary if the key doesn’t exist, or update the value if it does.  This allows you to make a thread-safe add-or-update. GetOrAdd() was added to attempt an thread-safe query/insert. Sometimes, you want to query for whether an item exists in the cache, and if it doesn’t insert a starting value for it.  This allows you to get the value if it exists and insert if not. Count, Keys, Values properties take a snapshot of the dictionary. Accessing these properties may interfere with add and update performance and should be used with caution. ToArray() returns a static snapshot of the dictionary. That is, the dictionary is locked, and then copied to an array as a O(n) operation.  GetEnumerator() is thread-safe and efficient, but allows dirty reads. Because reads require no locking, you can safely iterate over the contents of the dictionary.  The only downside is that, depending on timing, you may get dirty reads. Dirty reads during iteration The last point on GetEnumerator() bears some explanation.  Picture a scenario in which you call GetEnumerator() (or iterate using a foreach, etc.) and then, during that iteration the dictionary gets updated.  This may not sound like a big deal, but it can lead to inconsistent results if used incorrectly.  The problem is that items you already iterated over that are updated a split second after don’t show the update, but items that you iterate over that were updated a split second before do show the update.  Thus you may get a combination of items that are “stale” because you iterated before the update, and “fresh” because they were updated after GetEnumerator() but before the iteration reached them. Let’s illustrate with an example, let’s say you load up a concurrent dictionary like this: 1: // load up a dictionary. 2: var dictionary = new ConcurrentDictionary<string, int>(); 3:  4: dictionary["A"] = 1; 5: dictionary["B"] = 2; 6: dictionary["C"] = 3; 7: dictionary["D"] = 4; 8: dictionary["E"] = 5; 9: dictionary["F"] = 6; Then you have one task (using the wonderful TPL!) to iterate using dirty reads: 1: // attempt iteration in a separate thread 2: var iterationTask = new Task(() => 3: { 4: // iterates using a dirty read 5: foreach (var pair in dictionary) 6: { 7: Console.WriteLine(pair.Key + ":" + pair.Value); 8: } 9: }); And one task to attempt updates in a separate thread (probably): 1: // attempt updates in a separate thread 2: var updateTask = new Task(() => 3: { 4: // iterates, and updates the value by one 5: foreach (var pair in dictionary) 6: { 7: dictionary[pair.Key] = pair.Value + 1; 8: } 9: }); Now that we’ve done this, we can fire up both tasks and wait for them to complete: 1: // start both tasks 2: updateTask.Start(); 3: iterationTask.Start(); 4:  5: // wait for both to complete. 6: Task.WaitAll(updateTask, iterationTask); Now, if I you didn’t know about the dirty reads, you may have expected to see the iteration before the updates (such as A:1, B:2, C:3, D:4, E:5, F:6).  However, because the reads are dirty, we will quite possibly get a combination of some updated, some original.  My own run netted this result: 1: F:6 2: E:6 3: D:5 4: C:4 5: B:3 6: A:2 Note that, of course, iteration is not in order because ConcurrentDictionary, like Dictionary, is unordered.  Also note that both E and F show the value 6.  This is because the output task reached F before the update, but the updates for the rest of the items occurred before their output (probably because console output is very slow, comparatively). If we want to always guarantee that we will get a consistent snapshot to iterate over (that is, at the point we ask for it we see precisely what is in the dictionary and no subsequent updates during iteration), we should iterate over a call to ToArray() instead: 1: // attempt iteration in a separate thread 2: var iterationTask = new Task(() => 3: { 4: // iterates using a dirty read 5: foreach (var pair in dictionary.ToArray()) 6: { 7: Console.WriteLine(pair.Key + ":" + pair.Value); 8: } 9: }); The atomic Try…() methods As you can imagine TryAdd() and TryRemove() have few surprises.  Both first check the existence of the item to determine if it can be added or removed based on whether or not the key currently exists in the dictionary: 1: // try add attempts an add and returns false if it already exists 2: if (dictionary.TryAdd("G", 7)) 3: Console.WriteLine("G did not exist, now inserted with 7"); 4: else 5: Console.WriteLine("G already existed, insert failed."); TryRemove() also has the virtue of returning the value portion of the removed entry matching the given key: 1: // attempt to remove the value, if it exists it is removed and the original is returned 2: int removedValue; 3: if (dictionary.TryRemove("C", out removedValue)) 4: Console.WriteLine("Removed C and its value was " + removedValue); 5: else 6: Console.WriteLine("C did not exist, remove failed."); Now TryUpdate() is an interesting creature.  You might think from it’s name that TryUpdate() first checks for an item’s existence, and then updates if the item exists, otherwise it returns false.  Well, note quite... It turns out when you call TryUpdate() on a concurrent dictionary, you pass it not only the new value you want it to have, but also the value you expected it to have before the update.  If the item exists in the dictionary, and it has the value you expected, it will update it to the new value atomically and return true.  If the item is not in the dictionary or does not have the value you expected, it is not modified and false is returned. 1: // attempt to update the value, if it exists and if it has the expected original value 2: if (dictionary.TryUpdate("G", 42, 7)) 3: Console.WriteLine("G existed and was 7, now it's 42."); 4: else 5: Console.WriteLine("G either didn't exist, or wasn't 7."); The composite Add methods The ConcurrentDictionary also has composite add methods that can be used to perform updates and gets, with an add if the item is not existing at the time of the update or get. The first of these, AddOrUpdate(), allows you to add a new item to the dictionary if it doesn’t exist, or update the existing item if it does.  For example, let’s say you are creating a dictionary of counts of stock ticker symbols you’ve subscribed to from a market data feed: 1: public sealed class SubscriptionManager 2: { 3: private readonly ConcurrentDictionary<string, int> _subscriptions = new ConcurrentDictionary<string, int>(); 4:  5: // adds a new subscription, or increments the count of the existing one. 6: public void AddSubscription(string tickerKey) 7: { 8: // add a new subscription with count of 1, or update existing count by 1 if exists 9: var resultCount = _subscriptions.AddOrUpdate(tickerKey, 1, (symbol, count) => count + 1); 10:  11: // now check the result to see if we just incremented the count, or inserted first count 12: if (resultCount == 1) 13: { 14: // subscribe to symbol... 15: } 16: } 17: } Notice the update value factory Func delegate.  If the key does not exist in the dictionary, the add value is used (in this case 1 representing the first subscription for this symbol), but if the key already exists, it passes the key and current value to the update delegate which computes the new value to be stored in the dictionary.  The return result of this operation is the value used (in our case: 1 if added, existing value + 1 if updated). Likewise, the GetOrAdd() allows you to attempt to retrieve a value from the dictionary, and if the value does not currently exist in the dictionary it will insert a value.  This can be handy in cases where perhaps you wish to cache data, and thus you would query the cache to see if the item exists, and if it doesn’t you would put the item into the cache for the first time: 1: public sealed class PriceCache 2: { 3: private readonly ConcurrentDictionary<string, double> _cache = new ConcurrentDictionary<string, double>(); 4:  5: // adds a new subscription, or increments the count of the existing one. 6: public double QueryPrice(string tickerKey) 7: { 8: // check for the price in the cache, if it doesn't exist it will call the delegate to create value. 9: return _cache.GetOrAdd(tickerKey, symbol => GetCurrentPrice(symbol)); 10: } 11:  12: private double GetCurrentPrice(string tickerKey) 13: { 14: // do code to calculate actual true price. 15: } 16: } There are other variations of these two methods which vary whether a value is provided or a factory delegate, but otherwise they work much the same. Oddities with the composite Add methods The AddOrUpdate() and GetOrAdd() methods are totally thread-safe, on this you may rely, but they are not atomic.  It is important to note that the methods that use delegates execute those delegates outside of the lock.  This was done intentionally so that a user delegate (of which the ConcurrentDictionary has no control of course) does not take too long and lock out other threads. This is not necessarily an issue, per se, but it is something you must consider in your design.  The main thing to consider is that your delegate may get called to generate an item, but that item may not be the one returned!  Consider this scenario: A calls GetOrAdd and sees that the key does not currently exist, so it calls the delegate.  Now thread B also calls GetOrAdd and also sees that the key does not currently exist, and for whatever reason in this race condition it’s delegate completes first and it adds its new value to the dictionary.  Now A is done and goes to get the lock, and now sees that the item now exists.  In this case even though it called the delegate to create the item, it will pitch it because an item arrived between the time it attempted to create one and it attempted to add it. Let’s illustrate, assume this totally contrived example program which has a dictionary of char to int.  And in this dictionary we want to store a char and it’s ordinal (that is, A = 1, B = 2, etc).  So for our value generator, we will simply increment the previous value in a thread-safe way (perhaps using Interlocked): 1: public static class Program 2: { 3: private static int _nextNumber = 0; 4:  5: // the holder of the char to ordinal 6: private static ConcurrentDictionary<char, int> _dictionary 7: = new ConcurrentDictionary<char, int>(); 8:  9: // get the next id value 10: public static int NextId 11: { 12: get { return Interlocked.Increment(ref _nextNumber); } 13: } Then, we add a method that will perform our insert: 1: public static void Inserter() 2: { 3: for (int i = 0; i < 26; i++) 4: { 5: _dictionary.GetOrAdd((char)('A' + i), key => NextId); 6: } 7: } Finally, we run our test by starting two tasks to do this work and get the results… 1: public static void Main() 2: { 3: // 3 tasks attempting to get/insert 4: var tasks = new List<Task> 5: { 6: new Task(Inserter), 7: new Task(Inserter) 8: }; 9:  10: tasks.ForEach(t => t.Start()); 11: Task.WaitAll(tasks.ToArray()); 12:  13: foreach (var pair in _dictionary.OrderBy(p => p.Key)) 14: { 15: Console.WriteLine(pair.Key + ":" + pair.Value); 16: } 17: } If you run this with only one task, you get the expected A:1, B:2, ..., Z:26.  But running this in parallel you will get something a bit more complex.  My run netted these results: 1: A:1 2: B:3 3: C:4 4: D:5 5: E:6 6: F:7 7: G:8 8: H:9 9: I:10 10: J:11 11: K:12 12: L:13 13: M:14 14: N:15 15: O:16 16: P:17 17: Q:18 18: R:19 19: S:20 20: T:21 21: U:22 22: V:23 23: W:24 24: X:25 25: Y:26 26: Z:27 Notice that B is 3?  This is most likely because both threads attempted to call GetOrAdd() at roughly the same time and both saw that B did not exist, thus they both called the generator and one thread got back 2 and the other got back 3.  However, only one of those threads can get the lock at a time for the actual insert, and thus the one that generated the 3 won and the 3 was inserted and the 2 got discarded.  This is why on these methods your factory delegates should be careful not to have any logic that would be unsafe if the value they generate will be pitched in favor of another item generated at roughly the same time.  As such, it is probably a good idea to keep those generators as stateless as possible. Summary The ConcurrentDictionary is a very efficient and thread-safe version of the Dictionary generic collection.  It has all the benefits of type-safety that it’s generic collection counterpart does, and in addition is extremely efficient especially when there are more reads than writes concurrently. Tweet Technorati Tags: C#, .NET, Concurrent Collections, Collections, Little Wonders, Black Rabbit Coder,James Michael Hare

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• Did anyone experience negative SERP movement after implementing rel=author?

  - by raam86

  I am not intrested in why I don't see the picture in SERPs. So I know this is borderline off-limits but I turned every stone in the web (including DDgo) trying to find anybody experiencing a worse position in SERPs after implementing rel=author tags. In Google Webmaster Tools: Everything seems fine but the first results dropped 14 places in SERPs in the past two days. The original landing page went down from first page to 5th page in a few days. It is a useful site with original content concerning marriage laws. This specific page is no where to be found and now the first result leads to the home page. Assuming everything else is the same with no changes made to the site at all is there a reason the rel=author tag will cause such a plummet? Additional info that might be useful: The google+ account is as dead as a palm pilot.

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• SQL SERVER – Beginning New Weekly Series – Memory Lane – #002

  - by pinaldave

  Here is the list of curetted articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2006 Query to Find ByteSize of All the Tables in Database This was my second blog post and today I do not remember what was the business need which has made me build this query. It was built for SQL Server 2000 and it will not directly run on SQL Server 2005 or later version now. It measured the byte size of the tables in the database. This can be done in many different ways as well for example SP_HELPDB as well SP_HELP. I wish to build similar script in 2005 and later version. 2007 This week I had completed my – 1 Year (365 blogs) and very first 1 Million Views. I was pretty excited at that time with this new achievement. SQL SERVER Versions, CodeNames, Year of Release When I started with SQL Server I did not know all the names correctly for each version and I often used to get confused with this. However, as time passed by I started to remember all the codename as well. In this blog post I have not included SQL Server 2012′s code name as it was not released at the time. SQL Server 2012′s code name is Denali. Here is the question for you – anyone know what is the internal name of the SQL Server’s next version? Searching String in Stored Procedure I have already started to work with 2005 by this time and I was personally converting each of my stored procedures to SQL Server 2005 compatible. As we were upgrading from SQL Server 2000 to SQL Server 2005 we had to search each of the stored procedures and make sure that we remove incompatible code from it. For example, syscolumns of SQL Server 2000 was now being replaced by sys.columns of SQL Server 2005. This stored procedure was pretty helpful at that time. Later on I build few additional versions of the same stored procedure. Version 1: This version finds the Stored Procedures related to Table Version 2: This is specific version which works with SQL Server 2005 and later version 2008 Clear Drop Down List of Recent Connection From SQL Server Management Studio It happens to all of us when we connected to some remote client server and we never ever have to connect to it again. However, it keeps on bothering us that the name shows up in the list all the time. In this blog post I covered a quick tip about how we can remove the same. I also wrote a small article about How to Check Database Integrity for all Databases and there was a funny question from a reader requesting T-SQL code to refresh databases. 2009 Stored Procedure are Compiled on First Run – SP is taking Longer to Run First Time A myth is quite prevailing in the industry that Stored Procedures are pre-compiled and they should always run faster. It is not true. Stored procedures are compiled on very first execution of it and that is the reason why it takes longer when it executes first time. In this blog post I had a great time discussing the same concept. If you do not agree with it, you are welcome to read this blog post. Removing Key Lookup – Seek Predicate – Predicate – An Interesting Observation Related to Datatypes Performance Tuning is an interesting concept and my personal favorite one. In many blog posts I have described how to do performance tuning and how to improve the performance of the queries. In this quick quick tip I have explained how one can remove the Key Lookup and improve performance. Here are very relevant articles on this subject: Article 1 | Article 2 | Article 3 2010 Recycle Error Log – Create New Log file without a Server Restart During one of the consulting assignments I noticed DBA restarting server to create new log file. This is absolutely not necessary and restarting server might have many other negative impacts. There is a common sp_cycle_errorlog which can do the same task efficiently and properly. Have you ever used this SP or feature? Additionally I had a great time presenting on SQL Server Best Practices in SharePoint Conference. 2011 SSMS 2012 Reset Keyboard Shortcuts to Default It is very much possible that we mix up various SQL Server shortcuts and at times we feel like resetting it to default. In SQL Server 2012 it is not easy to do it, there is a process to follow and I enjoyed blogging about it. Fundamentals of Columnstore Index Columnstore index is introduced in SQL Server 2012 and have been a very popular subject. It increases the speed of the server dramatically as well can be an extremely useful feature with Datawharehousing. However updating the columnstore index is not as simple as a simple UPDATE statement. Read in a detailed blog post about how Update works with Columnstore Index. Additionally, you can watch a Quick Video on this subject. SQL Server 2012 New Features I had decided to explore SQL Server 2012 features last year and went through pretty much every single concept introduced in separate blog posts. Here are two blog posts where I describe how SQL Server 2012 functions works. Introduction to CUME_DIST – Analytic Functions Introduction to FIRST _VALUE and LAST_VALUE – Analytic Functions OVER clause with FIRST_VALUE and LAST_VALUE – Analytic Functions I indeed enjoyed writing about SQL Server 2012 functions last year. Have you gone through all the new features which are introduced in SQL Server 2012? If not, it is still not late to go through them. Reference: Pinal Dave (http://blog.sqlauthority.com)   Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Trying to format drive fails

  - by david

  since I will be doing an internship for which i need to use Windows software, I have decided to ruin my day trying to remove my Ubuntu 12.04, install Win XP SP3 (since the DualBoot theme from ubuntu suggests to first install Windows and then Ubuntu, for problems with the bootloader if you do it the other way around) and then reinstall Ubuntu 12.04 since I would like to keep using it as my primary operating system, using WinXP exclusively for the internship. Other than that, I would like to have a partition for the data, which can be used by both Ubuntu and Windows. So now, I have used the disk utility run from an ubuntu-live cd to format my drive with Master Boot Record (being conscious of the fact that this way I will lose all my data, which I have saved on an external drive before, and that my Ubuntu won't work anymore afterwards), creating partitions for Windows (NTFS), personal data (FAT, since as far as I know both Ubuntu and Windows can deal with this), a Swap partition for Linux, and one partition for Ubuntu (ext4); trying to install Win XP from cd gives me a blue screen, which stops the setup and telling me to remove all recently installed drives and to run CHKDSK. So I thought, that maybe Windows doesn't like pre-partitioned drives for its installation and thus I need to re-format my hard drive in order to have a completely "new" drive, which I can then, during the Windows-installation, partition in order to create the partitions I need. Trying to do this, though, the disk-utility run from the live-CD gives me this warning: Error creating partition table: helper exited with exit code 1: In part_create_partition_table: device_file=/dev/sda, scheme=0 got it got disk committed to disk BLKRRPART ioctl failed for /dev/sda: Device or resource busy I do not understand why it tells me that the hard-drive is busy, because, as stated above, I am doing all this from a live-CD. Thus, my questions are: How can I resolve the error given by the disk utility? Does it make sense to use four partitions in the way mentioned above? And if not so, which partitions should I create? Can I, theoretically, partition my drive from an Ubuntu live-cd in order to create the partitions I want and to install first Windows and then Ubuntu? Thanks for any help, David

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• VHOST not working in Apache

  - by Starx

  I got a LAMP server working in Ubuntu 11.04. Now the problem is that the websites have to enabled and disabled from the terminal. All all of them have to be accessed from http://localhost which is not so much efficient. So I created a VHOSTS, using some tutorials off the net. Here is the coding for it <VirtualHost *:80> ServerAdmin webmaster@localhost Servername site.com ServerAlias www.site.com DocumentRoot /home/starx/public_html/site/public <Directory /> Options FollowSymLinks AllowOverride None </Directory> <Directory /home/starx/public_html/site/public> Options Indexes FollowSymLinks MultiViews AllowOverride None Order allow,deny allow from all </Directory> ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/ <Directory "/usr/lib/cgi-bin"> AllowOverride None Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch Order allow,deny Allow from all </Directory> nGen ErrorLog ${APACHE_LOG_DIR}/site-error.log # Possible values include: debug, info, notice, warn, error, crit, # alert, emerg. LogLevel warn CustomLog ${APACHE_LOG_DIR}/site-access.log combined Alias /doc/ "/usr/share/doc/" <Directory "/usr/share/doc/"> Options Indexes MultiViews FollowSymLinks AllowOverride None Order deny,allow Deny from all Allow from 127.0.0.0/255.0.0.0 ::1/128 </Directory> </VirtualHost> Now, still I can't access the page in http://site.com but if i access using http://localhsot/ it is accessed. I have disabled all others site including default and have just enabled one site i.e. site How to fix this?

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• Membership in ASP.Net applications - part 2

  - by nikolaosk

  This is the second post in a series of posts regarding ASP.Net built in membership functionality,providers,controls. You can read the first one post one here . In order to follow this post, complete the steps in the first post. It will only take 10 minutes or so. 1) Launch Visual Studio 2005,2008/2010. Express editions will work fine. I am using Visual Studio 2010 Ultimate edition. 2) Follow all the steps in the first post of the series. 3) Run your application to make sure it runs. 4) Change the...(read more)

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• convert image to spritesheet of tiles for isometric map?

  - by Paul

  is there a way to convert an isometric image (like the first image) to a spritesheet (like the second image), in order to place each image on the isometric map with the code? The map looks like the first image, but some buildings are bigger than just one tile, so I need several squares (let's say the first image is a building, made of multiple tiles with different colors), and each square is placed with an offset of 64x32. The building is created in Blender and I save the image with the isometric perspective. But I have to split each square from this image in order to have the spritesheet, maybe there is smarter way, or a java software that would make the conversion for me?

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• Ubuntu 12.04.2 Dual boot UEFI Windows 8 Preinstalled CX21903W Ultrabook

  - by user180782

  Hi i have a problem trying to install ubuntu. The machine is a CX Ultrabook model CX.21903W Intel I5 with 500GB hard disk, 8 GB ram and 32 GB SSD. From Installing Ubuntu on a Pre-Installed Windows 8 (64-bit) System (UEFI Supported), and according to the steps guide: 1 - We create a partition from Win8 (70 GB) from the own win8 program. 2 - Confirm-SecureBootUEFI=True. 3 - From Win8, shift + Restart and from special menu we selected the UEFI Firmware Setting. 4 - From BIOS Option: ------Option 1) Disable Secure Boot. ------Option 2) Disable UEFI (Not Available) from Option 1: Three ways is available. With Secure Boot enable - We can't even boot ubuntu. A red windows saying Soft unproper signed. With Secure Boot disable - and this config in boot device order: ----1: UEFI: USB ----2: Windows Boot Manger ----3: Others and CSM (Compatibility Support Module): enable - GRUB appears and selecting try Ubuntu then a black windows appears and nothing happens. The same result if install ubuntu is selected. With Secure Boot disable - and this config in boot device order: ----1: USB (No UEFI) ----2: Windows Boot Manger ----3: Others and CSM (Compatibility Support Module): enable - GRUB appears and selecting try Ubuntu, - Ubuntu boots and we can install it even. 5 - Rebooting and just changing the boot order as ----1: Ubuntu [] ----2: Windows Boot Manger ----3: Others then nothings happens. 6 - Booting from LiveUSB again and, as per instructed, making Boot-Repair (A warning windows: Ubuntu is working in legacy mode.). 7 - Saving changes and rebooting, Grub works but selecting Ubuntu, a black windows appears and nothing happens. Selecting Win8, Win8 boots and works. Untill now we can't make the ubuntu installation. Any suggestion will be welcomed. kind regards and thanks in advance.

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