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• Master Note for Generic Data Warehousing

  - by lajos.varady(at)oracle.com

  ++++++++++++++++++++++++++++++++++++++++++++++++++++ The complete and the most recent version of this article can be viewed from My Oracle Support Knowledge Section. Master Note for Generic Data Warehousing [ID 1269175.1] ++++++++++++++++++++++++++++++++++++++++++++++++++++In this Document   Purpose   Master Note for Generic Data Warehousing      Components covered      Oracle Database Data Warehousing specific documents for recent versions      Technology Network Product Homes      Master Notes available in My Oracle Support      White Papers      Technical Presentations Platforms: 1-914CU; This document is being delivered to you via Oracle Support's Rapid Visibility (RaV) process and therefore has not been subject to an independent technical review. Applies to: Oracle Server - Enterprise Edition - Version: 9.2.0.1 to 11.2.0.2 - Release: 9.2 to 11.2Information in this document applies to any platform. Purpose Provide navigation path Master Note for Generic Data Warehousing Components covered Read Only Materialized ViewsQuery RewriteDatabase Object PartitioningParallel Execution and Parallel QueryDatabase CompressionTransportable TablespacesOracle Online Analytical Processing (OLAP)Oracle Data MiningOracle Database Data Warehousing specific documents for recent versions 11g Release 2 (11.2)11g Release 1 (11.1)10g Release 2 (10.2)10g Release 1 (10.1)9i Release 2 (9.2)9i Release 1 (9.0)Technology Network Product HomesOracle Partitioning Advanced CompressionOracle Data MiningOracle OLAPMaster Notes available in My Oracle SupportThese technical articles have been written by Oracle Support Engineers to provide proactive and top level information and knowledge about the components of thedatabase we handle under the "Database Datawarehousing".Note 1166564.1 Master Note: Transportable Tablespaces (TTS) -- Common Questions and IssuesNote 1087507.1 Master Note for MVIEW 'ORA-' error diagnosis. For Materialized View CREATE or REFRESHNote 1102801.1 Master Note: How to Get a 10046 trace for a Parallel QueryNote 1097154.1 Master Note Parallel Execution Wait Events Note 1107593.1 Master Note for the Oracle OLAP OptionNote 1087643.1 Master Note for Oracle Data MiningNote 1215173.1 Master Note for Query RewriteNote 1223705.1 Master Note for OLTP Compression Note 1269175.1 Master Note for Generic Data WarehousingWhite Papers Transportable Tablespaces white papers Database Upgrade Using Transportable Tablespaces:Oracle Database 11g Release 1 (February 2009) Platform Migration Using Transportable Database Oracle Database 11g and 10g Release 2 (August 2008) Database Upgrade using Transportable Tablespaces: Oracle Database 10g Release 2 (April 2007) Platform Migration using Transportable Tablespaces: Oracle Database 10g Release 2 (April 2007)Parallel Execution and Parallel Query white papers Best Practices for Workload Management of a Data Warehouse on the Sun Oracle Database Machine (June 2010) Effective resource utilization by In-Memory Parallel Execution in Oracle Real Application Clusters 11g Release 2 (Feb 2010) Parallel Execution Fundamentals in Oracle Database 11g Release 2 (November 2009) Parallel Execution with Oracle Database 10g Release 2 (June 2005)Oracle Data Mining white paper Oracle Data Mining 11g Release 2 (March 2010)Partitioning white papers Partitioning with Oracle Database 11g Release 2 (September 2009) Partitioning in Oracle Database 11g (June 2007)Materialized Views and Query Rewrite white papers Oracle Materialized Views  and Query Rewrite (May 2005) Improving Performance using Query Rewrite in Oracle Database 10g (December 2003)Database Compression white papers Advanced Compression with Oracle Database 11g Release 2 (September 2009) Table Compression in Oracle Database 10g Release 2 (May 2005)Oracle OLAP white papers On-line Analytic Processing with Oracle Database 11g Release 2 (September 2009) Using Oracle Business Intelligence Enterprise Edition with the OLAP Option to Oracle Database 11g (July 2008)Generic white papers Enabling Pervasive BI through a Practical Data Warehouse Reference Architecture (February 2010) Optimizing and Protecting Storage with Oracle Database 11g Release 2 (November 2009) Oracle Database 11g for Data Warehousing and Business Intelligence (August 2009) Best practices for a Data Warehouse on Oracle Database 11g (September 2008)Technical PresentationsA selection of ObE - Oracle by Examples documents: Generic Using Basic Database Functionality for Data Warehousing (10g) Partitioning Manipulating Partitions in Oracle Database (11g Release 1) Using High-Speed Data Loading and Rolling Window Operations with Partitioning (11g Release 1) Using Partitioned Outer Join to Fill Gaps in Sparse Data (10g) Materialized View and Query Rewrite Using Materialized Views and Query Rewrite Capabilities (10g) Using the SQLAccess Advisor to Recommend Materialized Views and Indexes (10g) Oracle OLAP Using Microsoft Excel With Oracle 11g Cubes (how to analyze data in Oracle OLAP Cubes using Excel's native capabilities) Using Oracle OLAP 11g With Oracle BI Enterprise Edition (Creating OBIEE Metadata for OLAP 11g Cubes and querying those in BI Answers) Building OLAP 11g Cubes Querying OLAP 11g Cubes Creating Interactive APEX Reports Over OLAP 11g CubesSelection of presentations from the BIWA website:Extreme Data Warehousing With Exadata  by Hermann Baer (July 2010) (slides 2.5MB, recording 54MB)Data Mining Made Easy! Introducing Oracle Data Miner 11g Release 2 New "Work flow" GUI   by Charlie Berger (May 2010) (slides 4.8MB, recording 85MB )Best Practices for Deploying a Data Warehouse on Oracle Database 11g  by Maria Colgan (December 2009)  (slides 3MB, recording 18MB, white paper 3MB )

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• Multiple calls to different page methods in same web page are not running in parallel (JQuery/Ajax/A

  - by Tony_Henrich

  I have several page methods defined in the code behind of an aspx page. I have several JS calls (see example below), one after the other, in the ready() method of JQuery to call these page methods. I noticed the javascript calls run asynchronously but the .NET page methods do not run in parallel. Page method 1 finishes first before page method 2 runs. Is there a way to get all the page methods to run all at the same time? My workaround is to put each method in its own aspx page or use iframes but I am looking for better solutions. $.ajax({ type: "POST", url: (page/methodname), data: "{}", contentType: "application/json; charset=utf-8", dataType: "json", success: function(msg) { .... } } });

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• Is it possible to tell IIS 7 to process the request queue in parallel?

  - by Uwe Keim

  Currently we are developing an ASMX, ASP 2.0, IIS 7 web service that does some calculations (and return a dynamically generated document) and will take approx. 60 seconds to run. Since whe have a big machine with multiple cores and lots of RAM, I expected that IIS tries its best to route the requests that arrive in its requests queue to all available threads of the app pool's thread pool. But we experience quiet the opposite: When we issue requests to the ASMX web service URL from multiple different clients, the IIS seems to serially process these requests. I.e. request 1 arrives, is being processed, then request 2 is being processed, then request 3, etc. Question: Is it possible (without changing the C# code of the web service) to configure IIS to process requests in parallel, if enough threads are available? If yes: how should I do it? It no: any workarounds/tips? Thanks Uwe

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• How can I run NUnit(Selenium Grid) tests in parallel?

  - by Benjamin Lee

  My current project uses NUnit for unit tests and to drive UATs written with Selenium. Developers normally run tests using ReSharper's test runner in VS.Net 2003 and our build box kicks them off via NAnt. We would like to run the UAT tests in parallel so that we can take advantage of Selenium Grid/RCs so that they will be able to run much faster. Does anyone have any thoughts on how this might be achieved? and/or best practices for testing Selenium tests against multiple browsers environments without writing duplicate tests automatically? Thank you.

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• facing outsourced wages, can i still eat and survive as a computing science major ?

  - by wefwgeweg

  offshore outsourced programmers charge fraction of what costs a North American developer. should I still pursue my major as computing science ? Why would companies spend more on North American/local developers where they can get the same quality if not better job done offshore ? I am just concerned for the development labor market, the free market wants the lowest cost provider. not just programming but many high skilled labor such as engineering, scientists, artists and etc. perhaps i should become a lawyer ?

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• Right way to have a thread in parallel to django project on wsgi.

  - by Enrico Carlesso

  Hi guys. I'm writing a django project, and I need to have a parallel thread which performs certain tasks. The project will be deployed in Apache2.2 with mod_wsgi. Actually my implementation consists on a thread with a while True - Sleep which is called from my django.wsgi file. Is this implementation correct? Two problems raises: does django.wsgi get called only once? Will I have just that instance of the thread running? And second, I need to "manually" visit at least a page to have the Thread run. Is there a workaround? Does anyone has some hints on better solutions? Thanks in advance.

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• Is Python appropriate for algorithms focused on scientific computing?

  - by gmatt

  My interests in programming lie mainly in algorithms, and lately I have seen many reputable researchers write a lot of their code in python. How easy and convenient is python for scientific computing? Does it have a library of algorithms that compares to matlab's? Is Python a scripting language or does it compile? Is it a great language for prototyping an algorithm? How long would it take me to learn enough of it to be productive provided I know C well and OO programming somewhat? Is it OO based? Sorry for the condensed format of questions, but I'm very curious and was hoping a more experienced programmer could help me out.

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• How to handle all unhandled exceptions when using Task Parallel Library?

  - by Buu Nguyen

  I'm using the TPL (Task Parallel Library) in .NET 4.0. I want to be able to centralize the handling logic of all unhandled exceptions by using the Thread.GetDomain().UnhandledException event. However, in my application, the event is never fired for threads started with TPL code, e.g. Task.Factory.StartNew(...). The event is indeed fired if I use something like new Thread(threadStart).Start(). This MSDN article suggests to use Task#Wait() to catch the AggregateException when working with TPL, but that is not I want because it is not "centralized" enough a mechanism. Does anyone experience same problem at all or is it just me? Do you have any solution for this?

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• What Use are Threads Outside of Parallel Problems on MultiCore Systesm?

  - by Robert S. Barnes

  Threads make the design, implementation and debugging of a program significantly more difficult. Yet many people seem to think that every task in a program that can be threaded should be threaded, even on a single core system. I can understand threading something like an MPEG2 decoder that's going to run on a multicore cpu ( which I've done ), but what can justify the significant development costs threading entails when you're talking about a single core system or even a multicore system if your task doesn't gain significant performance from a parallel implementation? Or more succinctly, what kinds of non-performance related problems justify threading? Edit Well I just ran across one instance that's not CPU limited but threads make a big difference: TCP, HTTP and the Multi-Threading Sweet Spot Multiple threads are pretty useful when trying to max out your bandwidth to another peer over a high latency network connection. Non-blocking I/O would use significantly less local CPU resources, but would be much more difficult to design and implement.

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• SQL Server (TSQL) - Is it possible to EXEC statements in parallel?

  - by Investor5555

  SQL Server 2008 R2 Here is a simplified example: EXECUTE sp_executesql N'PRINT ''1st '' + convert(varchar, getdate(), 126) WAITFOR DELAY ''000:00:10''' EXECUTE sp_executesql N'PRINT ''2nd '' + convert(varchar, getdate(), 126)' The first statement will print the date and delay 10 seconds before proceeding. The second statement should print immediately. The way T-SQL works, the 2nd statement won't be evaluated until the first completes. If I copy and paste it to a new query window, it will execute immediately. The issue is that I have other, more complex things going on, with variables that need to be passed to both procedures. What I am trying to do is: Get a record Lock it for a period of time while it is locked, execute some other statements against this record and the table itself Perhaps there is a way to dynamically create a couple of jobs? Anyway, I am looking for a simple way to do this without having to manually PRINT statements and copy/paste to another session. Is there a way to EXEC without wait / in parallel?

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• Noob question: Draw a quad parallel to the view.

  - by Jack

  Hi all, ok what I want to do is to draw a quad in the scene that lays on a plane parallel to the view. So it should appear flat. More in particular, I think I didn't get very well how the mechanism of gluLookAt works in comparison with the functions glTranslate and glRotate: If I position the view "manually" using the functions glTranslate and glRotate whenever I draw an object its position is relative to the current view. And I understand that this is due to the transformation matrix in the stack. However when I use the gluLookAt that should automatically set the view, the coordinates of the object I want to draw must be "absolute" to show it properly. Thanks in advance.

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• Multithreading - are the multi-core processors really doing parallel processing?

  - by so.very.tired

  Are the modern multi-core processors really doing parallel processing? Like, take for example, Intel's core i7 processors. some of them has #of Cores: 4 and #of Threads: 8 (taken from Intel's specifications pages). If I to write a program (say in Java or C) that has multiple threads of execution, will they really be processed concurrently? My instructor said that "it is not always the case with multi-core processors", but didn't gave to much details. And why do Intel have to specify both #of Cores and #of Threads? Isn't thread just a term that describe a program-related abstraction, unlike "cores" which are actual hardware? ("Every thread runs on different core").

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• How Can I Configure Selenium grid to test website in parallel?

  - by prakash.panjwani

  Hello Friends, I want to use selenium grid for my web page testing. I have successfully installed the demo of selenium grid on my PC and it is running fine. I have followed this link to install and run the selenium grid demo. I am trying to code a java program using selenium rc which can run with selenium grid for testing the web site, but I am not getting how does I make change on the selenium grid existing demo so that it will work for my web test. Can some body provide me any link/example so that I will do that?

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• What's the weirdest thing you've ever seen a non-techie do to a computing device?

  - by googletorp

  I thought it would be fun to bring out the stories on what people have done throughout the ages with computers due to their sometimes, to put it politely, less than perfect grasp of technology. I'll start out with a little story from my high-school days. After graduation, a classmate of mine, who took IT and subsequently scored an A in the subject, was sent an e-mail by a friend. She replied to his mail: "I'm sorry, but I can't reply your mail, since I don't have your email address." Till this day I still can't understand why she gave such a weird reply as she was a bright girl although not a techie. Now, let's hear those other battle stories from the real world...

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• parallel vms in VMWare Server - how to configure network so they can ping each other?

  - by IronGoofy

  I'm using VMWare Server (currently on Version 1.0.7) and have two VMs that I would like to run at the same time. However, I'm having problems in setting them up so they can ping each other. I've configured them to use 'Bridged' networking. They both obtain an IP address from the DHCP server on my network, but after that they can't ping each other. It seems that only the first one has a functioning network connection (I can ping it from the host machine and Internet connection works), but the other one does not. If it helps, both VMs are running XP SP 3. Any ideas? Thanks!

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• Are Uninterruptible Power Supply (UPS) at home really a worthwhile investment for home computing? [c

  - by Jian Lin

  Possible Duplicate: Is a UPS a good investment for a home machine? I have 2 Uninterruptible power supplies at home, but they seem to expire after 5 years or so. During this 5 years, it maybe saved the computer from turning off twice. But I wonder, I often save my documents every 10 minutes. So the most I can lose is 10 minute worth of work. Not to mention that, I may not be editing anything when the power is out. Also, when the UPS expires, one of them will give out beeping sound once in a while, probably signaling the changing of the battery. So I can either buy 2 new UPS or just buy 2 power outlets instead. 2 UPS, costing $160 to $250 roughly, can it be really worth it if it can save your computer from powering off for just 2 times? What are the alternatives?

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• How do I configure a C# web service client to send HTTP request header and body in parallel?

  - by Christopher

  Hi, I am using a traditional C# web service client generated in VS2008 .Net 3.5, inheriting from SoapHttpClientProtocol. This is connecting to a remote web service written in Java. All configuration is done in code during client initialization, and can be seen below: ServicePointManager.Expect100Continue = false; ServicePointManager.DefaultConnectionLimit = 10; var client = new APIService { EnableDecompression = true, Url = _url + "?guid=" + Guid.NewGuid(), Credentials = new NetworkCredential(user, password, null), PreAuthenticate = true, Timeout = 5000 // 5 sec }; It all works fine, but the time taken to execute the simplest method call is almost double the network ping time. Whereas a Java test client takes roughly the same as the network ping time: C# client ~ 550ms Java client ~ 340ms Network ping ~ 300ms After analyzing the TCP traffic for a session discovered the following: Basically, the C# client sent TCP packets in the following sequence. Client Send HTTP Headers in one packet. Client Waits For TCP ACK from server. Client Sends HTTP Body in one packet. Client Waits For TCP ACK from server. The Java client sent TCP packets in the following sequence. Client Sends HTTP Headers in one packet. Client Sends HTTP Body in one packet. Client Revieves ACK for first packet. Client Revieves ACK for second packet. Client Revieves ACK for second packet. Is there anyway to configure the C# web service client to send the header/body in parallel as the Java client appears to? Any help or pointers much appreciated.

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• Can someone look over the curriculum for this major & give me your thoughts? Computing & Security Te

  - by scottsharpejr

  My goal is to become a good web developer. I'm interested in learning how to build complex websites as well as how to write web applications. I want skills that will enable me to write apps for <--insert hottest web trend here-- (Facebook & iphone apps for example) This is one of my goals as far as Tech. is concerned. I'd also like to have a brod knowledge of different areas of IT. I'm looking into majoring in "Computing & Security Technology". The program is offered by Drexel in conjunction with my CC. It's a 4 year degree. Can someone take a look @ the pdf below. It outlines every course I must take. http://www.drexelatbcc.org/academics/PDF/CST_CT.pdf For degree requirments w/ links to course descriptiongs see drexel.edu/catalog/degree/ct.htm With electives I can go up to Web Development 4. Based on my goals of Web development & wanting a well rounding education in information technology, what do you think of the curriculum? How will I fare entering the job market with this degree? My goals here are a little different. I'd like to work for 2 to 3 companies over the course of 6-7 years. Working with and learning different areas of IT. I'd like to stay with a company an average of 2-3 years before moving on. My end goal is to go into business for myself (IT related). I appreciate any and all advice the community here can give me! :) Could someone also explain to me their interpretation of this major? thanks! P.S. I already know XHTML & CSS. I am just now starting to experiment with PHP.

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• How to compare 2 complex spreadsheets running in parallel for consistency with each other?

  - by tbone

  I am working on converting a large number of spreadsheets to use a new 3rd party data access library (converting from third party library #1 to third party library #2). fyi: a call to a UDF (user defined function) is placed in a cell, and when that is refreshed, it pulls the data into a pivot table below the formula. Both libraries behave the same and produce the same output, except, small irregularites can arise, such as an additional field being shown in the output pivot table using library #2, which can affect formulas on the sheet if data is being read from the pivot table without using GetPivotData. So I have ~100 of these very complicated (20+ worksheets per workbook) spreadsheets that I have to convert, and run in parallel for a period of time, to see if the output using the new data access library matches the old library. Is there some clever approach to do this, so I don't have to spend a large amount of time analyzing each sheet to determine the specific elements to compare? Two rough ideas that come to mind: 1. just create a Validator workbook that has the same # of worksheets, and simply do a Worbook1!Worksheet1!A1 - Worbook2!Worksheet3!A1 for every possible cell on each sheet 2. roughly the equivalent of #1, but just traverse the cells in the 2 books using VBA, and log any cells that do not match. I don't particularly like either idea, can anyone think of something better than this, maybe some 3rd party utility I could buy?

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• Should I learn two (or more) programming languages in parallel?

  - by c_maker

  I found entries on this site about learning a new programming language, however, I have not come across anything that talks about the advantages and disadvantages of learning two languages at the same time. Let's say my goal is to learn two new languages in a year. I understand that the definition of learning a new language is different for everyone and you can probably never know everything about a language. I believe in most cases the following things are enough to include the language in your resume and say that you are proficient in it (list is not in any particular order): Know its syntax so you can write a simple program in it Compare its underlying concepts with concepts of other languages Know best practices Know what libraries are available Know in what situations to use it Understand the flow of a more complex program At least know most of what you do not know I would probably look for a good book and pick an open source project for both of these languages to start with. My questions: Is it best to spend 5 months learning language#1 then 5 months learning language#2, or should you mix the two. Mixing them I mean you work on them in parallel. Should you pick two languages that are similar or different? Are there any advantages/disadvantages of let's say learning Lisp in tandem with Ruby? Is it a good idea to pick two languages with similar syntax or would it be too confusing? Please tell me what your experiences are regarding this. Does it make a difference if you are a beginner or a senior programmer?

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• Generic class for performing mass-parallel queries. Feedback?

  - by Aaron

  I don't understand why, but there appears to be no mechanism in the client library for performing many queries in parallel for Windows Azure Table Storage. I've created a template class that can be used to save considerable time, and you're welcome to use it however you wish. I would appreciate however, if you could pick it apart, and provide feedback on how to improve this class. public class AsyncDataQuery<T> where T: new() { public AsyncDataQuery(bool preserve_order) { m_preserve_order = preserve_order; this.Queries = new List<CloudTableQuery<T>>(1000); } public void AddQuery(IQueryable<T> query) { var data_query = (DataServiceQuery<T>)query; var uri = data_query.RequestUri; // required this.Queries.Add(new CloudTableQuery<T>(data_query)); } /// <summary> /// Blocking but still optimized. /// </summary> public List<T> Execute() { this.BeginAsync(); return this.EndAsync(); } public void BeginAsync() { if (m_preserve_order == true) { this.Items = new List<T>(Queries.Count); for (var i = 0; i < Queries.Count; i++) { this.Items.Add(new T()); } } else { this.Items = new List<T>(Queries.Count * 2); } m_wait = new ManualResetEvent(false); for (var i = 0; i < Queries.Count; i++) { var query = Queries[i]; query.BeginExecuteSegmented(callback, i); } } public List<T> EndAsync() { m_wait.WaitOne(); return this.Items; } private List<T> Items { get; set; } private List<CloudTableQuery<T>> Queries { get; set; } private bool m_preserve_order; private ManualResetEvent m_wait; private int m_completed = 0; private void callback(IAsyncResult ar) { int i = (int)ar.AsyncState; CloudTableQuery<T> query = Queries[i]; var response = query.EndExecuteSegmented(ar); if (m_preserve_order == true) { // preserve ordering only supports one result per query this.Items[i] = response.Results.First(); } else { // add any number of items this.Items.AddRange(response.Results); } if (response.HasMoreResults == true) { // more data to pull query.BeginExecuteSegmented(response.ContinuationToken, callback, i); return; } m_completed = Interlocked.Increment(ref m_completed); if (m_completed == Queries.Count) { m_wait.Set(); } } }

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• Show Notes: Architects in the Cloud

  - by Bob Rhubart

  Stephen G. Bennett and Archie Reed, the authors of Silver Clouds, Dark Linings: A Concise Guide to Cloud Computing,  discuss what’s new and what’s not so new about cloud computing, talk about how marketing hype has muddied understanding of what cloud is and what it can do, and explore other issues in the latest ArchBeat interview series. Listen to Part 1 Listen to Part 2 (December 22) Listen to Part 3 (December 29) Listen to Part 4 (January 5) Connect If you have questions, comments, or would otherwise like to interact directly with Steve or Archie, you can so through the following channels: Stephen G. Bennett Blog | Twitter | LinkedIn Archie Reed Blog | Twitter | LinkedIn Steve and Archie have also set up a Twitter account and blog specifically for their book: Twitter: @concisecloud Blog: concisecloud.com Of course, the book is available on Amazon: http://amzn.to/silverclouddarklinings Stay tuned: RSS Technorati Tags: oracle,otn,archbeat,cloud computing,podcast,. stephen bennett,archie reed del.icio.us Tags: oracle,otn,archbeat,cloud computing,podcast,. stephen bennett,archie reed

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• Programação paralela no .NET Framework 4 – Parte I

  - by anobre

  Introdução O avanço de tecnologia nos últimos anos forneceu, a baixo custo, acesso  a workstations com inúmeros CPUs. Facilmente encontramos hoje máquinas clientes com 2, 4 e até 8 núcleos, sem considerar os “super-servidores” com até 36 processadores :) Da wikipedia: A Unidade central de processamento (CPU, de acordo com as iniciais em inglês) ou o processador é a parte de um sistema de computador que executa as instruções de um programa de computador, e é o elemento primordial na execução das funções de um computador. Este termo tem sido usado na indústria de computadores pelo menos desde o início dos anos 1960[1]. A forma, desenho e implementação de CPUs têm mudado dramaticamente desde os primeiros exemplos, mas o seu funcionamento fundamental permanece o mesmo. Fazendo uma analogia, seria muito interessante delegarmos tarefas no mundo real que podem ser executadas independentemente a pessoas diferentes, atingindo desta forma uma  maior performance / produtividade na sua execução. A computação paralela se baseia na idéia que um problema maior pode ser dividido em problemas menores, sendo resolvidos de forma paralela. Este pensamento é utilizado há algum tempo por HPC (High-performance computing), e através das facilidades dos últimos anos, assim como a preocupação com consumo de energia, tornaram esta idéia mais atrativa e de fácil acesso a qualquer ambiente. No .NET Framework A plataforma .NET apresenta um runtime, bibliotecas e ferramentas para fornecer uma base de acesso fácil e rápido à programação paralela, sem trabalhar diretamente com threads e thread pool. Esta série de posts irá apresentar todos os recursos disponíveis, iniciando os estudos pela TPL, ou Task Parallel Library. Task Parallel Library A TPL é um conjunto de tipos localizados no namespace System.Threading e System.Threading.Tasks, a partir da versão 4 do framework. A partir da versão 4 do framework, o TPL é a maneira recomendada para escrever código paralelo e multithreaded. http://msdn.microsoft.com/en-us/library/dd460717(v=VS.100).aspx Task Parallelism O termo “task parallelism”, ou em uma tradução live paralelismo de tarefas, se refere a uma ou mais tarefas sendo executadas de forma simultanea. Considere uma tarefa como um método. A maneira mais fácil de executar tarefas de forma paralela é o código abaixo: Parallel.Invoke(() => TrabalhoInicial(), () => TrabalhoSeguinte()); O que acontece de verdade? Por trás nos panos, esta instrução instancia de forma implícita objetos do tipo Task, responsável por representar uma operação assíncrona, não exatamente paralela: public class Task : IAsyncResult, IDisposable É possível instanciar Tasks de forma explícita, sendo uma alternativa mais complexa ao Parallel.Invoke. var task = new Task(() => TrabalhoInicial()); task.Start(); Outra opção de instanciar uma Task e já executar sua tarefa é: var t = Task<int>.Factory.StartNew(() => TrabalhoInicialComValor());var t2 = Task<int>.Factory.StartNew(() => TrabalhoSeguinteComValor()); A diferença básica entre as duas abordagens é que a primeira tem início conhecido, mais utilizado quando não queremos que a instanciação e o agendamento da execução ocorra em uma só operação, como na segunda abordagem. Data Parallelism Ainda parte da TPL, o Data Parallelism se refere a cenários onde a mesma operação deva ser executada paralelamente em elementos de uma coleção ou array, através de instruções paralelas For e ForEach. A idéia básica é pegar cada elemento da coleção (ou array) e trabalhar com diversas threads concomitantemente. A classe-chave para este cenário é a System.Threading.Tasks.Parallel // Sequential version foreach (var item in sourceCollection) { Process(item); } // Parallel equivalent Parallel.ForEach(sourceCollection, item => Process(item)); Complicado né? :) Demonstração Acesse aqui um vídeo com exemplos (screencast). Cuidado! Apesar da imensa vontade de sair codificando, tome cuidado com alguns problemas básicos de paralelismo. Neste link é possível conhecer algumas situações. Abraços.

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• Best of "The Moth" 2009

  Not wanting to break the tradition (2004, 2005, 2006, 2007, 2008) below are some blog posts I picked from my blogging last year. As you can see by comparing with the links above, 2009 marks my lowest output yet with only 64 posts, but hopefully the quality has not been lowered ;-) 1. Parallel Computing was a strong focus of course. You can find links to most of that content aggregated in the post where I shared my entire parallelism session. Related to that was the link to the screencast I shared of the Parallel Computing Features Tour.2. Parallel Debugging is obviously part of the parallel computing links above, but I created more in depth content around that area of Visual Studio 2010 since it is the one I directly own. I aggregated all the links to that content in my post: Parallel Debugging.3. High Performance Computing through clusters is an area I'll be focusing more next year (besides parallelism on a single node on the client captured above) and I started introducing the topic on my blog this year. Read the (currently) 6 posts bottom up from my category on HPC.4. Windows 7 Task Manager. In April I shared a screenshot which was the most "borrowed" item from my blog (I should have watermarked it ;-)5. Windows Phone non-support in VS2010. Did my bit to spread clarification of the story.6. Window positions in Visual Studio is a long post, but one that I strongly advise all VS users to read and benefit from.7. Bug Triage gives you a glimpse into one thing all (Microsoft) product teams do.If you haven't yet, you can subscribe via one of the options on the left. Either way, thank you for staying tuned… Happy New Year! Comments about this post welcome at the original blog.

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• Parallelism in .NET – Part 8, PLINQ’s ForAll Method

  - by Reed

  Parallel LINQ extends LINQ to Objects, and is typically very similar.  However, as I previously discussed, there are some differences.  Although the standard way to handle simple Data Parellelism is via Parallel.ForEach, it’s possible to do the same thing via PLINQ. PLINQ adds a new method unavailable in standard LINQ which provides new functionality… LINQ is designed to provide a much simpler way of handling querying, including filtering, ordering, grouping, and many other benefits.  Reading the description in LINQ to Objects on MSDN, it becomes clear that the thinking behind LINQ deals with retrieval of data.  LINQ works by adding a functional programming style on top of .NET, allowing us to express filters in terms of predicate functions, for example. PLINQ is, generally, very similar.  Typically, when using PLINQ, we write declarative statements to filter a dataset or perform an aggregation.  However, PLINQ adds one new method, which provides a very different purpose: ForAll. The ForAll method is defined on ParallelEnumerable, and will work upon any ParallelQuery<T>.  Unlike the sequence operators in LINQ and PLINQ, ForAll is intended to cause side effects.  It does not filter a collection, but rather invokes an action on each element of the collection. At first glance, this seems like a bad idea.  For example, Eric Lippert clearly explained two philosophical objections to providing an IEnumerable<T>.ForEach extension method, one of which still applies when parallelized.  The sole purpose of this method is to cause side effects, and as such, I agree that the ForAll method “violates the functional programming principles that all the other sequence operators are based upon”, in exactly the same manner an IEnumerable<T>.ForEach extension method would violate these principles.  Eric Lippert’s second reason for disliking a ForEach extension method does not necessarily apply to ForAll – replacing ForAll with a call to Parallel.ForEach has the same closure semantics, so there is no loss there. Although ForAll may have philosophical issues, there is a pragmatic reason to include this method.  Without ForAll, we would take a fairly serious performance hit in many situations.  Often, we need to perform some filtering or grouping, then perform an action using the results of our filter.  Using a standard foreach statement to perform our action would avoid this philosophical issue: // Filter our collection var filteredItems = collection.AsParallel().Where( i => i.SomePredicate() ); // Now perform an action foreach (var item in filteredItems) { // These will now run serially item.DoSomething(); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This would cause a loss in performance, since we lose any parallelism in place, and cause all of our actions to be run serially. We could easily use a Parallel.ForEach instead, which adds parallelism to the actions: // Filter our collection var filteredItems = collection.AsParallel().Where( i => i.SomePredicate() ); // Now perform an action once the filter completes Parallel.ForEach(filteredItems, item => { // These will now run in parallel item.DoSomething(); }); This is a noticeable improvement, since both our filtering and our actions run parallelized.  However, there is still a large bottleneck in place here.  The problem lies with my comment “perform an action once the filter completes”.  Here, we’re parallelizing the filter, then collecting all of the results, blocking until the filter completes.  Once the filtering of every element is completed, we then repartition the results of the filter, reschedule into multiple threads, and perform the action on each element.  By moving this into two separate statements, we potentially double our parallelization overhead, since we’re forcing the work to be partitioned and scheduled twice as many times. This is where the pragmatism comes into play.  By violating our functional principles, we gain the ability to avoid the overhead and cost of rescheduling the work: // Perform an action on the results of our filter collection .AsParallel() .Where( i => i.SomePredicate() ) .ForAll( i => i.DoSomething() ); The ability to avoid the scheduling overhead is a compelling reason to use ForAll.  This really goes back to one of the key points I discussed in data parallelism: Partition your problem in a way to place the most work possible into each task.  Here, this means leaving the statement attached to the expression, even though it causes side effects and is not standard usage for LINQ. This leads to my one guideline for using ForAll: The ForAll extension method should only be used to process the results of a parallel query, as returned by a PLINQ expression. Any other usage scenario should use Parallel.ForEach, instead.

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