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  • suggest an algorithm for the following puzzle!!

    - by garima
    There are n petrol bunks arranged in circle. Each bunk is separated from the rest by a certain distance. You choose some mode of travel which needs 1litre of petrol to cover 1km distance. You can't infinitely draw any amount of petrol from each bunk as each bunk has some limited petrol only. But you know that the sum of litres of petrol in all the bunks is equal to the distance to be covered. ie let P1, P2, ... Pn be n bunks arranged circularly. d1 is distance between p1 and p2, d2 is distance between p2 and p3. dn is distance between pn and p1.Now find out the bunk from where the travel can be started such that your mode of travel never runs out of fuel.

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  • How to guard against memory leaks?

    - by just_wes
    I was recently interviewing for a C++ position, and I was asked how I guard against creating memory leaks. I know I didn't give a satisfactory answer to that question, so I'm throwing it to you guys. What are the best ways to guard against memory leaks? Thanks!

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  • Given a linked list of numbers. Swap every 2 adjacent links.

    - by Learner
    Given a linked list of numbers. Swap every 2 adjacent links. For eg if a linked list given to you is- a-b-c-d-e-f O/p expected- b-a-d-c-f-e Every 2 alternate links have to be swapped. I have written a solution here. Can you suggest me some other solution. Can you comment on my solution and help me better write it? void SwapAdjacentNodes (Node head) { if (head == null) return; if (head.next == null) return; Node curr = head; Node next = curr.Next; Node temp = next.Next; while (true) { temp = next.Next; next.Next = curr; curr.Next = temp; if (curr.Next != null) curr = curr.Next; else break; if (curr.Next.Next!=null) next = curr.Next.Next; else break; } }

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  • Shuffle array variables in a pre-specified order, without using extra memory of "size of input array"

    - by Eternal Learner
    Input : A[4] = {0,4,-1,1000} - Actual Array P[4] = {1,0,3,2} - Order to be reshuffled Output: A[4] = {4,0,1000,-1} Condition : Don't use an additional array as memory. Can use an extra variable or two. Problem : I have the below program in C++, but this fails for certain inputs of array P. #include<iostream> using namespace std; void swap(int *a_r,int *r) { int temp = *r; *r = *a_r; *a_r = temp; } int main() { int A[4] = {0,4,-1,1000}; int P[4] = {3,0,1,2}; int value = A[0] , dest = P[0]; for(int i=0; i<4;i++) { swap(&A[dest],&value); dest = P[dest]; } for(int i=0;i<4;i++) cout<<A[i]<<" "; }

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  • Compare two integer arrays with same length

    - by meta
    [Description] Given two integer arrays with the same length. Design an algorithm which can judge whether they're the same, the definition of "same" is that, if these two arrays are in sorted order, the elements in corresponding position should be the same. [Example] <1 2 3 4> = <3 1 2 4> <1 2 3 4> != <3 4 1 1> [Limitation] The algorithm should require constant extra space, and O(n) running time.

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  • Special simple random number generator

    - by psihodelia
    How to create a function, which on every call generates a random integer number? This number must be most random as possible (according to uniform distribution). It is only allowed to use one static variable and at most 3 elementary steps, where each step consists of only one basic arithmetic operation of arity 1 or 2. Example: int myrandom(void){ static int x; x = some_step1; x = some_step2; x = some_step3; return x; } Basic arithmetic operations are +,-,%,and, not, xor, or, left shift, right shift, multiplication and division. Of course, no rand(), random() or similar staff is allowed.

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  • What's up with this reversing bit order function?

    - by MattyW
    I'm rather ashamed to admit that I don't know as much about bits and bit manipulation as I probably should. I tried to fix that this weekend by writing some 'reverse the order of bits' and 'count the ON bits' functions. I took an example from here but when I implemented it as below, I found I had to be looping while < 29. If I loop while < 32 (as in the example) Then when I try to print the integer (using a printBits function i've written) I seem to be missing the first 3 bits. This makes no sense to me, can someone help me out? int reverse(int n) { int r = 0; int i = 0; for(i = 0; i < 29; i++) { r = (r << 1) + (n & 1); n >>=1; } return r; }

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  • Optimal strategy to make a C++ hash table, thread safe

    - by Ajeet
    (I am interested in design of implementation NOT a readymade construct that will do it all.) Suppose we have a class HashTable (not hash-map implemented as a tree but hash-table) and say there are eight threads. Suppose read to write ratio is about 100:1 or even better 1000:1. Case A) Only one thread is a writer and others including writer can read from HashTable(they may simply iterate over entire hash table) Case B) All threads are identical and all could read/write. Can someone suggest best strategy to make the class thread safe with following consideration 1. Top priority to least lock contention 2. Second priority to least number of locks My understanding so far is thus : One BIG reader-writer lock(semaphore). Specialize the semaphore so that there could be eight instances writer-resource for case B, where each each writer resource locks one row(or range for that matter). (so i guess 1+8 mutexes) Please let me know if I am thinking on the correct line, and how could we improve on this solution.

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  • Number of the different elements in an array.

    - by AB
    Is it possible to compute the number of the different elements in an array in linear time and constant space? Let us say it's an array of long integers, and you can not allocate an array of length sizeof(long). P.S. Not homework, just curious. I've got a book that sort of implies that it is possible.

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  • Find largest rectangle containing only zeros in an N&times;N binary matrix

    - by Rajendra
    Given an NxN binary matrix (containing only 0's or 1's), how can we go about finding largest rectangle containing all 0's? Example: I 0 0 0 0 1 0 0 0 1 0 0 1 II->0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 <--IV 0 0 1 0 0 0 IV is a 6×6 binary matrix; the return value in this case will be Cell 1: (2, 1) and Cell 2: (4, 4). The resulting sub-matrix can be square or rectangular. The return value can also be the size of the largest sub-matrix of all 0's, in this example 3 × 4.

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  • SQL SERVER – Weekly Series – Memory Lane – #039

    - by Pinal Dave
    Here is the list of selected 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. 2007 FQL – Facebook Query Language Facebook list following advantages of FQL: Condensed XML reduces bandwidth and parsing costs. More complex requests can reduce the number of requests necessary. Provides a single consistent, unified interface for all of your data. It’s fun! UDF – Get the Day of the Week Function The day of the week can be retrieved in SQL Server by using the DatePart function. The value returned by the function is between 1 (Sunday) and 7 (Saturday). To convert this to a string representing the day of the week, use a CASE statement. UDF – Function to Get Previous And Next Work Day – Exclude Saturday and Sunday While reading ColdFusion blog of Ben Nadel Getting the Previous Day In ColdFusion, Excluding Saturday And Sunday, I realize that I use similar function on my SQL Server Database. This function excludes the Weekends (Saturday and Sunday), and it gets previous as well as next work day. Complete Series of SQL Server Interview Questions and Answers Data Warehousing Interview Questions and Answers – Introduction Data Warehousing Interview Questions and Answers – Part 1 Data Warehousing Interview Questions and Answers – Part 2 Data Warehousing Interview Questions and Answers – Part 3 Data Warehousing Interview Questions and Answers Complete List Download 2008 Introduction to Log Viewer In SQL Server all the windows event logs can be seen along with SQL Server logs. Interface for all the logs is same and can be launched from the same place. This log can be exported and filtered as well. DBCC SHRINKFILE Takes Long Time to Run If you are DBA who are involved with Database Maintenance and file group maintenance, you must have experience that many times DBCC SHRINKFILE operations takes a long time but any other operations with Database are relatively quicker. mssqlsystemresource – Resource Database The purpose of resource database is to facilitates upgrading to the new version of SQL Server without any hassle. In previous versions whenever version of SQL Server was upgraded all the previous version system objects needs to be dropped and new version system objects to be created. 2009 Puzzle – Write Script to Generate Primary Key and Foreign Key In SQL Server Management Studio (SSMS), there is no option to script all the keys. If one is required to script keys they will have to manually script each key one at a time. If database has many tables, generating one key at a time can be a very intricate task. I want to throw a question to all of you if any of you have scripts for the same purpose. Maximizing View of SQL Server Management Studio – Full Screen – New Screen I had explained the following two different methods: 1) Open Results in Separate Tab - This is a very interesting method as result pan shows up in a different tab instead of the splitting screen horizontally. 2) Open SSMS in Full Screen - This works always and to its best. Not many people are aware of this method; hence, very few people use it to enhance performance. 2010 Find Queries using Parallelism from Cached Plan T-SQL script gets all the queries and their execution plan where parallelism operations are kicked up. Pay attention there is TOP 10 is used, if you have lots of transactional operations, I suggest that you change TOP 10 to TOP 50 This is the list of the all the articles in the series of computed columns. SQL SERVER – Computed Column – PERSISTED and Storage This article talks about how computed columns are created and why they take more storage space than before. SQL SERVER – Computed Column – PERSISTED and Performance This article talks about how PERSISTED columns give better performance than non-persisted columns. SQL SERVER – Computed Column – PERSISTED and Performance – Part 2 This article talks about how non-persisted columns give better performance than PERSISTED columns. SQL SERVER – Computed Column and Performance – Part 3 This article talks about how Index improves the performance of Computed Columns. SQL SERVER – Computed Column – PERSISTED and Storage – Part 2 This article talks about how creating index on computed column does not grow the row length of table. SQL SERVER – Computed Columns – Index and Performance This article summarized all the articles related to computed columns. 2011 SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Data Warehousing Concepts – Day 21 of 31 What is Data Warehousing? What is Business Intelligence (BI)? What is a Dimension Table? What is Dimensional Modeling? What is a Fact Table? What are the Fundamental Stages of Data Warehousing? What are the Different Methods of Loading Dimension tables? Describes the Foreign Key Columns in Fact Table and Dimension Table? What is Data Mining? What is the Difference between a View and a Materialized View? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Data Warehousing Concepts – Day 22 of 31 What is OLTP? What is OLAP? What is the Difference between OLTP and OLAP? What is ODS? What is ER Diagram? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Data Warehousing Concepts – Day 23 of 31 What is ETL? What is VLDB? Is OLTP Database is Design Optimal for Data Warehouse? If denormalizing improves Data Warehouse Processes, then why is the Fact Table is in the Normal Form? What are Lookup Tables? What are Aggregate Tables? What is Real-Time Data-Warehousing? What are Conformed Dimensions? What is a Conformed Fact? How do you Load the Time Dimension? What is a Level of Granularity of a Fact Table? What are Non-Additive Facts? What is a Factless Facts Table? What are Slowly Changing Dimensions (SCD)? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Data Warehousing Concepts – Day 24 of 31 What is Hybrid Slowly Changing Dimension? What is BUS Schema? What is a Star Schema? What Snow Flake Schema? Differences between the Star and Snowflake Schema? What is Difference between ER Modeling and Dimensional Modeling? What is Degenerate Dimension Table? Why is Data Modeling Important? What is a Surrogate Key? What is Junk Dimension? What is a Data Mart? What is the Difference between OLAP and Data Warehouse? What is a Cube and Linked Cube with Reference to Data Warehouse? What is Snapshot with Reference to Data Warehouse? What is Active Data Warehousing? What is the Difference between Data Warehousing and Business Intelligence? What is MDS? Explain the Paradigm of Bill Inmon and Ralph Kimball. SQL SERVER – Azure Interview Questions and Answers – Guest Post by Paras Doshi – Day 25 of 31 Paras Doshi has submitted 21 interesting question and answers for SQL Azure. 1.What is SQL Azure? 2.What is cloud computing? 3.How is SQL Azure different than SQL server? 4.How many replicas are maintained for each SQL Azure database? 5.How can we migrate from SQL server to SQL Azure? 6.Which tools are available to manage SQL Azure databases and servers? 7.Tell me something about security and SQL Azure. 8.What is SQL Azure Firewall? 9.What is the difference between web edition and business edition? 10.How do we synchronize On Premise SQL server with SQL Azure? 11.How do we Backup SQL Azure Data? 12.What is the current pricing model of SQL Azure? 13.What is the current limitation of the size of SQL Azure DB? 14.How do you handle datasets larger than 50 GB? 15.What happens when the SQL Azure database reaches Max Size? 16.How many databases can we create in a single server? 17.How many servers can we create in a single subscription? 18.How do you improve the performance of a SQL Azure Database? 19.What is code near application topology? 20.What were the latest updates to SQL Azure service? 21.When does a workload on SQL Azure get throttled? SQL SERVER – Interview Questions and Answers – Guest Post by Malathi Mahadevan – Day 26 of 31 Malachi had asked a simple question which has several answers. Each answer makes you think and ponder about the reality of the IT world. Look at the simple question – ‘What is the toughest challenge you have faced in your present job and how did you handle it’? and its various answers. Each answer has its own story. SQL SERVER – Interview Questions and Answers – Guest Post by Rick Morelan – Day 27 of 31 Rick Morelan of Joes2Pros has written an excellent blog post on the subject how to find top N values. Most people are fully aware of how the TOP keyword works with a SELECT statement. After years preparing so many students to pass the SQL Certification I noticed they were pretty well prepared for job interviews too. Yes, they would do well in the interview but not great. There seemed to be a few questions that would come up repeatedly for almost everyone. Rick addresses similar questions in his lucid writing skills. 2012 Observation of Top with Index and Order of Resultset SQL Server has lots of things to learn and share. It is amazing to see how people evaluate and understand different techniques and styles differently when implementing. The real reason may be absolutely different but we may blame something totally different for the incorrect results. Read the blog post to learn more. How do I Record Video and Webcast How to Convert Hex to Decimal or INT Earlier I asked regarding a question about how to convert Hex to Decimal. I promised that I will post an answer with Due Credit to the author but never got around to post a blog post around it. Read the original post over here SQL SERVER – Question – How to Convert Hex to Decimal. Query to Get Unique Distinct Data Based on Condition – Eliminate Duplicate Data from Resultset The natural reaction will be to suggest DISTINCT or GROUP BY. However, not all the questions can be solved by DISTINCT or GROUP BY. Let us see the following example, where a user wanted only latest records to be displayed. Let us see the example to understand further. 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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  • What do you do when you encounter an idiotic interview question?

    - by Senthil
    I was interviewing with a "too proud of my java skills"-looking person. He asked me "What is your knowledge on Java IO classes.. say.. hash maps?" He asked me to write a piece of java code on paper - instantiate a class and call one of the instance's methods. When I was done, he said my program wouldn't run. After 5 minutes of serious thinking, I gave up and asked why. He said I didn't write a main function so it wouldn't run. ON PAPER. [I am too furious to continue with the stupidity...] Believe me it wasn't trick questions or a psychic or anger management evaluation thing. I can tell from his face, he was proud of these questions. That "developer" was supposed to "judge" the candidates. I can think of several things: Hit him with a chair (which I so desperately wanted to) and walk out. Simply walk out. Ridicule him saying he didn't make sense. Politely let him know that he didn't make sense and go on to try and answer the questions. Don't tell him anything, but simply go on to try and answer the questions. So far, I have tried just 4 and 5. It hasn't helped. Unfortunately many candidates seem to do the same and remain polite but this lets these kind of "developers" just keep ascending up the corporate ladder, gradually getting the capacity to pi** off more and more people. How do you handle these interviewers without bursting your veins? What is the proper way to handle this, yet maintain your reputation if other potential employers were to ever get to know what happened here? Is there anything you can do or should you even try to fix this? P.S. Let me admit that my anger has been amplified many times by the facts: He was smiling like you wouldn't believe. I got so many (20 or so) calls from that company the day before, asking me to come to the interview, that I couldn't do any work that day. I wasted a paid day off.

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  • Working for free

    - by truncate
    Finances are making me take an extended period off of my college education. In my current state, I don't feel fully qualified to be employed by an iPhone software company. While I work on getting things back together, I'd like to try an work for a software company for free in my local area (I'm going to college out of state and have to move back as well). The economy has forced employers to be very picky about who they hire, if any at all. Since I'd like to continue refining my abilities, I was wondering on what the consensus is on working for free. It can't be considered an internship, as I would no longer be in school..., I guess an apprenticeship is more appropriate. Like I said, I don't think I'm qualified to be paid for my services, and I don't want to be. I just don't know how to ask, or if it's even appropriate to ask them to show me how to develop software in the real world. My thinking is that they would be willing to get some work done for free and if I prove myself, they could hire me. If not, there was no major loss. They get some free development, and lose a bit of time helping show me the ropes. I get either a job, or valuable experience that I need. The other alternative is that I try to work out things by myself on the iPhone platform, but that sounds terrifying. I appreciate any input the community has to offer.

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  • delayed_job :run_at is not working. all jobs set to run at current time

    - by jtwg
    I have installed the collectiveidea fork for delayed_job at git://github.com/collectiveidea/delayed_job.git but cannot get it to accept :run_at from my gemfile gem 'rails', '3.2.2' gem 'delayed_job_active_record' when I try it in the console 1.9.2-p318 :005 > Time.now => 2012-03-24 10:20:34 -0700 1.9.2-p318 :006 > User.delay.new :run_at => 5.days.from_now SQL (0.1ms) BEGIN SQL (1.6ms) INSERT INTO `delayed_jobs` (`attempts`, `created_at`, `failed_at`, `handler`, `last_error`, `locked_at`, `locked_by`, `priority`, `run_at`, `updated_at`) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?) [["attempts", 0], ["created_at", Sat, 24 Mar 2012 17:20:36 UTC +00:00], ["failed_at", nil], ["handler", "--- !ruby/object:Delayed::PerformableMethod\nobject: !ruby/class 'User'\nmethod_name: :new\nargs:\n- :run_at: 2012-03-29 17:20:36.876374000Z\n"], ["last_error", nil], ["locked_at", nil], ["locked_by", nil], ["priority", 0], ["run_at", Sat, 24 Mar 2012 17:20:36 UTC +00:00], ["updated_at", Sat, 24 Mar 2012 17:20:36 UTC +00:00]] (2.7ms) COMMIT => #<Delayed::Backend::ActiveRecord::Job id: 17, priority: 0, attempts: 0, handler: "--- !ruby/object:Delayed::PerformableMethod\nobject:...", last_error: nil, run_at: "2012-03-24 17:20:36", locked_at: nil, failed_at: nil, locked_by: nil, created_at: "2012-03-24 17:20:36", updated_at: "2012-03-24 17:20:36"> I see there is some UTC offset in the runtime, but based on Time.now, I can tell run_at is not going forward by 5 days. "run_at", Sat, 24 Mar 2012 17:20:36 UTC +00:00 Any ideas?

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  • Mgmt wants to re-title my position: Any help...? [closed]

    - by JohnFlyTN
    Management here wants to re-title my position, since I'm doing quite a bit of different work than was originally planned. They want my input. After a quick glance over my skill set and job duties, what would we need to describe this position as? I'll just list things I'm at least proficient in, I will not list things I have a passing knowledge of. About me : ~10 years software development. Languages : C, C++, Perl, PHP, C#, TCL, Unix shell scripting, SQL (TSQL, PLSQL) Systems : MS-Dos, Windows 3.1 to 7 for client, NT 4 to 2008 for server, OS/2, IBM MVS & z/OS, Linux ( multiple distros), AIX Current position: I do all sorts of in-house software. The range is single user apps to large systems spanning multiple OS's. One of the larger projects I've designed and coded is about 100k lines of C#, and a database where I have been the sole designer and maintainer. I have near total freedom to design as I see fit, restraints are usually budgetary. Skills required to replace me in my current role: Windows and Unix admin, Database design, .NET up to 3.5 (C#, ASP.NET), C++, Perl, good skills in designing large and efficient data processing systems. Given this small level of information what would you see this as being titled? (is more information required to render a decision?)

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  • Will an online degree get you a job that requires "CS or equivalent 4-year degree"? [on hold]

    - by qel
    I'm a nerdy slacker type who didn't get my life together till I was 30. I've had a real job for a couple years doing C#/SQL. I've gotten several raises, but I'm making less than most developers, and the atmosphere is ... not positive. Looking for a new job, I think my applications get thrown out because I don't have a degree. And I want to finish a Bachelor's just to feel like less of a loser. I have a lot of college credits from 1996-2003 and a low GPA, so I don't know if that's worth much. An online degree looks like a good option, but I just don't know what I should be looking at for online schools because they all look like fake degrees. If they had programs equivalent to a real Comp Sci degree, I don't think they would have weird sounding names like they do. University of Phoenix has a B.S./Information Technology-Software Engineering. DeVry has a B.S./Computer Engineering Technology program. But that's not CS, and most other things I see have even more fake-sounding names. Are these useless degrees? Some people say DeVry and UoP are acceptable, some people say they're a joke. I have enough experience now, though, that maybe all I'm missing is being able to check the box that I have a 4-year degree. Harvard Extension seems like a real degree, even if it isn't a real Harvard degree, but I'd have to live there at least 3 months, which kinda defeats the purpose of an online degree fitting around work.

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  • Is there a website that scrapes job postings to determine the popularity of web technologies? [closed]

    - by dB'
    I'm often in a position where I need to choose between a number of web technologies. These technologies might be programming languages, or web application frameworks, or types of databases, or some other kind of toolkit used by programmers. More often than not, after some doing research, I end up with a list of contenders that are all equally viable. They're all powerful enough to solve my problem, they're all popular and well supported, and they're all equally familiar/unfamiliar to me. There's no obvious rationale by which to choose between them. Still, I need to pick one, so at this point I usually ask myself a hypothetical question: which one of these technologies, if I invest in learning it, would be most helpful to me in a job search? Where can I go on the internet to answer this question? Is there a website/service that scrapes the texts of worldwide job postings and would allow me to compare, say, the number of employers looking for expertise in technology x vs. technology y? (Where x and y are Rails vs. Djando, Java vs. Python, Brainfuck vs. LOLCode, etc.)

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  • How do I tell my parents that landing a job is what actually counts?

    - by shovonr
    On one side, I just want to get a degree with a 3.0 GPA. On the other side, my parents want more than just a 3. Now here's the thing. I program with a passion. I spend day and night programming. And I ace all my programming courses. However, I do terrible on all my elective courses -- such as writing, history, and all that stuff -- which only leaves me with a 3.1 to 3.2 GPA. And my parents want more. They think that university is like high school, where you need super-stellar grades to get to the next level. But they don't realize that good enough grades will land me a job. And they don't realize that a programmer needs to practice to become good at programming, and that having good skills is what will land a job in a nice software development company. Thankfully, though, they don't threaten to beat me with a baseball bat or anything like that. They just occasionally give me the little "tsk-tsk". But even that little "tsk-tsk" makes me feel guilty for opening up an IDE. And on top of that, I procrastinate because of that feeling of guilt. So now, I want to come clean with them. I want to know what's a good way to do that. [Edit] OK, so now, I realized, I should aim for higher grades, as some have suggested below.

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  • SQL SERVER – Transcript of Learning SQL Server Performance: Indexing Basics – Interview of Vinod Kumar by Pinal Dave

    - by pinaldave
    Recently I just wrote a blog post on about Learning SQL Server Performance: Indexing Basics and I received lots of request that if we can share some insight into the course. Here is 200 seconds interview of Vinod Kumar I took right after completing the course. We have few free codes to watch the course, please your comment at http://facebook.com/SQLAuth and we will few of first ones, we will send the code. There are many people who said they would like to read the transcript of the video. Here I have generated the same. Pinal: Vinod, we recently released this course, SQL Server Indexing. It is about performance tuning. So tell me – how do indexes help performance? Vinod: I think what happens in the industry when it comes to performance is that developers and DBAs look at indexes first.  So that’s the first step for any performance tuning exercise, indexing is one of the most critical aspects and it is important to learn it the right way. Pinal: Correct. So what you mean to say is that if you know indexing you can pretty much tune any server and query. Vinod: So I might contradict my false statement now. Indexing is usually a stepping stone but it does not lead you to the end. But it’s good to start with indexing and there are lots of nuances to indexing that you need to understand, like how SQL uses indexing and how performance can improve because of the strategies that you have made. Pinal: But now I’m confused. First you said indexes are good, and then you said that indexes can degrade your performance.  So what is this course about?  I mean how does this course really make an impact? Vinod: Ok -so from the course perspective, what we are trying to do is give you a capsule which gives you a good start. Every journey needs a beginning, you need that first step.  This course is that first step in understanding. This is the most basic, fundamental course that we have tried to attack. This is the fundamentals of indexing, some of the key things that you must know about indexing.   Some of the basics of indexing are lesser known and so I think this course is geared towards each and every one of you out there who wants to understand little bit more about indexing. Pinal: So what I understand is that if I enrolled in this course I will have a minimum understanding about indexing when dealing with performance tuning.  Right? Vinod: Exactly. In this course is we have tried to give you a nice summary. We are talking about clustered indexing, non clustered indexing, too many indexes, too few indexes, over indexing, under indexing, duplicate indexing, columns tune indexing, with SQL Server 2012. There’s lot’s to learn. Pinal: You can see the URL [http://bit.ly/sql-index] of the course on the screen. Go ahead, attend, and let us know what you think about it. Thank you. Vinod: Thank you. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Index, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology, Video

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  • Building Simple Workflows in Oozie

    - by dan.mcclary
    Introduction More often than not, data doesn't come packaged exactly as we'd like it for analysis. Transformation, match-merge operations, and a host of data munging tasks are usually needed before we can extract insights from our Big Data sources. Few people find data munging exciting, but it has to be done. Once we've suffered that boredom, we should take steps to automate the process. We want codify our work into repeatable units and create workflows which we can leverage over and over again without having to write new code. In this article, we'll look at how to use Oozie to create a workflow for the parallel machine learning task I described on Cloudera's site. Hive Actions: Prepping for Pig In my parallel machine learning article, I use data from the National Climatic Data Center to build weather models on a state-by-state basis. NCDC makes the data freely available as gzipped files of day-over-day observations stretching from the 1930s to today. In reading that post, one might get the impression that the data came in a handy, ready-to-model files with convenient delimiters. The truth of it is that I need to perform some parsing and projection on the dataset before it can be modeled. If I get more observations, I'll want to retrain and test those models, which will require more parsing and projection. This is a good opportunity to start building up a workflow with Oozie. I store the data from the NCDC in HDFS and create an external Hive table partitioned by year. This gives me flexibility of Hive's query language when I want it, but let's me put the dataset in a directory of my choosing in case I want to treat the same data with Pig or MapReduce code. CREATE EXTERNAL TABLE IF NOT EXISTS historic_weather(column 1, column2) PARTITIONED BY (yr string) STORED AS ... LOCATION '/user/oracle/weather/historic'; As new weather data comes in from NCDC, I'll need to add partitions to my table. That's an action I should put in the workflow. Similarly, the weather data requires parsing in order to be useful as a set of columns. Because of their long history, the weather data is broken up into fields of specific byte lengths: x bytes for the station ID, y bytes for the dew point, and so on. The delimiting is consistent from year to year, so writing SerDe or a parser for transformation is simple. Once that's done, I want to select columns on which to train, classify certain features, and place the training data in an HDFS directory for my Pig script to access. ALTER TABLE historic_weather ADD IF NOT EXISTS PARTITION (yr='2010') LOCATION '/user/oracle/weather/historic/yr=2011'; INSERT OVERWRITE DIRECTORY '/user/oracle/weather/cleaned_history' SELECT w.stn, w.wban, w.weather_year, w.weather_month, w.weather_day, w.temp, w.dewp, w.weather FROM ( FROM historic_weather SELECT TRANSFORM(...) USING '/path/to/hive/filters/ncdc_parser.py' as stn, wban, weather_year, weather_month, weather_day, temp, dewp, weather ) w; Since I'm going to prepare training directories with at least the same frequency that I add partitions, I should also add that to my workflow. Oozie is going to invoke these Hive actions using what's somewhat obviously referred to as a Hive action. Hive actions amount to Oozie running a script file containing our query language statements, so we can place them in a file called weather_train.hql. Starting Our Workflow Oozie offers two types of jobs: workflows and coordinator jobs. Workflows are straightforward: they define a set of actions to perform as a sequence or directed acyclic graph. Coordinator jobs can take all the same actions of Workflow jobs, but they can be automatically started either periodically or when new data arrives in a specified location. To keep things simple we'll make a workflow job; coordinator jobs simply require another XML file for scheduling. The bare minimum for workflow XML defines a name, a starting point, and an end point: <workflow-app name="WeatherMan" xmlns="uri:oozie:workflow:0.1"> <start to="ParseNCDCData"/> <end name="end"/> </workflow-app> To this we need to add an action, and within that we'll specify the hive parameters Also, keep in mind that actions require <ok> and <error> tags to direct the next action on success or failure. <action name="ParseNCDCData"> <hive xmlns="uri:oozie:hive-action:0.2"> <job-tracker>localhost:8021</job-tracker> <name-node>localhost:8020</name-node> <configuration> <property> <name>oozie.hive.defaults</name> <value>/user/oracle/weather_ooze/hive-default.xml</value> </property> </configuration> <script>ncdc_parse.hql</script> </hive> <ok to="WeatherMan"/> <error to="end"/> </action> There are a couple of things to note here: I have to give the FQDN (or IP) and port of my JobTracker and NameNode. I have to include a hive-default.xml file. I have to include a script file. The hive-default.xml and script file must be stored in HDFS That last point is particularly important. Oozie doesn't make assumptions about where a given workflow is being run. You might submit workflows against different clusters, or have different hive-defaults.xml on different clusters (e.g. MySQL or Postgres-backed metastores). A quick way to ensure that all the assets end up in the right place in HDFS is just to make a working directory locally, build your workflow.xml in it, and copy the assets you'll need to it as you add actions to workflow.xml. At this point, our local directory should contain: workflow.xml hive-defaults.xml (make sure this file contains your metastore connection data) ncdc_parse.hql Adding Pig to the Ooze Adding our Pig script as an action is slightly simpler from an XML standpoint. All we do is add an action to workflow.xml as follows: <action name="WeatherMan"> <pig> <job-tracker>localhost:8021</job-tracker> <name-node>localhost:8020</name-node> <script>weather_train.pig</script> </pig> <ok to="end"/> <error to="end"/> </action> Once we've done this, we'll copy weather_train.pig to our working directory. However, there's a bit of a "gotcha" here. My pig script registers the Weka Jar and a chunk of jython. If those aren't also in HDFS, our action will fail from the outset -- but where do we put them? The Jython script goes into the working directory at the same level as the pig script, because pig attempts to load Jython files in the directory from which the script executes. However, that's not where our Weka jar goes. While Oozie doesn't assume much, it does make an assumption about the Pig classpath. Anything under working_directory/lib gets automatically added to the Pig classpath and no longer requires a REGISTER statement in the script. Anything that uses a REGISTER statement cannot be in the working_directory/lib directory. Instead, it needs to be in a different HDFS directory and attached to the pig action with an <archive> tag. Yes, that's as confusing as you think it is. You can get the exact rules for adding Jars to the distributed cache from Oozie's Pig Cookbook. Making the Workflow Work We've got a workflow defined and have collected all the components we'll need to run. But we can't run anything yet, because we still have to define some properties about the job and submit it to Oozie. We need to start with the job properties, as this is essentially the "request" we'll submit to the Oozie server. In the same working directory, we'll make a file called job.properties as follows: nameNode=hdfs://localhost:8020 jobTracker=localhost:8021 queueName=default weatherRoot=weather_ooze mapreduce.jobtracker.kerberos.principal=foo dfs.namenode.kerberos.principal=foo oozie.libpath=${nameNode}/user/oozie/share/lib oozie.wf.application.path=${nameNode}/user/${user.name}/${weatherRoot} outputDir=weather-ooze While some of the pieces of the properties file are familiar (e.g., JobTracker address), others take a bit of explaining. The first is weatherRoot: this is essentially an environment variable for the script (as are jobTracker and queueName). We're simply using them to simplify the directives for the Oozie job. The oozie.libpath pieces is extremely important. This is a directory in HDFS which holds Oozie's shared libraries: a collection of Jars necessary for invoking Hive, Pig, and other actions. It's a good idea to make sure this has been installed and copied up to HDFS. The last two lines are straightforward: run the application defined by workflow.xml at the application path listed and write the output to the output directory. We're finally ready to submit our job! After all that work we only need to do a few more things: Validate our workflow.xml Copy our working directory to HDFS Submit our job to the Oozie server Run our workflow Let's do them in order. First validate the workflow: oozie validate workflow.xml Next, copy the working directory up to HDFS: hadoop fs -put working_dir /user/oracle/working_dir Now we submit the job to the Oozie server. We need to ensure that we've got the correct URL for the Oozie server, and we need to specify our job.properties file as an argument. oozie job -oozie http://url.to.oozie.server:port_number/ -config /path/to/working_dir/job.properties -submit We've submitted the job, but we don't see any activity on the JobTracker? All I got was this funny bit of output: 14-20120525161321-oozie-oracle This is because submitting a job to Oozie creates an entry for the job and places it in PREP status. What we got back, in essence, is a ticket for our workflow to ride the Oozie train. We're responsible for redeeming our ticket and running the job. oozie -oozie http://url.to.oozie.server:port_number/ -start 14-20120525161321-oozie-oracle Of course, if we really want to run the job from the outset, we can change the "-submit" argument above to "-run." This will prep and run the workflow immediately. Takeaway So, there you have it: the somewhat laborious process of building an Oozie workflow. It's a bit tedious the first time out, but it does present a pair of real benefits to those of us who spend a great deal of time data munging. First, when new data arrives that requires the same processing, we already have the workflow defined and ready to run. Second, as we build up a set of useful action definitions over time, creating new workflows becomes quicker and quicker.

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  • How does a programmer who doesn't know how to program get a job ? [closed]

    - by A programmer
    I often read about this and I'm curious: if there programmers who can't program, how did they get a programming job in the first place? They must bring some value to the company they're working for, otherwise they would be fired. I don't think "programmers who don't know how to program" means "bad programmers" in this case ? Even if they are bad programmers, they still know (badly) how to write (bad) programs. So what defines programmers who can't program ?

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  • What stressors do programmers encounter on the job, and how do you deal with them? [closed]

    - by Matthew Rodatus
    Learning to manage stress is vital to staying healthy while working at any job. A necessary subtask is learning to recognize and limit the sources of stress. But, in the midst of the daily grind, it can be difficult to recognize sources of stress (especially for an intense, focused persona such as a programmer). What types of stressors should programmers look out for, and how can they be managed?

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