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  • SQL SERVER – Developer Training Resources and Summary Roundup

    - by pinaldave
    It is always pleasure for any author when other renowned authors in the industry write about you. Earlier I wrote a five part blog series on Developer Training and I have received a phenomenal response to the series. I have received plenty of comments, questions and feedback. I thought it would be nice to sum up the whole series as well answer a few of the questions received. Quick Recap Developer Training - Importance and Significance - Part 1 In this part we discussed the importance of training in the real world. The most important and valuable resource any company is its employee. Employees who have been well-trained will be better at their jobs and produce a better product.  An employee who is well trained obviously knows more about their job and all the technical aspects. I have a very high opinion about training employees and it is the most important task. Developer Training – Employee Morals and Ethics – Part 2 In this part we discussed the most crucial components of training. Often employees are expecting the company to pay for their training and the company expresses no interest in training the employee. Quite often training expenses are the real issue for both the employee and employer. There are companies that pay for 100% of the expenses and there are employees who opt for training on their own expense during their personal time. Training is often looked at as vacation by employee and employers and we need to change this mind-set. One of the ways is to report back the learning to your manager and implement newly learned knowledge in day-to-day work. Developer Training – Difficult Questions and Alternative Perspective - Part 3 This part was the most difficult to write as I tried to address a few difficult questions and answers. Training is such a sensitive issue that many developers when not receiving chance for training think about leaving the organization. The manager often feels pressure to accommodate every single employee for training even though his training budget is limited. It is indeed the responsibility of the developer to get maximum advantage from the training. Training immediately helps organizations but stays as a part of an employee’s knowledge forever. Developer Training – Various Options for Developer Training – Part 4 In this part I tried to explore a few methods and options for training. The generic feedback I received on this blog post was short and I should have explored each of the subject of the training in details. I believe there are two big buckets of training 1) Instructor Lead Training and 2) Self Lead Training. The common element between both the methods is “learning material”. Learning material can be of any format – videos, books, paper notes or just a plain black board. Instructor-led training is a very effective mode but not possible every single time. During the course of the developer’s career, one has to learn lots of new technology and it is almost impossible to have a quality trainer available on that subject at that time. Books are most effective and proven methods, however, it always helps if someone explains the concepts of the book with a demonstration. In recent times I have started to believe in online trainings which leads to a hybrid experience. Online trainings take the best part of the books and the best part of the instructor-led training and gives effective training in a matter of hours. Developer Training – A Conclusive Summary- Part 5 In this part, I shared what I was continuously thinking about developer training. There is no better teacher than oneself. There is no better motivation than a personal desire to learn new technology. Honestly there is nothing more personal learning. That “change is the only constant” and “adapt & overcome” are the essential lessons of life. One cannot stop the learning and resist the change. In the IT industry “ego of knowing all” and the “resistance to change” are the most challenging issues. Once someone overcomes them, life is much easier. I believe that proper and appropriate high quality training can help to address the burning issues. Opinion of Friends I invited a few of my friends to express their opinion about developer training and here are their opinions. I am listing them here in the order of the blog post publishing date. Nakul Vachhrajani - Developer Trainings-Importance, Benefits, Tips and follow-up Nakul’s sums of many of the concepts which are complementary to my blog posts. Nakul addresses the burning question of developer training with different angles. I am personally very impressed by his following statement - “Being skilled does not mean having just a stack of certifications, but it also means having an understanding about the internals of the products that you are working on – and using that knowledge to improve the efficiency & productivity at the workplace in turn resulting in better products, better consulting abilities and a happier self.” Nakul also suggests the online training options of Pluralsight. Vinod Kumar - Training–a necessity or bonus Vinod Kumar comes up with excellent follow up on developer training. Vinod is known for his inspirational writing about SQL Server. Vinod starts with a story of a student who is extremely eager to learn the wisdom of life from a monk but the monk does not accept him as a disciple for a long time. The conversation between student and monk is indeed an essence of all learning. We all want to learn quickly and be successful but the most important thing in life is to have the right attitude towards learning and more so towards life. The blog post end with a very important thought about how to avoid the famous excuse – “I don’t have enough time.” Ritesh Shah - Training – useful or useless? Ritesh brings up very important concept related to training. Ritesh in his meticulous style explains why training is an important and lifelong process. Training must not stop at any age but should continue forever. The moment training stops, progress stops along with. Paras Doshi - Professional Development Resource Paras is known for his to–the-point writing, and has summarized the five part series very precisely. He read the five part series and created a digest summary of the blog post. If you are in a rush and have no time to read my five series – I suggest you read his blog post. Training Resources I am often asked what the best resources for learning new technology are. This is the most difficult question EVER. There are plenty of good training resources available. When it is about training our needs are different, our preference of learning is different and we all have an opinion. Additionally, we all are located in different geographic locations worldwide and there is no way one solution will fit all. However, let me list a few of the training resources which I have built so far and you can consume them if you find it relevant to your need. SQL Server Books SQL Server Interview Questions and Answers SQL Wait Stats SQL Programming Joes 2 Pros SQL Server Video Tutorials SQL Server Questions and Answers SQL Server Performance: Indexing Basics SQL Server Performance: Introduction to Query Tuning SQL in Sixty Seconds Series of Sixty Seconds Learning Video on YouTube Trust me worldwide web is very big and there are plenty of high quality learning materials available worldwide – trainer-led as well online. I suggest you explore various options and make the best choice for yourself. Remember, training is your personal journey and it should never stop. Are you ready? Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Developer Training, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Installing software from source

    - by Learning
    I'm trying to understand the rational behind installing from software from source in Ubuntu 12.04. Obviously, I know I can download what I need from repos, but I want to develop a deeper understanding of Linux. As a Windows users, when I download a program I double click it, and it installs into the program files directory unless I specify otherwise. When I want to uninstall it, Windows has a tools that does that for me. When I install a program in Linux, where does it install to? How do I uninstall it afterwards? Are there residual files left over? How would I tell if it's been fully removed? For instance, I'm going to install LMMS (Linux Multimedia Studio) from source. I download and decompress the tar ball, and have a folder name lmms_XXX.tar (whatever). The folder is now on my desktop with an install file. If I run the install file from that location, does it install into that folder? If so, can I move that folder to where ever I want? I want thinking about putting it in /opt/lmms

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  • Evidence-Based-Scheduling - are estimations only as accurate as the work-plan they're based on?

    - by Assaf Lavie
    I've been using FogBugz's Evidence Based Scheduling (for the uninitiated, Joel explains) for a while now and there's an inherent problem I can't seem to work around. The system is good at telling me the probability that a given project will be delivered at some date, given the detailed list of tasks that comprise the project. However, it does not take into account the fact that during development additional tasks always pop up. Now, there's the garbage-can approach of creating a generic task/scheduled-item for "last minute hacks" or "integration tasks", or what have you, but that clearly goes against the idea of aggregating the estimates of many small cases. It's often the case that during the development stage of a project you realize that there's a whole area your planning didn't cover, because, well, that's the nature of developing stuff that hasn't been developed before. So now your ~3 month project may very well turn into a 6 month project, but not because your estimations were off (you could be the best estimator in the world, for those task the comprised your initial work plan); rather because you ended up adding a whole bunch of new tasks that weren't there to begin with. EBS doesn't help you with that. It could, theoretically (I guess). It could, perhaps, measure the amount of work you add to a project over time and take that into consideration when estimating the time remaining on a given project. Just a thought. In other words, EBS works on a task basis, but not on a project/release basis - but the latter is what's important. It's what your boss typically cares about - delivery date, not the time it takes to finish each task along the way, and not the time it would have taken, if your planning was perfect. So the question is (yes, there's a question here, don't close it): What's your methodology when it comes to using EBS in FogBugz and how do you solve the problem above, which seems to be a main cause of schedule delays and mispredictions? Edit Some more thoughts after reading a few answers: If it comes down to having to choose which delivery date you're comfortable presenting to your higher-ups by squinting at the delivery-probability graph and choosing 80%, or 95%, or 60% (based on what, exactly?) then we've resorted to plain old buffering/factoring of our estimates. In which case, couldn't we have skipped the meticulous case by case hour-sized estimation effort step? By forcing ourselves to break down tasks that take more than a day into smaller chunks of work haven't we just deluded ourselves into thinking our planning is as tight and thorough as it could be? People may be consistently bad estimators that do not even learn from their past mistakes. In that respect, having an EBS system is certainly better than not having one. But what can we do about the fact that we're not that good in planning as well? I'm not sure it's a problem that can be solved by a similar system. Our estimates are wrong because of tendencies to be overly optimistic/pessimistic about certain tasks, and because of neglect to account for systematic delays (e.g. sick days, major bug crisis) - and usually not because we lack knowledge about the work that needs to be done. Our planning, on the other hand, is often incomplete because we simply don't have enough knowledge in this early stage; and I don't see how an EBS-like system could fill that gap. So we're back to methodology. We need to find a way to accommodate bad or incomplete work plans that's better than voodoo-multiplication.

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  • Android passing an arraylist back to parent activity

    - by Nicklas O
    Hi there. I've been searching for a simple example of this with no luck. In my android application I have two activities: 1. The main activity which is launched at startup 2. A second activity which is launched by pressing a button on the main activty. When the second activity is finished (by pressing a button) I want it to send back an ArrayList of type MyObject to the main activity and close itself, which the main activity can then do whatever with it. How would I go about achieving this? I have been trying a few things but it is crashing my application when I start the second activity. When the user presses button to launch second activity: Intent i = new Intent(MainActivity.this, secondactivity.class); startActivityForResult(i, 1); The array which is bundled back after pressing a button on the second activity: Intent intent= getIntent(); Bundle b = new Bundle(); b.putParcelableArrayList("myarraylist", mylist); intent.putExtras(b); setResult(RESULT_OK, intent); finish(); And finally a listener on the main activity (although I'm not sure of 100% when this code launches...) protected void onActivityResult(int requestCode, int resultCode, Intent data) { super.onActivityResult(requestCode, resultCode, data); if(resultCode==RESULT_OK && requestCode==1){ Bundle extras = data.getExtras(); final ArrayList<MyObject> mylist = extras.getParcelableArrayList("myarraylist"); Toast.makeText(MainActivity.this, mylist.get(0).getName(), Toast.LENGTH_SHORT).show(); } } Any ideas where I am going wrong? The onActivityResult() seems to be crashing my application. EDIT: This is my class MyObject, its called plan and has a name and an id import android.os.Parcel; import android.os.Parcelable; public class Plan implements Parcelable{ private String name; private String id; public Plan(){ } public Plan(String name, String id){ this.name = name; this.id = id; } public String getName(){ return name; } public void setName(String name){ this.name = name; } public String getId(){ return id; } public void setId(String id){ this.id = id; } public String toString(){ return "Plan ID: " + id + " Plan Name: " + name; } @Override public int describeContents() { // TODO Auto-generated method stub return 0; } @Override public void writeToParcel(Parcel dest, int flags) { dest.writeString(id); dest.writeString(name); } public static final Parcelable.Creator<Plan> CREATOR = new Parcelable.Creator<Plan>() { public Plan createFromParcel(Parcel in) { return new Plan(); } @Override public Plan[] newArray(int size) { // TODO Auto-generated method stub return new Plan[size]; } }; } This is my logcat E/AndroidRuntime( 293): java.lang.RuntimeException: Unable to instantiate activ ity ComponentInfo{com.daniel.android.groupproject/com.me.android.projec t.secondactivity}: java.lang.NullPointerException E/AndroidRuntime( 293): at android.app.ActivityThread.performLaunchActiv ity(ActivityThread.java:2417) E/AndroidRuntime( 293): at android.app.ActivityThread.handleLaunchActivi ty(ActivityThread.java:2512) E/AndroidRuntime( 293): at android.app.ActivityThread.access$2200(Activi tyThread.java:119) E/AndroidRuntime( 293): at android.app.ActivityThread$H.handleMessage(Ac tivityThread.java:1863) E/AndroidRuntime( 293): at android.os.Handler.dispatchMessage(Handler.ja va:99) E/AndroidRuntime( 293): at android.os.Looper.loop(Looper.java:123) E/AndroidRuntime( 293): at android.app.ActivityThread.main(ActivityThrea d.java:4363) E/AndroidRuntime( 293): at java.lang.reflect.Method.invokeNative(Native Method) E/AndroidRuntime( 293): at java.lang.reflect.Method.invoke(Method.java:5 21) E/AndroidRuntime( 293): at com.android.internal.os.ZygoteInit$MethodAndA rgsCaller.run(ZygoteInit.java:860) E/AndroidRuntime( 293): at com.android.internal.os.ZygoteInit.main(Zygot eInit.java:618) E/AndroidRuntime( 293): at dalvik.system.NativeStart.main(Native Method) E/AndroidRuntime( 293): Caused by: java.lang.NullPointerException E/AndroidRuntime( 293): at com.daniel.android.groupproject.login.<init>( login.java:51) E/AndroidRuntime( 293): at java.lang.Class.newInstanceImpl(Native Method ) E/AndroidRuntime( 293): at java.lang.Class.newInstance(Class.java:1479) E/AndroidRuntime( 293): at android.app.Instrumentation.newActivity(Instr umentation.java:1021) E/AndroidRuntime( 293): at android.app.ActivityThread.performLaunchActiv ity(ActivityThread.java:2409) E/AndroidRuntime( 293): ... 11 more

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  • Get Unlimited Oracle Training for Your Team for an Entire Year

    - by KJones
    Written By Amit Kumar, Senior Director Oracle University Digital Training  Oracle University has been in the training business for a long time (over 30 years!) and has worked with many Oracle customers over the years.  We understand that getting your teams trained on the latest Oracle technologies is not always easy. Training becomes more challenging when you have remote teams, team members with different skill levels or experienced team members who just need the content that covers the latest product features. It can also be challenging to predict your training needs for the year, making it all the more difficult to provide training in a timely manner. Oracle Unlimited Learning Subscription is the Answer We’ve listened to our customers and we’ve worked hard to put together a flexible training solution that enables team members to get the training that addresses their individual needs, right when they need it. This new Oracle Unlimited Learning Subscription provides teams with one year of unlimited access to: •    All of Oracle's Training On Demand video courses for in-depth product training •    All of Oracle's Learning Streams, which provide fresh product content from Oracle experts for continuous learning •    Live connections with Oracle's top instructors  •    Dedicated labs for hands-on practice The Oracle Unlimited Learning Subscription is 100% digital, giving you maximum flexibility. It simplifies how you plan and budget for your team training.  Learning Oracle and staying connected with Oracle really has never been easier. Take a tour and contact your Oracle University representative today to learn more and request a demo. 

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  • How to implement Restricted access to application features

    - by DroidUser
    I'm currently developing a web application, that provides some 'service' to the user. The user will have to select a 'plan' according to which she/he will be allowed to perform application specific actions but up to a limit defined by the plan. A Plan will also limit access to certain features, which will not be available at all for some plans. As an example : say there are 3 plans, 2 actions throughout the application users in plan-1 can perform action-1 3 times, and they can't perform action-2 at all users in plan-2 can perform action-1 10 times, action-2 5 times users in plan-3 can perform action-1 20 times, action-2 10 times So i'm looking for the best way to get this done, and my main concerns besides implementing it, are the following(in no particular order) maintainability/changeability : the number of plans, and type of features/actions will change in the final product industry standard/best practice : for future readiness!! efficiency : ofcourse, i want fast code!! I have never done anything like this before, so i have no clue about how do i go about implementing these functionalities. Any tips/guides/patterns/resources/examples? I did read a little about ACL, RBAC, are they the patterns that i need to follow? Really any sort of feedback will help.

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  • Entity Framework vs. nHibernate for Performance, Learning Curve overall features

    - by hadi
    I know this has been asked several times and I have read all the posts as well but they all are very old. And considering there have been advancements in versions and releases, I am hoping there might be fresh views. We are building a new application on ASP.NET MVC and need to finalize on an ORM tool. We have never used ORM before and have pretty much boiled down to two - nHibernate & Entity Framework. I really need some advice from someone who has used both these tools and can recommend based on experience. There are three points that I am focusing on to finalize - Performance Learning Curve Overall Capability Your advice will be highly appreciated. Best Regards,

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  • Can learning a new language (Human not programming) help your career?

    - by Omar Kooheji
    I was wondering if anyone had any experience of learning a new language (a human language not a programming one) and whether is has helped you get ahead in your career. I'm assuming that the new language is one other than English which I think is fairly essential to programming as most programming resources seem to be english. The reason I ask is I speak Arabic and was told that it would give me an edge when I was looking for jobs, and yet so far in my current job it's completely irrelevant and in my last job I had it was used but I didn't get any special "appreciation" for speaking it.

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  • Where is the best place to start learning Java Socket Programming?

    - by MarcoBoomTing
    I wish to create a Java Socket server which can be connected to using Javascript and/or Flash. I have experience in Connecting to sockets in flash, and using a comet like system in Ajax. I wish to make a live communication system, which will intale multiple connections to the server from various clients, needing almost instant communication between peers. I coded a system like this in PHP but I want to convert it to Java, simply because I don't want the PHP engine to be tied up on this Sever, as it serves all the web stuff normally on the site, and i've heard is more powerful for this sort of thing. Just looking for advice on where I can start learning how to write this sort of system using Java? I have previous coding experience in PHP, Javascript, Adobe Air and AS3 if That helps?

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  • Partition Wise Joins II

    - by jean-pierre.dijcks
    One of the things that I did not talk about in the initial partition wise join post was the effect it has on resource allocation on the database server. When Oracle applies a different join method - e.g. not PWJ - what you will see in SQL Monitor (in Enterprise Manager) or in an Explain Plan is a set of producers and a set of consumers. The producers scan the tables in the the join. If there are two tables the producers first scan one table, then the other. The producers thus provide data to the consumers, and when the consumers have the data from both scans they do the join and give the data to the query coordinator. Now that behavior means that if you choose a degree of parallelism of 4 to run such query with, Oracle will allocate 8 parallel processes. Of these 8 processes 4 are producers and 4 are consumers. The consumers only actually do work once the producers are fully done with scanning both sides of the join. In the plan above you can see that the producers access table SALES [line 11] and then do a PX SEND [line 9]. That is the producer set of processes working. The consumers receive that data [line 8] and twiddle their thumbs while the producers go on and scan CUSTOMERS. The producers send that data to the consumer indicated by PX SEND [line 5]. After receiving that data [line 4] the consumers do the actual join [line 3] and give the data to the QC [line 2]. BTW, the myth that you see twice the number of processes due to the setting PARALLEL_THREADS_PER_CPU=2 is obviously not true. The above is why you will see 2 times the processes of the DOP. In a PWJ plan the consumers are not present. Instead of producing rows and giving those to different processes, a PWJ only uses a single set of processes. Each process reads its piece of the join across the two tables and performs the join. The plan here is notably different from the initial plan. First of all the hash join is done right on top of both table scans [line 8]. This query is a little more complex than the previous so there is a bit of noise above that bit of info, but for this post, lets ignore that (sort stuff). The important piece here is that the PWJ plan typically will be faster and from a PX process number / resources typically cheaper. You may want to look out for those plans and try to get those to appear a lot... CREDITS: credits for the plans and some of the info on the plans go to Maria, as she actually produced these plans and is the expert on plans in general... You can see her talk about explaining the explain plan and other optimizer stuff over here: ODTUG in Washington DC, June 27 - July 1 On the Optimizer blog At OpenWorld in San Francisco, September 19 - 23 Happy joining and hope to see you all at ODTUG and OOW...

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  • Books or other materials to overcome Linux learning curve?

    - by Marek Osvald
    I was born in 1989 and am an active Windows user since 1993. I've always struggled with Linux, not being able to configure the system the way I would like, snooping through blogs and forums for answers, never actually overcame the barrier. The books I've seen and read are either completely command line oriented (and don't get me wrong it's awesome to know this stuff when you're working on a server for example) but seems rather impractical to me on a desktop computer that's partially my development environment. The other kind are user manual describing step-by-step the controls of simplest applications like the Calculator, totally useless to me. What would you recommend for a programmer who needs to learn how to work with Linux but already knows the basics? What materials did you use to learn how to start with Linux?

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  • Effective books for learning the intricacies of business application development?

    - by OffApps Cory
    I am a self taught "developer". I use the term loosely because I only know enough to make myself dangerous. I have no theory background, and I only pick up things to get this little tool to work or make that control do what I want. That said, I am looking for some reading material that explains some of the theory behind application development especially from a business standpoint. Really I need to understand what all of these terms that float around really talk about. Business Logic Layer, UI abstraction level and all that. Anyone got a reading list that they feel helped them understand this stuff? I know how to code stuff up so that it works. It is not pretty mostly because I don't know the elegant way of doing it, and it is not planned out very well (I also don't know how to plan an application). Any help would be appreciated. I have read a number of books on what I thought was the subject, but they all seem to rehash basic coding and what-not. This doesn't have to be specific to VB.NET or WPF (or Entity Framework) but anything with those items would be quite helpful.

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  • What are the best tricks for learning how to -think- in Objective-C?

    - by Braintapper
    Before I get flamed out for not checking previous questions, I have read most of the tutorials, and have Hillegass' book, as well as O'Reilly's book on it. I'm not asking for tips on Cocoa or what IDE to use. Where my issue lies - my 'mental muscle memory' is making it hard for me to read Objective-C code. I have no problems at all reading Java and C code and understanding what's going on. Maybe I'm getting to old to learn a new syntax, but it's a struggle shifting mental gears and looking at Objective-C code and just "getting it" (I thought it might be an isolated case, but I have other friends who are seasoned devs who have said the same thing). Are there any tricks that any non-Objective-C programmers who now know Objective-C used to help process the syntactical differences when learning it? For some reason, I get dyslexic when reading Objective-C code. Maybe I'm not meant to be able to learn it (and that's ok too). I was hoping/wondering if there might be others who have had the same experience.

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  • Parallel programming, are we not learning from history again?

    - by mezmo
    I started programming because I was a hardware guy that got bored, I thought the problems being solved in the software side of things were much more interesting than those in hardware. At that time, most of the electrical buses I dealt with were serial, some moving data as fast as 1.5 megabit!! ;) Over the years these evolved into parallel buses in order to speed communication up, after all, transferring 8/16/32/64, whatever bits at a time incredibly speeds up the transfer. Well, our ability to create and detect state changes got faster and faster, to the point where we could push data so fast that interference between parallel traces or cable wires made cleaning the signal too expensive to continue, and we still got reasonable performance from serial interfaces, heck some graphics interfaces are even happening over USB for a while now. I think I'm seeing a like trend in software now, our processors were getting faster and faster, so we got good at building "serial" software. Now we've hit a speed bump in raw processor speed, so we're adding cores, or "traces" to the mix, and spending a lot of time and effort on learning how to properly use those. But I'm also seeing what I feel are advances in things like optical switching and even quantum computing that could take us far more quickly that I was expecting back to the point where "serial programming" again makes the most sense. What are your thoughts?

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  • learning C++ from java, trying to make a linked list.

    - by kyeana
    I just started learning c++ (coming from java) and am having some serious problems with doing anything :P Currently, i am attempting to make a linked list, but must be doing something stupid cause i keep getting "void value not ignored as it ought to be" compile errors (i have it marked where it is throwing it bellow). If anyone could help me with what im doing wrong, i would be very grateful :) Also, I am not used to having the choice of passing by reference, address, or value, and memory management in general (currently i have all my nodes and the data declared on the heap). If anyone has any general advice for me, i also wouldn't complain :P Key code from LinkedListNode.cpp LinkedListNode::LinkedListNode() { //set next and prev to null pData=0; //data needs to be a pointer so we can set it to null for //for the tail and head. pNext=0; pPrev=0; } /* * Sets the 'next' pointer to the memory address of the inputed reference. */ void LinkedListNode::SetNext(LinkedListNode& _next) { pNext=&_next; } /* * Sets the 'prev' pointer to the memory address of the inputed reference. */ void LinkedListNode::SetPrev(LinkedListNode& _prev) { pPrev=&_prev; } //rest of class Key code from LinkedList.cpp #include "LinkedList.h" LinkedList::LinkedList() { // Set head and tail of linked list. pHead = new LinkedListNode(); pTail = new LinkedListNode(); /* * THIS IS WHERE THE ERRORS ARE. */ *pHead->SetNext(*pTail); *pTail->SetPrev(*pHead); } //rest of class

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  • Cardinality Estimation Bug with Lookups in SQL Server 2008 onward

    - by Paul White
    Cost-based optimization stands or falls on the quality of cardinality estimates (expected row counts).  If the optimizer has incorrect information to start with, it is quite unlikely to produce good quality execution plans except by chance.  There are many ways we can provide good starting information to the optimizer, and even more ways for cardinality estimation to go wrong.  Good database people know this, and work hard to write optimizer-friendly queries with a schema and metadata (e.g. statistics) that reduce the chances of poor cardinality estimation producing a sub-optimal plan.  Today, I am going to look at a case where poor cardinality estimation is Microsoft’s fault, and not yours. SQL Server 2005 SELECT th.ProductID, th.TransactionID, th.TransactionDate FROM Production.TransactionHistory AS th WHERE th.ProductID = 1 AND th.TransactionDate BETWEEN '20030901' AND '20031231'; The query plan on SQL Server 2005 is as follows (if you are using a more recent version of AdventureWorks, you will need to change the year on the date range from 2003 to 2007): There is an Index Seek on ProductID = 1, followed by a Key Lookup to find the Transaction Date for each row, and finally a Filter to restrict the results to only those rows where Transaction Date falls in the range specified.  The cardinality estimate of 45 rows at the Index Seek is exactly correct.  The table is not very large, there are up-to-date statistics associated with the index, so this is as expected. The estimate for the Key Lookup is also exactly right.  Each lookup into the Clustered Index to find the Transaction Date is guaranteed to return exactly one row.  The plan shows that the Key Lookup is expected to be executed 45 times.  The estimate for the Inner Join output is also correct – 45 rows from the seek joining to one row each time, gives 45 rows as output. The Filter estimate is also very good: the optimizer estimates 16.9951 rows will match the specified range of transaction dates.  Eleven rows are produced by this query, but that small difference is quite normal and certainly nothing to worry about here.  All good so far. SQL Server 2008 onward The same query executed against an identical copy of AdventureWorks on SQL Server 2008 produces a different execution plan: The optimizer has pushed the Filter conditions seen in the 2005 plan down to the Key Lookup.  This is a good optimization – it makes sense to filter rows out as early as possible.  Unfortunately, it has made a bit of a mess of the cardinality estimates. The post-Filter estimate of 16.9951 rows seen in the 2005 plan has moved with the predicate on Transaction Date.  Instead of estimating one row, the plan now suggests that 16.9951 rows will be produced by each clustered index lookup – clearly not right!  This misinformation also confuses SQL Sentry Plan Explorer: Plan Explorer shows 765 rows expected from the Key Lookup (it multiplies a rounded estimate of 17 rows by 45 expected executions to give 765 rows total). Workarounds One workaround is to provide a covering non-clustered index (avoiding the lookup avoids the problem of course): CREATE INDEX nc1 ON Production.TransactionHistory (ProductID) INCLUDE (TransactionDate); With the Transaction Date filter applied as a residual predicate in the same operator as the seek, the estimate is again as expected: We could also force the use of the ultimate covering index (the clustered one): SELECT th.ProductID, th.TransactionID, th.TransactionDate FROM Production.TransactionHistory AS th WITH (INDEX(1)) WHERE th.ProductID = 1 AND th.TransactionDate BETWEEN '20030901' AND '20031231'; Summary Providing a covering non-clustered index for all possible queries is not always practical, and scanning the clustered index will rarely be optimal.  Nevertheless, these are the best workarounds we have today. In the meantime, watch out for poor cardinality estimates when a predicate is applied as part of a lookup. The worst thing is that the estimate after the lookup join in the 2008+ plans is wrong.  It’s not hopelessly wrong in this particular case (45 versus 16.9951 is not the end of the world) but it easily can be much worse, and there’s not much you can do about it.  Any decisions made by the optimizer after such a lookup could be based on very wrong information – which can only be bad news. If you think this situation should be improved, please vote for this Connect item. © 2012 Paul White – All Rights Reserved twitter: @SQL_Kiwi email: [email protected]

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  • sys.dm_exec_query_stats interaction with recompilation

    - by Sam Saffron
    We use sys.dm_exec_query_stats to track down slow queries and queries that are IO offenders. This works great, we get a lot of very insightful stats. It is clear this is not as accurate as running a profiler trace, as you have no idea when SQL Server will decide to chuck out a an execution plan. We have quite a few queries where the wrong execution plan is cached. For example queries like the following: SELECT TOP 30 a.Id FROM Posts a JOIN Posts q ON q.Id = a.ParentId JOIN PostTags pt ON q.Id = pt.PostId WHERE a.PostTypeId = 2 AND a.DeletionDate IS NULL AND a.CommunityOwnedDate IS NULL AND a.CreationDate @date AND LEN(a.Body) 300 AND pt.Tag = @tag AND a.Score 0 ORDER BY a.Score DESC The problem is that the ideal plan really depends on the date selected (screenshot of ideal plan): However if the wrong plan is cached, it totally chokes when the date range is big: (notice the big fat lines) To overcome this we were recommended to use either OPTION (OPTIMIZE FOR UNKNOWN) or OPTION (RECOMPILE) OPTIMIZE FOR UNKNOWN results in a slightly better plan, which is far from optimal. Executions are tracked in sys.dm_exec_query_stats. RECOMPILE results in the best plan being chosen, however no execution counts and stats are tracked in sys.dm_exec_query_stats. Is there another DMV we could use to track stats on queries with OPTION (RECOMPILE)? Is this behavior by-design? Is there another way we can for recompilation while keeping stats tracked in sys.dm_exec_query_stats? Note: the framework will always execute parameterized queries using sp_executesql

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  • ?Oracle????SELECT????UNDO

    - by Liu Maclean(???)
    ????????Oracle?????(dirty read),?Oracle??????Asktom????????Oracle???????, ???undo??????????(before image)??????Consistent, ???????????????Oracle????????????? ????????? ??,??,Oracle?????????????RDBMS,???????????? ?????????2?????: _offline_rollback_segments or _corrupted_rollback_segments ?2?????????Oracle???????????ORA-600[4XXX]???????????????,???2??????Undo??Corruption????????????,?????2????????????????? ??????????????_offline_rollback_segments ? _corrupted_rollback_segments ?2?????: ???????(FORCE OPEN DATABASE) ????????????(consistent read & delayed block cleanout) ??????rollback segment??? ?????:???????Oracle????????,??????????2?????,?????????????!! _offline_rollback_segments ? _corrupted_rollback_segments ???????????: ??2???????Undo Segments(???/???)????????online ?UNDO$???????????OFFLINE??? ???instance??????????????????? ??????Undo Segments????????active transaction????????????dead??SMON???(????????SMON??(?):Recover Dead transaction) _OFFLINE_ROLLBACK_SEGMENTS(offline undo segment list)????(hidden parameter)?????: ???startup???open database???????_OFFLINE_ROLLBACK_SEGMENTS????Undo segments(???/???),?????undo segments????????alert.log???TRACE?????,???????startup?? ?????????????,?ITL?????undo segments?: ???undo segments?transaction table?????????????????? ???????????commit,?????CR??? ????undo segments????(???corrupted??,???missed??)???????????alert.log,??????? ?DML?????????????????????????????????CPU,????????????????????? _CORRUPTED_ROLLBACK_SEGMENTS(corrupted undo segment list)??????????: ?????startup?open database???_CORRUPTED_ROLLBACK_SEGMENTS????undo segments(???/???)???????? ???????_CORRUPTED_ROLLBACK_SEGMENTS???undo segments????????????commit,???undo segments???drop??? ??????????? ??????????????????,?????????????????? ??bootstrap???????????,?????????ORA-00704: bootstrap process failure??,???????????(???Oracle????:??ORA-00600:[4000] ORA-00704: bootstrap process failure????) ??????_CORRUPTED_ROLLBACK_SEGMENTS????????????????????,??????????????? Oracle???????TXChecker??????????? ???????2?????,??????????????_CORRUPTED_ROLLBACK_SEGMENTS?????SELECT????UNDO???????: SQL> alter system set event= '10513 trace name context forever, level 2' scope=spfile; System altered. SQL> alter system set "_in_memory_undo"=false scope=spfile; System altered. 10513 level 2 event????SMON ??rollback ??? dead transaction _in_memory_undo ?? in memory undo ?? SQL> startup force; ORACLE instance started. Total System Global Area 3140026368 bytes Fixed Size 2232472 bytes Variable Size 1795166056 bytes Database Buffers 1325400064 bytes Redo Buffers 17227776 bytes Database mounted. Database opened. session A: SQL> conn maclean/maclean Connected. SQL> create table maclean tablespace users as select 1 t1 from dual connect by level exec dbms_stats.gather_table_stats('','MACLEAN'); PL/SQL procedure successfully completed. SQL> set autotrace on; SQL> select sum(t1) from maclean; SUM(T1) ---------- 501 Execution Plan ---------------------------------------------------------- Plan hash value: 1679547536 ------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 3 | 3 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 3 | | | | 2 | TABLE ACCESS FULL| MACLEAN | 501 | 1503 | 3 (0)| 00:00:01 | ------------------------------------------------------------------------------ Statistics ---------------------------------------------------------- 1 recursive calls 0 db block gets 3 consistent gets 0 physical reads 0 redo size 515 bytes sent via SQL*Net to client 492 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processe ???????????,????current block, ????????,consistent gets??3? SQL> update maclean set t1=0; 501 rows updated. SQL> alter system checkpoint; System altered. ??session A?commit; ???? session: SQL> conn maclean/maclean Connected. SQL> SQL> set autotrace on; SQL> select sum(t1) from maclean; SUM(T1) ---------- 501 Execution Plan ---------------------------------------------------------- Plan hash value: 1679547536 ------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 3 | 3 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 3 | | | | 2 | TABLE ACCESS FULL| MACLEAN | 501 | 1503 | 3 (0)| 00:00:01 | ------------------------------------------------------------------------------ Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 505 consistent gets 0 physical reads 108 redo size 515 bytes sent via SQL*Net to client 492 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed ?????? ?????????undo??CR?,???consistent gets??? 505 [oracle@vrh8 ~]$ ps -ef|grep LOCAL=YES |grep -v grep oracle 5841 5839 0 09:17 ? 00:00:00 oracleG10R25 (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq))) [oracle@vrh8 ~]$ kill -9 5841 ??session A???Server Process????,???dead transaction ????smon?? select ktuxeusn, to_char(sysdate, 'DD-MON-YYYY HH24:MI:SS') "Time", ktuxesiz, ktuxesta from x$ktuxe where ktuxecfl = 'DEAD'; KTUXEUSN Time KTUXESIZ KTUXESTA ---------- -------------------- ---------- ---------------- 2 06-AUG-2012 09:20:45 7 ACTIVE ???1?active rollback segment SQL> conn maclean/maclean Connected. SQL> set autotrace on; SQL> select sum(t1) from maclean; SUM(T1) ---------- 501 Execution Plan ---------------------------------------------------------- Plan hash value: 1679547536 ------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 3 | 3 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 3 | | | | 2 | TABLE ACCESS FULL| MACLEAN | 501 | 1503 | 3 (0)| 00:00:01 | ------------------------------------------------------------------------------ Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 411 consistent gets 0 physical reads 108 redo size 515 bytes sent via SQL*Net to client 492 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed ????? ????kill?? ???smon ??dead transaction , ???????????? ?????undo??????? ????active?rollback segment??? SQL> select segment_name from dba_rollback_segs where segment_id=2; SEGMENT_NAME ------------------------------ _SYSSMU2$ SQL> alter system set "_corrupted_rollback_segments"='_SYSSMU2$' scope=spfile; System altered. ? _corrupted_rollback_segments ?? ???2?rollback segment, ????????undo SQL> startup force; ORACLE instance started. Total System Global Area 3140026368 bytes Fixed Size 2232472 bytes Variable Size 1795166056 bytes Database Buffers 1325400064 bytes Redo Buffers 17227776 bytes Database mounted. Database opened. SQL> conn maclean/maclean Connected. SQL> set autotrace on; SQL> select sum(t1) from maclean; SUM(T1) ---------- 94 Execution Plan ---------------------------------------------------------- Plan hash value: 1679547536 ------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 3 | 3 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 3 | | | | 2 | TABLE ACCESS FULL| MACLEAN | 501 | 1503 | 3 (0)| 00:00:01 | ------------------------------------------------------------------------------ Statistics ---------------------------------------------------------- 228 recursive calls 0 db block gets 29 consistent gets 5 physical reads 116 redo size 514 bytes sent via SQL*Net to client 492 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 4 sorts (memory) 0 sorts (disk) 1 rows processed SQL> / SUM(T1) ---------- 94 Execution Plan ---------------------------------------------------------- Plan hash value: 1679547536 ------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 3 | 3 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 3 | | | | 2 | TABLE ACCESS FULL| MACLEAN | 501 | 1503 | 3 (0)| 00:00:01 | ------------------------------------------------------------------------------ Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 3 consistent gets 0 physical reads 0 redo size 514 bytes sent via SQL*Net to client 492 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed ?????? consistent gets???3,?????????????????,??ITL???UNDO SEGMENTS?_corrupted_rollback_segments????,???????????COMMIT??,????UNDO? ???????,?????????????????????????(????????????????????),????????????????? ???? , ?????

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  • When a professional should plan to leave a job ?

    - by Indigo Praveen
    Hi All, I don't know whether this should be asked or not but I think it happens with every programmer in his/her career. The question is when should someone start for looking another job. Some guys remain in one company for 10-15-20 years, mostlay in Europe. But if we see the trend in India guys are changing their jobs only in 1-2 years. If it's happening in India then there must be something behind it. So, I want to know the impacts on someone's career of changing jobs frequently. Please share your experiences.

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  • How much detail should be in a project plan or spec?

    - by DeanMc
    I have an issue that I feel many programmers can relate to... I have worked on many small scale projects. After my initial paper brain storm I tend to start coding. What I come up with is usually a rough working model of the actual application. I design in a disconnected fashion so I am talking about underlying code libraries, user interfaces are the last thing as the library usually dictates what is needed in the UI. As my projects get bigger I worry that so should my "spec" or design document. The above paragraph, from my investigations, is echoed all across the internet in one fashion or another. When a UI is concerned there is a bit more information but it is UI specific and does not relate to code libraries. What I am beginning to realise is that maybe code is code is code. It seems from my extensive research that there is no 1:1 mapping between a design document and the code. When I need to research a topic I dump information into OneNote and from there I prioritise features into versions and then into related chunks so that development runs in a fairly linear fashion, my tasks tend to look like so: Implement Binary File Reader Implement Binary File Writer Create Object to encapsulate Data for expression to the caller Now any programmer worth his salt is aware that between those three to do items could be a potential wall of code that could expand out to multiple files. I have tried to map the complete code process for each task but I simply don't think it can be done effectively. By the time one mangles pseudo code it is essentially code anyway so the time investment is negated. So my question is this: Am I right in assuming that the best documentation is the code itself. We are all in agreement that a high level overview is needed. How high should this be? Do you design to statement, class or concept level? What works for you?

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  • Where can I find a good software implementation plan template?

    - by Corpsekicker
    This is not "programming" related as much as it is "software engineering" related. I am required to produce an implementation for additional functionality to a complete system. All I am armed with is knowledge of the existing architecture and a functional spec with visual requirements, user stories and use cases. Is there a standardised way to go about this? I suck at documentation.

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