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• SQL SERVER – Backing Up and Recovering the Tail End of a Transaction Log – Notes from the Field #042

  - by Pinal Dave

  [Notes from Pinal]: The biggest challenge which people face is not taking backup, but the biggest challenge is to restore a backup successfully. I have seen so many different examples where users have failed to restore their database because they made some mistake while they take backup and were not aware of the same. Tail Log backup was such an issue in earlier version of SQL Server but in the latest version of SQL Server, Microsoft team has fixed the confusion with additional information on the backup and restore screen itself. Now they have additional information, there are a few more people confused as they have no clue about this. Previously they did not find this as a issue and now they are finding tail log as a new learning. Linchpin People are database coaches and wellness experts for a data driven world. In this 42nd episode of the Notes from the Fields series database expert Tim Radney (partner at Linchpin People) explains in a very simple words, Backing Up and Recovering the Tail End of a Transaction Log. Many times when restoring a database over an existing database SQL Server will warn you about needing to make a tail end of the log backup. This might be your reminder that you have to choose to overwrite the database or could be your reminder that you are about to write over and lose any transactions since the last transaction log backup. You might be asking yourself “What is the tail end of the transaction log”. The tail end of the transaction log is simply any committed transactions that have occurred since the last transaction log backup. This is a very crucial part of a recovery strategy if you are lucky enough to be able to capture this part of the log. Most organizations have chosen to accept some amount of data loss. You might be shaking your head at this statement however if your organization is taking transaction logs backup every 15 minutes, then your potential risk of data loss is up to 15 minutes. Depending on the extent of the issue causing you to have to perform a restore, you may or may not have access to the transaction log (LDF) to be able to back up those vital transactions. For example, if the storage array or disk that holds your transaction log file becomes corrupt or damaged then you wouldn’t be able to recover the tail end of the log. If you do have access to the physical log file then you can still back up the tail end of the log. In 2013 I presented a session at the PASS Summit called “The Ultimate Tail Log Backup and Restore” and have been invited back this year to present it again. During this session I demonstrate how you can back up the tail end of the log even after the data file becomes corrupt. In my demonstration I set my database offline and then delete the data file (MDF). The database can’t become more corrupt than that. I attempt to bring the database back online to change the state to RECOVERY PENDING and then backup the tail end of the log. I can do this by specifying WITH NO_TRUNCATE. Using NO_TRUNCATE is equivalent to specifying both COPY_ONLY and CONTINUE_AFTER_ERROR. It as its name says, does not try to truncate the log. This is a great demo however how could I achieve backing up the tail end of the log if the failure destroys my entire instance of SQL and all I had was the LDF file? During my demonstration I also demonstrate that I can attach the log file to a database on another instance and then back up the tail end of the log. If I am performing proper backups then my most recent full, differential and log files should be on a server other than the one that crashed. I am able to achieve this task by creating new database with the same name as the failed database. I then set the database offline, delete my data file and overwrite the log with my good log file. I attempt to bring the database back online and then backup the log with NO_TRUNCATE just like in the first example. I encourage each of you to view my blog post and watch the video demonstration on how to perform these tasks. I really hope that none of you ever have to perform this in production, however it is a really good idea to know how to do this just in case. It really isn’t a matter of “IF” you will have to perform a restore of a production system but more of a “WHEN”. Being able to recover the tail end of the log in these sever cases could be the difference of having to notify all your business customers of data loss or not. If you want me to take a look at your server and its settings, or if your server is facing any issue we can Fix Your SQL Server. Note: Tim has also written an excellent book on SQL Backup and Recovery, a must have for everyone. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: Notes from the Field, PostADay, SQL, SQL Authority, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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• How often should we write unit tests?

  - by Midnight Blue

  Hi, I am recently introduced to the test-driven approach to development by my mentor at work, and he encourages me to write an unit-test whenenver "it makes sense." I understand some benefits of having a throughout unit-test suite for both regression testing and refractoring, but I do wonder how often and how throughout we should write unit-test. My mentor/development lead asks me to write a new unit test-case for a newly written control flow in a method that is already being tested by the exsisting test class, and I think it is an overkill. How often do you write your unit tests, and how detailed do you think your unit tests should be? Thanks!

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• testtesttest testesetset [closed]

  - by test

  testtesttesttesttesttest

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• SQL SERVER – #TechEdIn – Presenting Tomorrow on Speed Up! – Parallel Processes and Unparalleled Performance at TechEd India 2012

  - by pinaldave

  Performance tuning is always a very hot topic when it is about SQL Server. SQL Server Performance Tuning is a very challenging subject that requires expertise in Database Administration and Database Development. I always have enjoyed talking about SQL Server Performance tuning subject. However, in India, it’s actually the very first time someone is presenting on this interesting subject, so this time I had the biggest challenge to present this session. Frequently enough, we get these two kind of questions: How to turn off parallelism as it is reducing performance? How to turn on parallelism as I want more performance? The reality is that not everyone knows what exactly is needed by their system. In this session, I have attempted to answer this very question. I’ve decided to provide a balanced view but stay away from theory, which leads us to say “It depends”. The session will have a clear message about this towards its end. Deck Details Slides: 45+ Demos: 7+ Bonus Quiz: 5 Images: 10+ Session delivery time: 52 Mins + 8 Mins of Q & A I have presented this session a couple of times to my friends and so far have received good feedback. Oftentimes, when people hear that I am going to present 45 slides, they all say it is too much to cover. However, when I am done with the session the usual reaction is that I truly gave justice to those slides. Action Item Here are a few of the action items for all of those who are going to attend this session: If you want to attend the session, just come early. There’s a good chance that you may not get a seat because right before me, there is a session from SQL Guru Vinod Kumar. He performs a powerful delivery of million concepts in just a little time. Quiz. I will be asking few questions during the session as well as before the session starts. If you get the correct answer, I will give unique learning material for you. You may not want to miss this learning opportunity at any cosst. Session Details Title: Speed Up! – Parallel Processes and Unparalleled Performance (Add to Calendar) Abstract: “More CPU, More Performance” – A  very common understanding is that usage of multiple CPUs can improve the performance of the query. To get a maximum performance out of any query, one has to master various aspects of the parallel processes. In this deep-dive session, we will explore this complex subject with a very simple interactive demo. Attendees will walk away with proper understanding of CX_PACKET wait types, MAXDOP, parallelism threshold and various other concepts. Date and Time: March 23, 2012, 12:15 to 13:15 Location: Hotel Lalit Ashok - Kumara Krupa High Grounds, Bengaluru – 560001, Karnataka, India. Add to Calendar Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Interview Questions and Answers, SQL Query, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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• test is null in the controller upon post

  - by user281180

  I have the following codes and the test value is always null in the controller after the post. What is wrong with the following code: Model: public class Suitcase { public string Color { get; set; } public string[] Size { get; set; } public List<string> Clothes { get; set; } public List<Test> test { get; set; } } public class Test { public string Name { get; set; } public int ID { get; set; } } The view: <fieldset> <legend>All about my baggage</legend> <div class="editor-label"> <%: Html.LabelFor(model => model.Color) %> </div> <div class="editor-field"> <%: Html.TextBoxFor(model => model.Color) %> </div> <br /> <div class="editor-label"> Width, Height, Depth: </div> <div class="editor-field"> ml.TextBoxFor(model => model.Depth, new { style = "width:50px;" })%> </div> <br /> <div class="editor-label">Suitcase Contents</div> <div class="editor-field"> <div id="clothes-editor"> Clothing Item: <input type="text" id="new-clothes-item" style="width:150px" /> <button id="add-clothes">Add to suitcase</button> </div> <b>Items currently in suitcase:</b> <ul id="clothes-list"> </ul> </div> <p> <button id="pack-it">Put on Baggage Carosel</button> </p> </fieldset> <script type="text/javascript" language="javascript"> $(function () { $("button").button(); // allow users to add items to the suitcase $("#add-clothes").click(function () { var clothesText = $("#new-clothes-item"); $("#clothes-list").append("<li>" + clothesText.val() + "</li>"); clothesText.val("").focus(); }); // pack the suitcase up and send it to the baggage carosel...erm...controller $("#pack-it").click(function () { var clothesList = []; $("#clothes-list li").each(function () { clothesList.push($(this).text()) }); var SizeList = []; SizeList[0] = "Medium"; SizeList[1] = "Large"; SizeList[2] = "small"; var Data = new Object(); Data.test = []; var reading = {}; reading.Name = "Micheal" reading.ID = 123; Data.test[0] = reading; reading.Name = "Rowen" reading.ID = 1234; Data.test[1] = reading; $.ajax({ type: 'POST', traditional: true, data: { Color: $("#Color").val(), Size: SizeList, Clothes: clothesList, test: Data.test } }); }); }); </script> Controller: [HttpPost] public EmptyResult Suitcase(Suitcase lookWhatIPacked) { return new EmptyResult(); }

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• Skype performance in IPSEC VPN

  - by dunxd

  I've been challenged to "improve Skype performance" for calls within my organisation. Having read the Skype IT Administrators Guide I am wondering whether we might have a performance issue where the Skype Clients in a call are all on our WAN. The call is initiated by a Skype Client at our head office, and terminated on a Skype Client in a remote office connected via IPSEC VPN. Where this happens, I assume the trafficfrom Client A (encrypted by Skype) goes to our ASA 5510, where it is furtehr encrypted, sent to the remote ASA 5505 decrypted, then passed to Client B which decrypts the Skype encryption. Would the call quality benefit if the traffic didn't go over the VPN, but instead only relied on Skype's encryption? I imagine I could achieve this by setting up a SOCKS5 proxy in our HQ DMZ for Skype traffic. Then the traffic goes from Client A to Proxy, over the Skype relay network, then arrives at Cisco ASA 5505 as any other internet traffic, and then to Client B. Is there likely to be any performance benefit in doing this? If so, is there a way to do it that doesn't require a proxy? Has anyone else tackled this?

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• How do I improve my incremental-backup performance?

  - by Alistair Bell

  I'm currently using the traditional rsync+cp -al method to create incremental/snapshot backups of our server tree. The backups are going onto a pair of eight-disk towers connected to the backup machine (a Sandy Bridge machine with 16 GB of RAM, running CentOS 5.5) via four eSATA connections (four disks per connection). Each disk is a regular 2 TB disk, so we have 32 TB of disk space connected to the backup machine. We're backing up about 20 TB of data on the servers with this. The problem is that each daily backup is taking more than 24 hours, and the real time-killer isn't the actual rsync, but the time it takes to perform a cp -al of the tree locally on the backup machine. It's taking more than 12 hours just to make the shadow copy of the tree, and as far as I can tell the performance backlog is at the disk (top shows the cp using a lot of RAM but not a lot of CPU and mostly in uninterruptible-sleep state) We have the server data split into four major volumes (and a few minor ones), and each of these backups runs in parallel (with some offsets in the cron to try to get some disks' cp done first). There are two volumes on the backup drive, both striped LVM volumes of 16 TB each. So obviously I need to improve the performance because it's unusable as it stands. The first question is: when CentOS 6 comes out, with support for btrfs, will making snapshots of subvolumes with btrfs substantially increase this performance? The second is: is there a way, with ext3 or something else supported in CentOS 5 or 6, to 'encourage' it to put the directories/inodes in one part of a volume (which could happen to be the part that's on an SSD, via LVM) and the files in another? That would presumably solve the problem, but I don't know of ways to hint ext3 like that.

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• Poor SSL performance with vsftpd

  - by petrus

  I'm trying to tweak vsftpd to achieve maximum performance for my usage: I have only one or two clients that connect to the server. File size is between ~15MB and 1GB. Typical transfer batch represent between 1 and 2GB of data. For testing purposes, I'm using a tmpfs on both sides (thus eliminating any disks bottleneck) with a single 1GB file. When SSL is disabled, performance is good, with a transfer rate at ~120MB/s (reaching the limits of gigabit networking). With SSL enabled only for control traffic (and not data traffic), performance drops at about 112MB/s, which is still within the acceptable limits. However, when SSL is enabled for data flows, the transfer speed drops dramatically: 6.7MB/s using 3DES & SHA (ssl_ciphers=DES-CBC3-SHA in vsftpd.conf) 16MB/s using DES & SHA (ssl_ciphers=DES-CBC-SHA) I didn't tested other ciphers, but from what I can see from the CPU usage during the transfer, it seems that vsftpd is only using a single cpu/core per client. While this can fit for large ftp sites with hundreds of clients, I'd like to avoid this behavior and use more ressources on the server. On a side note, if you have any ideas regarding other openssl ciphers...

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• Performance degrades for more than 2 threads on Xeon X5355

  - by zoolii

  Hi All, I am writing an application using boost threads and using boost barriers to synchronize the threads. I have two machines to test the application. Machine 1 is a core2 duo (T8300) cpu machine (windows XP professional - 4GB RAM) where I am getting following performance figures : Number of threads :1 , TPS :21 Number of threads :2 , TPS :35 (66 % improvement) further increase in number of threads decreases the TPS but that is understandable as the machine has only two cores. Machine 2 is a 2 quad core ( Xeon X5355) cpu machine (windows 2003 server with 4GB RAM) and has 8 effective cores. Number of threads :1 , TPS :21 Number of threads :2 , TPS :27 (28 % improvement) Number of threads :4 , TPS :25 Number of threads :8 , TPS :24 As you can see, performance is degrading after 2 threads (though it has 8 cores). If the program has some bottle neck , then for 2 thread also it should have degraded. Any idea? , Explanations ? , Does the OS has some role in performance ? - It seems like the Core2duo (2.4GHz) scales better than Xeon X5355 (2.66GHz) though it has better clock speed. Thank you -Zoolii

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• Improve wireless performance

  - by djechelon

  Hello, I have a Trust Speedshare Turbo Pro router, which is running on channel 6. I found that the wireless signal (and network performance) dramatically drops from my PDA (I can barely attach to the network, even if I set the PDA's energy settings to maximum wireless performance) when I even exit my room, and I don't have shielded walls or something like that. I can't even stream a SD video from my desktop (connected via LAN) to my laptop using WiFi, while via LAN it works fine. I read that changing router's channel could improve performance due to interference reducing. I found that almost all wireless networks around here run on channels 6 and 11. I tried to go to my router's settings page to change channel, but I found that the combo box only allows me to select 6!! I'm not sure, but I may have been able in the past to change channel, though not to all of the available channels. A few minutes ago I tried a firmware upgrade, but it didn't solve my problem. My question is Is it possible that my router is someway locked to its channel? I bought it on my own, I didn't receive it from my ISP Apart from boosting the antenna power to the maximum (which, by the way, increases the EM radiation my and my family's bodies absorb 24/7 and is little more environment-unfriendly), do you have any tips on getting high quality transmission up to 5 metres from the antenna? Thank you

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• Developing high-performance and scalable zend framework website [on hold]

  - by Daniel

  We are going to develop an ads website like http://www.gumtree.com/ (it will not be like this one but just to give you an ideea) and we are having some issues regarding performance and scalability. We are planning on using Zend Framework for this project but this is all that I'm sure off at this point. I don't think a classic approch like Zend Framework (PHP) + MySQL + Memcache + jQuery (and I would throw Doctrine 2 in there to) will fix result in a high-performance application. I was thinking on making this a RESTful application (with Zend Framework) + NGINX (or maybe MongoDB) + Memcache (or eAccelerator -- I understand this will create problems with scalability on multiple servers) + jQuery or maybe throw Backbone.js in there, a CDN for static content, a server for images and a scalable server for the requests and the rest. My questions are: - What do you think about my approch? - What solutions would you recommand for developing an high performance, scalable application expected to have a lot of traffic using PHP(Zend Framework 2)...I would be interested in your approch. I should note that I'm a Zend developer, I'm working with Zend for over 3 years, this is why I'm choosing it.

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• WSUS performance for unneeded updates

  - by mhouston100

  We have a WSUS server serving around 300 PC's and a couple of dozen servers and a discussion came up at work as to what products to include. We have a single SQL 2005 instance on one of the servers and it has NEVER been updated. My first thought was to just tick the box for SQL 2005 and let WSUS do it's thing to upgrade to the latest service pack at least. One of the other guys here has the opinion that having updates that are relevant to only a small selection of hosts would effect the performance of WSUS as a whole, claiming that each update does a 'check' against all the hosts or something similar. My argument is that manually updating these servers is obviously not working as the admins are not paying attention to what is needed. So my question is: Do updates that only effect a sub-set of the hosts effect the overall performance of the WSUS server in relation to ALL the hosts? (disk space is not an issue at this point) Is there any performance justification for or against manually updating small amounts of products? Basically I'm needing a rebuttal against his argument and I'm unable to find any concrete documentation to prove him wrong.

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• Write your Tests in RSpec with IronRuby

  - by kazimanzurrashid

  [Note: This is not a continuation of my previous post, treat it as an experiment out in the wild. ] Lets consider the following class, a fictitious Fund Transfer Service: public class FundTransferService : IFundTransferService { private readonly ICurrencyConvertionService currencyConvertionService; public FundTransferService(ICurrencyConvertionService currencyConvertionService) { this.currencyConvertionService = currencyConvertionService; } public void Transfer(Account fromAccount, Account toAccount, decimal amount) { decimal convertionRate = currencyConvertionService.GetConvertionRate(fromAccount.Currency, toAccount.Currency); decimal convertedAmount = convertionRate * amount; fromAccount.Withdraw(amount); toAccount.Deposit(convertedAmount); } } public class Account { public Account(string currency, decimal balance) { Currency = currency; Balance = balance; } public string Currency { get; private set; } public decimal Balance { get; private set; } public void Deposit(decimal amount) { Balance += amount; } public void Withdraw(decimal amount) { Balance -= amount; } } We can write the spec with MSpec + Moq like the following: public class When_fund_is_transferred { const decimal ConvertionRate = 1.029m; const decimal TransferAmount = 10.0m; const decimal InitialBalance = 100.0m; static Account fromAccount; static Account toAccount; static FundTransferService fundTransferService; Establish context = () => { fromAccount = new Account("USD", InitialBalance); toAccount = new Account("CAD", InitialBalance); var currencyConvertionService = new Moq.Mock<ICurrencyConvertionService>(); currencyConvertionService.Setup(ccv => ccv.GetConvertionRate(Moq.It.IsAny<string>(), Moq.It.IsAny<string>())).Returns(ConvertionRate); fundTransferService = new FundTransferService(currencyConvertionService.Object); }; Because of = () => { fundTransferService.Transfer(fromAccount, toAccount, TransferAmount); }; It should_decrease_from_account_balance = () => { fromAccount.Balance.ShouldBeLessThan(InitialBalance); }; It should_increase_to_account_balance = () => { toAccount.Balance.ShouldBeGreaterThan(InitialBalance); }; } and if you run the spec it will give you a nice little output like the following: When fund is transferred » should decrease from account balance » should increase to account balance 2 passed, 0 failed, 0 skipped, took 1.14 seconds (MSpec). Now, lets see how we can write exact spec in RSpec. require File.dirname(__FILE__) + "/../FundTransfer/bin/Debug/FundTransfer" require "spec" require "caricature" describe "When fund is transferred" do Convertion_Rate = 1.029 Transfer_Amount = 10.0 Initial_Balance = 100.0 before(:all) do @from_account = FundTransfer::Account.new("USD", Initial_Balance) @to_account = FundTransfer::Account.new("CAD", Initial_Balance) currency_convertion_service = Caricature::Isolation.for(FundTransfer::ICurrencyConvertionService) currency_convertion_service.when_receiving(:get_convertion_rate).with(:any, :any).return(Convertion_Rate) fund_transfer_service = FundTransfer::FundTransferService.new(currency_convertion_service) fund_transfer_service.transfer(@from_account, @to_account, Transfer_Amount) end it "should decrease from account balance" do @from_account.balance.should be < Initial_Balance end it "should increase to account balance" do @to_account.balance.should be > Initial_Balance end end I think the above code is self explanatory, treat the require(line 1- 4) statements as the add reference of our visual studio projects, we are adding all the required libraries with this statement. Next, the describe which is a RSpec keyword. The before does exactly the same as NUnit's Setup or MsTest’s TestInitialize attribute, but in the above we are using before(:all) which acts as ClassInitialize of MsTest, that means it will be executed only once before all the test methods. In the before(:all) we are first instantiating the from and to accounts, it is same as creating with the full name (including namespace)  like fromAccount = new FundTransfer.Account(.., ..), next, we are creating a mock object of ICurrencyConvertionService, check that for creating the mock we are not using the Moq like the MSpec version. This is somewhat an interesting issue of IronRuby or maybe the DLR, it seems that it is not possible to use the lambda expression that most of the mocking tools uses in arrange phase in Iron Ruby, like: currencyConvertionService.Setup(ccv => ccv.GetConvertionRate(Moq.It.IsAny<string>(), Moq.It.IsAny<string>())).Returns(ConvertionRate); But the good news is, there is already an excellent mocking tool called Caricature written completely in IronRuby which we can use to mock the .NET classes. May be all the mocking tool providers should give some thought to add the support for the DLR, so that we can use the tool that we are already familiar with. I think the rest of the code is too simple, so I am skipping the explanation. Now, the last thing, how we are going to run it with RSpec, lets first install the required gems. Open you command prompt and type the following: igem sources -a http://gems.github.com This will add the GitHub as gem source. Next type: igem install uuidtools caricature rspec and at last we have to create a batch file so that we can execute it in the Notepad++, create a batch like in the IronRuby bin directory like my previous post and put the following in that batch file: @echo off cls call spec %1 --format specdoc pause Next, add a run menu and shortcut in the Notepad++ like my previous post. Now when we run it it will show the following output: When fund is transferred - should decrease from account balance - should increase to account balance Finished in 0.332042 seconds 2 examples, 0 failures Press any key to continue . . . You will complete code of this post in the bottom. That's it for today. Download: RSpecIntegration.zip

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• Contricted A* problem

  - by Ragekit

  I've got a little problem with an A* algorithm that I need to constrict a little bit. Basically : I use an A* to find the shortest path between 2 randomly placed room in 3D space, and then build a corridor between them. The problem I found is that sometimes it makes chimney like corridors that are not ideal, so I constrict the A* so that if the last movement was up or down, you go sideways. Everything is fine, but in some corner cases, it fails to find a path (when there is obviously one). Like here between the blue and red dot : (i'm in unity btw, but i don't think it matters) Here is the code of the actual A* (a bit long, and some redundency) while(current != goal) { //add stair up / stair down foreach(Node<GridUnit> test in current.Neighbors) { if(!test.Data.empty && test != goal) continue; //bug at arrival; if(test == goal && penul !=null) { Vector3 currentDiff = current.Data.bounds.center - test.Data.bounds.center; if(!Mathf.Approximately(currentDiff.y,0)) { //wanna drop on the last if(!coplanar(test.Data.bounds.center,current.Data.bounds.center,current.Data.parentUnit.bounds.center,to.Data.bounds.center)) { continue; } else { if(Mathf.Approximately(to.Data.bounds.center.x, current.Data.parentUnit.bounds.center.x) && Mathf.Approximately(to.Data.bounds.center.z, current.Data.parentUnit.bounds.center.z)) { continue; } } } } if(current.Data.parentUnit != null) { Vector3 previousDiff = current.Data.parentUnit.bounds.center - current.Data.bounds.center; Vector3 currentDiff = current.Data.bounds.center - test.Data.bounds.center; if(!Mathf.Approximately(previousDiff.y,0)) { if(!Mathf.Approximately(currentDiff.y,0)) { //you wanna drop now : continue; } if(current.Data.parentUnit.parentUnit != null) { if(!coplanar(test.Data.bounds.center,current.Data.bounds.center,current.Data.parentUnit.bounds.center,current.Data.parentUnit.parentUnit.bounds.center)) { continue; }else { if(Mathf.Approximately(test.Data.bounds.center.x, current.Data.parentUnit.parentUnit.bounds.center.x) && Mathf.Approximately(test.Data.bounds.center.z, current.Data.parentUnit.parentUnit.bounds.center.z)) { continue; } } } } } g = current.Data.g + HEURISTIC(current.Data,test.Data); h = HEURISTIC(test.Data,goal.Data); f = g + h; if(open.Contains(test) || closed.Contains(test)) { if(test.Data.f > f) { //found a shorter path going passing through that point test.Data.f = f; test.Data.g = g; test.Data.h = h; test.Data.parentUnit = current.Data; } } else { //jamais rencontré test.Data.f = f; test.Data.h = h; test.Data.g = g; test.Data.parentUnit = current.Data; open.Add(test); } } closed.Add (current); if(open.Count == 0) { Debug.Log("nothingfound"); //nothing more to test no path found, stay to from; List<GridUnit> r = new List<GridUnit>(); r.Add(from.Data); return r; } //sort open from small to biggest travel cost open.Sort(delegate(Node<GridUnit> x, Node<GridUnit> y) { return (int)(x.Data.f-y.Data.f); }); //get the smallest travel cost node; Node<GridUnit> smallest = open[0]; current = smallest; open.RemoveAt(0); } //build the path going backward; List<GridUnit> ret = new List<GridUnit>(); if(penul != null) { ret.Insert(0,to.Data); } GridUnit cur = goal.Data; ret.Insert(0,cur); do{ cur = cur.parentUnit; ret.Insert(0,cur); } while(cur != from.Data); return ret; You see at the start of the foreach i constrict the A* like i said. If you have any insight it would be cool. Thanks

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• Constrained A* problem

  - by Ragekit

  I've got a little problem with an A* algorithm that I need to Constrained a little bit. Basically : I use an A* to find the shortest path between 2 randomly placed room in 3D space, and then build a corridor between them. The problem I found is that sometimes it makes chimney like corridors that are not ideal, so I constrict the A* so that if the last movement was up or down, you go sideways. Everything is fine, but in some corner cases, it fails to find a path (when there is obviously one). Like here between the blue and red dot : (i'm in unity btw, but i don't think it matters) Here is the code of the actual A* (a bit long, and some redundency) while(current != goal) { //add stair up / stair down foreach(Node<GridUnit> test in current.Neighbors) { if(!test.Data.empty && test != goal) continue; //bug at arrival; if(test == goal && penul !=null) { Vector3 currentDiff = current.Data.bounds.center - test.Data.bounds.center; if(!Mathf.Approximately(currentDiff.y,0)) { //wanna drop on the last if(!coplanar(test.Data.bounds.center,current.Data.bounds.center,current.Data.parentUnit.bounds.center,to.Data.bounds.center)) { continue; } else { if(Mathf.Approximately(to.Data.bounds.center.x, current.Data.parentUnit.bounds.center.x) && Mathf.Approximately(to.Data.bounds.center.z, current.Data.parentUnit.bounds.center.z)) { continue; } } } } if(current.Data.parentUnit != null) { Vector3 previousDiff = current.Data.parentUnit.bounds.center - current.Data.bounds.center; Vector3 currentDiff = current.Data.bounds.center - test.Data.bounds.center; if(!Mathf.Approximately(previousDiff.y,0)) { if(!Mathf.Approximately(currentDiff.y,0)) { //you wanna drop now : continue; } if(current.Data.parentUnit.parentUnit != null) { if(!coplanar(test.Data.bounds.center,current.Data.bounds.center,current.Data.parentUnit.bounds.center,current.Data.parentUnit.parentUnit.bounds.center)) { continue; }else { if(Mathf.Approximately(test.Data.bounds.center.x, current.Data.parentUnit.parentUnit.bounds.center.x) && Mathf.Approximately(test.Data.bounds.center.z, current.Data.parentUnit.parentUnit.bounds.center.z)) { continue; } } } } } g = current.Data.g + HEURISTIC(current.Data,test.Data); h = HEURISTIC(test.Data,goal.Data); f = g + h; if(open.Contains(test) || closed.Contains(test)) { if(test.Data.f > f) { //found a shorter path going passing through that point test.Data.f = f; test.Data.g = g; test.Data.h = h; test.Data.parentUnit = current.Data; } } else { //jamais rencontré test.Data.f = f; test.Data.h = h; test.Data.g = g; test.Data.parentUnit = current.Data; open.Add(test); } } closed.Add (current); if(open.Count == 0) { Debug.Log("nothingfound"); //nothing more to test no path found, stay to from; List<GridUnit> r = new List<GridUnit>(); r.Add(from.Data); return r; } //sort open from small to biggest travel cost open.Sort(delegate(Node<GridUnit> x, Node<GridUnit> y) { return (int)(x.Data.f-y.Data.f); }); //get the smallest travel cost node; Node<GridUnit> smallest = open[0]; current = smallest; open.RemoveAt(0); } //build the path going backward; List<GridUnit> ret = new List<GridUnit>(); if(penul != null) { ret.Insert(0,to.Data); } GridUnit cur = goal.Data; ret.Insert(0,cur); do{ cur = cur.parentUnit; ret.Insert(0,cur); } while(cur != from.Data); return ret; You see at the start of the foreach i constrict the A* like i said. If you have any insight it would be cool. Thanks

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• Hyperthreading vs. SQL Server & PostgreSQL

  - by IanC

  I have read that hyperthreading is a "performance killer" when it comes to DBs. However, what I read didn't state which CPUs. Further, it mostly indicated that I/O was "cut to < 10% performance". That logically doesn't make sense since I/O is primarily a function of controllers and disks, not CPUs. But then no one ever said bugs made sense. What I read also stated that SQL Server could put two parallel query ops onto 1 logical core (2 threads), thereby degrading performance. I have a hard time believing SQL Server's architects would have made such an obvious miscalculation. Does anyone have and data on how hyperthreading on current generation CPUs affects either of the RDBMSs I mentioned?

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• aligning truecrypt partition on 1.5TB 4kB sector drive

  - by pQd

  hi, aligning partitions to start at real physical sector of ssds / stripped raids / 4kB drives is a 'good thing to do'. but i've run into a problems when trying to do it for a truecrypt partition that will contain ext3 on it. or so it seems. when drive is question is partitioned properly and formatted with ext3 i get very reasonable write speeds around 70-80MB/s, but when i put truecrypt and ext3 on the top of it write performance becomes very unstable and goes between 1-25MB/s with very high io-wait. on the same server i dont have any performance issues with ext3 on the top of truecrypt on regular 512B-sector 500GB sata disks. so my best guess is that iowaits are caused by misalignment but i cannot really find reliable information on how to calculate optimal partition beginning. i've tried to start it at 128 logical sector, i've also tried 8132 sector as suggested here but both gave me very bad and unstable performance. do you have any experience with similar setup? thanks!

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• What is Peformance Monitor telling me when my page faults / second are high?

  - by David Robison

  I have a Windows 7 x64 computer that is having performance issues. After some investigation, I have discovered that the page faults / second on it, as reported by Performance Monitor, are really high. Everything else seems to be normal. Resource Monitor reports no hard faults and lots of available memory. Is this a potential cause for problems, or is it a red herring? If it is something that could be causing problems, what should I do next to figure out what is causing it? Here is a screen shot of the Performance Monitor. Notice that the average page faults / second is 75,887. On another computer that does not have problems, this number is closer to 3,000. Here is a screen shot of the Resource Monitor, sorted by hard faults / second, which is currently 0 for all processes.

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• When to use Nginx PHP Fast CGI with a TCP socket instead of a UNIX socket?

  - by user64204

  I've followed this guide to setup PHP in FastCGI mode with Nginx. This guide describes 2 ways of doing it: TCP socket and UNIX socket. I've ran some Apache Benchmark on my locale machine and here are the results: Below tests ran multiple times to get better average statistics: $ ab -c 200 -n 100000 http://.... APACHE: 1800 req/sec NGINX (TCP socket): 2500 req/sec NGINX (UNIX socket): 15000 req/sec As far as I understand, there is overhead with using a TCP socket rather than a UNIX socket, hence the better performance with the latter. However I was not expecting such a performance difference given that the TCP socket is on the localhost, and therefore would like to ask the following question: Q: Given the huge performance gain with using a UNIX socket, what are the configuration scenarios where it would make sense to use a TCP socket instead?

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• Processor upgrade on a laptop vs. Ram upgrade. Also does ram always matter?

  - by Evan

  I have a Dell Inspiron 14r (N4110) with an Intel Core i3 and 4gb of ram. It runs very smoothly, however gaming on this laptop is very limited. This is mostly because of integrated graphics but i have seen a computer with a Core i5, and very similar specs otherwise, run games that the N4110 cannot. This other computer has integrated graphics and 6gb of ram. I am wondering whether upgrading ram or upgrading the processor make the most difference in performance. Which setup would get better performance, an i5 with 4gb of ram or an i3 with 8 gb of ram? (Both with integrated graphics) Also, is there a certain point at which you have too much ram for the computer to ever possibly use? For instance is there really any difference in performance between 8 gb and 16 gb of ram?

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• Xen Disk Performence Issues

  - by user98651

  I'm currently using Xen PV on CentOS 5 with my domU's as flat files running on a hardware RAID controlled (write cache enabled) formatted with XFS. On the dom0 I can get about 500MB/s in a 2GB dd write from /dev/zero however on the domU's I'm lucky if I get 10MB/s (it is usually around half that). I've tried changing the disk scheduling to NOOP on the domU's, changed some mount parameters and tweaked the performance allocations of both the dom0 (prioritize CPU) and domU's (increase RAM and VCPU allocations). None of these steps have produced any noticeable change in performance. My instinct here is that it is not a hardware problem, due to the solid performance of the dom0. Any ideas on what might be causing this problem? I'm considering moving to LVM based domU's.

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• Perfmon quick rundown

  - by anon

  I've known quite along while about performance monitor on Windows. I have decided now to create a scheduled performance monitoring of my entire system so I can find bottlenecks for future improvements. So as you can imagine this is going to run 24/7 so I can identify peak utilization. With performance monitor on Windows 7 for example where are the logs stored (c:\perfmon)? Is there a log size? Even better is the a website that can get me up to speed with scheduling and best practices of perfmon? (I don't need an explanation of what I can monitor)

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• How to unit test asynchronous APIs?

  - by Ben Clayton

  Hi all. I have installed Google Toolbox for Mac (http://code.google.com/p/google-toolbox-for-mac/) into Xcode and followed the instructions to set up unit testing found here (http://code.google.com/p/google-toolbox-for-mac/wiki/iPhoneUnitTesting). It all works great, and I can test my synchronous methods on all my objects absolutely fine. However, most of the complex APIs I actually want to test return results asynchronously via calling a method on a delegate - for example a call to a file download and update system will return immediately and then run a -fileDownloadDidComplete: method when the file finishes downloading. How would I test this as a unit test? It seems like I'd want to the testDownload function, or at least the test framework to 'wait' for fileDownloadDidComplete: method to run. Any ideas much appreciated!

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• Where to place unit test project

  - by Karsten

  I'm thinking about where to put the unit/integration test project. I follow the 1 test project pr. project convention I can think of 3 ways, that all seems good to me, which make it kind of hard to choose :-) Test project is put under a Tests sub folder to the project it tests. Test project is put next to the project it tests, in a "project".Tests folder. I believe this is what Roy Osherove recommends. Put all test projects in a sub folder in the root. e.g. \Tests\"project".Tests Something else? What you choose and why?

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• Unit test class inherited from ContextBoundObject and decorated with ContextAttribute

  - by Joel Cunningham

  I am trying to retrofit unit tests on to some existing code base. Both the class and method I want to unit test is decorated with custom attributes that are inherited from ContextBoundObject and ContextAttribute. I dont want them to run as part of the unit test. The only solution I have come up with is to compile the attribute out when I want to unit test. I dont really like this solution and would prefer to either replace it with a mocked attribute at runtime or prevent the attribute from running in a more elegant way. How do you unit test code that has class and method attributes that inherit from ContextBoundObject and ContextAttribute that you dont want to run as part of a unit test? Thanks in advance.

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