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  • Understanding Linux SCSI queue depths

    - by Troels Arvin
    I'm experimenting with the effects of different SCSI queue depth values on a Dell server running CentOS Linux 5.4 (x86_64). The server has two QLogic QLE2560 FC HBAs connected via multipathing to a storage system. The storage system has allocated two LUNs to the server, each connected through four paths in an active-active-active-active round-robin configuration. All in all, the two LUNs exist as eight /dev/sdX devices, represented by two devices in /dev/mpath. I currently adjust the queue depth values in /etc/modprobe.conf and check the result (after rebooting) by looking in the seventh column of /proc/scsi/sg/devices. Two questions related to that: Is there a way to adjust queue depths without rebooting or unloading the qla2xxx kernel module? E.g., can I echo a new queue depth value into some /proc or /sys-like file to update the queue depth? If I set the queue depth to 128, is that 128 in total for all devices handled by the qla2xxx module?, or 128 for each HBA? (256 in total), or 128 for each of the eight /dev/sdX devices (1024 in toal)?, or 128 for each of the two /dev/mpath/... devices (256 in total)? This is important for me to know so that my server doesn't flood the storage system, affecting other servers connected to it.

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  • What's throttling the database?

    - by Troels Arvin
    Hardware: Intel x86_64 with 192GB of RAM. OS: CentOS 5.4 x86_64. DBMS: DB2 v. 9.7.1 64 bit. During certain special workloads (e.g. parallel REORGs/RUNSTATs), I've seen the server transporting 450MB/s with 25000IO/s (yes, there is probably some storage system caching happening here) while all CPU cores were happily working in an even mix of usermode/wait. And disk benchmark tools can also bring some very satisfying bandwith and IO/s numbers to the table. On the other hand, we also have another scenario: A single rather complex query with at least one large table scan. db2's "list applications" reports that the query is Executing (not locked). IO: At most 10MB/s, 500 IO/s; CPU: two cores in 99.9% wait state, all other cores 100% idle. The tables which the query reads from have been altered to have LOCKSIZE=TABLE, so I would think that lock list work is zero. What's going on in such a situation? What tools/snapshots/... can I use to gain better insight in such a case?

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  • MSSQL: Choice of service accounts

    - by Troels Arvin
    When installing MS SQL Server 2008, one needs to associate a service account with the installation (possibly even several accounts, one for the SQL Server Agent, one for Analysis Services, ..., but let's leave that for the case of simplicity). The service account may be local account, or a Windows domain account. If a domain account is used: Can MSSQL start, if connectivity to the domain controllers is temporarily down? If the answer is yes: Should each DBMS instance on each server have a separate account, or does it make sense to use a particular "MSSQL" domain account on all MSSQL-installations in the organization? If separate accounts are used for each instance on each server: Does it make sense to create a special MSSQL security group in the domain and place all the MSSQL service accounts in that group, perhaps to ease replication, etc? Is there a common, generally accepted naming convention for MSSQL service account(s)?

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  • How to select the nth row in a SQL database table?

    - by Charles Roper
    I'm interested in learning some (ideally) database agnostic ways of selecting the nth row from a database table. It would also be interesting to see how this can be achieved using the native functionality of the following databases: SQL Server MySQL PostgreSQL SQLite Oracle I am currently doing something like the following in SQL Server 2005, but I'd be interested in seeing other's more agnostic approaches: WITH Ordered AS ( SELECT ROW_NUMBER() OVER (ORDER BY OrderID) AS RowNumber, OrderID, OrderDate FROM Orders) SELECT * FROM Ordered WHERE RowNumber = 1000000 Credit for the above SQL: Firoz Ansari's Weblog Update: See Troels Arvin's answer regarding the SQL standard. Troels, have you got any links we can cite?

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  • FileNotFoundException Java

    - by Troels Hansen
    Hi, I'm trying to make a simple highscore system for a minesweeper game. However i keep getting a file not found exception, and i've tried to use the full path for the file aswell. package minesweeper; import java.io.*; import java.util.*; public class Highscore{ public static void submitHighscore(String difficulty) throws IOException{ int easy = 99999; int normal = 99999; int hard = 99999; //int newScore = (int) MinesweeperView.getTime(); int newScore = 10; File f = new File("Highscores.dat"); if (!f.exists()){ f.createNewFile(); } Scanner input = new Scanner(f); PrintStream output = new PrintStream(f); if (input.hasNextInt()){ easy = input.nextInt(); normal = input.nextInt(); hard = input.nextInt(); } output.flush(); if(difficulty.equals("easy")){ if (easy > newScore){ easy = newScore; } }else if (difficulty.equals("normal")){ if (normal > newScore){ normal = newScore; } }else if (difficulty.equals("hard")){ if (hard > newScore){ hard = newScore; } } output.println(easy); output.println(normal); output.println(hard); } //temporary main method used for debugging public static void main(String[] args) throws IOException { submitHighscore("easy"); } }

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  • Javascript global object calls function?

    - by Troels
    Hello stackoverflow I have a very odd problem with javascript. My code is rather long so here is an example of the structure and the problem: var x = new function f() { this.id = ""; } function g(obj) { if (x.id == "") { ... obj.firstChild.setAttribute("onclick", "javascript:o();"); ... x.id = obj.id; } else if (x.id != obj.id) { ... x.id = ""; g(obj); } } function o() { ... if (something == something) { ... } else { ... x.id = ""; // if-statement of the g() function is called here? } } As you can see, the if-statement of the g() function is for some reason called or re-run upon x.id being changed. I simply cannot understand this, because they are not in the same scope, and changing a variable should under no circumstances trigger anything? Any help would be greatly appreciated.

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  • ASP.NET mvcConf Videos Available

    - by ScottGu
    Earlier this month the ASP.NET MVC developer community held the 2nd annual mvcConf event.  This was a free, online conference focused on ASP.NET MVC – with more than 27 talks that covered a wide variety of ASP.NET MVC topics.  Almost all of the talks were presented by developers within the community, and the quality and topic diversity of the talks was fantastic. Below are links to free recordings of the talks that you can watch (and optionally download): Scott Guthrie Keynote The NuGet-y Goodness of Delivering Packages (Phil Haack) Industrial Strenght NuGet (Andy Wahrenberger) Intro to MVC 3 (John Petersen) Advanced MVC 3 (Brad Wilson) Evolving Practices in Using jQuery and Ajax in ASP.NET MVC Applications (Eric Sowell) Web Matrix (Rob Conery) Improving ASP.NET MVC Application Performance (Steven Smith) Intro to Building Twilio Apps with ASP.NET MVC (John Sheehan) The Big Comparison of ASP.NET MVC View Engines (Shay Friedman) Writing BDD-style Tests for ASP.NET MVC using MSTestContrib (Mitch Denny) BDD in ASP.NET MVC using SpecFlow, WatiN and WatiN Test Helpers (Brandon Satrom) Going Postal - Generating email with View Engines (Andrew Davey) Take some REST with WCF (Glenn Block) MVC Q&A (Jeffrey Palermo) Deploy ASP.NET MVC with No Effort (Troels Thomsen) IIS Express (Vaidy Gopalakrishnan) Putting the V in MVC (Chris Bannon) CQRS and Event Sourcing with MVC 3 (Ashic Mahtab) MVC 3 Extensibility (Roberto Hernandez) MvcScaffolding (Steve Sanderson) Real World Application Development with Mvc3 NHibernate, FluentNHibernate and Castle Windsor (Chris Canal) Building composite web applications with Open frameworks (Sebastien Lambla) Quality Driven Web Acceptance Testing (Amir Barylko) ModelBinding derived types using the DerivedTypeModelBinder in MvcContrib (Steve Hebert) Entity Framework "Code First": Domain Driven CRUD (Chris Zavaleta) Wrap Up with Jon Galloway & Javier Lozano I’d like to say a huge thank you to all of the speakers who presented, and to Javier Lozano, Eric Hexter and Jon Galloway for all their hard work in organizing the event and making it happen. Hope this helps, Scott P.S. I am also now using Twitter for quick updates and to share links. Follow me at: twitter.com/scottgu

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