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  • how do i design a high pass filters in matlab without using the builtin function?

    - by noura
    hello everyone, i'm just not sure how to draw the frequency response (H) of the high pass filter? after drawing the frequency response i can get the b coefficient by taking the ifft of (H). so yeah, for a low pass filter, with a cutoff frequency of say pi/2 : the frequency response code will be H = exp(-1*j*w*4).*(((0 <= w) & (w<= pi/2)) | ((2*pi - pi/2 <= w) & (w<=2*pi)); sincr the response is "1" between 0 and pi/2 and between (2*pi - pi/2) and 2*pi. can you help me write H for a high pass filter? thanx in advance.

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  • How to know the level of a symlink in linux?

    - by ???
    For example, if a symlink a -> b b -> c c -> d say, the symlink level of a is 3. Then, is there any utility to get this info? And, also I want to get the expansion detail of a symlink, which will show me something like: 1. /abc/xyz is expanded to /abc/xy/z (lrwx--x--x root root) 2. /abc/xy/z is expanded to /abc/xy-1.3.2/z (lrwx--x--x root root) 3. /abc/xy-1.3.2/z is expanded to /abc/xy-1.3.2/z-4.6 (lrwx--x--x root root) 4. /abc/xy-1.3.2/z-4.6 is expanded to /storage/121/43/z_4_6 (lrwx--x--x root root) 5. /storage/121/43/z_4_6 is expanded to /media/kitty_3135/43/z_4_6 (lrwx--x--x root root) So I can diagnostic with the symlinks. Any idea?

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  • Why is Rake not able to invoke multiple tasks consecutively?

    - by PandaWood
    I have a Rake task which I have simplified below. I'm using Ruby 1.9 on Windows. Perhaps you would like to guess the outcome of calling the Rake task "list_all_levels" below? It should be: "Hello level 1" "Hello level 2" "Hello level 3" But for reasons unknown to me, it prints only "Hello level 1" and then stops. That is, it always invokes only the first task. If I change the first line to pass the arg "42", it would print "Hello level 42" and then stop. I'm wondering why does it not invoke the task 3 times and print all 3 lines? And is there any way to get it to work how I would expect? task :list_all_levels => [] do Rake::Task[:list].invoke 1 Rake::Task[:list].invoke 2 Rake::Task[:list].invoke 3 end task :list, [:level] => [] do |t, args| puts "Hello level #{args.level}" end

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  • Can an SSD notify the hosting OS that its wear level is getting high?

    - by Tony_Henrich
    I read a lot about SSDs and I am interested in them for server use. My biggest concern is their reliability. A lot of writes shortens their life span. I can mitigate this problem if I can run some kind of diagnostics on a regular basis on the SSD or if the SSD can automatically warn the OS that its reliability is reaching a critical level. Think of this as S.M.A.R.T or software like SpinRite for SSDs. Does anything I mentioned exist now? Which kind/brand of SSD does this? I don't mind swapping out a tired SSD for a newer one once a while. I am pretty sure that SSDs life is calculated in years and not in few months? For me, the improved performance will pay for the SSD over and over. I am planning to use plenty of RAM as well.

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  • When machine code is generated from a program how does it translates to hardware level operations ??

    - by user553492
    Like if say the instruction is something like 100010101 1010101 01010101 011101010101. Now how is this translating to an actual job of deleting something from memory? Memory consists of actual physical transistors the HOLD data. What causes them to lose that data is some external signal? I want to know how that signal is generated. Like how some binary numbers change the state of a physical transistor. Is there a level beyond machine code that isn't explicitly visible to a programmer? I have heard of microcode that handle code at hardware level, even below assembly language. But still I pretty much don't understand. Thanks!

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  • Will the next iPhone Simulator be able to simulate the high resolution of iPhone 4?

    - by dontWatchMyProfile
    As a follow-up to this question, the next one is: Will we be able to simulate our interfaces how they look on the new high resolution display, even without owning an iPhone 4? I guess that there is a formula that we can use to calculate the exact needed distance between our monitors and our eyes, to achieve the exact same visual effect of the Retina Display. This would help a lot to get things right. The first thing we need is an high resolution iPhone Simulator. I can't get any sleep until I know.

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  • How to write php code to input jsonstring and insert to sql server

    - by Romi
    i am trying to OUTPUT a Json String from the phone and to get it uploaded to the sql server i have. I Do not know how to get the output Json and write the php code... i tried many methods but couldnt find a solution. public void post(String string) { HttpClient httpclient = new DefaultHttpClient(); HttpPost httppost = new HttpPost( "http://www.hopscriber.com/xoxoxox/testphp.php"); try { List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(); nameValuePairs.add(new BasicNameValuePair("myJson", string)); httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs)); HttpResponse response = httpclient.execute(httppost); String str = inputStreamToString(response.getEntity().getContent()) .toString(); Log.w("SENCIDE", str); } catch (Exception e) { Toast.makeText(getBaseContext(), "notwork", Toast.LENGTH_LONG) .show(); } } private Object inputStreamToString(InputStream is) { // TODO Auto-generated method stub String line = ""; StringBuilder total = new StringBuilder(); // Wrap a BufferedReader around the InputStream BufferedReader rd = new BufferedReader(new InputStreamReader(is)); // Read response until the end try { while ((line = rd.readLine()) != null) { total.append(line); } } catch (IOException e) { e.printStackTrace(); } // Return full string return total; } it outputs a json string as [myJson=[{"name":"FriendTracker","user":"amjgp000000000000000","pack":"org.siislab.tutorial.friendtracker","perm":"org.siislab.tutorial.permission.READ_FRIENDS","level":"Normal"},{"name":"FriendTracker","user":"amjgp000000000000000","pack":"org.siislab.tutorial.friendtracker","perm":"org.siislab.tutorial.permission.WRITE_FRIENDS","level":"Normal"},{"name":"FriendTracker","user":"amjgp000000000000000","pack":"org.siislab.tutorial.friendtracker","perm":"org.siislab.tutorial.permission.FRIEND_SERVICE","level":"Normal"},{"name":"FriendTracker","user":"amjgp000000000000000","pack":"org.siislab.tutorial.friendtracker","perm":"org.siislab.tutorial.permission.FRIEND_NEAR","level":"Dangerous"},{"name":"FriendTracker","user":"amjgp000000000000000","pack":"org.siislab.tutorial.friendtracker","perm":"org.siislab.tutorial.permission.BROADCAST_FRIEND_NEAR","level":"Normal"},{"name":"FriendTracker","user":"amjgp000000000000000","pack":"org.siislab.tutorial.friendtracker","perm":"android.permission.RECEIVE_BOOT_COMPLETED","level":"Normal"},{"name":"FriendTracker","user":"amjgp000000000000000","pack":"org.siislab.tutorial.friendtracker","perm":"android.permission.READ_CONTACTS","level":"Dangerous"},{"name":"FriendTracker","user":"amjgp000000000000000","pack":"org.siislab.tutorial.friendtracker","perm":"android.permission.ACCESS_FINE_LOCATION","level":"Dangerous"},{"name":"FriendTracker","user":"amjgp000000000000000","pack":"org.siislab.tutorial.friendtracker","perm":"android.permission.WRITE_EXTERNAL_STORAGE","level":"Dangerous"},{"name":"FriendTracker","user":"amjgp000000000000000","pack":"org.siislab.tutorial.friendtracker","perm":"android.permission.READ_PHONE_STATE","level":"Dangerous"},{"name":"Tesing","user":"amjgp000000000000000","pack":"com.example.tesing","perm":"null","level":"null"},{"name":"Action Bar","user":"amjgp000000000000000","pack":"name.brucephillips.actionbarexample","perm":"null","level":"null"},.......

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  • Load different levels in XML

    - by Anearion
    my question is more about a theoretical gener than a pratical way to make things happen. I'm about start developing a game for android, text based so i won't need sprites or animation, nor a game engine. Let's say is similar to a sudoku game, where each level is an harder version of sudoku and each level has some question to be asnwered over the sudoku itself. I was wondering if the better way is to have only one XML and then inside all the different levels, each one with his meta-tags, or if the different approach of making n xml files where each one is a level is preferred. At the moment a level should have those tags: <level> <question>Question_1</question> <hint1>what does it do?</hint1> <hint2>where...</hint2> .... <hintN>how...</hintN> </level> So each level could have some items to read and that's what made me think that maybe different files are better cuz if i have to load lvl 10 i can read only the 10.xml file. I hope my question isn't too stupind. Thanks in advance

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  • Problem displaying tiles using tiled map loader with SFML

    - by user1905192
    I've been searching fruitlessly for what I did wrong for the past couple of days and I was wondering if anyone here could help me. My program loads my tile map, but then crashes with an assertion error. The program breaks at this line: spacing = atoi(tilesetElement-Attribute("spacing")); Here's my main game.cpp file. #include "stdafx.h" #include "Game.h" #include "Ball.h" #include "level.h" using namespace std; Game::Game() { gameState=NotStarted; ball.setPosition(500,500); level.LoadFromFile("meow.tmx"); } void Game::Start() { if (gameState==NotStarted) { window.create(sf::VideoMode(1024,768,320),"game"); view.reset(sf::FloatRect(0,0,1000,1000));//ball drawn at 500,500 level.SetDrawingBounds(sf::FloatRect(view.getCenter().x-view.getSize().x/2,view.getCenter().y-view.getSize().y/2,view.getSize().x, view.getSize().y)); window.setView(view); gameState=Playing; } while(gameState!=Exiting) { GameLoop(); } window.close(); } void Game::GameLoop() { sf::Event CurrentEvent; window.pollEvent(CurrentEvent); switch(gameState) { case Playing: { window.clear(sf::Color::White); window.setView(view); if (CurrentEvent.type==sf::Event::Closed) { gameState=Exiting; } if ( !ball.IsFalling() &&!ball.IsJumping() &&sf::Keyboard::isKeyPressed(sf::Keyboard::Space)) { ball.setJState(); } ball.Update(view); level.Draw(window); ball.Draw(window); window.display(); break; } } } And here's the file where the error happens: /********************************************************************* Quinn Schwab 16/08/2010 SFML Tiled Map Loader The zlib license has been used to make this software fully compatible with SFML. See http://www.sfml-dev.org/license.php This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software. Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions: 1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required. 2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software. 3. This notice may not be removed or altered from any source distribution. *********************************************************************/ #include "level.h" #include <iostream> #include "tinyxml.h" #include <fstream> int Object::GetPropertyInt(std::string name) { int i; i = atoi(properties[name].c_str()); return i; } float Object::GetPropertyFloat(std::string name) { float f; f = strtod(properties[name].c_str(), NULL); return f; } std::string Object::GetPropertyString(std::string name) { return properties[name]; } Level::Level() { //ctor } Level::~Level() { //dtor } using namespace std; bool Level::LoadFromFile(std::string filename) { TiXmlDocument levelFile(filename.c_str()); if (!levelFile.LoadFile()) { std::cout << "Loading level \"" << filename << "\" failed." << std::endl; return false; } //Map element. This is the root element for the whole file. TiXmlElement *map; map = levelFile.FirstChildElement("map"); //Set up misc map properties. width = atoi(map->Attribute("width")); height = atoi(map->Attribute("height")); tileWidth = atoi(map->Attribute("tilewidth")); tileHeight = atoi(map->Attribute("tileheight")); //Tileset stuff TiXmlElement *tilesetElement; tilesetElement = map->FirstChildElement("tileset"); firstTileID = atoi(tilesetElement->Attribute("firstgid")); spacing = atoi(tilesetElement->Attribute("spacing")); margin = atoi(tilesetElement->Attribute("margin")); //Tileset image TiXmlElement *image; image = tilesetElement->FirstChildElement("image"); std::string imagepath = image->Attribute("source"); if (!tilesetImage.loadFromFile(imagepath))//Load the tileset image { std::cout << "Failed to load tile sheet." << std::endl; return false; } tilesetImage.createMaskFromColor(sf::Color(255, 0, 255)); tilesetTexture.loadFromImage(tilesetImage); tilesetTexture.setSmooth(false); //Columns and rows (of tileset image) int columns = tilesetTexture.getSize().x / tileWidth; int rows = tilesetTexture.getSize().y / tileHeight; std::vector <sf::Rect<int> > subRects;//container of subrects (to divide the tilesheet image up) //tiles/subrects are counted from 0, left to right, top to bottom for (int y = 0; y < rows; y++) { for (int x = 0; x < columns; x++) { sf::Rect <int> rect; rect.top = y * tileHeight; rect.height = y * tileHeight + tileHeight; rect.left = x * tileWidth; rect.width = x * tileWidth + tileWidth; subRects.push_back(rect); } } //Layers TiXmlElement *layerElement; layerElement = map->FirstChildElement("layer"); while (layerElement) { Layer layer; if (layerElement->Attribute("opacity") != NULL)//check if opacity attribute exists { float opacity = strtod(layerElement->Attribute("opacity"), NULL);//convert the (string) opacity element to float layer.opacity = 255 * opacity; } else { layer.opacity = 255;//if the attribute doesnt exist, default to full opacity } //Tiles TiXmlElement *layerDataElement; layerDataElement = layerElement->FirstChildElement("data"); if (layerDataElement == NULL) { std::cout << "Bad map. No layer information found." << std::endl; } TiXmlElement *tileElement; tileElement = layerDataElement->FirstChildElement("tile"); if (tileElement == NULL) { std::cout << "Bad map. No tile information found." << std::endl; return false; } int x = 0; int y = 0; while (tileElement) { int tileGID = atoi(tileElement->Attribute("gid")); int subRectToUse = tileGID - firstTileID;//Work out the subrect ID to 'chop up' the tilesheet image. if (subRectToUse >= 0)//we only need to (and only can) create a sprite/tile if there is one to display { sf::Sprite sprite;//sprite for the tile sprite.setTexture(tilesetTexture); sprite.setTextureRect(subRects[subRectToUse]); sprite.setPosition(x * tileWidth, y * tileHeight); sprite.setColor(sf::Color(255, 255, 255, layer.opacity));//Set opacity of the tile. //add tile to layer layer.tiles.push_back(sprite); } tileElement = tileElement->NextSiblingElement("tile"); //increment x, y x++; if (x >= width)//if x has "hit" the end (right) of the map, reset it to the start (left) { x = 0; y++; if (y >= height) { y = 0; } } } layers.push_back(layer); layerElement = layerElement->NextSiblingElement("layer"); } //Objects TiXmlElement *objectGroupElement; if (map->FirstChildElement("objectgroup") != NULL)//Check that there is atleast one object layer { objectGroupElement = map->FirstChildElement("objectgroup"); while (objectGroupElement)//loop through object layers { TiXmlElement *objectElement; objectElement = objectGroupElement->FirstChildElement("object"); while (objectElement)//loop through objects { std::string objectType; if (objectElement->Attribute("type") != NULL) { objectType = objectElement->Attribute("type"); } std::string objectName; if (objectElement->Attribute("name") != NULL) { objectName = objectElement->Attribute("name"); } int x = atoi(objectElement->Attribute("x")); int y = atoi(objectElement->Attribute("y")); int width = atoi(objectElement->Attribute("width")); int height = atoi(objectElement->Attribute("height")); Object object; object.name = objectName; object.type = objectType; sf::Rect <int> objectRect; objectRect.top = y; objectRect.left = x; objectRect.height = y + height; objectRect.width = x + width; if (objectType == "solid") { solidObjects.push_back(objectRect); } object.rect = objectRect; TiXmlElement *properties; properties = objectElement->FirstChildElement("properties"); if (properties != NULL) { TiXmlElement *prop; prop = properties->FirstChildElement("property"); if (prop != NULL) { while(prop) { std::string propertyName = prop->Attribute("name"); std::string propertyValue = prop->Attribute("value"); object.properties[propertyName] = propertyValue; prop = prop->NextSiblingElement("property"); } } } objects.push_back(object); objectElement = objectElement->NextSiblingElement("object"); } objectGroupElement = objectGroupElement->NextSiblingElement("objectgroup"); } } else { std::cout << "No object layers found..." << std::endl; } return true; } Object Level::GetObject(std::string name) { for (int i = 0; i < objects.size(); i++) { if (objects[i].name == name) { return objects[i]; } } } void Level::SetDrawingBounds(sf::Rect<float> bounds) { drawingBounds = bounds; cout<<tileHeight; //Adjust the rect so that tiles are drawn just off screen, so you don't see them disappearing. drawingBounds.top -= tileHeight; drawingBounds.left -= tileWidth; drawingBounds.width += tileWidth; drawingBounds.height += tileHeight; } void Level::Draw(sf::RenderWindow &window) { for (int layer = 0; layer < layers.size(); layer++) { for (int tile = 0; tile < layers[layer].tiles.size(); tile++) { if (drawingBounds.contains(layers[layer].tiles[tile].getPosition().x, layers[layer].tiles[tile].getPosition().y)) { window.draw(layers[layer].tiles[tile]); } } } } I really hope that one of you can help me and I'm sorry if I've made any formatting issues. Thanks!

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  • Query a Log4Net-database

    - by pinhack
    So if you use Log4Net to log into a database (i.e. using the AdoNetAppender), how can you conveniently get an overview of what has happend ? Well, you could try the following Query ( T-SQL ):   SELECT convert(varchar(10),LogDB.Date,121) as Datum, LogDB.Level, LogDB.Logger,COUNT(LogDB.Logger) as Counter From Log4Net.dbo.Log as LogDB  where Level <> 'DEBUG' AND convert(varchar(10),LogDB.Date,121) like '2010-03-25' GROUP BY convert(varchar(10),LogDB.Date,121),LogDB.Level,LogDB.Logger ORDER BY counter desc This query will give you the number of events by the Logger at a specified date - and it's easy to customize, just adjust the Date and the Level to your needs. You need a bit more information than that? How about this query:  Select  convert(varchar(10),LogDB.Date,121) as Datum,LogDB.Level,LogDB.Message,LogDB.Logger ,count(LogDB.Message) as counter From Log4Net.dbo.Log as LogDB where Level <> 'DEBUG' AND convert(varchar(10),LogDB.Date,121) like '2010-03-25' GROUP BY convert(varchar(10),LogDB.Date,121),LogDB.Level,LogDB.Message,LogDB.Logger ORDER BY counter desc Similar to the first one, but inclusive the Message - which will return a much larger resultset.

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  • Alternatives to Pessimistic Locking in Cluster Applications

    - by amphibient
    I am researching alternatives to database-level pessimistic locking to achieve transaction isolation in a cluster of Java applications going against the same database. Synchronizing concurrent access in the application tier is clearly not a solution in the present configuration because the same database transaction can be invoked from multiple JVMs concurrently. Currently, we are subject to occasional race conditions which, due to the optimistic locking we have in place via Hibernate, cause a StaleObjectStateException exception and data loss. I have a moderately large transaction within the scope of my refactoring project. Let's describe it as updating one top-level table row and then making various related inserts and/or updates to several of its child entities. I would like to insure exclusive access to the top-level table row and all of the children to be affected but I would like to stay away from pessimistic locking at the database level for performance reasons mostly. We use Hibernate for ORM. Does it make sense to start a single (perhaps synchronous) message queue application into which this method could be moved to insure synchronized access as opposed to each cluster node using its own, which is a clear race condition hazard? I am mentioning this approach even though I am not confident in it because both the top-level table row and its children could also be updated from other system calls, not just the mentioned transaction. So I am seeking to design a solution where the top-level table row and its children will all somehow be pseudo-locked (exclusive transaction isolation) but at the application and not the database level. I am open to ideas and suggestions, I understand this is not a very cut and dried challenge.

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  • SQL SERVER – Simple Example of Snapshot Isolation – Reduce the Blocking Transactions

    - by pinaldave
    To learn any technology and move to a more advanced level, it is very important to understand the fundamentals of the subject first. Today, we will be talking about something which has been quite introduced a long time ago but not properly explored when it comes to the isolation level. Snapshot Isolation was introduced in SQL Server in 2005. However, the reality is that there are still many software shops which are using the SQL Server 2000, and therefore cannot be able to maintain the Snapshot Isolation. Many software shops have upgraded to the later version of the SQL Server, but their respective developers have not spend enough time to upgrade themselves with the latest technology. “It works!” is a very common answer of many when they are asked about utilizing the new technology, instead of backward compatibility commands. In one of the recent consultation project, I had same experience when developers have “heard about it” but have no idea about snapshot isolation. They were thinking it is the same as Snapshot Replication – which is plain wrong. This is the same demo I am including here which I have created for them. In Snapshot Isolation, the updated row versions for each transaction are maintained in TempDB. Once a transaction has begun, it ignores all the newer rows inserted or updated in the table. Let us examine this example which shows the simple demonstration. This transaction works on optimistic concurrency model. Since reading a certain transaction does not block writing transaction, it also does not block the reading transaction, which reduced the blocking. First, enable database to work with Snapshot Isolation. Additionally, check the existing values in the table from HumanResources.Shift. ALTER DATABASE AdventureWorks SET ALLOW_SNAPSHOT_ISOLATION ON GO SELECT ModifiedDate FROM HumanResources.Shift GO Now, we will need two different sessions to prove this example. First Session: Set Transaction level isolation to snapshot and begin the transaction. Update the column “ModifiedDate” to today’s date. -- Session 1 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN UPDATE HumanResources.Shift SET ModifiedDate = GETDATE() GO Please note that we have not yet been committed to the transaction. Now, open the second session and run the following “SELECT” statement. Then, check the values of the table. Please pay attention on setting the Isolation level for the second one as “Snapshot” at the same time when we already start the transaction using BEGIN TRAN. -- Session 2 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that the values in the table are still original values. They have not been modified yet. Once again, go back to session 1 and begin the transaction. -- Session 1 COMMIT After that, go back to Session 2 and see the values of the table. -- Session 2 SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that the values are yet not changed and they are still the same old values which were there right in the beginning of the session. Now, let us commit the transaction in the session 2. Once committed, run the same SELECT statement once more and see what the result is. -- Session 2 COMMIT SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that it now reflects the new updated value. I hope that this example is clear enough as it would give you good idea how the Snapshot Isolation level works. There is much more to write about an extra level, READ_COMMITTED_SNAPSHOT, which we will be discussing in another post soon. If you wish to use this transaction’s Isolation level in your production database, I would appreciate your comments about their performance on your servers. I have included here the complete script used in this example for your quick reference. ALTER DATABASE AdventureWorks SET ALLOW_SNAPSHOT_ISOLATION ON GO SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 1 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN UPDATE HumanResources.Shift SET ModifiedDate = GETDATE() GO -- Session 2 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 1 COMMIT -- Session 2 SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 2 COMMIT SELECT ModifiedDate FROM HumanResources.Shift GO Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Transaction Isolation

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  • SQL SERVER – Simple Example of Snapshot Isolation – Reduce the Blocking Transactions

    - by pinaldave
    To learn any technology and move to a more advanced level, it is very important to understand the fundamentals of the subject first. Today, we will be talking about something which has been quite introduced a long time ago but not properly explored when it comes to the isolation level. Snapshot Isolation was introduced in SQL Server in 2005. However, the reality is that there are still many software shops which are using the SQL Server 2000, and therefore cannot be able to maintain the Snapshot Isolation. Many software shops have upgraded to the later version of the SQL Server, but their respective developers have not spend enough time to upgrade themselves with the latest technology. “It works!” is a very common answer of many when they are asked about utilizing the new technology, instead of backward compatibility commands. In one of the recent consultation project, I had same experience when developers have “heard about it” but have no idea about snapshot isolation. They were thinking it is the same as Snapshot Replication – which is plain wrong. This is the same demo I am including here which I have created for them. In Snapshot Isolation, the updated row versions for each transaction are maintained in TempDB. Once a transaction has begun, it ignores all the newer rows inserted or updated in the table. Let us examine this example which shows the simple demonstration. This transaction works on optimistic concurrency model. Since reading a certain transaction does not block writing transaction, it also does not block the reading transaction, which reduced the blocking. First, enable database to work with Snapshot Isolation. Additionally, check the existing values in the table from HumanResources.Shift. ALTER DATABASE AdventureWorks SET ALLOW_SNAPSHOT_ISOLATION ON GO SELECT ModifiedDate FROM HumanResources.Shift GO Now, we will need two different sessions to prove this example. First Session: Set Transaction level isolation to snapshot and begin the transaction. Update the column “ModifiedDate” to today’s date. -- Session 1 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN UPDATE HumanResources.Shift SET ModifiedDate = GETDATE() GO Please note that we have not yet been committed to the transaction. Now, open the second session and run the following “SELECT” statement. Then, check the values of the table. Please pay attention on setting the Isolation level for the second one as “Snapshot” at the same time when we already start the transaction using BEGIN TRAN. -- Session 2 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that the values in the table are still original values. They have not been modified yet. Once again, go back to session 1 and begin the transaction. -- Session 1 COMMIT After that, go back to Session 2 and see the values of the table. -- Session 2 SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that the values are yet not changed and they are still the same old values which were there right in the beginning of the session. Now, let us commit the transaction in the session 2. Once committed, run the same SELECT statement once more and see what the result is. -- Session 2 COMMIT SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that it now reflects the new updated value. I hope that this example is clear enough as it would give you good idea how the Snapshot Isolation level works. There is much more to write about an extra level, READ_COMMITTED_SNAPSHOT, which we will be discussing in another post soon. If you wish to use this transaction’s Isolation level in your production database, I would appreciate your comments about their performance on your servers. I have included here the complete script used in this example for your quick reference. ALTER DATABASE AdventureWorks SET ALLOW_SNAPSHOT_ISOLATION ON GO SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 1 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN UPDATE HumanResources.Shift SET ModifiedDate = GETDATE() GO -- Session 2 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 1 COMMIT -- Session 2 SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 2 COMMIT SELECT ModifiedDate FROM HumanResources.Shift GO Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Transaction Isolation

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  • How use DNS server to create simple HA (High availability) of my website?

    - by marc22
    Welcome, How can i use DNS server to create simple HA (High availability) of website ? For example if my web-server ( for better understanding i use internal IP in real it will be other hosting companies) 192.168.0.120 :80 (is offline) traffic go to 192.168.0.130 :80 You have right, i use bad word "hight avability" of course i was thinking about failover. Using few IP in A records is good for simple load-balancing. But not in case, if i want notice user about failure (for example display page, Oops something is wrong without our server, we working on it) against "can't establish connection". I was thinking about setting up something like this 2 DNS servers, one installed on www server Both have low TTL on my domain, set up 2 ns records first for DNS with my apache server second to other dns If user try connect he will get ip of www server using first dns, if that dns is offline (probably www server is also down) so it will try second NS record, what will point to another dns, that dns will point to "backup" page. That's what i would like to do. If You have other idea please share. Reverse proxy is not option, because IP of server can change, or i can use other country for backup.

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  • Server load high, CPU idle. NFS the cause?

    - by Mech Software
    I am running into a scenario where I'm seeing a high server load (sometimes upwards of 20 or 30) and a very low CPU usage (98% idle). I'm wondering if these wait states are coming as part of an NFS filesystem connection. Here is what I see in VMStat procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 2 1 0 1298784 0 0 0 0 16 5 0 9 1 1 97 2 0 0 1 0 1308016 0 0 0 0 0 0 0 3882 4 3 80 13 0 0 1 0 1307960 0 0 0 0 120 0 0 2960 0 0 88 12 0 0 1 0 1295868 0 0 0 0 4 0 0 4235 1 2 84 13 0 6 0 0 1292740 0 0 0 0 0 0 0 5003 1 1 98 0 0 4 0 0 1300860 0 0 0 0 0 120 0 11194 4 3 93 0 0 4 1 0 1304576 0 0 0 0 240 0 0 11259 4 3 88 6 0 3 1 0 1298952 0 0 0 0 0 0 0 9268 7 5 70 19 0 3 1 0 1303740 0 0 0 0 88 8 0 8088 4 3 81 13 0 5 0 0 1304052 0 0 0 0 0 0 0 6348 4 4 93 0 0 0 0 0 1307952 0 0 0 0 0 0 0 7366 5 4 91 0 0 0 0 0 1307744 0 0 0 0 0 0 0 3201 0 0 100 0 0 4 0 0 1294644 0 0 0 0 0 0 0 5514 1 2 97 0 0 3 0 0 1301272 0 0 0 0 0 0 0 11508 4 3 93 0 0 3 0 0 1307788 0 0 0 0 0 0 0 11822 5 3 92 0 0 From what I can tell when the IO goes up the waits go up. Could NFS be the cause here or should I be worried about something else? This is a VPS box on a fiber channel SAN. I'd think the bottleneck wouldn't be the SAN. Comments?

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  • What privilege level is required on a Windows client workstation on an ActiveDomain to break file lo

    - by Mike Burton
    I'm not sure if I should be asking this here or on StackOverflow, but here goes: I'm part of a team maintaining a document management application, and I'm trying to figure out Windows file locking permissions. We use a utility somebody downloaded years ago called psunlock to remotely close all locks on a file. We recently discovered that this does not work across different domains on our VPN. A little bit of digging lead me to the samba manual's discussion of file locking. I still don't really "get it", though. Does anyone have any insight to share into how the process of locking and breaking locks on files works in a network context? My thinking is that privileges are required both on the file appliance and on the client workstations which hold locks. Is that accurate? Can anyone give a more specific version? Ideally I'm looking for something along the lines of A user must have privilege level X in order to break locks held from a client workstation. In practice I'd be happy with a hotlink to a good white paper on the subject.

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  • Downmix surround to Dolby Pro-Logic at the OS/driver level in Windows 7?

    - by davr
    First off, I'm talking about Dolby Pro-Logic, a really old tech for encoding 4 audio channels (L/R/C/SR) into two analog outputs, and then extracting them again. It was used in surround sound systems in the last century. I have a modern PC that can output 5.1 analog audio (Three outputs on the back carry six channels of audio). But I have a really old surround sound reciever that only has a two-channel, L/R input, which it extracts 4 channels of audio from, and outputs to 5.1 speakers. What I want is some way for the OS, Windows 7, to act as if I really had 5.1 audio channels available, so applications produce surround audio, but before outputting it out of the back of my PC, apply Dolby Pro-Logic matrix encoding so that it outputs over only two channels. These two channels would then get sent to my receiver via a RCA cable, which would decode it again and drive the surround speakers. Is anything like this possible? I'm pretty sure I could do it at an application / codec level, but I'm looking for something that I just have to set once.

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  • How to fix high Load_Cycle_Count laptop drive (TOSHIBA MK6006GAH in Vaio TX1XP)?

    - by Sam Brightman
    Hoping someone knows exactly what's going on here. It seems this drive has some combination of aggressive power saving settings and Ubuntu defaults that has massively increased the Load_Cycle_Count for the drive: https://wiki.ubuntu.com/DanielHahler/Bug59695 So the drive is now so slow that it cannot boot because it takes long enough to access the data that the kernel will not recognise it properly. I'm not worried about the data on the drive, but would really like to keep the laptop functioning. There is some indication that this is possible because the figure is still low 200,000s and most drives supposedly go to 600,000. Additionally, SMART tests pass and consider the drive healthy and without errors. But the really surprising thing was when I ran mhdd... Every single read came up red (slow) until I pressed 'R' for reset drive. I noticed the next read was normal speed, so held down 'R'. Magically the drive read perfectly for as long as I held the key BUT resumed slow (and noisy) seeking/reading after releasing. I don't think the source code to mhdd is available, so I'm not exactly sure what this means (besides, I don't know enough low-level HDD stuff either). It seems like the drive should be able to work, but is stuck trying to power save or something. There are no BIOS options on the laptop. Does anyone know how I can stop the drive from doing extremely slow/noisy operations like this? Or is constantly resetting the drive also damanging, and only causing it to work well by luck (i.e. not a suggestion that it's fixable)?

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  • Is there a way to do a sector level copy/clone from one hard drive to another?

    - by irrational John
    Without going into distracting details, I'm attempting to duplicate the contents of the 500GB drive in my MacBook to another 500GB drive. But this is turning out to be an unexpected hassle because the drive contains both the OS X partition and an NTFS partition with Win 7 via Apple's Boot Camp. With the exception of Clonezilla, the tools I have looked at so far all have some limitation. The Mac tools don't want to deal with the NTFS partition. The Windows tools are totally clueless about either the HFS+ partition and/or the hybrid MBR/GPT Boot Camp partitioning. Clonezilla looked like it would do what I want but apparently I can't figure out how to use it. After doing what I thought was a sector to sector copy I found that only the NTFS partition had been migrated. The others were apparently empty. (And frankly, I'm not positive Clonezilla migrated the partition table correctly either). Note: It takes over 2 hours using SATA to read/write all sectors with these drives. So I'm not up for using trial & error to narrow in on the right combination of Clonezilla options to use. I'm beginning to think that maybe the answer is to boot Linux (probably Ubuntu) and then use some ancient BSD command. Trouble is I don't know what command (or parameters to use) in order to do a sector level copy from one drive to another. As far as I know the drives have the same number of sectors so this should be trivial. Sigh.

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  • Does a high run queue length average result in poor performance for a web server?

    - by Domino
    I'm trying to narrow down the list of suspects of web servers that perform moderately well most of the time with occasional bouts of poor performance. I'm analyzing the data collected and summarized by sar. I've noticed a few things, one of which is high number of tasks in the run queue. 10:15:01 AM runq-sz plist-sz ldavg-1 ldavg-5 ldavg-15 blocked 10:25:01 AM 2 150 0.05 0.05 0.06 0 10:35:01 AM 4 149 0.08 0.12 0.09 0 10:45:01 AM 6 150 0.13 0.19 0.15 0 10:55:01 AM 1 150 0.08 0.10 0.13 0 11:05:01 AM 4 150 0.20 0.35 0.23 0 11:15:01 AM 3 149 0.02 0.09 0.15 0 11:25:01 AM 7 149 0.04 0.05 0.11 0 11:35:01 AM 4 150 0.14 0.15 0.13 0 11:45:01 AM 6 150 0.27 0.18 0.16 0 11:55:01 AM 5 150 0.08 0.10 0.13 0 12:05:01 PM 3 149 0.35 0.40 0.26 0 12:15:01 PM 19 155 0.02 0.10 0.16 1 12:25:01 PM 2 150 0.00 0.07 0.12 0 12:35:02 PM 3 151 0.58 0.24 0.17 0 12:45:01 PM 8 150 0.02 0.13 0.15 0 12:55:01 PM 6 149 0.81 0.29 0.18 0 01:05:01 PM 3 148 0.00 0.09 0.13 0 01:15:01 PM 7 149 0.00 0.04 0.11 0 I believe these are 10 minute averages. Is this an indicator that the web server is not performing as fast as it could if the average run queue length was lower?

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  • Is there a Mac utility that does low level drive integrity check and repair?

    - by Puzzled Late at Night
    The PGP Whole Disk Encryption for Mac OS X Quick Start User Guide version 10.0 contains the following remarks: PGP Corporation deliberately takes a conservative stance when encrypting drives, to prevent loss of data. It is not uncommon to encounter Cyclic Redundancy Check (CRC) errors while encrypting a hard disk. If PGP WDE encounters a hard drive with bad sectors, PGP WDE will, by default, pause the encryption process. This pause allows you to remedy the problem before continuing with the encryption process, thus avoiding potential disk corruption and lost data. To avoid disruption during encryption, PGP Corporation recommends that you start with a healthy disk by correcting any disk errors prior to encrypting. and As a best practice, before you attempt to use PGP WDE, use a third-party scan disk utility that has the ability to perform a low-level integrity check and repair any inconsistencies with the drive that could lead to CRC errors. These software applications can correct errors that would otherwise disrupt encryption. The PGP WDE Windows user guide suggests SpinRite or Norton Disk Doctor. What recourse do I have on the Mac?

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  • How to implement an experience system?

    - by Roflcoptr
    I'm currently writing a small game that is based on earning experiences when killing enemies. As usual, each level requires more experience gain than the level before, and on higher levels killing enemies awards more experience. But I have problem balancing this system. Are there any prebuild algorithms that help to caculate how the experience curve required for each level should look like? And how much experience an average enemy on a specific level should provide?

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