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  • B-trees, databases, sequential inputs, and speed.

    - by IanC
    I know from experience that b-trees have awful performance when data is added to them sequentially (regardless of the direction). However, when data is added randomly, best performance is obtained. This is easy to demonstrate with the likes of an RB-Tree. Sequential writes cause a maximum number of tree balances to be performed. I know very few databases use binary trees, but rather used n-order balanced trees. I logically assume they suffer a similar fate to binary trees when it comes to sequential inputs. This sparked my curiosity. If this is so, then one could deduce that writing sequential IDs (such as in IDENTITY(1,1)) would cause multiple re-balances of the tree to occur. I have seen many posts argue against GUIDs as "these will cause random writes". I never use GUIDs, but it struck me that this "bad" point was in fact a good point. So I decided to test it. Here is my code: SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[T1]( [ID] [int] NOT NULL CONSTRAINT [T1_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO CREATE TABLE [dbo].[T2]( [ID] [uniqueidentifier] NOT NULL CONSTRAINT [T2_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO declare @i int, @t1 datetime, @t2 datetime, @t3 datetime, @c char(300) set @t1 = GETDATE() set @i = 1 while @i < 2000 begin insert into T2 values (NEWID(), @c) set @i = @i + 1 end set @t2 = GETDATE() WAITFOR delay '0:0:10' set @t3 = GETDATE() set @i = 1 while @i < 2000 begin insert into T1 values (@i, @c) set @i = @i + 1 end select DATEDIFF(ms, @t1, @t2) AS [Int], DATEDIFF(ms, @t3, getdate()) AS [GUID] drop table T1 drop table T2 Note that I am not subtracting any time for the creation of the GUID nor for the considerably extra size of the row. The results on my machine were as follows: Int: 17,340 ms GUID: 6,746 ms This means that in this test, random inserts of 16 bytes was almost 3 times faster than sequential inserts of 4 bytes. Would anyone like to comment on this? Ps. I get that this isn't a question. It's an invite to discussion, and that is relevant to learning optimum programming.

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  • side effect of zsh echo?

    - by Mirai
    For some reason this script will work with all of the 'echo's at the end, but without them $wall is an empty string. This seems like really odd behaviour. #!/bin/zsh if [ ! -n "$1" ] ; then files=(~/pictures/backgrounds/*jpg) else while [ $1 ] ; do files+=(`echo $1/*jpg`) shift done fi echo $files N=${#files} echo $N ((N=RANDOM%N)) echo $N wall=${files[$N]} echo $wall cp $wall ~/wall.jpg

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  • KeyNotFound Exception in Dictionary(of T)

    - by C Patton
    I'm about ready to bang my head against the wall I have a class called Map which has a dictionary called tiles. class Map { public Dictionary<Location, Tile> tiles = new Dictionary<Location, Tile>(); public Size mapSize; public Map(Size size) { this.mapSize = size; } //etc... I fill this dictionary temporarily to test some things.. public void FillTemp(Dictionary<int, Item> itemInfo) { Random r = new Random(); for(int i =0; i < mapSize.Width; i++) { for(int j=0; j<mapSize.Height; j++) { Location temp = new Location(i, j, 0); int rint = r.Next(0, (itemInfo.Count - 1)); Tile t = new Tile(new Item(rint, rint)); tiles[temp] = t; } } } and in my main program code Map m = new Map(10, 10); m.FillTemp(iInfo); Tile t = m.GetTile(new Location(2, 2, 0)); //The problem line now, if I add a breakpoint in my code, I can clearly see that my instance (m) of the map class is filled with pairs via the function above, but when I try to access a value with the GetTile function: public Tile GetTile(Location location) { if(this.tiles.ContainsKey(location)) { return this.tiles[location]; } else { return null; } } it ALWAYS returns null. Again, if I view inside the Map object and find the Location key where x=2,y=2,z=0 , I clearly see the value being a Tile that FillTemp generated.. Why is it doing this? I've had no problems with a Dictionary such as this so far. I have no idea why it's returning null. and again, when debugging, I can CLEARLY see that the Map instance contains the Location key it says it does not... very frustrating. Any clues? Need any more info? Help would be greatly appreciated :)

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  • sybase trigger to find the deleted querry

    - by vinod
    hi , In my sybase server, some rows of a table (TBL_RESOURCE) are deleting from unknown source at random intervals.I tried a lot, but i cannot able to locate from which source/file/process this data is deleting.Is there any mechanism to locate this problem !! i need to find out who is deleting this rows.. how we can find out who is deleted it and from which file ... can we use triger to find the source of deletion ..?

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  • how to work with datagridview if need show many columns data (approx 1Mio)

    - by ruprog
    is a problem to display data in Datagridview. A large amount of data (stock quotes) data to be displayed from left to right Tell me what to do to display an array of data in datagridviev Public dat As New List(Of act) Public Class act Public time As Date Public price As Integer End Class Sub work() Dim r As New Random For x As Integer = 0 To 1000000 Dim el As New act el.time = Now el.price = r.Next(0, 1000) dat.Add(New act) Next End Sub

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  • What's the worst name you've seen for a product? [closed]

    - by Dean J
    (Community wiki from the start.) What's the worst name you've seen for a product? It might be a euphemism the company didn't know about, maybe something like Penetrode (from Office Space). It might be something impossible to do a web search on, like the band named "Download". It might be some combination of random syllables that's just awful. But no matter what, it's bad. What's the worst you've seen?

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  • Rendering problem with UITableview

    - by Spider-Paddy
    I have a very strange problem with a UITableview within a navigation controller on the iPhone simulator. Of the cells displayed, only some are correctly rendered. They are all supposed to look the same but the majority are missing the accessory I've set, scrolling the view changes which cell has the accessory so I suspect it's some sort of cell caching happening, although the contents are correct for each cell. I also set an image as the background and that was also only displaying sporadically but I fixed that by changing cell.backgroundView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"yellow-bar_short.png"]]; (which also only rendered a random cell with the background) to cell.backgroundColor = [[UIColor alloc] initWithPatternImage:[UIImage imageNamed:@"yellow-bar_short.png"]]; I now need to fix the problem with the accessory only showing on a random cell. I tried moving the code from cellForRowAtIndex to willDisplayCell but it made no difference. I put in a log command to confirm that it is running through each frame. Basically it's a table view (UITableViewCellStyleSubtitle) that gets its info from a server & is then updated by a delegate method calling reload. Code is: -(void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath { NSLog(@"%@", [NSString stringWithFormat:@"Setting colours for cell %i", indexPath.row]); // Set cell background // cell.backgroundView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"yellow-bar_short.png"]]; cell.backgroundColor = [[UIColor alloc] initWithPatternImage:[UIImage imageNamed:@"yellow-bar_short.png"]]; cell.textLabel.backgroundColor = [UIColor clearColor]; cell.detailTextLabel.backgroundColor = [UIColor clearColor]; // detailTableViewAccessory is a view containing an imageview in this view's nib // i.e. nib <- view <- imageview <- image cell.accessoryView = detailTableViewAccessory; } // Called by data fetching object when done -(void)listDataTransferComplete:(ArticleListParser *)articleListParserObject { NSLog(@"Data parsed, reloading detail table"); self.currentTotalResultPages = (((articleListParserObject.currentArticleCount - 1) / 10) + 1); self.detailTableDataSource = [articleListParserObject.returnedArray copy]; // make a local copy of the returned array // Render table again with returned array data (neither of these 2 fixed it) [self.detailTableView performSelectorOnMainThread:@selector(reloadData) withObject:nil waitUntilDone:NO]; // [self.detailTableView reloadData]; // Re-enable necessary buttons (including table cells) letUserSelectRow = TRUE; [btnByName setEnabled:TRUE]; [btnByPrice setEnabled:TRUE]; // Remove please wait message NSLog(@"Removing please wait view"); [pleaseWaitViewControllerObject.view removeFromSuperview]; } I only included code that I thought was relevant, can supply more if needed. I can't test it on an iPhone yet so I don't know if it's maybe just a simulator anomaly or a bug in my code. I've always gotten good feedback from questions, any ideas?

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  • RSA PKCS1 implementation in Python

    - by user307016
    I'm working on the RSA PKCS1 implementation in Python,here's the message block i got: m = [0,2,random paddings,0,message integers] I read the RFC2313,and get a equation seems for transforming the message block object into an big-edian integer. I just get confused about how to transform it in Python. Any help would be appreciated.

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  • Code Golf: Countdown Number Game

    - by Noldorin
    Challenge Here is the task, inspired by the well-known British TV game show Countdown. The challenge should be pretty clear even without any knowledge of the game, but feel free to ask for clarifications. And if you fancy seeing a clip of this game in action, check out this YouTube clip. It features the wonderful late Richard Whitely in 1997. You are given 6 numbers, chosen at random from the set {1, 2, 3, 4, 5, 6, 8, 9, 10, 25, 50, 75, 100}, and a random target number between 100 and 999. The aim is to make use the six given numbers and the four common arithmetic operations (addition, subtraction, multiplication, division; all over the rational numbers) to generate the target - or as close as possible either side. Each number may only be used once at most, while each arithmetic operator may be used any number of times (including zero.) Note that it does not matter how many numbers are used. Write a function that takes the target number and set of 6 numbers (can be represented as list/collection/array/sequence) and returns the solution in any standard numerical notation (e.g. infix, prefix, postfix). The function must always return the closest-possible result to the target, and must run in at most 1 minute on a standard PC. Note that in the case where more than one solution exists, any single solution is sufficient. Examples: {50, 100, 4, 2, 2, 4}, target 203 e.g. 100 * 2 + 2 + (4 / 4) e.g. (100 + 50) * 4 * 2 / (4 + 2) {25, 4, 9, 2, 3, 10}, target 465 e.g. (25 + 10 - 4) * (9 * 2 - 3) {9, 8, 10, 5, 9, 7), target 241 e.g. ((10 + 9) * 9 * 7) + 8) / 5 Rules Other than mentioned in the problem statement, there are no further restrictions. You may write the function in any standard language (standard I/O is not necessary). The aim as always is to solve the task with the smallest number of characters of code. Saying that, I may not simply accept the answer with the shortest code. I'll also be looking at elegance of the code and time complexity of the algorithm! My Solution I'm attempting an F# solution when I find the free time - will post it here when I have something! Format Please post all answers in the following format for the purpose of easy comparison: Language Number of characters: ??? Fully obfuscated function: (code here) Clear (ideally commented) function: (code here) Any notes on the algorithm/clever shortcuts it takes.

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  • What causes POCO proxy entities to only sometimes be created in Entity Framework 4.

    - by Kohan
    I have set up my POCOs and I have marked their public properties as virtual and I am successfully getting Proxies most of the time (95%) but randomly I am getting EF return some proxies and some non-proxies. Recycling the app pool when this happens will then fix this instance of the error and it will go away for an amount of time. Then it will re-occur in some other random (it seems) place. What can cause this sort of behaviour? Thanks, Kohan

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  • Finding databases for use in applications

    - by JonF
    Does anyone have some recommendations on how I can find databases for random things that I might want to use in my application. For example, a database of zip code locations, area code cities, car engines, IP address locations, or whatever. I'm just asking generally when you decide you need a bunch of data where are some good places to start looking other than google?

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  • What does this line of code mean?

    - by Victor
    Hi, I am wondering what this line of code mean? b = (gen_rand_uniform()>0.5)?1:0; The gren_rand_uniform() is a function to generate random 0 and 1 numbers. However I don't get the meaning for >0.5 and 1:0. I know this is supposed to be a basic question, please bear with me. Thanks!

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  • Save/Load jFreechart TimeSeriesCollection chart from XML

    - by IMAnis_tn
    I'm working with this exemple wich put rondom dynamic data into a TimeSeriesCollection chart. My problem is that i can't find how to : 1- Make a track of the old data (of the last hour) when they pass the left boundary (because the data point move from the right to the left ) of the view area just by implementing a horizontal scroll bar. 2- Is XML a good choice to save my data into when i want to have all the history of the data? public class DynamicDataDemo extends ApplicationFrame { /** The time series data. */ private TimeSeries series; /** The most recent value added. */ private double lastValue = 100.0; public DynamicDataDemo(final String title) { super(title); this.series = new TimeSeries("Random Data", Millisecond.class); final TimeSeriesCollection dataset = new TimeSeriesCollection(this.series); final JFreeChart chart = createChart(dataset); final ChartPanel chartPanel = new ChartPanel(chart); final JPanel content = new JPanel(new BorderLayout()); content.add(chartPanel); chartPanel.setPreferredSize(new java.awt.Dimension(500, 270)); setContentPane(content); } private JFreeChart createChart(final XYDataset dataset) { final JFreeChart result = ChartFactory.createTimeSeriesChart( "Dynamic Data Demo", "Time", "Value", dataset, true, true, false ); final XYPlot plot = result.getXYPlot(); ValueAxis axis = plot.getDomainAxis(); axis.setAutoRange(true); axis.setFixedAutoRange(60000.0); // 60 seconds axis = plot.getRangeAxis(); axis.setRange(0.0, 200.0); return result; } public void go() { final double factor = 0.90 + 0.2 * Math.random(); this.lastValue = this.lastValue * factor; final Millisecond now = new Millisecond(); System.out.println("Now = " + now.toString()); this.series.add(new Millisecond(), this.lastValue); } public static void main(final String[] args) throws InterruptedException { final DynamicDataDemo demo = new DynamicDataDemo("Dynamic Data Demo"); demo.pack(); RefineryUtilities.centerFrameOnScreen(demo); demo.setVisible(true); while(true){ demo.go(); Thread.currentThread().sleep(1000); } } }

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  • KeyNotFound Exception in CSsharp

    - by C Patton
    I'm about ready to bang my head against the wall I have a class called Map which has a dictionary called tiles. class Map { public Dictionary<Location, Tile> tiles = new Dictionary<Location, Tile>(); public Size mapSize; public Map(Size size) { this.mapSize = size; } //etc... I fill this dictionary temporarily to test some things.. public void FillTemp(Dictionary<int, Item> itemInfo) { Random r = new Random(); for(int i =0; i < mapSize.Width; i++) { for(int j=0; j<mapSize.Height; j++) { Location temp = new Location(i, j, 0); int rint = r.Next(0, (itemInfo.Count - 1)); Tile t = new Tile(new Item(rint, rint)); tiles[temp] = t; } } } and in my main program code Map m = new Map(10, 10); m.FillTemp(iInfo); Tile t = m.GetTile(new Location(2, 2, 0)); //The problem line now, if I add a breakpoint in my code, I can clearly see that my instance (m) of the map class is filled with pairs via the function above, but when I try to access a value with the GetTile function: public Tile GetTile(Location location) { if(this.tiles.ContainsKey(location)) { return this.tiles[location]; } else { return null; } } it ALWAYS returns null. Again, if I view inside the Map object and find the Location key where x=2,y=2,z=0 , I clearly see the value being a Tile that FillTemp generated.. Why is it doing this? I've had no problems with a Dictionary such as this so far. I have no idea why it's returning null. and again, when debugging, I can CLEARLY see that the Map instance contains the Location key it says it does not... very frustrating. Any clues? Need any more info? Help would be greatly appreciated :)

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  • Who owns forum users or are user grabbers legal?

    - by Eugene
    Hi, I am not very strong in "legal or not" questions so I hope someone can help me here. How legal is the following: I create my forum, then choose a random existing forum (not mine), take a user from that forum (username, avatar, etc) and create an identical account at my forum. I know that this is extremely hard to prove and everything but anyway: how legal are the described actions? Thanks!

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