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• JVM tuning on Amazon EC2

  - by Shadowman

  We will be deploying a production application to Amazon EC2 very shortly. Initially, we'll just be using a "small" instance, but have plans to scale up not long afterwards. My question is, has any investigation been done on JVM tuning for the EC2 environment? Are there any specific changes that we should make to our JVM parameters to compensate for quirks/characteristics of Amazon EC2? Or, do the normal tuning methodologies apply here as they would in a physical environment? Our application will be deployed on Tomcat 6.x. It is built using JBoss Seam 2.2.x, and uses PostgreSQL 8.x as the backend database. Any advice you can give is greatly appreciated!

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• Mysql count how many queries per second are executed, is there any way ?

  - by Nikos

  Hello, i have a busy web server with LAMP installed, and i was wondering, is there any way to count how many queries per second (mysql) are executed in the server ? Thank you.

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• SQL indexing on varchar

  - by alex

  I have a table whose columns are varchar(50) and a float - I need to (very quickly) look get the float associated with a given string. Even with indexing, this is rather slow. I know, however, that each string is associated with an integer, which I know at the time of lookup, so that each string maps to a unique integer, but each integer does not map to a unique string. One might think of it as a tree structure. Is there anything to be gained by adding this integer to the table, indexing on it, and using a query like SELECT floatval FROM mytable WHERE phrase=givenstring AND assoc=givenint? This is Postgres, and if you couldn't tell, I have very little experience with databases.

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• Suggested (simple) approach for drawing large numbers of visual elements in WPF?

  - by Ender

  I'm writing an interface that features a large (~50000px width) "canvas"-type area that is used to display a lot of data in a fairly novel way. This involves lots of lines, rectangles, and text. The user can scroll around to explore the entire canvas. At the moment I'm just using a standard Canvas panel with various Shapes placed on it. This is nice and easy to do: construct a shape, assign some coordinates, and attach it to the Canvas. Unfortunately, it's pretty slow (to construct the children, not to do the actual rendering). I've looked into some alternatives, it's a bit intimidating. I don't need anything fancy - just the ability to efficiently construct and place objects in a coordinate plane. If all I get are lines, colored rectangles, and text, I'll be happy. Do I need Geometry instances inside of Geometry Groups inside of GeometryDrawings inside of some Panel container? Note: I'd like to include text and graphics (i.e. colored rectangles) in the same space, if possible.

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• Why use only a few webpage AJAX to load content ?

  - by nusbit

  Hey My Question is: Why don't use more webpages AJAX to load the Webpage content? Because of the fact that you can switch off JS or is there a thought about some security problem ?

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• Select a certain amount of checkbox arrays on the page

  - by Joris Tobebech

  Hi guys, so i wrote a function to select a certain amount of checkboxes on the page, the number retrieves fine when i message box it but no checkboxes are checked. here is my function function checkAmount(number) { alert(number); var boxes = document.getElementsByTagName("input"); for (var i = 0; i < number; i++) { if (boxes[i].name == "vote[]") { boxes[i].checked = true; } } } and here is my execution code OnClick="checkAmount(document.getElementById(\'ammount\').value)"

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• Increasing speed of webservice - howto

  - by Koran

  Hi, Our client-server product has the protocol between them as XML over HTTP. Here, the client asks a GET/POST query to the web server and the server responds with XML. The server is written using django. The server has to be on the web because there are many clients across the world using this. The server code uses extensive memoization and also there is very less db queries - most queries dont have any db queries, some of them has max 1. The biggest problem is the speed. Every query takes close to 5 seconds for the reply. The data replied is also very less - in the range of 4-6 Kb. What are the mechanisms to improve speed of the web service? Is this the usual way of writing a client-server? Are there other technologies and are we missing out on it? Thank you K

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• Where should the partitioning column go in the primary key on SQL Server?

  - by Bialecki

  Using SQL Server 2005 and 2008. I've got a potentially very large table (potentially hundreds of millions of rows) consisting of the following columns: CREATE TABLE ( date SMALLDATETIME, id BIGINT, value FLOAT ) which is being partitioned on column date in daily partitions. The question then is should the primary key be on date, id or value, id? I can imagine that SQL Server is smart enough to know that it's already partitioning on date and therefore, if I'm always querying for whole chunks of days, then I can have it second in the primary key. Or I can imagine that SQL Server will need that column to be first in the primary key to get the benefit of partitioning. Can anyone lend some insight into which way the table should be keyed?

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• Optimizing a shared buffer in a producer/consumer multithreaded environment

  - by Etan

  I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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• Table and Image in a single page of QTextDocument in Qt4

  - by liaK

  Hi, I want to display a table and a image side by side. i.e Left side the image and right side the table. I want this because the image is the reference image for the data present in the table. I want that output in pdf. So I am using QTextDocument, QTextCursor and QPrinter to get the output in pdf. So how it is possible to display the image and table in QtextDocument i.e within a single page of the pdf? I am using Qt 4.5.3 and Windows Xp. Any pointers regarding this are welcome.

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• [C++]Advantage of using a static member function instead of an equivalent non-static member function

  - by jonathanasdf

  I was wondering whether there's any advantages to using a static member function when there is a non-static equivalent. Will it result in faster execution (because of not having to care about all of the member variables), or maybe less use of memory (because of not being included in all instances)? Basically, the function I'm looking at is an utility function to rotate an integer array representing pixel colours an arbitrary number of degrees around an arbitrary centre point. It is placed in my abstract Bullet base class, since only the bullets will be using it and I didn't want the overhead of calling it in some utility class. It's a bit too long and used in every single derived bullet class, making it probably not a good idea to inline. How would you suggest I define this function? As a static member function of Bullet, of a non-static member function of Bullet, or maybe not as a member of Bullet but defined outside of the class in Bullet.h? What are the advantages and disadvantages of each?

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• NHibernate slow mapping

  - by Rob A

  My question is what can I do to determine the cause of the slowness, or what can I do to speed it up without knowing the exact cause. I am running a simple query and it appears that the mapping back to the entities is taking taking forever. The result set is 350, which is not much data in my opinion. IRepository repo = ObjectFactory.GetInstance<IRepository>(); var q = repo.Query<Order>(item => item.Ordereddate > DateTime.Now.AddDays(-40)); foreach (var order in q) { Console.WriteLine(order.TransactionNumber); } The profiler is telling me it is executing the query 7ms / 35257ms, I am assuming that the former is the actual response from the db and the latter is the time it takes NH to do it's magic. 35 seconds is too long. This is a simple mapping, one table, nested components, using fluent interface to do mappings. I just start up a simple console app and run the one query, the slowness is measured after the SessionFactory is initialized, there should only be one session, and I am not using a transaction. Thanks

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• Flash causing jerky javascript animations

  - by Matt Brailsford

  Hi Guys, I'm developing a site which has a flash background playing a small video loop scaled to fill the whole background. Over the top I have a number of HTML elements which are animated using javascript. The problem I am having is that (predominantly in FF, but also in others to a lesser degree) the flash seems to be causing my javascript animations to run rather jerky, and in some cases missing the animation altogether and just jumping to the end state. Does anybody have any thoughts on how to make the 2 work together nicely? Many thanks Matt

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• mysql query building output taking a long time

  - by user121196

  I have a simple query that does select * from t limit 1; on a remote mysql server. I use squirrel(mysql client) to run it, it shows: Query 1 of 1 elapsed time (seconds) - Total: 22.047, SQL query: 1.047, Building output: 21 why does building output take such a long time? what does this process do? when running from mysql command line, the whole process takes 0.3 secs (also remotely)

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• How to recognize what indexes are not used?

  - by tomaszs

  I have a table in MySQL with 7 indexes, most of them are on more than one column. I think here is too much indexes. Is there any way to get statistics of what indexes are used more by all thousands of queries to this database and what are less worthy so I know what index to consider to remove in first place?

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• Is it wise to use temporary tables?

  - by Industrial

  Hi guys, We have a mySQL database table for products. We are utilizing a cache layer to reduce database load, but we think that it's a good idea to minimize the actual data needed to be stored in the cache layer to speed up the application further. All the products in the database, that is visible to visitors have a price attached to them: The prices are stored in a different table, called prices . There are multiple price categories depending on which discount level each visitor (customer) applies to. From time to time, there are campaigns which means that a special price for each product is available. The special prices are stored in a table called specials. Is it a bad to make a temp table that binds the tables together? It would only have the neccessary information and would ofcourse be cached. -------------|-------------|------------ | productId | hasPrice | hasSpecial -------------|-------------|------------ 1 | 1 | 0 2 | 1 | 1 By doing such, it would be super easy to know if the specific product really has a price, without having to iterate through the complete prices or specials table each time a product should be listed or presented. Are temp tables a common thing for web applications or is it just bad design?

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• What's the quickest way to remove an element from a Map by value in Java?

  - by Supertux

  What's the quickest way to remove an element from a Map by value in Java? Currently I'm using: DomainObj valueToRemove = new DomainObj(); String removalKey = null; for (Map.Entry<String, DomainObj> entry : map.entrySet()) { if (valueToRemove.equals(entry.getValue())) { removalKey = entry.getKey(); break; } } if (removalKey != null) { map.remove(removalKey); }

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• Algorithm for Search page

  - by Geetha

  Hi All, I am creating a search page where we can find the product by entering the text. ex: Brings on the night. My query bring the records which contain atleast word from this. Needs: 1. First row should contains the record with the given sentence. 2. Second most matching....etc How to achieve this. Is there any algorithm for this. It will be more helpful if anyone share your idea. Geetha

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• WCF high instance count: anyone knows negative sideffects?

  - by Alex

  Hi there! Did anyone experience or know of negative side effects from having a high service instance count like 60k? Aside from the memory consumption of course. I am planning to increase the threshold for the maximum allowed instance count in our production environments. I am basically sick of severe production incidents just because "something" forgot to close a proxy properly. I plan to go to something like 60k instances which will allow the service to survive using default session timeouts at a call rate average for our clients. Thanks, Alex

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• Hitting a memory limit slows down the .Net application

  - by derdo

  We have a 64bit C#/.Net3.0 application that runs on a 64bit Windows server. From time to time the app can use large amount of memory which is available. In some instances the application stops allocating additional memory and slows down significantly (500+ times slower).When I check the memory from the task manager the amount of the memory used barely changes. The application keeps on running very slowly and never gives an out of memory exception. Any ideas? Let me know if more data is needed.

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• comparing two cursors in oracle instead of using MINUS

  - by Omnipresent

  The following query takes more than 3 minutes to run because tables contain massive amounts of data: SELECT RTRIM(LTRIM(A.HEAD)), A.EFFECTIVE_DATE, FROM TABLE_1 A WHERE A.TYPE_OF_ACTION='6' AND A.EFFECTIVE_DATE >= ADD_MONTHS(SYSDATE,-15) MINUS SELECT RTRIM(LTRIM(B.head)), B.EFFECTIVE_DATE, FROM TABLE_2 B In our system a query gets killed if it is running for more than 8 seconds. Is there a way to run the queries individually ..put them in cursors..compare and then get the results? that way each query will be ran individually rather than as one massive query which takes 3 minutes. How would two cursors be compared to mimic the MINUS?

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• Efficiency of iteration: NSArray vs C array of pointers?

  - by morgancodes

  I'm working at the audio buffer level, mixing audio signals created by a colleciton of objects. Since I'm looping through these objects at 44.1khz, efficiency is crucial. Is there any difference in the efficiency of iterating over an NSArray vs a C array of pointers? How about NSMutableArray?

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• What are the internal limits to WCF

  - by ligos

  WCF has lots of limits imposed on it to protect against DoS attacks and other developer brainlessness. What are these limits? And how can they be overriden? Specifically, if I was to try to send a large number of messages in a short period of time to a variety of different clients, what are the internal WCF limits they may cause messages to be sent slowly. PS: this question is a much shorter version of my previous question that did not get much attention. EDIT I have answered the original question. The issue being my async calls were being turned into synchronous ones.

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• detect page refresh jQuery or C# ASP.Net

  - by Marco

  Hello, I was searching for a way of detecting in my C# code if the page had been refreshed (f5). First I don’t know if a jQuery/JavaScript solution would be better than a fully C# ASP.Net. So... the first question would be: What would make you choose one over the other? And the third, and most important part, is if someone would help me with this. Some good tutorial, or article… anything. I tried some solutions out there… but maybe, because of my lack of knowledge they didn’t work. Thanks in advance.

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• Make jQuery-ui draggable handle cover entire page

  - by Acorn

  What would be the best way to make an element draggable when clicking anywhere in the window? Would I have to use a container <div> that covers the whole window? I tried making the body draggable but that didn't work. The problem with using a container <div> is that it moves and therefore doesn't cover the whole of the screen any more after it has been dragged. What about making a really vast container <div> that spans a large number of pixels in every direction so you would never get to the edge of it. Is that a bad idea? The idea (simplified) is to have a page with a square in the middle that can be dragged by dragging any part of the window. Here's a wonderfully unnecessary mockup :)

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