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• java virtual machine - how does it allocate resources?

  - by Will

  I am testing the performance of a data streaming system that supports continuous queries. This is how it works: - There is a polling service which sends data to my system. - As data passes into the system, each query evaluates based on a window of the stream at the current time. - The window slides as data passes in. My problem is this, when I add more queries to the system, I should expect the throughput to decrease because it can't cope the data rate. However, I actually observe an increase in throughput. I can't understand why this is the case and I am guessing that it's something to do with the way the JVM allocates CPU, memory etc. Can anyone shed any light to my problem?

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• Design cache mechanism

  - by Delashmate

  Hi All, I got assignment to write design for cache mechanism, This is my first time writing a design document, Our program display images for doctors, and we wan't to reduce the parsing time of the images So we want to save the parsed data in advance (in files or inside database) Currently I have several design key ideas Handle locks - each shared data structure should be handled, also files Test - add test to verify the data from the cache is equal to the data from the files To decouple the connection to the database- not to call directly to the database Cleanup mechanisem- to delete old files if the cahce directory exceed configurable threshold Support config file Support performance tool in the feature I will also add class diagram, data flow charts, and workflow What do you think I should add to the key ideas? Do you know good link to atricales about design? Thanks in advance, Dan

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• Can I Use EF Across Multiple DBs in One SQLServer Instance?

  - by thomashubschman

  Hello, I have been searching the blogs and articles but I have not found much support for this scenario. I have been poking around EF and realized that I could create views that contained data from multiple databases and then build the EF object model off of those views. Although it works I am not sure about the usual issues of performance, scalability, maintainability. The way I am achieving the connection between databases is by creating associations in the EF model. Does anyone have any information about this type of implementation? Either another solution or commentary on this proposed solution? Thanks, Tom

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• How to setup a http(s) proxy with record/replay functionality?

  - by superb

  The use case is: I want to do some android app performance tests and I want to fix the data when app got from web. The solution I come up with is to setup a local http proxy, which can first record all http traffic, and later replay then app is running perf tests. I found http://mitmproxy.org/, which has exactly the features I want. but seems with the default settings it cannot be used as a https proxy. I tried using it as proxy and login to facebook but doesn't work. I am not familiar with the https protocol and how cert things work. Any one can provide some help? Thanks a lot.

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• "Remember" last three MySql queries; Cookie, passed variable or other method?

  - by Camran

  I have a classified website, with pretty sophisticated searching, and I am about to implement a function where the last three queries is displayed for the user, so that the user can go back easier through the queries. This because for each query the user has to provide a lot of input. I have four questions for you: I wonder, how can I save the actual query (SELECT * FROM etc etc)...? Do I need to add some form of encryption to be on the safe side? How will this affect performance? (I don't like the fact that cookies slow websites down) Anything else to think about? If you need more input, let me know... Btw, the website is PHP based. Thanks

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• What scenarios/settings will result in a query on SQL Server (2008) return stale data

  - by s1mm0t

  Most applications rarely need to display 100% accurate data. For example if this stack overflow question displays that there have been 0 views, when there have really been 10, it doesn't really matter. This is one way that the (perceived) performance of applications can be improved, by caching results and therefore sometimes not showing 100% accurate results. There are some cases where the data does need to be 100% accurate though. So if I run the query select * from Foo I want to be sure that the results are not stale. Now depending on how my database is set up, other activity on the database, use of transactions and isolation levels etc this query may or may not be a true reflection of the world. What scenario's and settings can people think of that will result in this query returning stale results or given that another connection is part way through a transaction that has updated this table, how can I guarantee that when the above query returns, the results will be accurate.

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• One on One table relation - is it harmful to keep relation in both tables?

  - by EBAGHAKI

  I have 2 tables that their rows have one on one relation.. For you to understand the situation, suppose there is one table with user informations and there is another table that contains a very specific informations and each user can only link to one these specific kind of informations ( suppose second table as characters ) And that character can only assign to the user who grabs it, Is it against the rules of designing clean databases to hold the relation key in both tables? User Table: user_id, name, age, character_id Character Table: character_id, shape, user_id I have to do it for performance, how do you think about it?

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• How can I edit a js file sent by the server before it gets to my browser?

  - by pstone

  During a normal browsing session I want to edit a specific javascript file before the browser receives since once it gets there it's impossible to edit. Is there are any tool for this? For what I need it I can't just save it and edit it on my disk. I'm ready to learn how to program it myself but if anyone can point out more or less what I have to do I'd be very grateful. I'd have to intercept the packets until I have the whole file while blocking the browser from receiving it any part of it, then edit it manually and forward it to the same port. I don't think I can do this by just using pcap, I've read a bit about scapy but I'm not sure if it can help me either. Thanks in advance.

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• Facing problem in configuring Reporting Server

  - by idrees99

  Hi all, I am using Sql server 2005 express edition and i want to Install and configure Reporting server on my local machine.Now i have installed the reporting server but the issue is that i am unable to configure it properly.when ever i go to start the reporting services it gives me the following message: THE SQL SERVER REPORTING SERVICE(SQLEXPRESS)service on Local computer started and then stopped. Some services stop automatically if they have no work to do, for example, the performance Logs and Alerts service. I am using WindowsXp Professional. plz help me out as i have just started using sql server and i dont have any idea.

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• Optimal search queries

  - by Macros

  Following on from my last question http://stackoverflow.com/questions/2788082/sql-server-query-performance, and discovering that my method of allowing optional parameters in a search query is sub optimal, does anyone have guidelines on how to approach this? For example, say I have an application table, a customer table and a contact details table, and I want to create an SP which allows searching on some, none or all of surname, homephone, mobile and app ID, I may use something like the following: select * from application a inner join customer c on a.customerid = a.id left join contact hp on (c.id = hp.customerid and hp.contacttype = 'homephone') left join contact mob on (c.id = mob.customerid and mob.contacttype = 'mobile') where (a.ID = @ID or @ID is null) and (c.Surname = @Surname or @Surname is null) and (HP.phonenumber = @Homphone or @Homephone is null) and (MOB.phonenumber = @Mobile or @Mobile is null) The schema used above isn't real, and I wouldn't be using select * in a real world scenario, it is the construction of the where clause I am interested in. Is there a better approach, either dynamic sql or an alternative which can achieve the same result, without the need for many nested conditionals. Some SPs may have 10 - 15 criteria used in this way

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• Is it possible to exclude folders from a web application project in vs 2010?

  - by JL

  I had previously asked this question. At the time I was working with VS 2008. To restate the question. I have a web application that generates 1000's of small xml files in a certain directory. I would like to exclude this directory from the web application project in visual studio 2010. With vs 2008 it was not possible. Has anything changed? Besides the general wait for VS to iterate through this directory and add an item in the solution explorer for each file, it also strains my system resources, so I would like to exclude it from the project, but the dir and files need to physically exist on disk, because they are part of the application. Any OOB VS 2010 solutions, or any good workarounds? Thanks Update: This also sums up the issue nicely http://forums.asp.net/t/1179077.aspx

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• Which NoSQL db to use with C?

  - by systemsfault

  Hello all, I'm working on an application that I'm going to write with C and i am considering to use a nosql db for storing timeseries data with at most 8 or 9 fields. But in every 5 minutes there will huge write operations such as 2-10 million rows and then there will be reads(but performance is not as crucial in read as in the write operation). I'm considering to use a NoSQL db here in order to store the data but couldn't decide on which one to use. Couchdb seems to have a stable driver called pillowtalk for C; but Mongo's driver doesn't look as promising as pillowtalk. I'm also open to other suggestions. What is your recommendation?

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• InvalidCastException: System.Web.UI.PartialCachingControl -> MyCustomControl when OutputCaching

  - by marcinn

  The problem: I am unable to use OutputCaching with my controls which derives from MyCustomControl. Controls are loaded dynamically using definitions from database with Page.LoadControl method. When I add to ascx <%@ OutputCache VaryByParam="*" Duration="3600"% the "InvalidCastException: System.Web.UI.PartialCachingControl - MyCustomControl" exception is thrown. I am unable to modify assembly witch contains dynamic loading controls logic. Is there any way to fix it in derived controls? The second question is about iis7 and native output caching - is it resolves this problem? (I tried to set up several performance counters and I saw that cache wasn't hit...)

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• How do you use the C language to produce a ruby gem?

  - by DJTripleThreat

  I would like to see some source code or maybe a link to some that gives at least a stub for writing ruby gems in the C languages (C++?? is that possible too?) Also, some of you may know that Facebook compiles some of their code natively as php extensions for better performance. Is anyone doing this in Rails? If so, what has been your experience with it? Have you found it to be useful? Thanks. Edit: I guess I'll answer my own question with some stuff I learned today but I'm going to leave the question open for another answer because I'd like to see what others have to say on this topic

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• "Inlining" (kind of) functions at runtime in C

  - by fortran

  Hi, I was thinking about a typical problem that is very JIT-able, but hard to approach with raw C. The scenario is setting up a series of function pointers that are going to be "composed" (as in maths function composition) once at runtime and then called lots and lots of times. Doing it the obvious way involves many virtual calls, that are expensive, and if there are enough nested functions to fill the CPU branch prediction table completely, then the performance with drop considerably. In a language like Lisp, I could probably process the code and substitute the "virtual" call by the actual contents of the functions and then call compile to have an optimized version, but that seems very hacky and error prone to do in C, and using C is a requirement for this problem ;-) So, do you know if there's a standard, portable and safe way to achieve this in C? Cheers

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• PHP, better to set the variable before if or use if/else?

  - by DssTrainer

  So a simple one that I just never could find a straight answer on. What is better (performance or otherwise): $var = false; If ($a == $b) { $var = true; } or If ($a == $b) { $var = true; } else { $var = false; } I've heard arguments for both ways. I find the first cleaner to ensure I have it set, and a little less code too. The pro being that you may only need to set it once without conditional. But the con being that if the argument is true, it gets set twice. I am assuming the second way is probably best practice

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• "Volkswagen Passat" Navigation

  - by joe_midi

  http://web.vw.com/all-new-passat-experience/ The navigation on this .swf is very impressive, and I was wondering how I would go about replicating it. The way each of the sections Design / Technology / Safety / Performance I want to know how each section can expand and still fit together. I've started with MOUSE_OVER events, but I'm not entirely sure how to order them so each section is the right size for every mouse over Event. This is the code I have for each "Section", I have created a movie clip with a Mask that expands on mouse over and brings the selected clip to the highest depth. this.firstButton01.addEventListener(MouseEvent.MOUSE_OVER, firstButton01OVER) function firstButton01OVER(e:Event):void { this.firstButton01.gotoAndPlay(2); this.setChildIndex(firstButton01,this.numChildren-1); }

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• [Bash] Save part of matching pattern to variable

  - by Ben

  I want to extract a substring matching a pattern and save it to a file. An example string: Apr 12 19:24:17 PC_NMG kernel: sd 11:0:0:0: [sdf] Attached SCSI removable disk I want to extract the part between the brackets, in this case []. I tried to do something like grep -e '[$subtext]' to save the text in the brackets to a variable. Of course it doesn't work, but I am looking for a way similar to this. It would be very elegant to include a variable in a regex like this. What can I do best? Thanks!

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• Error in SQL. Can not find it.

  - by kmsboy

  Error in SQL. Can not find it. DECLARE @year VARCHAR (4), @month VARCHAR (2), @day VARCHAR (2), @weekday VARCHAR (2), @hour VARCHAR (2), @archivePath VARCHAR (128), @archiveName VARCHAR (128), @archiveFullName VARCHAR (128) SET @year = CAST(DATEPART(yyyy, GETDATE()) AS VARCHAR) SET @month = CAST(DATEPART(mm, GETDATE()) AS VARCHAR) SET @day = CAST(DATEPART(dd, GETDATE()) AS VARCHAR) SET @weekday = CAST(DATEPART (dw, GETDATE()) AS VARCHAR) SET @hour = CAST(DATEPART (hh, GETDATE()) AS VARCHAR) SET @archivePath = 'd:\1c_new\backupdb\' SET @archiveName = 'TransactionLog_' + @year + '_' + @month + '_' + @day + '_' + @hour + '.bak' SET @archiveFullName = @archivePath + @archiveName BACKUP LOG [xxx] TO DISK = @archiveFullName WITH INIT , NOUNLOAD , NAME = N'?????????? ??? ??????????', SKIP , STATS = 10, DESCRIPTION = N'?????????? ??? ??????????', NOFORMAT

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• What machine learning algorithms can be used in this scenario?

  - by ExceptionHandler

  My data consists of objects as follows. Obj1 - Color - shape - size - price - ranking So I want to be able to predict what combination of color/shape/size/price is a good combination to get high ranking. Or even a combination could work like for eg: in order to get good ranking, the alg predicts best performance for this color and this shape. Something like that. What are the advisable algorithms for such a prediction? Also may be if you can briefly explain how I can approach towards the model building I would really appreciate it. Say for eg: my data looks like Blue pentagon small $50.00 #5 Red Squre large $30.00 #3 So what is a useful prediction model that I should look at? What algorithm should I try to predict like say highest weightage is for price followed by color and then size. What if I wanted to predict in combinations like a Red small shape is less likely to higher rank compared to pink small shape . (In essence trying to combine more than one nominal values column to make the prediction)

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• Fastest way to convert a binary file to SQLite database

  - by chown

  I've some binary files and I'm looking for a way to convert each of those files to a SQLite database. I've already tried C# but the performance is too slow. I'm seeking an advice on how and what programming language should be the best to perform this kind of conversion. Though I prefer any Object Oriented Language more (like C#, Java etc), I'm open for any programming language that boosts up the conversion. I don't need a GUI frontend for the conversion, running the script/program from console is okay. Thanks in advance

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• Java exception translations

  - by user3079275

  Apologies if this has been discussed on other threads but I find it helps clarify my thinking when I am forced to write down my questions. I am trying to properly understand the concept of checked vs unchecked exceptions and exception translation in Java but I am getting confused. So far I understood that checked exceptions are exceptions that need to be always caught in a try/catch block otherwise I get a compile time error. This is to force programmers to think about abnormal situations that might happen at run time (like disk full etc). Is this right? What I did not get was why we have unchecked exceptions, when are they useful? Is it only during development time to debug code that might access an illegal array index etc? This confusion is because I see that Error exceptions are also unchecked as is RunTimeException but its not clear to me why they are both lumped together into an unchecked category?

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• CouchDB: How to change view function via javascript?

  - by osti

  Hello Guys, I am playing around with CouchDB to test if it is "possible" [1] to store scientific data (simulated and experimental raw data + metadata). A big pro is the schema-less approach of CouchDB: we have to be very flexible with the metadata, as the set of parameters changes very often. Up to now I have some code to feed raw data, plots (both as attachments), and hierarchical metadata (as JSON) into CouchDB documents, and have written some prototype Javascript for filtering and showing. But the filtering is done on the client side (a.k.a. browser): The map function simply returns everything. How could I change the (or push a second) map function of a specific _design-document with simple browser-JS? I do not think that a temporary view would yield any performance gain... Thanks for your time and answers. [1]: of course it is possible, but is it also useful? feasible? reasonable?

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• What language should I use to parse a lot of text?

  - by BicMan

  My company's proprietary software generates a log file that is much easier to use if it is parsed. The log parser we all use was written by another employee as a side project, and it has horrible performance. These log files can grow to 10s of megabytes very quickly, and the parser we currently use has issues if a log file is bigger than 1 megabyte. So, I want to write a program that can parse this massive amount of text in the shortest amount of time possible. We use Windows exclusively, so running on Windows is a must. Our current implementation runs on a local web server, and I'm convinced that running it as an application would have to be faster. All suggestions will be helpful. Thanks.

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• Serialization of a TChan String

  - by J Fritsch

  I have declared the following type KEY = (IPv4, Integer) type TPSQ = TVar (PSQ.PSQ KEY POSIXTime) type TMap = TVar (Map.Map KEY [String]) data Qcfg = Qcfg { qthresh :: Int, tdelay :: Rational, cwpsq :: TPSQ, cwmap :: TMap, cw chan :: TChan String } deriving (Show) and would like this to be serializable in a sense that Qcfg can either be written to disk or be sent over the network. When I compile this I get the error No instances for (Show TMap, Show TPSQ, Show (TChan String)) arising from the 'deriving' clause of a data type declaration Possible fix: add instance declarations for (Show TMap, Show TPSQ, Show (TChan String)) or use a standalone 'deriving instance' declaration, so you can specify the instance context yourself When deriving the instance for (Show Qcfg) I am now not quite sure whether there is a chance at all to serialize my TChan although all individual nodes in it are members of the show class. For TMap and TPSQ I wonder whether there are ways to show the values in the TVar directly (because it does not get changed, so there should no need to lock it) without having to declare an instance that does a readTVar ?

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