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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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• 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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• 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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• 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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• In Python, is it better to use list comprehensions or for-each loops?

  - by froadie

  Which of the following is better to use and why? Method 1: for k, v in os.environ.items() print "%s=%s" % (k, v) Method 2: print "\n".join(["%s=%s" % (k, v) for k,v in os.environ.items()]) I tend to lead towards the first as more understandable, but that might just be because I'm new to Python and list comprehensions are still somewhat foreign to me. Is the second way considered more Pythonic? I'm assuming there's no performance difference, but I may be wrong. What would be the advantages and disadvantages of these 2 techniques? (Code taken from Dive into Python)

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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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• 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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• 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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• Clarifying... So Background Jobs don't Tie Up Application Resources (in Rails)?

  - by viatropos

  I'm trying to get a better grasp of the inner workings of background jobs and how they improve performance. I understand that the goal is to have the application return a response to the user as fast as it can, so you don't want to, say, parse a huge feed that would take 10 seconds because it would prevent the application from being able to process any other requests. So it's recommended to put any operations that take more than say 500ms to execute, into a queued background job. What I don't understand is, doesn't that just delay the same problem? I know the user who invoked that background job will get an immediate response, but what if another user comes right when that background job starts (and it takes 10 seconds to finish), wont that user have to wait? Or is the main issue that, requests are the only thing that can happen one-at-a-time, while on the other hand a request can start while one+ background jobs are in the middle of running? Is that correct?

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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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• 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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• 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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• Choosing an alternative ( visual basic) high level programming language

  - by user370244

  I used to be visual basic 6 programmer, i was pleased with visual basic : it is high level language that do stuff fast,easy to learn, easy to do stuff in,you can drag and drop stuff to the form and write your code,it is simply amazing.however microsoft buried VB6 and pointed us to VB.NET which is so different that it is not the old VB anymore.I didn't like what microsoft did and would like to look somewhere AWAY from microsoft and from any other proprietary language . I would like to look into a similar language that is easy,cross platform (windows / Linux), object oriented, visual design, non proprietary and compile (for some guarding against reverse engineering). i am freelancer so the choice is entirely mine,i don't care about performance of programs, the time taken to develop a given programs is much more important. desktop / database / GUI /networking programming is what i am looking for. so any such language offered by our open source community ? thank you so much

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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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• How does a cmdlet know when it really should call WriteVerbose()?

  - by Roman Kuzmin

  How does a cmdlet know when it really should call WriteVerbose(), WriteDebug() and etc.? Perhaps I miss something simple but I cannot find the answer. All cmdlet implementations I have seen so far just call WriteVerbose() without any hesitation. I know that it is correct to do so, but it is not effective. Performance suffers when verbose mode is off but a cmdlet still prepares data for WriteVerbose() call, that is, for nothing. In other words, in a cmdlet I would like to be able to: if (<VerboseMode>) { .... data preparation, sometimes expensive ... WriteVerbose(...); } But I don't know how to get this if (<VerboseMode>). Any ideas?

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• Excel Interop: Fastest way to change color of portions of text in a huge range of cells

  - by Kyopaxa

  There some articles about the fastest way to write data using Excel interop assigning directly an Array of data to the value of the range. Like: string[,] multidimensionalArrayData = new string[200, 3]; // (...) Fill multidimensionalArrayData with your data dataSheet.Range["A1:C200"].Value = multidimensionalArrayData; There are also some articles about how to change the Font color of a specific portion of text, for example (VB this time): With ActiveCell.Characters(Start:=3, Length:=3).Font .Name = "Arial" .FontStyle = "Regular" .Size = 10 .Color = "Red" .ThemeFont = xlThemeFontNone End With The question now is, what would be the fastest way to change the color of specific portions of text for thousands of cells? Currently, in my C# code, I have to do it cell by cell, with a horrible performance hit. Is there a way to fill an array of 'Characters' objects in C# and pass that array to a range in one go? Any other solutions?

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• I want to make a wrapped acces type for certain internals of one of classes and I have some performa

  - by Alex

  I am writing an abstract matrix class (and some concrete subclasses) for use on very differing hardwares/architectures, etc. and I want to write a row and column type that provides a transparent reference to the rows and columns of the matrix. However, I want to tune for performance, so I'd like this class to be essentially a compiler construct. In other words, I'm willing to sacrifice some dev time to making the overhead of these classes as small as possible. I assume all (small) methods would want to be virtual? Keep the structure small? Any other suggestions?

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• Eclipse debug - line: not available

  - by Mike

  I can't seem to find anything on google telling me why this might be and what the resolution is. I'm Stepping through third party code (that I have the source for) and would really like to see the current line being executed... Looking at javac compile flags, I see the -g:none flag. If this flag is set, would this be enough to explain why I'm not able to see line numbers? If so, why would someone do this, are there performance implications? Do I need to recompile the jar myself to attach the missing debug info (if possible)? Thanks!

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• How often does memcache on Google AppEngine lose data?

  - by Freed

  Memcache in general and on AppEngine in specific is unreliable in the sense that my data may be deleted from the cache for whatever reason at any point in time. However, in some cases there might be cases where a small risk may be worth the added performance using memcache could give, such as updating some data in memcache that gets saved periodically to some other, more reliable storage. Are there any numbers from Google that could give me an indication of the actual probability that a memcache entry would be lost from the cache before its expiration time, given that I keep within my quotas? Are there any reasons other than hardware failure and administrative operations such as machines at the data centers being upgraded/moved/replaced that would cause entries to be removed from memcache prematurely?

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• Any efficient way to read datas from large binary file?

  - by limi

  Hi, I need to handle tens of Gigabytes data in one binary file. Each record in the data file is variable length. So the file is like: <len1><data1><len2><data2>..........<lenN><dataN> The data contains integer, pointer, double value and so on. I found python can not even handle this situation. There is no problem if I read the whole file in memory. It's fast. But it seems the struct package is not good at performance. It almost stuck on unpack the bytes. Any help is appreciated. Thanks.

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• try finally block around every Object.Create?

  - by max

  Hi, I have a general question about best practice in OO Delphi. Currently, I but a try finally block around everywhere, where I create an object, to free that object after usage (to avoid memory leaks). E.g.: aObject := TObject.Create; try aOBject.AProcedure(); ... finally aObject.Free; end; instead of: aObject := TObject.Create; aObject.AProcedure(); .. aObject.Free; To you think, it is good practice, or too much overhead? And what about the performance?

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• which is the cleaner way to do this simple while?

  - by user363834

  I'm learning c++ and I want to make clean and readable code and I was wondering which way is better (while is supposed to make the factorial of 9) : 1 - int main(){ int i = 1,r = i; while (i < 10) { r *= ++i; } 2 - int main(){ int i = 1,r = i; while (i < 10) { i++ r *= i } 1 may be harder to understand but it's 1 less line, is it worth it? and what about performance. Obviously it wouldn't matter in such a trivial example but it would be a good practice to make fast code from the begining.

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• Merging DataTable(s) Column by Column.

  - by Omky

  Hello All, I want to merge two or more DataTables Colum by Column. I am developing C# Windows Application. My use case is below: I have empty data grid in my application. user will drag and drop one column from available column list box into data grid. The data grid will start displaying data for that column. Now, I will drag another column into data grid and now grid should get populated data of two columns. This will repeat till user feels that he has dropped all necessary columns. What is best way to do this? Is there any performance hits with large number of rows typically 1 million? Please help. Thanks, Omky

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• Language D compared to C++?

  - by Henrik

  Anyone here with experience of the language D? I was just reading through its presentation at http://www.d-programming-language.org/ and at Wikipedia and it seems like a good (better) alternative to C++. With good/better I mean that it seem simpler yet it has all the good stuff within C/C++. But without some of the difficulties that make C++ more difficult to learn and use in a good and efficient way. So anyone with comments/experience with the language D? Performance?

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• Why would you use a MyObject[] internally, but expose a List<MyObject>?

  - by timmyd

  I have come across a class that has an immutable property: MyObject[] allObjs The property is initialized like this: List<MyObject> objs = createAllMyObjects(); allObjs = objs.toArray(new MyObject[objs.size()]); When it is exposed through the accessor, it's done as a List: public List<MyObject> getAllMyObjects() { return Collections.unmodifiableList(Arrays.asList(allObjs)); } Why would a programmer do this? Is there a benefit that I don't know about? Performance is not a concern, as the array of objs will only ever number in a few dozen elements. It seems that we are going round and round in circles. The class is a sort of factory, so it's got a private constructor and exposes only static methods (not sure if this could be a reason for the madness).

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