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• [MySQL] Efficiently store last X records per item

  - by Saif Bechan

  I want to store the last X records in an MySQL database in an efficient way. So when the 4th record is stored the first should be deleted. The way I do this not is first run a query getting the items. Than check what I should do then insert/delete. There has to be a better way to do this. Any suggestions? Edit I think I should add that the records stored do not have a unique number. They have a mixed par. For example article_id and user_id. Then I want to make a table with the last X items for user_x. Just selecting the article from the table grouped by user and sorted by time is not an option for me. The table where I do the sort and group on has millions of records and gets hit a lot for no reason. So making a table in between with the last X records is way more effient. PS. I am not using this for articles and users.

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• MySQL More Tables or More Rows

  - by Pez Cuckow

  I am working on a game that I am going to open to the public to have on their game. The game stores lots of information (about 300 rows) per website and spends a lot of time updating values within this MySQL database. Is it better (faster/efficient) to add a new table for every website or to just have 1000's of rows in one table and add a column "website_id" or similar?

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• String Parsing in C#

  - by Betamoo

  What is the most efficient way to parse a C# string in the form of "(params (abc 1.3)(sdc 2.0)....)" into a struct in the form struct Params { double abc,sdc....; } Thanks EDIT The structure always have the same parameters (number and names).. but the order is not granted..

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• Cuda program results are always zero in HW, correct in EMU??

  - by Orion Nebula

  Hi all! I am having a weird problem .. I have written a CUDA code which executes correctly in emulation and all results show up.. however, when executed on hardware "G210" .. the results in the result memory are always 0 I am passing two vectors to the kernel, one with random variables the other is initialized to zero, the code copies the first vector to shared memory, does some swapping and other operations and then writes back the results on the second vector (the one with the initial 0's) I am using double precision, the -arch sm13 flag is used, all memory allocation also use sizeof(double) .. I have checked if the kernel is invoked, it does .. so no problems here .. the cudaMemCpy has no problems .. what could be the problem .. :( why would it work in emulation but not on HW I am quite confused .. any ideas?

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• Random List of millions of elements in Python Efficiently

  - by eWizardII

  Hello, I have read this answer potentially as the best way to randomize a list of strings in Python. I'm just wondering then if that's the most efficient way to do it because I have a list of about 30 million elements via the following code: import json from sets import Set from random import shuffle a = [] for i in range(0,193): json_data = open("C:/Twitter/user/user_" + str(i) + ".json") data = json.load(json_data) for j in range(0,len(data)): a.append(data[j]['su']) new = list(Set(a)) print "Cleaned length is: " + str(len(new)) ## Take Cleaned List and Randomize it for Analysis shuffle(new) If there is a more efficient way to do it, I'd greatly appreciate any advice on how to do it. Thanks,

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• When to use Vanilla Javascript vs. jQuery?

  - by jondavidjohn

  I have noticed while monitoring/attempting to answer common jQuery questions, that there are certain practices using javascript, instead of jQuery, that actually enable you to write less and do ... well the same amount. And may also yield performance benefits. A specific example $(this) vs this Inside a click event referencing the clicked objects id jQuery $(this).attr("id"); Javascript this.id; Are there any other common practices like this? Where certain Javascript operations could be accomplished easier, without bringing jQuery into the mix. Or is this a rare case? (of a jQuery "shortcut" actually requiring more code) EDIT : While I appreciate the answers regarding jQuery vs. plain javascript performance, I am actually looking for much more quantitative answers. While using jQuery, instances where one would actually be better off (readability/compactness) to use plain javascript instead of using $(). In addition to the example I gave in my original question.

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• Writing shorter code/algorithms, is more efficient (performance)?

  - by Carlos

  After coming across the code golf trivia around the site it is obvious people try to find ways to write code and algorithms as short as the possibly can in terms of characters, lines and total size, even if that means writing something like: n=input() while n>1:n=(n/2,n*3+1)[n%2];print n So as a beginner I start to wonder whether size actually matters :D. It is obviously a very subjective question highly dependent on the actual code being used, but what is the rule of thumb in the real world. In the case that size wont matter, how come then we don't focus more on performance rather than size?

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• Most Efficient way to set Register to 1 or (-1)

  - by Bob

  I am taking an assembly course now, and the guy who checks our home assignments is a very pedantic old-school optimization freak. For example he deducts 10% if he sees: mov ax, 0 instead of: xor ax,ax even if it's only used once. I am not a complete beginner in assembly programing but I'm not an optimization expert, so I need your help in something (might be a very stupid question but I'll ask anyway): if I need to set a register value to 1 or (-1) is it better to use: mov ax, 1 or do something like: xor ax,ax inc ax I really need a good grade, so I'm trying to get it as optimized as possible. ( I need to optimize both time and code size)

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• Combining two-part SQL query into one query

  - by user332523

  Hello, I have a SQL query that I'm currently solving by doing two queries. I am wondering if there is a way to do it in a single query that makes it more efficient. Consider two tables: Transaction_Entries table and Transactions, each one defined below: Transactions - id - reference_number (varchar) Transaction_Entries - id - account_id - transaction_id (references Transactions table) Notes: There are multiple transaction entries per transaction. Some transactions are related, and will have the same reference_number string. To get all transaction entries for Account X, then I would do SELECT E.*, T.reference_number FROM Transaction_Entries E JOIN Transactions T ON (E.transaction_id=T.id) where E.account_id = X The next part is the hard part. I want to find all related transactions, regardless of the account id. First I make a list of all the unique reference numbers I found in the previous result set. Then for each one, I can query all the transactions that have that reference number. Assume that I hold all the rows from the previous query in PreviousResultSet UniqueReferenceNumbers = GetUniqueReferenceNumbers(PreviousResultSet) // in Java foreach R in UniqueReferenceNumbers // in Java SELECT * FROM Transaction_Entries where transaction_id IN (SELECT * FROM Transactions WHERE reference_number=R Any suggestions how I can put this into a single efficient query?

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• How to see what objects lie in which generation in YourKit?

  - by prams

  I am using YourKit (11.0) to try to profile my j2ee app. The app uses java 6 and running on 64-bit linux (centos). I was told that YourKit possibly tells us which objects exist in which generation (eden, old, etc) at any given point of time. On a side note, I am trying to chase a problem where memory usage keeps increasing until a major collection happens (every 4 hrs) and I am suspicious about few particular objects, so I am interested to know where those objects lie at different times. Fortunately I know lot of memory is being consumed in one particular area of code (so other objects are possibly directly being put into the old gen), but don't exactly know how much of that memory is being put into eden space, how much is being collected by the minor collections, etc. Thanks.

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• figuring out which field to look for a value in with SQL and perl

  - by Micah

  I'm not too good with SQL and I know there's probably a much more efficient way to accomplish what I'm doing here, so any help would be much appreciated. Thanks in advance for your input! I'm writing a short program for the local school high school. At this school, juniors and seniors who have driver's licenses and cars can opt to drive to school rather than ride the bus. Each driver is assigned exactly one space, and their DLN is used as the primary key of the driver's table. Makes, models, and colors of cars are stored in a separate cars table, related to the drivers table by the License plate number field. My idea is to have a single search box on the main GUI of the program where the school secretary can type in who/what she's looking for and pull up a list of results. Thing is, she could be typing a license plate number, a car color, make, and model, someone driver's name, some student driver's DLN, or a space number. As the programmer, I don't know what exactly she's looking for, so a couple of options come to mind for me to build to be certain I check everywhere for a match: 1) preform a couple of SELECT * FROM [tablename] SQL statements, one per table and cram the results into arrays in my program, then search across the arrays one element at a time with regex, looking for a matched pattern similar to the search term, and if I find one, add the entire record that had a match in it to a results array to display on screen at the end of the search. 2) take whatever she's looking for into the program as a scaler and prepare multiple select statements around it, such as SELECT * FROM DRIVERS WHERE DLN = $Search_Variable SELECT * FROM DRIVERS WHERE First_Name = $Search_Variable SELECT * FROM CARS WHERE LICENSE = $Search_Variable and so on for each attribute of each table, sticking the results into a results array to show on screen when the search is done. Is there a cleaner way to go about this lookup without having to make her specify exactly what she's looking for? Possibly some kind of SQL statement I've never seen before?

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• more efficient way to pickle a string

  - by gatoatigrado

  The pickle module seems to use string escape characters when pickling; this becomes inefficient e.g. on numpy arrays. Consider the following z = numpy.zeros(1000, numpy.uint8) len(z.dumps()) len(cPickle.dumps(z.dumps())) The lengths are 1133 characters and 4249 characters respectively. z.dumps() reveals something like "\x00\x00" (actual zeros in string), but pickle seems to be using the string's repr() function, yielding "'\x00\x00'" (zeros being ascii zeros). i.e. ("0" in z.dumps() == False) and ("0" in cPickle.dumps(z.dumps()) == True)

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• Is converting this ArrayList to a Generic List efficient?

  - by Greg

  The code I'm writing receives an ArrayList from unmanaged code, and this ArrayList will always contain one or more objects of type Grid_Heading_Blk. I've considered changing this ArrayList to a generic List, but I'm unsure if the conversion operation will be so expensive as to nullify the benefits of working with the generic list. Currently, I'm just running a foreach (Grid_Heading_Blk in myArrayList) operation to work with the ArrayList contents after passing the ArrayList to the class that will use it. Should I convert the ArrayList to a generic typed list? And if so, what is the most efficient way of doing so?

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• Algorithm to pick values from set to match target value?

  - by CSharperWithJava

  I have a fixed array of constant integer values about 300 items long (Set A). The goal of the algorithm is to pick two numbers (X and Y) from this array that fit several criteria based on input R. Formal requirement: Pick values X and Y from set A such that the expression X*Y/(X+Y) is as close as possible to R. That's all there is to it. I need a simple algorithm that will do that. Additional info: The Set A can be ordered or stored in any way, it will be hard coded eventually. Also, with a little bit of math, it can be shown that the best Y for a given X is the closest value in Set A to the expression X*R/(X-R). Also, X and Y will always be greater than R From this, I get a simple iterative algorithm that works ok: int minX = 100000000; int minY = 100000000; foreach X in A if(X<=R) continue; else Y=X*R/(X-R) Y=FindNearestIn(A, Y);//do search to find closest useable Y value in A if( X*Y/(X+Y) < minX*minY/(minX+minY) ) then minX = X; minY = Y; end end end I'm looking for a slightly more elegant approach than this brute force method. Suggestions?

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• Most efficient way to fetch and output Content with 2-Level Comments?

  - by awegawef

  I have some content with up to 2-levels of replies. I am wondering what the most efficient way to fetch and output the replies. I should note that I am planning on storing the comments with fields content_id and reply_to, where reply_to refers to which comment it is in reply to (if any). Any criticism on this design is welcome. In pseudo-code (ish), my first attempt would be: # in outputting content CONTENT_ID all_comments = fetch all comments where content_id == CONTENT_ID root_comments = filter all_comments with reply_to == None children_comments = filter all_comments with reply_to != None output_comments = list() for each root_comment children = filter children_comments, reply_to == root_comment.id output_coments.append( (root_comment, children) ) send output_comments to template Is this the best way to do this? Thanks in advance. Edit: On second thought, I'll want to preserve date-order on the comments, so I'll have to do this a bit differently, or at least just sort the comments afterward.

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• Whats the most common waste of computing power in javascipt

  - by qwertymk

  We've all seen people who do this jQuery('a').each(function(){ jQuery(this)[0].innerHTML += ' proccessed'; }); function letsPoluteNS() { polute = ''; for (morePolution = 0; morePolution < arguments.length; morePolution++) polute.join(arguments[morePolution]); return polute; } and so on. I was wondering what people have seen the most common javascript/jQuery technique that is slowing down the page and/or wasting time for the javascript engine. PS I know that this question may not seem to fit into whats an accepted question, yet I'm asking for what the most common accepted waste is

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• What is the lightest way to make a huge chess-like grid?

  - by Sotkra

  Hey there I'm working on a browser-game and I can't help but wonder about what's the lightest way to make the grid/board on which the game takes place. Right now, as a mere sample, I'll show you this: http://sotkra.com/game/ Now, as the grid gets bigger and bigger, the table and its td's create a very heavy filepage which in turn...sucks in more resources from the browser engine and computer. So, is a table with td's the most lightweight way to craft a huge grid-like board or is there something lighter that you recommend? Cheers Sotkra

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• sharpziplib - can you add a file without it copying the entire zip first?

  - by schmoopy

  Im trying to add an existing file to a .zip file using sharpziplib - problem is, the zip file is 1GB in size. When i try to add 1 small file (400k) sharpziplib creates a copy/temp of the orig zip file before adding the new file - this poses a problem when the amount of free disk space is less than 2x the zip file you are trying to update. for example: 1GB zip myfile.zip 1GB zip myfile.zip.tmp.293 ZipFile zf = new ZipFile(path); zf.BeginUpdate(); zf.Add(file); // Adding a 400k file here causes a 1GB temp file to be created zf.EndUpdate(); zf.Close(); Is there a more efficient way to do this? Thanks :-)

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• What's the best way to write to more files than the kernel allows open at a time?

  - by Elpezmuerto

  I have a very large binary file and I need to create separate files based on the id within the input file. There are 146 output files and I am using cstdlib and fopen and fwrite. FOPEN_MAX is 20, so I can't keep all 146 output files open at the same time. I also want to minimize the number of times I open and close an output file. How can I write to the output files effectively? I also must use the cstdlib library due to legacy code.

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• What is the best file format to parse?

  - by anxiety

  Scenario: I'm working on a rails app that will take data entry in the form of uploaded text-based files. I need to parse these files before importing the data. I can choose the file type uploaded to the app; the software used by those uploading has several export options regarding file type. While it may be insignificant, I was wondering if there is a specific file type that is most efficiently parsed. This question can be viewed as language-independent, I believe. (While XML is commonly parsed, it is not a feasible file type for sake of this project.)

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• Correct way to add objects to an ArrayList

  - by ninjasense

  I am trying to add an object to an arraylist but when I view the results of the array list, it keeps adding the same object over and over to the arraylist. I was wondering what the correct way to implement this would be. public static ArrayList<Person> parsePeople(String responseData) { ArrayList<Person> People = new ArrayList<Person>(); try { JSONArray jsonPeople = new JSONArray(responseData); if (!jsonPeople.isNull(0)) { for (int i = 0; i < jsonPeople.length(); i++) { Person.add(new Person(jsonPeople.getJSONObject(i))); } } } catch (JSONException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (Exception e) { } return People; } I have double checked my JSONArray data and made sure they are not duplicates. It seems to keep adding the first object over and over.

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• read files from directory and filter files from Java

  - by Adnan

  The following codes goes through all directories and sub-directories and outputs just .java files; import java.io.File; public class DirectoryReader { private static String extension = "none"; private static String fileName; public static void main(String[] args ){ String dir = "C:/tmp"; File aFile = new File(dir); ReadDirectory(aFile); } private static void ReadDirectory(File aFile) { File[] listOfFiles = aFile.listFiles(); if (aFile.isDirectory()) { listOfFiles = aFile.listFiles(); if(listOfFiles!=null) { for(int i=0; i < listOfFiles.length; i++ ) { if (listOfFiles[i].isFile()) { fileName = listOfFiles[i].toString(); int dotPos = fileName.lastIndexOf("."); if (dotPos > 0) { extension = fileName.substring(dotPos); } if (extension.equals(".java")) { System.out.println("FILE:" + listOfFiles[i] ); } } if(listOfFiles[i].isDirectory()) { ReadDirectory(listOfFiles[i]); } } } } } } Is this efficient? What could be done to increase the speed? All ideas are welcome.

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• How can I make Emacs start-up faster?

  - by Colin

  I use Emacs v. 22 (the console version, either remotely with PuTTY or locally with Konsole) as my primary text editor on Linux. It takes a while to load up each time I start it though, probably almost a second, although I never timed it. I tend to open and close Emacs a lot, because I'm more comfortable using the Bash command-line for file/directory manipulation and compiling. How can I speed up the start-up time?

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• FacesMessages and rich:effect?

  - by user331747

  I'd like to be able to make an Ajax call using JSF/Seam/RichFaces and have the page update with the relevant h:messages component. That works with no problem. I'm able to perform the appropriate reRender. However, I'd also like to be able to make use of rich:effect to make it a bit prettier. Ideally, I'd like to be able to have the messages fade in and then disappear when the user clicks on them. However, I've been unable to get this working thus far. Has anyone gotten such a scenario working? Does anyone who knows JSF/Seam a bit better than me have any good advice? Thanks in advance!

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• Dynamic allocated array is not freed

  - by Stefano

  I'm using the code above to dynamically allocate an array, do some work inside the function, return an element of the array and free the memory outside of the function. But when I try to deallocate the array it doesn't free the memory and I have a memory leak. The debugger pointed to the myArray variable shows me the error CXX0030. Why? struct MYSTRUCT { char *myvariable1; int myvariable2; char *myvariable2; .... }; void MyClass::MyFunction1() { MYSTRUCT *myArray= NULL; MYSTRUCT *myElement = this->MyFunction2(myArray); ... delete [] myArray; } MYSTRUCT* MyClass::MyFunction2(MYSTRUCT *array) { array = (MYSTRUCT*)operator new(bytesLength); ... return array[X]; }

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