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• Emulating a transaction-safe SEQUENCE in MySQL

  - by Michael Pliskin

  We're using MySQL with InnoDB storage engine and transactions a lot, and we've run into a problem: we need a nice way to emulate Oracle's SEQUENCEs in MySQL. The requirements are: - concurrency support - transaction safety - max performance (meaning minimizing locks and deadlocks) We don't care if some of the values won't be used, i.e. gaps in sequence are ok. There is an easy way to archieve that by creating a separate InnoDB table with a counter, however this means it will take part in transaction and will introduce locks and waiting. I am thinking to try a MyISAM table with manual locks, any other ideas or best practices?

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• Result of Long Positive Integers & Search and element in array..

  - by AGeek

  Hi, I have two Questions for which I cannot find answers by googling, but I find these questions very important for preparation.. Kindly explain only the logic, I will be able to code. In Search of Efficient Logic..... in terms of Memory and Time. WAP to add two long positive integers. What Data structure / data type we can use to store the numbers and result. What is the best way to search an element from an array in shortest time. Size of the array could be large enough, and any elements could be stored in the array(i.e. no range). Thanks.

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• building a pairwise matrix in scipy/numpy in Python from dictionaries

  - by user248237

  I have a dictionary whose keys are strings and values are numpy arrays, e.g.: data = {'a': array([1,2,3]), 'b': array([4,5,6]), 'c': array([7,8,9])} I want to compute a statistic between all pairs of values in 'data' and build an n by x matrix that stores the result. Assume that I know the order of the keys, i.e. I have a list of "labels": labels = ['a', 'b', 'c'] What's the most efficient way to compute this matrix? I can compute the statistic for all pairs like this: result = [] for elt1, elt2 in itertools.product(labels, labels): result.append(compute_statistic(data[elt1], data[elt2])) But I want result to be a n by n matrix, corresponding to "labels" by "labels". How can I record the results as this matrix? thanks.

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• mysql does not utilize my cpu and ram enough?

  - by vick

  Hello Everyone! I am importing a 2.5gb csv file to a mysql table. My storage engine is innodb. Here is the script: use xxx; DROP TABLE IF EXISTS `xxx`.`xxx`; CREATE TABLE `xxx`.`xxx` ( `xxx_id` int(10) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(128) NOT NULL, `yy` varchar(128) NOT NULL, `yyy` varchar(64) NOT NULL, `yyyy` varchar(2) NOT NULL, `yyyyy` varchar(10) NOT NULL, `url` varchar(64) NOT NULL, `p` varchar(10) NOT NULL, `pp` varchar(10) NOT NULL, `category` varchar(256) NOT NULL, `flag` varchar(4) NOT NULL, PRIMARY KEY (`xxx_id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; set autocommit = 0; load data local infile '/home/xxx/raw.csv' into table company fields terminated by ',' optionally enclosed by '"' lines terminated by '\r\n' ( name, yy, yyy, yyyy, yyyyy, url, p, pp, category, flag ); commit; Why does my PC (core i7 920 with 6gb ram) only consume 9% cpu power and 60% ram when running these queries?

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• python dictionary with constant value-type

  - by s.kap

  hi there, I bumped into a case where I need a big (=huge) python dictionary, which turned to be quite memory-consuming. However, since all of the values are of a single type (long) - as well as the keys, I figured I can use python (or numpy, doesn't really matter) array for the values ; and wrap the needed interface (in: x ; out: d[x]) with an object which actually uses these arrays for the keys and values storage. I can use a index-conversion object (input -- index, of 1..n, where n is the different-values counter), and return array[index]. I can elaborate on some techniques of how to implement such an indexing-methods with reasonable memory requirement, it works and even pretty good. However, I wonder if there is such a data-structure-object already exists (in python, or wrapped to python from C/++), in any package (I checked collections, and some Google searches). Any comment will be welcome, thanks.

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• How to search for closest value in a lookup table?

  - by CSharperWithJava

  I have a simple one dimmensional array of integer values that represent a physical set of part values I have to work with. I then calculate and ideal value mathematically. How could I write an efficient search algorithm that will find the smallest abosulte difference from my ideal value in the array? The array is predetermined and constant, so it can be sorted however I need. Example Lookup array: 100, 152, 256, 282, 300 Searching for an ideal value of 125 would find 100 in the array, whereas 127 would find 152. The actual lookup array will be about 250 items long and never change.

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• Fast, Vectorizable method of taking floating point number modulus of special primes?

  - by caffiend

  Is there a fast method for taking the modulus of a floating point number? With integers, there are tricks for Mersenne primes, so that its possible to calculate y = x MOD 2^31 without needing division. Can any similar tricks be applied for floating point numbers? Preferably, in a way that can be converted into vector/SIMD operations, or moved into GPGPU code. The primes I'm interested in would be 2^7 and 2^31, although if there are more efficient ones for floating point numbers, those would be welcome.

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• Fastest way to sort files

  - by Werner

  Hi, I have a huge text file with lines like: -568.563626 159 33 -1109.660591 -1231.295129 4.381508 -541.181308 159 28 -1019.279615 -1059.115975 4.632301 -535.370812 155 29 -1033.071786 -1152.907805 4.420473 -533.547101 157 28 -1046.218277 -1063.389677 4.423696 What I want is to sort the file, depending on the 5th column, so I would get -568.563626 159 33 -1109.660591 -1231.295129 4.381508 -535.370812 155 29 -1033.071786 -1152.907805 4.420473 -533.547101 157 28 -1046.218277 -1063.389677 4.423696 -541.181308 159 28 -1019.279615 -1059.115975 4.632301 For this I use: for i in file.txt ; do sort -k5n $i ; done I wonder if this is the fastest or more efficient way Thanks

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• Pass Session data to a Class Library without using a bunch of constructors?

  - by sah302

  Hi all, I've got my application here where literally every object has a lastUpdatedBy property. The information I put into here is the person's username, which is retrieved from the session("username") variable. How can I pass this data to my DAL in the class library? At first I was just passing in the value into each method, but this is ridiculous I thought, there should be no reason to do that every time a method is called. Then I thought well if I just put it in a constructor for each of the DAL related classes, that will make it even easier. However, even still on any given page, I've got a plethora of New() declarations, for which every single line I need to pass in the session username casted as a string. Is there an even still more efficient way of doing this so that I could only declare this in one place, and everything will know what it is and I can pass it to classes in a class library?

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• Secondary keys in a B-tree

  - by Phenom

  Let's say that there is a file that contains an unsorted list of student information, which includes a student ID number as well as other information. I want to make a program that retrieves student information based on student ID number. In order to make it efficient, I store the student IDs in a B-tree. So when I enter a student ID number, it searches the B-tree to see if its there or not. It also does one more thing. If it finds the student ID number, then it also returns where in the file that student's information is. This is the secondary key. The program uses this information to locate the rest of the student's information and prints it to screen. Can this be done? Is this how a b-tree works?

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• What data structure would be the least painful DataTable replacement?

  - by MatthewMartin

  I'm storing a lot of sorted ~10 row 2 column/key value pairs in ASP.NET cache-- they're the data for dropdownlists. Right now they are all DataTables, which isn't very space efficient (the rule of thumb is 10x increase in size when data is strored in a dataset). Old Code DataTable table = dataAccess.GetDataTable(); dropDownList.DataSource = table; Hoped for new Code Unknown data = dataAccess.GetSomethingMoreSpaceEfficient(); dropDownList.DataSource = data; What pre-existing datastructures are similar enough to DataTable that would minimize code breakage and reduce the serialized size when stored in ASP.NET cache?

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• How does Photoshop (Or drawing programs) blit?

  - by user146780

  I'm getting ready to make a drawing application in Windows. I'm just wondering, do drawing programs have a memory bitmap which they lock, then set each pixel, then blit? I don't understand how Photoshop can move entire layers without lag or flicker without using hardware acceleration. Also in a program like Expression Design, I could have 200 shapes and move them around all at once with no lag. I'm really wondering how this can be done without GPU help. I don't think super efficient algorithms could justify that? Thanks

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• Why it is necessary to put comments on check-ins? [closed]

  - by Mik Kardash

  In fact, I always have something to put in when I perform a check-in of my code. However, the question I have is - Is it really so necessary? Does it help so much? How? From one point of view, comments can help you to keep track of changes performed with every check-in. Thus, I will be able to analyze the changes and identify a hypothetic problem a little bit quicker. On the other hand, it takes some time to write useful information into check-in. Is it worth it? What are the pros and cons of writing comments to every check-in? Is there any way to write "efficient" check-in comments?

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• Please suggest me the best way to design my database.

  - by Raymond Ho

  I have a table named "Pages" and a table named "Categories". Each entry of the table "Pages" is linked to the table "Categories". The "Categories" table have 5 entries, they are: "Car", "Websites", "Technology", "Mobile Phones", and "Interest". So each time I put an entry to the "Pages" table, I need to map it to the "Categories" table so are arranged properly. Here's my table: Pages ______ id [PK] name url Categories ______ id [PK] Categoryname Pages2Categories ______ Pages.id Categories.id So my question is, is this the most efficient way to create this kind of relationships between tables? It seems very amateur

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• Copy an array backwards? Array.Copy?

  - by daniel

  I have a List<T> that I want to be able to copy to an array backwards, meaning start from List.Count and copy maybe 5 items starting at the end of the list and working its way backwards. I could do this with a simple reverse for loop; however there is probably a faster/more efficient way of doing this so I thought I should ask. Can I use Array.Copy somehow? Originally I was using a Queue as that pops it off in the correct order I need, but I now need to pop off multiple items at once into an array and I thought a list would be faster.

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• e-commerce product data/metadata schemas

  - by Shreko

  Trying to figure out how is product data/metadata schema designed. For example, how does an e-commerce site enter a product spec. Does it copy and paste from mfg spec sheet, enters it in their own fields or something else? Here is an example, looking at the D3000 Nikon DSLR Manufacturer: http://nikon.ca/en/Product.aspx?m=17300&disp=Specs futureshop.ca: www.futureshop.ca/en-CA/product/nikon-nikon-d3000-10-2mp-dslr-camera-with-18-55mm-lens-kit-d3000/10128435.aspx?path=865c2348a1542e848982c9dbd9253483en02 memoryexpress.com: www.memoryexpress.com/Products/PID-MX25539%28ME%29.aspx They are all slightly different in order or in parent/child field? What's storage is used for this type of info rdbms or xml?

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• Getting Older PHP Extensions

  - by maSnun

  Hello All, It happens that I need the GD, SQLite and a few more extensions for php 5.1. But I can't find out where to get them. I am using WinBinder to develop some desktop applications for Windows with php. The minimal php 5.1 pack has the winbinder extension only. I need other extensions for enhanced features like image editing or data storage. Can anybody help? I really need this very much. Thanks and Regards, Masnun

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• Determining the order of a list of numbers (possibly without sorting)

  - by Victor Liu

  I have an array of unique integers (e.g. val[i]), in arbitrary order, and I would like to populate another array (ord[i]) with the the sorted indexes of the integers. In other words, val[ord[i]] is in sorted order for increasing i. Right now, I just fill in ord with 0, ..., N, then sort it based on the value array, but I am wondering if we can be more efficient about it since ord is not populated to begin with. This is more of a question out of curiousity; I don't really care about the extra overhead from having to prepopulate a list and then sort it (it's small, I use insertion sort). This may be a silly question with an obvious answer, but I couldn't find anything online.

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• Sql Server XML-type column duplicate entry detection

  - by aaaa bbbb

  In Sql Server I am using an XML type column to store a message. I do not want to store duplicate messages. I only will have a few messages per user. I am currently querying the table for these messages, converting the XML to string in my C# code. I then compare the strings with what I am about to insert. Unfortunately, Sql Server pretty-prints the data in the XML typed fields. What you store into the database is not necessarily exactly the same string as what you get back out later. It is functionally equivalent, but may have white space removed, etc. Is there an efficient way to compare an XML string that I am considering inserting with those that are already in the database? As an aside, if I detect a duplicate I need to delete the older message then insert the replacement.

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• High level programming logic, design, pattern

  - by Muhammad Shahzad

  I have been doing programming from last 7 years, getting better and better, but still i think that am lacking something. I have been doing work in JOOMLA, MAGENTO, WP, Custom PHP, Opencart, laravel, codeignitor. Sometimes i need to design logic for a huge database application, in the applications we need nesting loops and queries, although i follow OOPS standards, ORM etc, still i feel i need more robust coding designs. I need to know how can i improve these things, so that code remain neat, efficient and faster. Also how big webapps like facebook twitter tests there code speed? How high level programmers choose design patterns. If you can help me find something useful with examples?

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• Android and PHP - Do I need to use sessions?

  - by jtnire

  I have created an Android App that communicates with a PHP web server. They both send JSON to each other. My App is almost finished, however there is one thing left to do: authentication. Since the user's username and password will be stored in Android SharedPreferences, is there any need to use PHP sessions, given that the user won't need to enter the username/password at every request? Since I can just send the username and password in the HTTP POST header for every request, and that I will be using SSL, is this sufficient? I guess I could add an extra field in the header called 'random' that just adds a random value, just to use as a salt so that the encrypted SSL payload will be different everytime. The reason why I don't want to use sessions is that my Android App would either have to handle cookies, or managed the storage of the session ID. If there are some serious cons to using my method above, then I'm more than happy to use sessions, however all advice is appreciated. Thanks

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• What is faster: multiple `send`s or using buffering?

  - by dauerbaustelle

  I'm playing around with sockets in C/Python and I wonder what is the most efficient way to send headers from a Python dictionary to the client socket. My ideas: use a send call for every header. Pros: No memory allocation needed. Cons: many send calls -- probably error prone; error management should be rather complicated use a buffer. Pros: one send call, error checking a lot easier. Cons: Need a buffer :-) malloc/realloc should be rather slow and using a (too) big buffer to avoid realloc calls wastes memory. Any tips for me? Thanks :-)

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• IE 8 prompts user on "slow" jQuery script

  - by Jason

  I have a form with over 100 list items that I must reorder on submit. The following code works to reorder my list without any apparent problems in Firefox; however, IE prompts with the message "A script on this page is causing Internet Explorer to run slowly. If it continues to run, your computer may become unresponsive. Do you want to abort the script?" If the user clicks 'No', the script will work as expected. var listitems = $(form).find('li').get(); listitems.sort(function(a, b) { var compA = $(a).attr('id'); var compB = $(b).attr('id'); return (compA - compB); }); Any ideas on how to make this more efficient?

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• How can a string timestamp with hours 0 to 24 be parsed

  - by user897052

  I am trying to parse a string timestamp of format "yyyyMMddHHmmss" with DateTime.ParseExact(). The catch is I must allow for an hour value of "24" (i.e. hours can be from 0 to 24; Note: I can't control the input values.) and, of course, that results in an exception. Are there any settings/properties I can set instead of manually parsing/using regex's? If not, any efficient parsing ideas? ex. DateTime.ParseExact("20120911240000", "yyyyMMddHHmmss", System.Globalization.CultureInfo.InvariantCulture); hour 24 means hour 0 of next day (so day + 1, hour = 0)

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• Logging NHibernate SQL queries

  - by GuestMVCAsync

  Is there a way to access the full SQL query, including the values, inside my code? I am able to log SQL queries using log4net: <logger name="NHibernate.SQL" additivity="false"> <level value="ALL"/> <appender-ref ref="NHibernateSQLFileLog"/> </logger> However, I would like to find a way to log SQL queries from the code also. This way I will log the specific SQL query that causes an exception in my try/catch statement. Right now I have to data-mine the SQLFileLog to find the query that caused the exception when an exception occurs and it is not efficient.

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