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• Keeping historic of modification in a database.

  - by mada

  Hi, Im a j2ee developper & we are using hibernatne mapping with a postgres databasae. We have to keep track of any changes occurs in the databse , in others words alls previous & current value of any field should be saved & field can be various types (bytea, int, char...) With a simple table it is easy but we a graph of objets things are more difficult So we have , speaking in a UML point of view, a graph of objects to store in the database with every changes & the user. Any idea or pattern how to do that ? Thanks in advance.

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• where to store information like gender and year of birth?

  - by fayer

  i have users and i need them to specify a gender (male, female) and year of birth (1930, 1931...1999, 2000). i wonder where i should store these values: in the database? in php file? if i store them in the database i have to manually create all entries first. but a good thing is that the user table will have constraints so the gender field will always be male or female, it cannot be something else. if i store them in the php file (eg. as html) then i can easily add/remove values. but a con is that i dont have the constraints in database, so another value could be stored as gender by mistake, even though i could add validation in php backend so even if someone hacked the html it is not stored unless it's either male or female. what is best practice to do this? thanks

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• SQL Database dilemma : Optimize for Querying or Writing?

  - by Harry

  I'm working on a personal project (Search engine) and have a bit of a dilemma. At the moment it is optimized for writing data to the search index and significantly slow for search queries. The DTA (Database Engine Tuning Adviser) recommends adding a couple of Indexed views inorder to speed up search queries. But this is to the detriment of writing new data to the DB. It seems I can't have one without the other! This is obviously not a new problem. What is a good strategy for this issue?

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• JavaScript Profiler in IE

  - by Daniel Silveira

  Does anyone know a tool for Profiling JavaScript in IE? List available: IE8 (Internet Explorer 8 only) JavaScript Profiler YUI!

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• JavaScript: Is there a better way to retain your array but efficiently concat or replace items?

  - by Michael Mikowski

  I am looking for the best way to replace or add to elements of an array without deleting the original reference. Here is the set up: var a = [], b = [], c, i, obj; for ( i = 0; i < 100000; i++ ) { a[ i ] = i; b[ i ] = 10000 - i; } obj.data_list = a; Now we want to concatenate b INTO a without changing the reference to a, since it is used in obj.data_list. Here is one method: for ( i = 0; i < b.length; i++ ) { a.push( b[ i ] ); } This seems to be a somewhat terser and 8x (on V8) faster method: a.splice.apply( a, [ a.length, 0 ].concat( b ) ); I have found this useful when iterating over an "in-place" array and don't want to touch the elements as I go (a good practice). I start a new array (let's call it keep_list) with the initial arguments and then add the elements I wish to retain. Finally I use this apply method to quickly replace the truncated array: var keep_list = [ 0, 0 ]; for ( i = 0; i < a.length; i++ ){ if ( some_condition ){ keep_list.push( a[ i ] ); } // truncate array a.length = 0; // And replace contents a.splice.apply( a, keep_list ); There are a few problems with this solution: there is a max call stack size limit of around 50k on V8 I have not tested on other JS engines yet. This solution is a bit cryptic Has anyone found a better way?

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• C++, using one byte to store two variables

  - by 2di

  Hi All I am working on representation of the chess board, and I am planning to store it in 32 bytes array, where each byte will be used to store two pieces. (That way only 4 bits are needed per piece) Doing it in that way, results in a overhead for accessing particular index of the board. Do you think that, this code can be optimised or completely different method of accessing indexes can be used? c++ char getPosition(unsigned char* c, int index){ //moving pointer c+=(index>>1); //odd number if (index & 1){ //taking right part return *c & 0xF; }else { //taking left part return *c>>4; } } void setValue(unsigned char* board, char value, int index){ //moving pointer board+=(index>>1); //odd number if (index & 1){ //replace right part //save left value only 4 bits *board = (*board & 0xF0) + value; }else { //replacing left part *board = (*board & 0xF) + (value<<4); } } int main() { char* c = (char*)malloc(32); for (int i = 0; i < 64 ; i++){ setValue((unsigned char*)c, i % 8,i); } for (int i = 0; i < 64 ; i++){ cout<<(int)getPosition((unsigned char*)c, i)<<" "; if (((i+1) % 8 == 0) && (i > 0)){ cout<<endl; } } return 0; } I am equally interested in your opinions regarding chess representations, and optimisation of the method above, as a stand alone problem. Thanks a lot

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• Rails: Thread won't affect database unless joined to main Thread

  - by hatboysam

  I have a background operation I would like to occur every 20 seconds in Rails given that some condition is true. It kicked off when a certain controller route is hit, and it looks like this def startProcess argId = self.id t = Thread.new do while (Argument.isRunning(argId)) do Argument.update(argId) Argument.markVotes(argId) puts "Thread ran" sleep 20 end end end However, this code does absolutely nothing to my database unless I call "t.join" in which case my whole server is blocked for a long time (but it works). Why can't the read commit ActiveRecords without being joined to the main thread? The thread calls methods that look something like def sample model = Model.new() model.save() end but the models are not saved to the DB unless the thread is joined to the main thread. Why is this? I have been banging my head about this for hours.

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• Styled Javascript Popup that Conncects to Database

  - by user269799

  I want to create a javascript popup box that contains text fields. I want to be able to style this box - using CSS - and I want the textfield entries to be Inserted into a MySQL database. Is this possible? I would be familiar with doing this through web forms and server side scripting but I need it to be a bit more client side this time to make things seem a bit faster. I am thinking I may need to learn some AJAX but any pointers would be a help. GF

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• How to find root cause for "too many connections" error in MySQL/PHP

  - by Nir

  I'm running a web service which runs algorithms that serve millions of calls daily and run some background processing as well. Every now and than I see "Too many connections" error in attempts to connect to the MySQL box" for a few seconds. However this is not necessarily attributed to high traffic times or anything I can put my finger on. I want to find the bottleneck causing it. Other than in the specific times this happens the server isn't too loaded in terms of CPU and Memory, and has 2-3 connections (threads) open and everything works smoothly. (I use Zabbix for monitoring) Any creative ideas on how to trace it?

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• migrate/ update core data app without erasing user data!

  - by treasure

  hello, i have a very complicated problem that i would like to share with you and maybe someone can answer it for me. before i start i have to say that i am very new in this. So, i have a coredata iphone app (much like the recipes app) that uses a pre-populated sql database. The user can add/edit his own data but the default data cannot be deleted. the useres data are ALL saved in the same sql database. QUESTION: what do i have to do in order to: - update some (not all) of the default data that are stored in the sql database without "touching" the user's data? (the model will stay the same - no new entities etc-) (if the user uninstall the app and then reinstall the new version everything will be ok but i dont want to do this, obviously). can someone PLEASE help in coding level?

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• Is is faster to filter and get data or filter then get data ?

  - by remi bourgarel

  Hi I have this kind of request : SELECT myTable.ID, myTable.Adress, -- 20 more columns of all kind of type FROM myTable WHERE EXISTS(SELECT * FROM myLink WHERE myLink.FID = myTable.ID and myLink.FID2 = 666) myLink has a lot of rows. Do you think it's faster to do like this : SELECT myLink.FID INTO @result FROM myLink WHERE myLink.FID2 = 666 UPDATE @result SET Adress = myTable.Adress, -- 20 more columns of all kind of type FROM myTable WHERE myTable.ID = @result.ID

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• C: using a lot of structs can make a program slow?

  - by nunos

  I am coding a breakout clone. I had one version in which I only had one level deep of structures. This version runs at 70 fps. For more clarity in the code I decided the code should have more abstractions and created more structs. Most of the times I have two two three level deep of structures. This version runs at 30 fps. Since there are some other differences besides the structures, I ask you: Does using a lot of structs in C can slow down the code significantly? Thanks.

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• Display Fees details from database In Table Format

  - by Suryakavitha

  Hi , I am using a website(C#) for inserting fees details for I std to V std into a database... next i want to display in that details in next page as a table format which is mentioned below..... ClassName Class I ClassII ClassIII ClassIV ClassV TutionFees 1000 1000 1100 1100 1100 ExamFees 500 500 500 550 600 Bookfees 200 200 300 300 300 How shall i Do like this format? can any one tell me the solution Of this? plz.. Thanks in advance..

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• Speed up :visible:input selector avoiding filter

  - by macca1

  I have a jQuery selector that is running way too slow on my unfortunately large page: $("#section").find(":visible:input").filter(":first").focus(); Is there a quicker way to select the first visible input without having to find ALL the visible inputs and then filtering THAT selection for the first? I want something like :visible:input:first but that doesn't seem to work.

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• VB.Net Create Database table from class property

  - by joeb

  I'm trying to create an inheritable class(OF t) in vb.net that I will pass it a class of objects. Inside the class of objects I want to use the class properties to create a corresponding database table. Like below Public Class SampleClass #Region "Properties" Private newPropertyValue As String Public Property NewProperty() As String Get Return newPropertyValue End Get Set(ByVal value As String) newPropertyValue = value End Set End Property #End Region Public Sub New() End Sub End Class I'm new to vb.net so I don't know my way around exactly. I was looking into class attributes for this action but they do not fully make sense to me yet. Thanks in advance.

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• How can I update a field in a MySQL database table by addition in MySQL database in a single query

  - by undefined

  I have a table that stores a value that will be added to over time. When I want to add to the value I would like to do so in a single query rather than - Get oldValue from database newValue = oldValue + X update row with newValue $query1 = "SELECT value FROM table WHERE id = thisID"; $result1 = mysql_query($query1); while($row=mysql_fetch_array($result)) { $oldValue = $row['value']; } $newValue = $oldValue + x $query1 = "UPDATE table SET value = $newValue WHERE id = thisID"; Can this be done in a single query?

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• finding long repeated substrings in a massive string

  - by Will

  I naively imagined that I could build a suffix trie where I keep a visit-count for each node, and then the deepest nodes with counts greater than one are the result set I'm looking for. I have a really really long string (hundreds of megabytes). I have about 1 GB of RAM. This is why building a suffix trie with counting data is too inefficient space-wise to work for me. To quote Wikipedia's Suffix tree: storing a string's suffix tree typically requires significantly more space than storing the string itself. The large amount of information in each edge and node makes the suffix tree very expensive, consuming about ten to twenty times the memory size of the source text in good implementations. The suffix array reduces this requirement to a factor of four, and researchers have continued to find smaller indexing structures. And that was wikipedia's comments on the tree, not trie. How can I find long repeated sequences in such a large amount of data, and in a reasonable amount of time (e.g. less than an hour on a modern desktop machine)? (Some wikipedia links to avoid people posting them as the 'answer': Algorithms on strings and especially Longest repeated substring problem ;-) )

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• How expensive are variables in JavaScript?

  - by Tom

  How expensive are local variables (var v), global variables (window.v) and cross-global variables (parent.v) in JavaScript, in the major browsers? Has anyone performed any good tests on this one?

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• Help me choose between XML or SQL Lite on android

  - by Ngetha

  I have an android app that periodically, say once a week downloads content from a server in XML. The content is used by the app, different Acitivities use different parts of the content. My question is a design one, should I save the data in SQlite or just keep it as an XML file, which one would be faster to read? The app can only use one content piece at a time, which means subsequent XML content downloads replace the old one.

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• sql query is too slow, how to improve speed

  - by user1289282

  I have run into a bottleneck when trying to update one of my tables. The player table has, among other things, id, skill, school, weight. What I am trying to do is: SELECT id, skill FROM player WHERE player.school = (current school of 4500) AND player.weight = (current weight of 14) to find the highest skill of all players returned from the query UPDATE player SET starter = 'TRUE' WHERE id = (highest skill) move to next weight and repeat when all weights have been completed move to next school and start over all schools completed, done I have this code implemented and it works, but I have approximately 4500 schools totaling 172000 players and the way I have it now, it would take probably a half hour or more to complete (did not wait it out), which is way too slow. How to speed this up? Short of reducing the scale of the system, I am willing to do anything that gets the intended result. Thanks! *the weights are the standard folk style wrestling weights ie, 103, 113, 120, 126, 132, 138, 145, 152, 160, 170, 182, 195, 220, 285 pounds

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• Counting context switches per thread

  - by Sarmun

  Is there a way to see how many context switches each thread generates? (both in and out if possible) Either in X/s, or to let it run and give aggregated data after some time. (either on linux or on windows) I have found only tools that give aggregated context-switching number for whole os or per process. My program makes many context switches (50k/s), probably a lot not necessary, but I am not sure where to start optimizing, where do most of those happen.

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• Converting keys of an array/object-tree to lowercase

  - by tstenner

  Im currently optimizing a PHP application and found one function being called around 10-20k times, so I'd thought I'd start optimization there. function keysToLower($obj) { if(!is_object($obj) && !is_array($obj)) return $obj; foreach($obj as $key=>$element) { $element=keysToLower($element); if(is_object($obj)) { $obj->{strtolower($key)}=$element; if(!ctype_lower($key)) unset($obj->{$key}); } else if(is_array($obj) && ctype_upper($key)) { $obj[strtolower($key)]=$element; unset($obj[$key]); } } return $obj; } Most of the time is spent in recursive calls (which are quite slow in PHP), but I don't see any way to convert it to a loop. What would you do?

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• Cannot add App_Data SQL Server database

  - by Interfector

  Hello, Using Visual Studio 2010 10.0.20319.1 RTMRel and SQL Server Express 10.50.1600.1 I'm trying to add a new SQL Server Database .mdf, however, I receive the following error: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 25 – Connection string is not valid) I have enabled TCP/IP and Named Pipelines, added Firewall Exceptions for Sql Server, I am successfully connecting from VS in the Server Explorer window. I would appreciate if someone can pint me to a solution to my problem. Thank you.

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• Styled Javascript Popup that Connects to Database

  - by user269799

  I want to create a javascript popup box that contains text fields. I want to be able to style this box - using CSS - and I want the textfield entries to be Inserted into a MySQL database. Is this possible? I would be familiar with doing this through web forms and server side scripting but I need it to be a bit more client side this time to make things seem a bit faster. I am thinking I may need to learn some AJAX but any pointers would be a help. GF

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• Slow first page load on asp.net site

  - by Tabloo Quijico

  Hi, Every now and then (always after a long period of idle-time, e.g. overnight) when I access a site built using asp.net - it takes around 15 seconds to load the page (15 seconds before I see any progress whatsoever, then the page comes up fast). Further pages on that site, or refreshes, are quick as usual - they are also fast on other machines, only the first one seems to take the 'hit'. Page tracing never through anything up (whole cycle was a fraction of a second) So my question is where else should I be looking? Perhaps IIS? Or could it still be my asp.net app and I'm just looking in the wrong place (the trace) for clues? As I don't have much control over the IIS server, anything I can check through asp.net would be more helpful, before I go ask that particular admin. cheers :D

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