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• Is it possible to load an entire SQL Server CE database into RAM?

  - by DanM

  I'm using LinqToSql to query a small SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table via a foreign key, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of the appeal of LinqToSql. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view.

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• Can I share code & resources between Android projects without using a library?

  - by Tom

  The standard advice for sharing code & resources between Android projects is to use a library. Personally I find this works poorly if (a) the shared code changes a lot, or (b) your computer isn't fast enough. I also don't want to get into deploying multiple APK's, which seems to be necessary when I use dependent projects (i.e. Java Build Path, Projects Tab). On the other hand, sharing a folder of source code by using the Eclipse linked source feature works great (Java Build Path, Source tab, Link Source button), but for these two issues: 1) I can't use the same technique to share resources. I can create the link to the resources parent folder but then things get wonky and the shared resources don't get compiled (I'm using ADT 21). 2) So then I settle for copying the shared resources into each project, but this doesn't work because either. The shared code can't import the copy of its resources because it doesn't know the package name of the project that uses it. The solution I've been using is to access the resources dynamically, but that has become cumbersome as the number of resources grows. So, I need a solution to either (1) or (2), or I'll have to go back to a library project. (Or maybe there is another option I haven't thought of?)

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• Deterministic floating point and .NET

  - by code2code

  How can I guarantee that floating point calculations in a .NET application (say in C#) always produce the same bit-exact result? Especially when using different versions of .NET and running on different platforms (x86 vs x86_64). Inaccuracies of floating point operations do not matter. In Java I'd use strictfp. In C/C++ and other low level languages this problem is essentially solved by accessing the FPU / SSE control registers but that's probably not possible in .NET. Even with control of the FPU control register the JIT of .NET will generate different code on different platforms. Something like HotSpot would be even worse in this case... Why do I need it? I'm thinking about writing a real-time strategy (RTS) game which heavily depends on fast floating point math together with a lock stepped simulation. Essentially I will only transmit user input across the network. This also applies to other games which implement replays by storing the user input. Not an option are: decimals (too slow) fixed point values (too slow and cumbersome when using sqrt, sin, cos, tan, atan...) update state across the network like an FPS: Sending position information for hundreds or a few thousand units is not an option Any ideas?

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• Creating a network adapter - how hard is it?

  - by Vilx-

  I'm interested in building a little (commercial) device on top of Arduino. I want it to be able to interface with network. Network as in standard Ethernet, Cat5, RJ-45, etc. I know that there is an Ethernet Shield, but it costs even more than the Arduino itself, and it's pretty big. Naturally, I want my device to be as small and as cheap as possible. So I'm thinking about recreating an Ethernet module myself. The problem is - I haven't got any experience with Ethernet, nor do I have a good idea where to start looking. Thus I can't even say if my ideas are feasible. Ultimately I would like the device to have three ports - one for incoming signal, two for outgoing, so the device is essentially a little switch where it is plugged in itself as well. The switching capabilities need not be very fast - the volume of data will be low. 10Mbit is more than enough, can be even slower. If that is not possible, a single port for controlling the device itself will also do. Another possibility I'm considering is power line communications - sending information through power lines. That's another area I've no experience with. What hardware should I be looking at, and where can I find information about the necessary software? So - can anyone tell me if these ideas are feasible, and if yes - where should I start looking?

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• Does NSClassFromString affect performance?

  - by Tomen

  I want to create a controller that depends on the class of a given instance of a model -(BaseController *)getControllerForModel:(Model *)model { BaseController *controller = nil; Class controllerClass = [BaseController class]; //the default value //find the right controller if ([model isMemberOfClass:[ModelClass1 class]]) controllerClass = [ConcreteController1 class]; else if ([model isMemberOfClass:[ModelClass2 class]]) controllerClass = [ConcreteController2 class]; else if ([model isMemberOfClass:[ModelClass3 class]]) controllerClass = [ConcreteController3 class]; ... else if ([model isMemberOfClass:[ModelClassX class]]) controllerClass = [ConcreteControllerX class]; else Trace(TRACELEVEL_WARNING, @"Unrecognized model type: %@", NSStringFromClass([model class])); //Now instantiate it with the model controller = [[[controllerClass alloc] initWithModel:model] autorelease]; return slotController; } I want to find a more flexible solution to this and thought of having a dictionary, which maps Model-Classes to Controller-Classes and then NSClassFromString could give me the right instance. My question is this: Is NSClassFromString using much of my applications performance if i use it several times (say, 100 times at once)? Or would it be about as fast as the above approach?

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• Fasted way to develop data entry screens for a .NET backend ?

  - by jay23

  I am a .NET / C# back end guy. I am working on a app that will have about 200 different data entry screens. For me exposing DTO as a collection for CRUD (IUpdatable and IQueryable) is the easy part, can do it in sleep :-). What I am trying to decide is what type of front end technology will allow me to develop these data entry screens fast. They don't have to be fancy but they are not just plain grid either and on average they have about 15 form fields and some client side data validation (no db look up) Options I am looking at are Use ExtJS on the front and REST / JSON on the back. ASP.NET RIA but I do not know SL (Well XAML) Plain ASP.NET / MVC One idea I had was the DTO will contain the meta data about the form (As Attributes) and the form can be dynamically generated, but i do not want to reinvent the wheel if their is an easy way. I have looked at RAD software but all of them look at the DB and generate screens. I rather want some thing that can look at my DTO and generate screens. Jay

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• Listening UDP or switch to TCP in a MFC application

  - by Alexander.S

  I'm editing a legacy MFC application, and I have to add some basic network functionalities. The operating side has to receive a simple instruction (numbers 1,2,3,4...) and do something based on that. The clients wants the latency to be as fast as possible, so naturally I decided to use datagrams (UDP). But reading all sorts of resources left me bugged. I cannot listen to UDP sockets (CAsyncSocket) in MFC, it's only possible to call Receive which blocks and waits. Blocking the UI isn't really a smart. So I guess I could use some threading technique, but since I'm not all that experienced with MFC how should that be implemented? The other part of the question is should I do this, or revert to TCP, considering reliability and implementation issues. I know that UDP is unreliable, but just how unreliable is it really? I read that it is up to 50% faster, which is a lot for me. References I used: http://msdn.microsoft.com/en-us/library/09dd1ycd(v=vs.80).aspx

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• I want to build a Google-friendly web app, where should I start?

  - by ronii

  I have only very basic experience with HTML/CSS and have quite a bit of experience with testing software and web apps from a consumer perspective. I'd love to launch a web application that plays nicely with Google services, similar to some of the apps you'd find on the Google Apps Marketplace, such as ManyMoon, time to note, Socialwok, etc. I'm a huge Google fan and would like to build something that's well integrated with other Google services. If you were a total beginner and wanted to build a complex app like one of examples above (project management, CRM, etc), where would you start? If you worked your ass off 18 hours a day, 24/7, how fast could you do it? I've dabbled into various languages and development frameworks, and read about which apps are using what languages but it's hard to figure out what would be most beneficial to jump into. Ruby on Rails, PHP, Google Web Toolkit, AppEngine. The list goes on and on. I want to be able to build and launch my own scalable web app. Thanks.

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• Design for fastest page download

  - by mexxican

  I have a file with millions of URLs/IPs and have to write a program to download the pages really fast. The connection rate should be at least 6000/s and file download speed at least 2000 with avg. 15kb file size. The network bandwidth is 1 Gbps. My approach so far has been: Creating 600 socket threads with each having 60 sockets and using WSAEventSelect to wait for data to read. As soon as a file download is complete, add that memory address(of the downloaded file) to a pipeline( a simple vector ) and fire another request. When the total download is more than 50Mb among all socket threads, write all the files downloaded to the disk and free the memory. So far, this approach has been not very successful with the rate at which I could hit not shooting beyond 2900 connections/s and downloaded data rate even less. Can somebody suggest an alternative approach which could give me better stats. Also I am working windows server 2008 machine with 8 Gig of memory. Also, do we need to hack the kernel so as we could use more threads and memory. Currently I can create a max. of 1500 threads and memory usage not going beyond 2 gigs [ which technically should be much more as this is a 64-bit machine ]. And IOCP is out of question as I have no experience in that so far and have to fix this application today. Thanks Guys!

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• Optimization of a c++ matrix/bitmap class

  - by Andrew

  I am searching a 2D matrix (or bitmap) class which is flexible but also fast element access. The contents A flexible class should allow you to choose dimensions during runtime, and would look something like this (simplified): class Matrix { public: Matrix(int w, int h) : data(new int[x*y]), width(w) {} void SetElement(int x, int y, int val) { data[x+y*width] = val; } // ... private: // symbols int width; int* data; }; A faster often proposed solution using templates is (simplified): template <int W, int H> class TMatrix { TMatrix() data(new int[W*H]) {} void SetElement(int x, int y, int val) { data[x+y*W] = val; } private: int* data; }; This is faster as the width can be "inlined" in the code. The first solution does not do this. However this is not very flexible anymore, as you can't change the size anymore at runtime. So my question is: Is there a possibility to tell the compiler to generate faster code (like when using the template solution), when the size in the code is fixed and generate flexible code when its runtime dependend? I tried to achieve this by writing "const" where ever possible. I tried it with gcc and VS2005, but no success. This kind of optimization would be useful for many other similar cases.

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• Fixing an SQL where statement that is ugly and confusing

  - by Mike Wills

  I am directly querying the back-end MS SQL Server for a software package. The key field (vehicle number) is defined as alpha though we are entering numeric value in the field. There is only one exception to this, we place an "R" before the number when the vehicle is being retired (which means we sold it or the vehicle is junked). Assuming the users do this right, we should not run into a problem using this method. (Right or wrong isn't the issue here) Fast forward to now. I am trying to query a subset of these vehicle numbers (800 - 899) for some special processing. By doing a range of '800' to '899' we also get 80, 81, etc. If I cast the vehicle number into an INT, I should be able to get the right range. Except that these "R" vehicles are kicking me in the butt now. I have tried where vehicleId not like 'R%' and cast(vehicleId as int) between 800 and 899 however, I get a casting error on one of these "R" vehicles. What does work is where vehicleId not between '800' and '899' and cast(vehicleId as int) between 800 and 899', but I feel there has to be a better way and less confusing way. I have also tried other variations with HAVING and a sub-query all producing a casting error.

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• optimized search using ajax and keypress

  - by ooo

  i have the following code as i want to search a database as a user is typing into a textbox. This code below works fine but it seems a little inefficient as if a user is typing really fast, i am potentially doing many more searches than necessary. So if a user is typing in "sailing" i am searching on "sail", "saili", "sailin", and "sailing" i wanted to see if there was a way to detect any particular time between keypresses so only search if user stops typing for 500 milliseconds or something like this. is there a best practices for something like this? $('#searchString').keypress(function(e) { if (e.keyCode == 13) { var url = '/Tracker/Search/' + $("#searchString").val(); $.get(url, function(data) { $('div#results').html(data); $('#results').show(); }); } else { var existingString = $("#searchString").val(); if (existingString.length > 2) { var url = '/Tracker/Search/' + existingString; $.get(url, function(data) { $('div#results').html(data); $('#results').show(); }); } }

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• Coldfusion 8 and HTTP PUT - is there a way to PUT an object?

  - by ciaranarcher

  Hi all We are using EHCache with CF 8 to cache stuff on a central server using a RESTful interface over HTTP. I am trying to cache a cfquery object to the cache server. I can get this to work if I call EHCache direct (i.e. store it in a local cache) but if I try to cache on a remote server over HTTP I am running into problems. The code I am using is as follows: <cfhttp url="http://localhost:8080/myCache/myKey" method="put" result="r" timeout="2" throwonerror="true" > <cfhttpparam type="body" value="#ARGUMENTS.item#" /> </cfhttp> CF doesn't like this reference to #ARGUMENTS.item# and it complains Complex object types cannot be converted to simple values. Can anyone give me an example of how to put an object over http using CF? If this is not possible with CF then a Java example would be the next best thing. Many thanks in advance! PS: I do not want to use serialization to text/JSON etc. as this approach has issues with data integrity and most importantly it's not fast enough.

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• Why Can't Businesses Upgrade their Browsers from IE6/IE7?

  - by viatropos

  I have read lots these past few weeks on IE6, seeing if it was really that bad to make it look right. I have just learned HTML and CSS this past year so I've been spoiled to start with basically CSS3 and HTML5, and I can do some really cool stuff super fast. I'm no IE6 master and I don't have years of experience with IE. So I thought it'd take a little time to figure out all the hacks to IE6/7 discovered and just implement them. But it's way harder than that (or maybe just way too much work). I'd have to either completely rebuild my design using "Internet Explorer 'Principles'", or cut out a lot of the neat things I could do using more recent technologies. For a million and one other reasons, everyone who builds things online seems to think IE should die. My question is, why can't businesses upgrade their browsers? When I work with businesses, they almost always resist the first time I ask, but 5 seconds later I'll show them what it looks like on my computer and talk about how great the latest stuff is (how much more secure later browser are, all the famous IE security cases, how much smoother and faster they new browsers are, how the IE team has basically missed the boat entirely, how much smoother business processes run, etc.), and they get excited! And within a few seconds they're up and running with Chrome or something. So can businesses not upgrade for some reasons? What are the reasons a business cannot upgrade? The main reason I think of is because they have an old version of windows. But a) wasn't there a legal case against this? and b) somebody must have figured out how to install Chrome or Firefox on ancient versions of Windows by now.

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• How would I compare two Lists(Of <CustomClass>) in VB?

  - by Kumba

  I'm working on implementing the equality operator = for a custom class of mine. The class has one property, Value, which is itself a List(Of OtherClass), where OtherClass is yet another custom class in my project. I've already implemented the IComparer, IComparable, IEqualityComparer, and IEquatable interfaces, the operators =, <>, bool and not, and overriden Equals and GetHashCode for OtherClass. This should give me all the tools I need to compare these objects, and various tests comparing two singular instances of these objects so far checks out. However, I'm not sure how to approach this when they are in a List. I don't care about the list order. Given: Dim x As New List(Of OtherClass) From {New OtherClass("foo"), New OtherClass("bar"), New OtherClass("baz")} Dim y As New List(Of OtherClass) From {New OtherClass("baz"), New OtherClass("foo"), New OtherClass("bar")} Then (x = y).ToString should print out True. I need to compare the same (not distinct) set of objects in this list. The list shouldn't support dupes of OtherClass, but I'll have to figure out how to add that in later as an exception. Not interested in using LINQ. It looks nice, but in the few examples I've played with, adds a performance overhead in that bugs me. Loops are ugly, but they are fast :) A straight code answer is fine, but I'd like to understand the logic needed for such a comparison as well. I'm probably going to have to implement said logic more than a few times down the road.

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• problem with a very simple tile based game

  - by newbieguy

  Hello, I am trying to create a pacman-like game. I have an array that looks like this: array: 1111111111111 1000000000001 1111110111111 1000000000001 1111111111111 1 = Wall, 0 = Empty space I use this array to draw tiles that are 16x16 in size. The Game character is 32x32. Initially I represented the character's position in array indexes, [1,1] etc. I would update his position if array[character.new_y][charater.new_x] == 0 Then I translated these array coordinates to pixels, [y*16, x*16] to draw him. He was lining up nicely, wouldn't go into walls, but I noticed that since I was updating him by 16 pixels each, he was moving very fast. I decided to do it in reverse, to store the game character's position in pixels instead, so that he could use less than 16 pixels per move. I thought that a simple if statement such as this: if array[(character.new_pixel_y)/16][(character.new_pixel_x)/16] == 0 would prevent him from going into walls, but unfortunately he eats a bit of the bottom and right side walls. Any ideas how would I properly translate pixel position to the array indexes? I guess this is something simple, but I really can't figure it out :(

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• Worth website that a web developer must surf daily?

  - by I Like PHP

  Hello All, this may be not a right place to ask this question, but i can get best answer only from here, so i m posting here. i m a web developer and working with technology PHP,MySQL, JavaScript,jQuery,AJAX, CSS, HTML, JSON i daily surf few websites regarding web development , i know there are a lot of website with very good knowledge but we are not aware of that so i think we have to share with each other.i m mentioning some useful links that we must surf daily for gaining knowledge and do better/fast development. please you also suggest some good links which you surf regularly and best in their field. i surf belows links regularly - [Stack Overflow][1] // No doubt, it is best - [Delicious][2]// best social bookmarking website - [Smashing Magazine][3] // Best site to improve knowledege for a web developer - [Net tuts][4] // Best tutorail wesbsite with full explanation - [Official PHP site ][5] // i think nothing to mention about it( just superb) - [Javascript Debugger][6] // U can filter your javascript/jquery code here - [jQuery Official site][7] // best to learn jQuery i m waiting for you great response. i also need any good and trusted website on mysql, i think mysql officail website is very confusing, i had to search a lot to find a single thing, if u have any good regarding mysql then share please. Thanks alwayz.

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• 2-column table with two foreign keys. Performance/design question.

  - by Emanuel

  Hello everyone! I recently ran into a quite complex problem and after looking around a lot I couldn't find a solution to it. I've found answers to my questions many times before on stackoverflow.com, so I decided to post here. So I'm making a user/group managment system for a web-based project, and I'm storing all related data into a postgreSQL database. This system relies on three tables: USERS GROUPS GROUP_USERS The two first tables simply define all the users and all the groups on the site, and the last table, GROUP_USERS, stores the groups every user is part of. It only has two columns: USER_ID GROUP_ID Since every user can be a member of several groups, I decided to make a separate table for this purpose, rather than storing a comma separated column in the USERS-table. Now, both columns are foreign keys, and I want to make them both primary keys as well, this since each combination of USER_ID and GROUP_ID has to be unique, and if I give them the constraint UNIQUE pgAdmin tells me that each table should have at least one Primary key. But now I am stuck with what seems to be a lot of indexes and relations to a very small table only containing numbers. In the end, I want this table to be as fast as possible, even if containing tens of thousands of rows. Size on disk shouldn't be a problem since its just all numbers anyway, but it feels quite stupid to have a full-sized index refering to a smaller table. Should I stick with my current solution, store comma-separated values in a column in the USERS-table or is there any other solution I should be aware of. PS. I don't want to use an array-column, even if they are supported by postgreSQL. I want to be as generic as possible so I can switch database later on, if necessary. EDIT: I other words, will using a compound primary key and two foreign keys in one table with only two columns have a negative impact on performance rather than the opposite due to the size of the generated index? Thank you!

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• Windows Azure Worldwide availability

  - by Insomniac

  Hi, I've been reviewing Windows Azure platform for some time, and can't find answer to one very important question. If I deploy my application within a cloud, how it will be reached from different places worldwide? For example if I have a web application with a database and want it to be accessible to users in UK, US, China and etc. Can I be sure that any user in the world will get almost the same request processing time? I think of it this way. 1. User sends request (navigates in browser to my web site) 2. This request gets in a cloud in a nearest location (closest to user MS Data Center?) 3. It is processed by an instance of my web application (in nearest location, with request to my centralized DB which can be far away but SQL request goes via MS internal network, which I believe should be very fast). 4. Response sent to user. Please let me know if I'm wrong. Thanks.

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• getting string.substring(N) not to choke when N > string.length

  - by aape

  I'm writing some code that takes a report from the mainframe and converts it to a spreadsheet. They can't edit the code on the MF to give me a delimited file, so I'm stuck dealing with it as fixed width. It's working okay now, but I need to get it more stable before I release it for testing. My problem is that in any given line of data, say it could have three columns of numbers, each five chars wide at positions 10, 16, and 22. If on this one particular row, there's no data for the last two cols, it won't be padded with spaces; rather, the length of the string will be only 14. So, I can't just blindly have dim s as string = someStream.readline a = s.substring(10, 5) b = s.substring(16, 5) c = s.substring(22, 5) because it'll choke when it substrings past the length of the string. I know I could test the length of the string before processing each row, and I have automated the filling of some of the vsariables using a counter and a loop, and using the counter*theWidthOfTheGivenVariable to jump around, but this project was a dog to start with (come on! turning a report into a spreadsheet?), but there are many different types of rows (it's not just a grid), and the code's getting ugly fast. I'd like this to be clean, clear, and maintainable for the poor sucker that gets this after me. If it matters, here's my code so far (it's really crufty at the moment). You can see some of my/its idiocy in the processSection#data subs So, I'm wondering 1) is there a way baked in to .NET to have string.substring not error when reading past the end of a string without wrapping it in a try...catch? and 2) would it be appropriate in this situation to write a new string class that inherits from string that has a more friendly substring function in it? ETA: Thanks for all the advice and knowledge everyone. I'll go with the extension. Hopefully one of these years, I'll get my chops up enough to pay someone back in kind. :)

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• Choosing approach for an IM client-server app

  - by John

  Update: totally re-wrote this to be more succint. I'm looking at a new application, one part of which will be very similar to standard IM clients, i.e text chat, ability to send attachments, maybe some real-time interaction like a multi-user whiteboard. It will be client-server, i.e all traffic goes through my central server. That means if I want to support cross-communication with other IM systems, I am still free to pick any protocol for my own client<--server communication - my server can use XMPP or whatever to talk to other systems. Clients are expected to include desktop apps, but probably also browser-based as well either through Flex/Silverlight or HTML/AJAX. I see 3 options for my own client-server communication layer: XMPP. The benefits are clients already exist as do open-source servers. However it requires the most up-front research/learning and also appears like it might raise legal issues due to GPL. Custom sockets. A server app makes connections with the clients, allowing any text/binary data to be sent very fast. However this approach requires building said server from scratch, and also makes a JS client tricky Servlets (or similar web server). Using tried and tested Java web-stack, clients send HTTP requests similar to AJAX-based websites. The benefit is the server is easy to write using well-established technologies, and easy to talk to. But what restrictions would this bring? Is it appropriate technology for real-time communication? Advice and suggests are welcome, especially what pros and cons surround using a web-server approach as compared to a socket-based approach.

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• Logic: Best way to sample & count bytes of a 100MB+ file

  - by Jami

  Let's say I have this 170mb file (roughly 180 million bytes). What I need to do is to create a table that lists: all 4096 byte combinations found [column 'bytes'], and the number of times each byte combination appeared in it [column 'occurrences'] Assume two things: I can save data very fast, but I can update my saved data very slow. How should I sample the file and save the needed information? Here're some suggestions that are (extremely) slow: Go through each 4096 byte combinations in the file, save each data, but search the table first for existing combinations and update it's values. this is unbelievably slow Go through each 4096 byte combinations in the file, save until 1 million rows of data in a temporary table. Go through that table and fix the entries (combine repeating byte combinations), then copy to the big table. Repeat going through another 1 million rows of data and repeat the process. this is faster by a bit, but still unbelievably slow This is kind of like taking the statistics of the file. NOTE: I know that sampling the file can generate tons of data (around 22Gb from experience), and I know that any solution posted would take a bit of time to finish. I need the most efficient saving process

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• log activity. intrusion detection. user event notification ( interraction ). messaging

  - by Julian Davchev

  Have three questions that I somehow find related so I put them in same place. Currently building relatively large LAMP system - making use of messaging(activeMQ) , memcache and other goodies. I wonder if there are best practices or nice tips and tricks on howto implement those. System is user aware - meaning all actions done can be bind to particular logged user. 1. How to log all actions/activities of users? So that stats/graphics might be extracted later for analysing. At best that will include all url calls, post data etc etc. Meaning tons of inserts. I am thinking sending messages to activeMQ and later cron dumping in DB and cron analysing might be good idea here. Since using Zend Framework I guess I may use some request plugin so I don't have to make the log() call all over the code. 2.How to log stuff so may be used for intrusion detection? I know most things might be done on http level using apache mods for example but there are also specific cases like (5 failed login attempts in a row (leads to captcha) etc etc..) This also would include tons of inserts. Here I guess direct usage of memcache might be best approach as data don't seem vital to be permanantly persisted. Not sure if cannot use data from point 1. 3.System will notify users of some events. Like need approval , something broke..whatever.Some events will need feedback(action) from user, others are just informational. Wonder if there is common solutions for needs like this. Example: Based on occuring event(s) user will be notifed (user inbox for example) what happend. There will be link or something to lead him to details of thingy that happend and take action accordingly. Those seem trivial at first look but problem I see if coding it directly is becoming really fast hard to maintain.

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• Why is DivMod Limited to Words (<=65535)?

  - by Andreas Rejbrand

  In Delphi, the declaration of the DivMod function is procedure DivMod(Dividend: Cardinal; Divisor: Word; var Result, Remainder: Word); Thus, the divisor, result, and remainder cannot be grater than 65535, a rather severe limitation. Why is this? Why couldn't the delcaration be procedure DivMod(Dividend: Cardinal; Divisor: Cardinal; var Result, Remainder: Cardinal); The procedure is implemented using assembly, and is therefore probably extremely fast. Would it not be possible for the code PUSH EBX MOV EBX,EDX MOV EDX,EAX SHR EDX,16 DIV BX MOV EBX,Remainder MOV [ECX],AX MOV [EBX],DX POP EBX to be adapted to cardinals? How much slower is the naïve attempt procedure DivModInt(const Dividend: integer; const Divisor: integer; out result: integer; out remainder: integer); begin result := Dividend div Divisor; remainder := Dividend mod Divisor; end; that is not (?) limited to 16-bit integers?

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• Parallelize or vectorize all-against-all operation on a large number of matrices?

  - by reve_etrange

  I have approximately 5,000 matrices with the same number of rows and varying numbers of columns (20 x ~200). Each of these matrices must be compared against every other in a dynamic programming algorithm. In this question, I asked how to perform the comparison quickly and was given an excellent answer involving a 2D convolution. Serially, iteratively applying that method, like so list = who('data_matrix_prefix*') H = cell(numel(list),numel(list)); for i=1:numel(list) for j=1:numel(list) if i ~= j eval([ 'H{i,j} = compare(' char(list(i)) ',' char(list(j)) ');']); end end end is fast for small subsets of the data (e.g. for 9 matrices, 9*9 - 9 = 72 calls are made in ~1 s). However, operating on all the data requires almost 25 million calls. I have also tried using deal() to make a cell array composed entirely of the next element in data, so I could use cellfun() in a single loop: # who(), load() and struct2cell() calls place k data matrices in a 1D cell array called data. nextData = cell(k,1); for i=1:k [nextData{:}] = deal(data{i}); H{:,i} = cellfun(@compare,data,nextData,'UniformOutput',false); end Unfortunately, this is not really any faster, because all the time is in compare(). Both of these code examples seem ill-suited for parallelization. I'm having trouble figuring out how to make my variables sliced. compare() is totally vectorized; it uses matrix multiplication and conv2() exclusively (I am under the impression that all of these operations, including the cellfun(), should be multithreaded in MATLAB?). Does anyone see a (explicitly) parallelized solution or better vectorization of the problem?

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