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  • MySQL table organization and optimization (Rails)

    - by aguynamedloren
    I've been learning Ruby on Rails over the past few months with no prior programming experience. Lately, I've been thinking about database optimization and table organization. I know there are great books on the subject, but I typically learn by example / as I go. Here's a hypothetical situation: Let's say I am building a social network for a niche community with 250,000 members (users). The users have the ability to attend events. Let's say there are 50,000 past/present/future events. Much like Facebook events, a user can attend any number of events and an event can have any number of attendees. In the database, there would be a table for users and a table for events. Somehow I would have to create an association between the users and events. I could create an "events" column in the users table such that each user row would contain a hash of event IDs, or I could create an "attendees" column in the events table such that each event row would contain a hash of user IDs. Neither of these solutions seem ideal, however. On a users profile page, I want to display the list of events they are associated with, which would require scanning the 50,000 event rows for the user ID of said user if I include an "attendees" column in the events table. Likewise, on an event page, I want to display a list of attendees for the event, which would require scanning the 250,000 user rows for the event ID of said event if I include an "events" column in the users table. Option 3 would be to create a third table that contains the attendee information for each and every event - but I don't see how this would solve any problems. Are these non-issues? Rails makes accessing all of this information easy, but I guess I'm worried about scale. It is entirely possible that I am under-estimating the speed and processing power of modern databases / servers / etc. How long would it take to scan 250,000 user rows for specific event IDs - 10ms? 100ms? 1,000ms? I guess that's not that bad. Am I just over-thinking this?

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  • Great UIKit/Objective-C one-Liners

    - by Nissan Fan
    New to Objective-C iPhone/iPod touch/iPad development, but I'm starting to discover lots of power in one-liners of code such as this: [UIApplication sharedApplication].applicationIconBadgeNumber = 10; Which will display that distinctive red notification badge on your app iphone with the number 10. Please share you favorite one-liners in Objective-C for the iPhone/iPod touch/iPad here.

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  • RegEx, Php, Preg_match, Phone numbers, Oh my!

    - by Kirk
    How do I find phone number of the following format and store them to a variable. It needs to match 3334445555, 333.444.5555, 333-444-5555, 333 444 5555, (333) 444 5555 and all combinations thereof. Here is the frame of it $regex = expression; if (preg_match ('/$regex/', matches)) { $phone = matches[1]; }

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  • Passcode functionality for iPhone app?

    - by David Liu
    I was thinking about putting in PIN number functionality within my iPhone app (various examples can be seen here http://forums.mint.com/showthread.php?t=5956 ), but I was kinda stumped how to go about it. Should I just go with a hidden textfield and simulate the inputs with images?

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  • Python Expand Tabs Length Calculation

    - by Mithrill
    I'm confused by how the length of a string is calculated when expandtabs is used. I thought expandtabs replaces tabs with the appropriate number of spaces (with the default number of spaces per tab being 8). However, when I ran the commands using strings of varying lengths and varying numbers of tabs, the length calculation was different than I thought it would be (i.e., each tab didn't always result in the string length being increased by 8 for each instance of "/t"). Below is a detailed script output with comments explaining what I thought should be the result of the command executed above. Would someone please explain the how the length is calculated when expand tabs is used? IDLE 2.6.5 >>> s = '\t' >>> print len(s) 1 >>> #the length of the string without expandtabs was one (1 tab counted as a single space), as expected. >>> print len(s.expandtabs()) 8 >>> #the length of the string with expandtabs was eight (1 tab counted as eight spaces). >>> s = '\t\t' >>> print len(s) 2 >>> #the length of the string without expandtabs was 2 (2 tabs, each counted as a single space). >>> print len(s.expandtabs()) 16 >>> #the length of the string with expandtabs was 16 (2 tabs counted as 8 spaces each). >>> s = 'abc\tabc' >>> print len(s) 7 >>> #the length of the string without expandtabs was seven (6 characters and 1 tab counted as a single space). >>> print len(s.expandtabs()) 11 >>> #the length of the string with expandtabs was NOT 14 (6 characters and one 8 space tabs). >>> s = 'abc\tabc\tabc' >>> print len(s) 11 >>> #the length of the string without expandtabs was 11 (9 characters and 2 tabs counted as a single space). >>> print len(s.expandtabs()) 19 >>> #the length of the string with expandtabs was NOT 25 (9 characters and two 8 space tabs). >>>

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  • Google Analytics API and Internal Search question

    - by Am
    I'm trying to use Google Analytics API to query internal searches that happen on my site. I'd like to be able to query the keywords and the number of times that keyword was used in internal search, based on URL of a page on the site. The idea is to find out which keywords direct the user to a particular page. Does anyone know which dimensions and metrics must use to query that information?

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  • Help with ASP.NET 4.0 routing and subfolders

    - by pixel3cs
    If I use routing with 2 query parameters, like this: System.Web.Routing.RouteTable.Routes.MapPageRoute("HomeRoute", "home/{f1}/{f2}", "~/Home.aspx"); My image does not appear on my Home.aspx page: <img src="~/img/img.jpg" /> or <img src="img/img.jpg" /> But it does appear when I access the http://localhost:3760/Website/Home.aspx URL I tried using Routing.Ignore with no luck. I look for a solution wich should work for an unlimited number of subfolders: "home/{f1}/{f2}/.../{fn}"

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  • Permutations of Varying Size

    - by waiwai933
    I'm trying to write a function in PHP that gets all permutations of all possible sizes. I think an example would be the best way to start off: $my_array = array(1,1,2,3); Possible permutations of varying size: 1 1 // * See Note 2 3 1,1 1,2 1,3 // And so forth, for all the sets of size 2 1,1,2 1,1,3 1,2,1 // And so forth, for all the sets of size 3 1,1,2,3 1,1,3,2 // And so forth, for all the sets of size 4 Note: I don't care if there's a duplicate or not. For the purposes of this example, all future duplicates have been omitted. What I have so far in PHP: function getPermutations($my_array){ $permutation_length = 1; $keep_going = true; while($keep_going){ while($there_are_still_permutations_with_this_length){ // Generate the next permutation and return it into an array // Of course, the actual important part of the code is what I'm having trouble with. } $permutation_length++; if($permutation_length>count($my_array)){ $keep_going = false; } else{ $keep_going = true; } } return $return_array; } The closest thing I can think of is shuffling the array, picking the first n elements, seeing if it's already in the results array, and if it's not, add it in, and then stop when there are mathematically no more possible permutations for that length. But it's ugly and resource-inefficient. Any pseudocode algorithms would be greatly appreciated. Also, for super-duper (worthless) bonus points, is there a way to get just 1 permutation with the function but make it so that it doesn't have to recalculate all previous permutations to get the next? For example, I pass it a parameter 3, which means it's already done 3 permutations, and it just generates number 4 without redoing the previous 3? (Passing it the parameter is not necessary, it could keep track in a global or static). The reason I ask this is because as the array grows, so does the number of possible combinations. Suffice it to say that one small data set with only a dozen elements grows quickly into the trillions of possible combinations and I don't want to task PHP with holding trillions of permutations in its memory at once.

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  • How to check if string is a valid XML element name?

    - by xsaero00
    I need a regex or a function in PHP that will validate a string to be a good XML element name. Form w3schools: XML elements must follow these naming rules: Names can contain letters, numbers, and other characters Names cannot start with a number or punctuation character Names cannot start with the letters xml (or XML, or Xml, etc) Names cannot contain spaces I can write a basic regex that will check for rules 1,2 and 4, but it won't account for all punctuation allowed and won't account for 3rd rule \w[\w0-9-]

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  • Total stack sizes of threads in one process

    - by David
    I use pthreads_attr_getthreadsizes() to get default stack size of one thread, 8MB on my machine. But when I create 8 threads and allocate a very large stack size to them, say hundreds of MB, the program crash. So, I guess, shall ("Number of threads" x "stack size of per thread") shall less than a value(virtual memory size)?

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  • Regular Expression for Decimal or Blank

    - by Phil P
    Sorry for the potentially dumb question but I am trying to pull together a regular expression that will allow: A number with 1 or 2 numbers before a decimal point, and 0-6 numbers after the decimal point. However I also need to allow the field to be blank if so required. Valid Examples 0.952321 1.20394 12.12 25 Blank Invalid Examples 123.45678 1.1234567 Please can anyone help?

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  • Running a python script on all the files in a directory.

    - by S1syphus
    I have a Python script that reads through a text csv file and creates a playlist file. However I can only do one at a time, like: python playlist.py foo.csv foolist.txt However, I have a directory of files that need to be made into a playlist, with different names, and sometimes a different number of files. So far I have looked at creating a txt file with a list of all the names of the file in the directory, then loop through each line of that, however I know there must be an easier way to do it.

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  • Apache rewrite URL replace characters

    - by Tim Cooper
    It's been a while since I've done anything with mod_write, so I was hoping I could help some help on this. I would like a URL like this: http://example.com/qwerty/xyz/ to be directed to querty.xyz.php, where the number of slashes and alpha characters between the slashes is not explicitly set.

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  • scripts on Cshell

    - by lego69
    hello, I've got some problem, I have list of data in the file: 053-37878 03828008 Moskovitch James 500 052-34363 01234567 Mendelson Kippi 450 053-32322 03828008 Jameson Shula 350 054-39238 03333333 Merden Moshe 300 is it possible rewrite this list in the same file (without using temporary file) but without last number thanks in advance for any help (I'm talking about C-Shell scripts)

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  • What is the best way to handle this type of inclusive logic in Ruby?

    - by Steve McLelland
    Is there a better way of handling this in Ruby, while continuing to use the symbols? pos = :pos1 # can be :pos2, :pos3, etc. if pos == :pos1 || pos == :pos2 || pos == :pos3 puts 'a' end if pos == :pos1 || pos == :pos2 puts 'b' end if pos == :pos1 puts 'c' end The obvious way would be swapping out the symbols for number constants, but that's not an option. pos = 3 if pos >= 1 puts 'a' end if pos >= 2 puts 'b' end if pos >= 3 puts 'c' end Thanks.

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  • JDBC profiling tools

    - by antispam
    We need to profile the JDBC operations of several web applications, number of queries, time spent, rows returned, ... Have you used any free/commercial JDBC profiling tool? What are your experiences? Thank you.

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  • Alternatives to requiring users to register for an account?

    - by jamieb
    I'm working on a side project to build a new web app idea of mine. For the sake of discussion, let's say this app displays a random photograph of a famous work of art. On a scale of 1 to 5, users are asked to rate how well they like each piece of art, and then are shown the next photo. Eventually, the app is able to get an sense of the person's style and is able to recommend artwork that he/she may find pleasing. The whole concept is similar to Netflix. I understand how to do all the preference matching logic (although not as sophisticated as Netflix). But I'd like to find a way to do this without requiring that users create an account first. This is a novelty website that a typical user might use only a handful of times. Requiring registration is overkill and will likely drastically reduce it's utility. I'd like to allow people to begin rating artwork within five seconds of their initial pageview, yet maintain the integrity of the voting (since recommendations are predicated on how other people have rated the various pieces of artwork). Can it be done? Some ideas: OpenID. The perfect solution except for the fact that it's not wildly used and my target audience isn't the most technically adept demographic. Text message. User inputs phone number and is texted a four digit code to key into the web app. Quick, easy, and great way to limit abuse. However, privacy concerns abound... people are probably even less likely to give me their phone number than their email address. Facebook login. I personally don't have a Facebook account due to privacy concerns. And I'd really hate to support such a proprietary platform. Hash code/Bookmark. Vistor's initial pageview generates a 5 or 6 digit alphanumeric code that is embedded in each subsequent URL. They can bookmark any page to save their state. Good: Very simple system that doesn't require any user action. Bad: Very easy to stuff the ballot box, might be difficult to account for users sharing the link containing their ID code via email or social networking sites.

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  • When to address managed heap fragmentation

    - by emddudley
    I was reading a blog entry by Josh Smith where he used a cache mechanism in order to "reduce managed heap fragmentation". His caching reduces the number of short-lived objects being created at the cost of slightly slower execution speed. How much of a problem is managed heap fragmentation in a managed language like C#? How can you diagnose if it's an issue? In what situations would you typically need to address it?

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  • Are hash collisions with different file sizes just as likely as same file size?

    - by rwmnau
    I'm hashing a large number of files, and to avoid hash collisions, I'm also storing a file's original size - that way, even if there's a hash collision, it's extremely unlikely that the file sizes will also be identical. Is this sound (a hash collision is equally likely to be of any size), or do I need another piece of information (if a collision is more likely to also be the same length as the original). Or, more generally: Is every file just as likely to produce a particular hash, regardless of original file size?

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