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  • Building "isolated" and "automatically updated" caches (java.util.List) in Java.

    - by Aidos
    Hi Guys, I am trying to write a framework which contains a lot of short-lived caches created from a long-living cache. These short-lived caches need to be able to return their entier contents, which is a clone from the original long-living cache. Effectively what I am trying to build is a level of transaction isolation for the short-lived caches. The user should be able to modify the contents of the short-lived cache, but changes to the long-living cache should not be propogated through (there is also a case where the changes should be pushed through, depending on the Cache type). I will do my best to try and explain: master-cache contains: [A,B,C,D,E,F] temporary-cache created with state [A,B,C,D,E,F] 1) temporary-cache adds item G: [A,B,C,D,E,F] 2) temporary-cache removes item B: [A,C,D,E,F] master-cache contains: [A,B,C,D,E,F] 3) master-cache adds items [X,Y,Z]: [A,B,C,D,E,F,X,Y,Z] temporary-cache contains: [A,C,D,E,F] Things get even harder when the values in the items can change and shouldn't always be updated (so I can't even share the underlying object instances, I need to use clones). I have implemented the simple approach of just creating a new instance of the List using the standard Collection constructor on ArrayList, however when you get out to about 200,000 items the system just runs out of memory. I know the value of 200,000 is excessive to iterate, but I am trying to stress my code a bit. I had thought that it might be able to somehow "proxy" the list, so the temporary-cache uses the master-cache, and stores all of it's changes (effectively a Memento for the change), however that quickly becomes a nightmare when you want to iterate the temporary-cache, or retrieve an item at a specific index. Also given that I want some modifications to the contents of the list to come through (depending on the type of the temporary-cache, whether it is "auto-update" or not) and I get completly out of my depth. Any pointers to techniques or data-structures or just general concepts to try and research will be greatly appreciated. Cheers, Aidos

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  • Patterns: Local Singleton vs. Global Singleton?

    - by Mike Rosenblum
    There is a pattern that I use from time to time, but I'm not quite sure what it is called. I was hoping that the SO community could help me out. The pattern is pretty simple, and consists of two parts: A singleton factory, which creates objects based on the arguments passed to the factory method. Objects created by the factory. So far this is just a standard "singleton" pattern or "factory pattern". The issue that I'm asking about, however, is that the singleton factory in this case maintains a set of references to every object that it ever creates, held within a dictionary. These references can sometimes be strong references and sometimes weak references, but it can always reference any object that it has ever created. When receiving a request for a "new" object, the factory first searches the dictionary to see if an object with the required arguments already exits. If it does, it returns that object, if not, it returns a new object and also stores a reference to the new object within the dictionary. This pattern prevents having duplicative objects representing the same underlying "thing". This is useful where the created objects are relatively expensive. It can also be useful where these objects perform event handling or messaging - having one object per item being represented can prevent multiple messages/events for a single underlying source. There are probably other reasons to use this pattern, but this is where I've found this useful. My question is: what to call this? In a sense, each object is a singleton, at least with respect to the data it contains. Each is unique. But there are multiple instances of this class, however, so it's not at all a true singleton. In my own personal terminology, I tend to call the factory method a "global singleton". I then call the created objects "local singletons". I sometimes also say that the created objects have "reference equality", meaning that if two variables reference the same data (the same underlying item) then the reference they each hold must be to the same exact object, hence "reference equality". But these are my own invented terms, and I am not sure that they are good ones. Is there standard terminology for this concept? And if not, could some naming suggestions be made? Thanks in advance...

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  • Perl CGI that sends a temporary loading page to client then later sends the actual results page

    - by Kurt W. Leucht
    I've wasted at least a half day of my company's time searching the Internet for an answer and I'm getting wrapped around the axle here. I can't figure out the difference between all the different technology choices (long polling, ajax streaming, comet, XMPP, etc.) and I can't get a simple hello world example working on my PC. I am running Apache 2.2 and ActivePerl 5.10.0. JavaScript is completely acceptable for this solution. All I want to do is write a simple Perl CGI script that when accessed, it immediately returns some HTML that tells the user to wait or maybe sends an animated GIF. Then without any user intervention (no mouse clicks or anything) I want the CGI script to at some time later replace the wait message or the animated GIF with the actual HTML results from their query. I know this is simple stuff and websites do it all the time, but I can't find a single working example that I can cut and paste onto my machine that will work. Here is my simple Hello World example that I've compiled from various Internet sources, but it doesn't seem to work. When I refresh this CGI URL in my web browser it prints nothing for 5 seconds, then it prints the PLEASE BE PATIENT web page, but not the results web page. What am I doing wrong? #!C:\Perl\bin\perl.exe use CGI; use CGI::Carp qw/fatalsToBrowser warningsToBrowser/; sub Create_HTML { my $html = <<EOHTML; <html> <head> <meta http-equiv="pragma" content="no-cache" /> <meta http-equiv="expires" content="-1" /> <script type="text/javascript" > var xmlhttp=false; /*@cc_on @*/ /*@if (@_jscript_version >= 5) // JScript gives us Conditional compilation, we can cope with old IE versions. // and security blocked creation of the objects. try { xmlhttp = new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try { xmlhttp = new ActiveXObject("Microsoft.XMLHTTP"); } catch (E) { xmlhttp = false; } } @end @*/ if (!xmlhttp && typeof XMLHttpRequest!='undefined') { try { xmlhttp = new XMLHttpRequest(); } catch (e) { xmlhttp=false; } } if (!xmlhttp && window.createRequest) { try { xmlhttp = window.createRequest(); } catch (e) { xmlhttp=false; } } </script> <title>Ajax Streaming Connection Demo</title> </head> <body> Some header text. <p> <div id="response">PLEASE BE PATIENT</div> <p> Some footer text. </body> </html> EOHTML return $html; } my $cgi = new CGI; print $cgi->header; print Create_HTML(); sleep(5); print "<script type=\"text/javascript\">\n"; print "\$('response').innerHTML = 'Here are your results!';\n"; print "</script>\n";

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  • MongoDB vs. Redis vs. Cassandra for a fast-write, temporary row storage solution

    - by Mark Bao
    Hi there, I'm building a system that tracks and verifies ad impressions and clicks. This means that there are a lot of insert commands (about 90/second average, peaking at 250) and some read operations, but the focus is on performance and making it blazing-fast. The system is currently on MongoDB, but I've been introduced to Cassandra and Redis since then. Would it be a good idea to go to one of these two solutions, rather than stay on MongoDB? Why or why not? Thank you

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  • Using wix3 SqlScript to run generated temporary sql-script files.

    - by leiflundgren
    I am starting to write an installer which will use the SqlScript-element. That takes a reference to the Binary-table what script to run. I would like to dynamically generate the script during the installation. I can see three possibilities: Somehow to get SqlScript to read it data from a file rather then a Binary entry. Inject my generated script into the Binary table Using SqlString Which will cause the need to place some rather long strings into Properties, but I guess that shouldn't really be a prolem. Any advice? Regards Leif (My reason, should anyone be interested is that the database should have a job set up, that calls on an installed exe-file. I prefer to create the job using sqlscript. And the path of that file is not known until InstallDir has been choosen.)

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  • How can I use geoalchemy with elixir autoload tables?

    - by Dan Ellis
    I'm using geoalchemy and autoloaded tables, but I'd like to use Elixir, because it has a nicer query syntax. Does anyone know how to get them to work together? I did get it working with this code -- http://pastie.textmate.org/private/y3biyvosuejkrtxbpdv1a -- but that still gives the ugly warning about not recognising the geometry column when the table is reflected. Ideally, what I'd like to do is to get SQLAlchemy's own table reflection to recognise the geometry columns. How would I plumb them together?

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  • MySQL INSERT data does not get stored in proper db, only temporary?

    - by greye
    I'm having trouble with MySQL or Python and can't seem to isolate the problem. INSERTs only seem to last the run of the script and are not stored in the database. I have this script: import MySQLdb db = MySQLdb.connect(host="localhost", user="user", passwd="password", db="example") dbcursor = db.cursor() dbcursor.execute("select * from tablename") temp = dbcursor.fetchall() print 'before: '+str(temp) dbcursor.execute('INSERT INTO tablename (data1, data2, data3) VALUES ("1", "a", "b")') dbcursor.execute("select * from tablename") temp = dbcursor.fetchall() print 'after: '+str(temp) The first time I run it I get the expected output: >>> before: () after: ((1L, 'a', 'b'),) The problem is that if I run it again, the before comes out empty when it should already have the entry in it and the after doesn't break (data 1 is primary key). >>> before: () after: ((1L, 'a', 'b'),) >>> before: () after: ((1L, 'a', 'b'),) >>> before: () after: ((1L, 'a', 'b'),) If I try running the insert command twice in the same script it will break ("Duplicate entry for PRIMARY KEY") Any idea what might be happening here?

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  • What can map database tables like LINQ to SQL did?

    - by trnTash
    A good thing in LINQ to SQL was a fast and reliable way to map database tables and convert them into classes accessible from c# project. However it is no longer recommended to create projects using LINQ to SQL. What is its substitute? What kind of tool should I use in VS 2010 today if I want to have the same functionality as I had with LINQ to SQL?

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  • Different behavior between IE6 and Firefox for HTML Tables?

    - by YogoZuno
    I'm doing the first bit of web-page development I've done in years, in VS2008, using VB.net. I have a fairly simple layout, which is using several nested tables. IE6 displays the layout just fine, but Firefox for some reason shows the whole thing in a small panel at the top of the page, with a scrollbar. Can anyone suggest something basic I am likely missing?

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  • How can I compare tables in two different databases using SQL?

    - by chama
    I'm trying to compare the schemas of two tables that exist in different databases. So far, I have this query SELECT * FROM sys.columns WHERE object_id = OBJECT_ID('table1') The only thing is that I don't know how to use the sys.columns to reference a database other than the one that the query is connected to. I tried this SELECT * FROM db.sys.columns WHERE object_id = OBJECT_ID('table1') but it didn't find anything. I'm using SQL Server 2005 Any suggestions? thanks!

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  • How to capture a click on a link on a temporary layer that is hidden when the focus changes

    - by hstoerr
    We have a layer that appears when a certain text input has the focus and that should dissappear when the input loses the focus. I tried to do it like this: <input type="text" onblur="document.getElementById('hideme').style.display='none'" /> <div id="hideme">Textextext <a href="http://disney.com/">disney</a> text</div> My problem is: when the user clicks on the link link, the browser does not follow this link. It seems the layer disappears before the browser checks where the click goes. What can I do here? One idea would be to watch whether the mouse enters the hideme div and not to close it when the mouse cursor is in there, but this seems way to complicated. Do you have a better idea? By the way: you can try it out very easy by pasting this into the Tryit Editor of w3schools. :-)

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  • User has many computers, computers have many attributes in different tables, best way to JOIN?

    - by krismeld
    I have a table for users: USERS: ID | NAME | ---------------- 1 | JOHN | 2 | STEVE | a table for computers: COMPUTERS: ID | USER_ID | ------------------ 13 | 1 | 14 | 1 | a table for processors: PROCESSORS: ID | NAME | --------------------------- 27 | PROCESSOR TYPE 1 | 28 | PROCESSOR TYPE 2 | and a table for harddrives: HARDDRIVES: ID | NAME | ---------------------------| 35 | HARDDRIVE TYPE 25 | 36 | HARDDRIVE TYPE 90 | Each computer can have many attributes from the different attributes tables (processors, harddrives etc), so I have intersection tables like this, to link the attributes to the computers: COMPUTER_PROCESSORS: C_ID | P_ID | --------------| 13 | 27 | 13 | 28 | 14 | 27 | COMPUTER_HARDDRIVES: C_ID | H_ID | --------------| 13 | 35 | So user JOHN, with id 1 owns computer 13 and 14. Computer 13 has processor 27 and 28, and computer 13 has harddrive 35. Computer 14 has processor 27 and no harddrive. Given a user's id, I would like to retrieve a list of that user's computers with each computers attributes. I have figured out a query that gives me a somewhat of a result: SELECT computers.id, processors.id AS p_id, processors.name AS p_name, harddrives.id AS h_id, harddrives.name AS h_name, FROM computers JOIN computer_processors ON (computer_processors.c_id = computers.id) JOIN processors ON (processors.id = computer_processors.p_id) JOIN computer_harddrives ON (computer_harddrives.c_id = computers.id) JOIN harddrives ON (harddrives.id = computer_harddrives.h_id) WHERE computers.user_id = 1 Result: ID | P_ID | P_NAME | H_ID | H_NAME | ----------------------------------------------------------- 13 | 27 | PROCESSOR TYPE 1 | 35 | HARDDRIVE TYPE 25 | 13 | 28 | PROCESSOR TYPE 2 | 35 | HARDDRIVE TYPE 25 | But this has several problems... Computer 14 doesnt show up, because it has no harddrive. Can I somehow make an OUTER JOIN to make sure that all computers show up, even if there a some attributes they don't have? Computer 13 shows up twice, with the same harddrive listet for both. When more attributes are added to a computer (like 3 blocks of ram), the number of rows returned for that computer gets pretty big, and it makes it had to sort the result out in application code. Can I somehow make a query, that groups the two returned rows together? Or a query that returns NULL in the h_name column in the second row, so that all values returned are unique? EDIT: What I would like to return is something like this: ID | P_ID | P_NAME | H_ID | H_NAME | ----------------------------------------------------------- 13 | 27 | PROCESSOR TYPE 1 | 35 | HARDDRIVE TYPE 25 | 13 | 28 | PROCESSOR TYPE 2 | 35 | NULL | 14 | 27 | PROCESSOR TYPE 1 | NULL | NULL | Or whatever result that make it easy to turn it into an array like this [13] => [P_NAME] => [0] => PROCESSOR TYPE 1 [1] => PROCESSOR TYPE 2 [H_NAME] => [0] => HARDDRIVE TYPE 25 [14] => [P_NAME] => [0] => PROCESSOR TYPE 1

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  • How do I link ASP.NET membership/role users to tables in db?

    - by SnapConfig.com
    I am going to use forms authentication but I want to be able to link the asp.net users to some tables in the db for example If I have a class and students (as roles) I'll have a class students table. I'm planning to put in a Users table containing a simple int userid and ASP.NET username in there and put userid wherever I want to link the users. Does that sound good? any other options of modeling this? it does sound a bit convoluted?

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  • How to display a non-model, temporary pop-up message in Android?

    - by chefgon
    For an example of what I'm looking for, hit the Home button while you're composing a message in the Gmail app. A little message will pop up at the bottom of the screen for a moment that says "Message saved as Draft." I can't figure out how to display one of those messages myself, and I'm not sure what to call it so I can't do a search for it.

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  • How do I conditionally select a field from one of two tables?

    - by freakwincy
    I have two tables invoices and pending_payments both of which have the following rows in common: invoice_id and balance. I want to do a select in MySQL that'll work thus: [pseudo-code] if(invoice_id exists in pending_payments table) { select balance from pending_payments where invoice_id = yadayadayada } else { select balance from invoices where invoice_id = yadayadayada } Is this even doable in MySQL? If so, how?

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  • Does deleting temporary symlinks interrupt current downloads/access to that symlink?

    - by Joe
    I am using symlinks generated in PHP. They are generated when someone requests a download, and I want them to expire at the end of each day. The problem is, what if someone starts downloading a symlink 1 minute before the end of the day and then I delete the symlink while they are downloading it... My question is, to your knowledge will that individual downloading the symlink, right before I delete it, still be able to "download" the file? I am not worried about "resumable download" capability.. but will it make their download stop or break in some way?

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