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• Keeping track of dirty blocks on a block device

  - by mikeY

  I'm looking for a way to keep track of what blocks on a block device are modified after a point in time. How I eventually want to use this for is to keep two 2TB disks in sync, one which only comes online (connected through USB) once a month. Without knowing what blocks have been modified, I have to go through the whole 2TB every time. I'm using a recent GNU/Linux OS and have C and Python experience. I'm hoping to avoid writing kernel level code as I don't have any experience in that area whatsoever. My current theory is that there should be some hooks somewhere where my code can get called when a disk flush is performed. Any ideas?

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• .NET Performance: Deep Recursion vs Queue

  - by JeffN825

  I'm writing a component that needs to walk large object graphs, sometimes 20-30 levels deep. What is the most performant way of walking the graph? A. Enqueueing "steps" so as to avoid deep recursion or B. A DFS (depth first search) which may step many levels deep and have a "deep" stack trace at times. I guess the question I'm asking is: Is there a performance hit in .NET for doing a DFS that causes a "deep" stack trace? If so, what is the hit? And would I better better off with some BFS by means of queueing up steps that would have been handled recursively in a DFS? Sorry if I'm being unclear. Thanks.

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• Fill data gaps - UNION, PARTITION BY, or JOIN?

  - by Dave Jarvis

  Problem There are data gaps that need to be filled. Would like to avoid UNION or PARTITION BY if possible. Query Statement The select statement reads as follows: SELECT count( r.incident_id ) AS incident_tally, r.severity_cd, r.incident_typ_cd FROM report_vw r GROUP BY r.severity_cd, r.incident_typ_cd ORDER BY r.severity_cd, r.incident_typ_cd Data Sources The severity codes and incident type codes are from: severity_vw incident_type_vw The columns are: incident_tally severity_cd incident_typ_cd Actual Result Data 36 0 ENVIRONMENT 1 1 DISASTER 27 1 ENVIRONMENT 4 2 SAFETY 1 3 SAFETY Required Result Data 36 0 ENVIRONMENT 0 0 DISASTER 0 0 SAFETY 27 1 ENVIRONMENT 0 1 DISASTER 0 1 SAFETY 0 2 ENVIRONMENT 0 2 DISASTER 4 2 SAFETY 0 3 ENVIRONMENT 0 3 DISASTER 1 3 SAFETY Question How would you use UNION, PARTITION BY, or LEFT JOIN to fill in the zero counts?

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• $.get sends prototype functions in request URL?

  - by pimvdb

  I have some prototype functions added to Object which in my opinion were practical in certain scenarios. However, I noticed that when I executed a $.get, the prototype functions are handled as data members and are sent like http://...?prototypefunc=false. This is rather useless as I don't supply these as data members, but they are added to the query string. To be exact, I have this code: Object.prototype.in = function() { for(var i=0; i<arguments.length; i++) if(arguments[i] == this) return true; return false; } $.get('http://localhost/test.php', {'test': 'foo'}, function(text) { }); The corresponding URL constructed is: http://localhost/test.php?test=foo&in=false How can I avoid this?

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• What are the common patterns in web programming?

  - by lankerisms

  I have been trying to write my first big web app (more than one cgi file) and as I kept moving forward with the rough prototype, paralelly trying to predict more tasks, this is the todo that got accumulated (In no particular order). * Validations and input sanitizations * Object versioning (to avoid edit conflicts. I dont want hard locks) * Exception handling * memcache * xss and injection protections * javascript * html * ACLs * phonetics in search, match and find duplicates (for form validation) * Ajaxify!!! (I have snipped off the project specific items.) I know that each todo will be quite tied up to its project and technologies used. What I am wondering though, is if there is a pattern in your todo items as well as the sequence in which you experienced guys have come across them.

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• PHP: Safe way to store decryptable passwords

  - by Jammer

  I'm making an application in PHP and there is a requirement that it must be possible to decrypt the passwords in order to avoid problems in the future with switching user database to different system. What encryption/decryption algorithm would you suggest? Is it good idea to just store the encrypted value and then compare the future authentication attempts to that value? Are the passwords still as safe as MD5/SHA1 when the private key is not available to the attacker (Hidden in USB drive for example)? I should still use salting, right? What encryption libraries should I use for PHP?

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• Updating Activity UI from Different Activity Method?

  - by stormin986

  I have a tab widget where one of the tabs is a chat-type feature. I want to update the chat data at an interval (variable depending on whether the chat tab is active or not). The best approach seemed to be using an AsyncTask in my main TabActivity class, as that would avoid any issues of the chat activity being destroyed while in the background, while an AsyncTask was running. I wanted to ensure that the Activity isn't destroyed and recreated, thus causing my AsyncTask to be unable to modify the actual active Activity's data. However, now that my AsyncTask is in the TabActivity activity, I don't have a direct way to call my Chat's ListAdapter notifyDataSetChanged() from my onPostExecute() method anymore. Is there a way to get a reference to a given Tab's current Activity from the TabHost/TabActivity? Or, alternatively, can I assume my chat activity will never be destroyed as a child activity of the TabActivity activity (well, never destroyed while the TabActivity is active at least), and then just put the AsyncTask in the Chat Activity?

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• does it make sense to send password information during email communication from websites

  - by Samuel

  Most of the online sites on registration do send a link to activate the site and on any further correspondence with the end user they provide information about the site and also provide the login credentials with password in clear text (as given below) Username - [email protected] Password - mysecretpassword What would you do in such a case? From a usability perspective does it make sense to send the password information in clear text or should you just avoid sending this information. I was under the impression that most of the passwords are MD5 hashed before storing in the database and hence the service provider will not have any access to clear text passwords, is this a security violation?

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• Is it possible to match with decomposed sequences in F#?

  - by Ball

  I seem to remember an older version of F# allowing structural decomposition when matching sequences just like lists. Is there a way to use the list syntax while keeping the sequence lazy? I'm hoping to avoid a lot of calls to Seq.head and Seq.skip 1. I'm hoping for something like: let decomposable (xs:seq<'a>) = match xs with | h :: t -> true | _ -> false seq{ 1..100 } |> decomposable But this only handles lists and gives a type error when using sequences. When using List.of_seq, it seems to evaluate all the elements in the sequence, even if it is infinite.

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• C++ containers on classes, returning pointers

  - by otneil

  Hello, I'm having some trouble to find the best way to accomplish what I have in mind due to my inexperience. I have a class where I need to a vector of objects. So my first question will be: is there any problem having this: vector< AnyType container* and then on the constructor initialize it with new (and deleting it on the destructor)? Another question is: if this vector is going to store objects, shouldn't it be more like vector< AnyTipe* so they could be dynamically created? In that case how would I return an object from a method and how to avoid memory leaks (trying to use only STL)?

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• Importing a spreadsheet, but having trouble.

  - by Chris Phelps

  I have a form that allows a user to import a spreadsheet. This spreadsheet is generally static when it comes to column headers, but now the users want to be able to include an optional column (called Notes). My code crashes when I try to read the column from the spreadsheet if it doesn't exist. Dim objCommand As New OleDbCommand() objCommand = ExcelConnection() 'function that opens spreadsheet and returns objCommand Dim reader As OleDbDataReader reader = objCommand.ExecuteReader() While reader.Read() Dim Employee As String = Convert.ToString(reader("User")) Dim SerialNUM As String = Convert.ToString(reader("serialno")) **Dim Notes As String = Convert.ToString(reader("notes"))** If the spreadsheet contains a Notes column, all goes well. If not, crash. How can I check to see if the Notes column exists in the spreadsheet to avoid the crash?

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• Issues running python scripts in Command Prompt (Specifically with command line arguments)?

  - by dmanatunga

  I am trying to run my python scripts in DOS without calling python.exe first. I am specifically doing this in relation to running django-admin.py. I have C:\Python26 and C:\Python26\Scripts in my PATH. However, if I try running django-admin.py by doing: django-admin.py startproject helloworld I get the message: Type 'django-admin.py help' for usage. Now, after some experimentation, I realized the problem is that the secondary arguments to these scripts are not being passed for some reason, since I tried it with a some other python scripts I have. I know I could avoid this problem by simply doing: python C:\Python26\Scripts\django-admin.py startproject helloworld But I know it should be possible to run the first command only and get it to work, because I had it working before. I've looked everywhere, and not many places have been helpful so any idea would be useful for me at this point.

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• Exposing a "dumbed-down", read-only instance of a Model in GAE

  - by Blixt

  Does anyone know a clever way, in Google App Engine, to return a wrapped Model instance that only exposes a few of the original properties, and does not allow saving the instance back to the datastore? I'm not looking for ways of actually enforcing these rules, obviously it'll still be possible to change the instance by digging through its __dict__ etc. I just want a way to avoid accidental exposure/changing of data. My initial thought was to do this (I want to do this for a public version of a User model): class ReadOnlyUser(db.Model): display_name = db.StringProperty() @classmethod def kind(cls): return 'User' def put(self): raise SomeError() Unfortunately, GAE maps the kind to a class early on, so if I do ReadOnlyUser.get_by_id(1) I will actually get a User instance back, not a ReadOnlyUser instance.

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• Can I change the database server and database a report is pointing to dynamically?

  - by Randy Minder

  I have a Crystal 2008 report that will be deployed to an InfoView server. There are four different databases the user might want to execute the report against. Each of the four databases have exactly the same schema. Only the data in each is different. Each database corresponds to a plant we have around the world. Instead of creating four different reports (each one connected to one of the four databases), am I able to dynamically change the server/database the report hits based on a value the user enters into a parameter? I'm really trying to avoid having to create four identical reports except for the database connection on each. If this isn't possible, how do developers typically deal with this sort of scenario? I would imagine it's fairly common. Thanks very much.

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• bitfield mask calculation macro

  - by Aidan Cully

  We have a set of C macros, here, for using the preprocessor to do bitfield operations, and we run into warnings when attempting to use these macros in visual studio. The problem can be demonstrated very easily: #define BITFIELD_WIDTHMASK(Width) \ ((Width) >= 32 ? ~0x0ul : (1ul << (Width)) - 1) unsigned long foo(void) { return BITFIELD_WIDTHMASK(32); } Compiling this with MSVC yields the warning: test.c(12) : warning C4293: '<<' : shift count negative or too big, undefined behavior This isn't a behavior problem - the << operator won't be used in this case, and that should be detected at compile time. But does anyone have any suggestions about how to rewrite the macro to avoid the warning? Or, failing that, how to redesign the macro interface for this? Thanks in advance

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• CoreData and many NSArrayController

  - by unixo

  In my CoreData Application, I've an outline view on left of main window, acting as source list (like iTunes); on the right I display a proper view, based on outline selection. Each view has its components, such as table view, connected to array controller, owned by the specific view. Very often different views display same data, for example, a table view of the same entity. From a performance point of view, is better to have a single array controller per entity and share it between all views or does CoreData cache avoid memory waste?

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• Audio input via HTML5?

  - by tibbon

  We have a VoIP application imVOX, and we are looking at various ways of expanding our reach. Part of that is writing an HTML5 application, but it requires the use of audio input from the browser (and also push to talk buttons from the browser, even if another app is focused). On the audio side, with HTML5 is there any way of taking audio input from the browser to compress and send to our servers? I know with Flash such is possible, but we're trying to avoid flash for mobile compatibility and generally looking toward the future.

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• Can I join between two MySQL tables stores on separate machines?

  - by CuriousCoder

  I have a relatively light query that needs information from a local MySQL table along with another MySQL table which is stored on a physically separate machine (on the same network). I'm keen to avoid setting up replication just to facilitate this light query that only needs executed once a day. Is there any way that I can join with a table on a remote machine using one query? Or run a SELECT INTO into a local table. Notes I'm using C# & .NET 4.

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• VB.NET generates properties in the release build

  - by dattebayo

  I have a form and i drag and drop a control in VB.NET. I have a line say, private WithEvents radioButton RadioButton Also, I have a handler like, private void click(.....) Handles radioButton.Click { ... } Now, When I build this is .NET 3.5 in release mode, and see the generated code in reflector tool, the code is something like, Private Overridable Property radioButton As RadioButton . . . <AccessedThroughProperty("radioButton")> _ Private _radioButton As RadioButton Can someone tell me what is going on here? And how do I avoid the generation of new properties and fields? -datte

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• BASH Expression to replace beginning and ending of a string in one operation?

  - by swestrup

  Here's a simple problem that's been bugging me for some time. I often find I have a number of input files in some directory, and I want to construct output file names by replacing beginning and ending portions. For example, given this: source/foo.c source/bar.c source/foo_bar.c I often end up writing BASH expressions like: for f in source/*.c; do a="obj/${f##*/}" b="${a%.*}.obj" process "$f" "$b" done to generate the commands process "source/foo.c" "obj/foo.obj" process "source/bar.c "obj/bar.obj" process "source/foo_bar.c "obj/foo_bar.obj" The above works, but its a lot wordier than I like, and I would prefer to avoid the temporary variables. Ideally there would be some command that could replace the beginning and ends of a string in one shot, so that I could just write something like: for f in source/*.c; do process "$f" "obj/${f##*/%.*}.obj"; done Of course, the above doesn't work. Does anyone know something that will? I'm just trying to save myself some typing here.

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• Cookie is setting twice (dublicated)

  - by Erik Larsson

  I'm new to cookies, and im trying to set a cookie where to store the referer (the org ref). But when i try this function: function do_it_cookie() { // Check if cookie exists if (isset($_COOKIE['ref'])) { // It dose exist, do nothing or anything... } else { setcookie ('ref', $_SERVER['HTTP_REFERER'], time() + 60, '/'); header ("Location: http://www.nyttforetag.com/mind-your-own-business/"); } } I want to store the cookie on the user computer for 30 days, if the return i want to know the initial refereeing url. But when i use this and lets say i go to another page in my site and then go back to the homepage its sets a new cookie with the exact same name and with the ref of the previous page. Is there away to avoid this?

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• ant: iterator over properties file

  - by scheibenkleister

  Hi, all my projects and their versions are defined in a properties file like this: ProjectNameA=0.0.1 ProjectNameB=1.4.2 I'd like to iterate over all projects and use there names and versions in an ant script. Right now, I read the entire properties file in help of the property task. Then I iterate over a given list in a for loop like this: <for list="ProjectNameA,ProjectNameB" param="project"> <sequential> <echo message="@{project} has version ${@{project}}" /> </sequential> </for> How can I avoid the duplication of the project names in the for loop. So basically iterate over each line and extract the name and the version of a project. Thanks.

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• Creating a virtual, data-driven section of a Wordpress-powered site

  - by lgomez

  Hello all, I want to create a plugin for wordpress to automatically serve pages containing data pulled from a provider's API. The API returns one or more records containing data for that record and I simply want to have the plugin intercept the request, call the API with parameters pulled from the request URI and display the data using a template that I can either let them upload to the server or let them copy and paste into the plugins admin settings. For example, I may want one of my wordpress installations to show products pulled from such an API under the url "example.com/products". The plugin would catch that request, extract the variables from the URL, call the API and render the template with the returned results. I'd like to avoid requiring editing the .htaccess file like some caching plugins do. Some of the admins of these pages won't know how to do that or simply won't have access to the .htaccess file. Thanks!

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• What is the effect on record size of reordering columns in PostgreSQL?

  - by Summer

  Since Postgres can only add columns at the end of tables, I end up re-ordering by adding new columns at the end of the table, setting them equal to existing columns, and then dropping the original columns. So, what does PostgreSQL do with the memory that's freed by dropped columns? Does it automatically re-use the memory, so a single record consumes the same amount of space as it did before? But that would require a re-write of the whole table, so to avoid that, does it just keep a bunch of blank space around in each record? Thanks! ~S

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• How to use switch statement with Enumerations C#

  - by Maximus Decimus

  I want to use a switch statement in order to avoid many if's. So I did this: public enum Protocol { Http, Ftp } string strProtocolType = GetProtocolTypeFromDB(); switch (strProtocolType) { case Protocol.Http: { break; } case Protocol.Ftp: { break; } } but I have a problem of comparing an Enum and a String. So if I added Protocol.Http.ToString() there is another error because it allows only CONSTANT evaluation. If I change it to this switch (Enum.Parse(typeof(Protocol), strProtocolType)) It's not possible also. So, it's possible to use in my case a switch statement or not?

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