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• Load Balancing and Failover for Read-Only PostgreSQL Database

  - by Eric J.

  Scenario Multiple application servers host web services written in Java, running in SpringSource dm Server. To implement a new requirement, they will need to query a read-only PostgreSQL database. Issue To support redundancy, at least two PostgreSQL instances will be running. Access to PostgreSQL must be load balanced and must auto-fail over to currently running instances if an instance should go down. Auto-discovery of newly running instances is desirable but not required. Research I have reviewed the official PostgreSQL documentation on this issue. However, that focuses on the more general case of read/write access to the database. Top google results tend to lead to older newsgroup messages or dead projects such as Sequoia or DB Balancer, as well as one active project PG Pool II Question What are your real-world experiences with PG Pool II? What other simple and reliable alternatives are available?

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• WPF DataGrid Vs Windows Forms DataGridView

  - by Mrk Mnl

  I have experience in WPF and Windows Forms, however have only used the Windows Forms DataGridView and not the WPF DataGrid (which was only included in .Net 4 or could be added to .Net 3.5 from Codeplex, I understand). I am about to devlop an app using one of these controls heavily for large amounts of data and have read performance is an issue with the WPF DataGrid so I may stick to the Windows Forms DataGridView.. Is this the case? I do not want to use a 3rd party control. Does the Windows Forms DataGridView offer significant performance over the WPF DataGrid for large amounts of data? If I were to use WPF I would prefer to use .Net 3.5S SP1, unless the DataGrid in the .Net 4 is significantly better? Also I want to use ADO with DataTable's which I feel is better suited to Windows Forms..

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• Automatic exit from bash shell script on error

  - by radman

  Hi, I've been writing some shell script and I would find it useful if there was the ability to halt the execution of said shell script if any of the commands failed. See below for an example: #!/bin/bash cd some_dir ./configure --some-flags make make install So in this case if the script can't change to the indicated directory then it would certainly not want to do a ./configure afterward it fails. Now I'm well aware that I could have an if check for each command (which I think is a hopeless solution), but is there a global setting to make the script exit if one of the commands fails?

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• Why is this not a bug in qmail?

  - by jemfinch

  I was reading DJB's "Some thoughts on security after ten years of Qmail 1.0" and he listed this function for moving a file descriptor: int fd_move(to,from) int to; int from; { if (to == from) return 0; if (fd_copy(to,from) == -1) return -1; close(from); return 0; } It occurred to me that this code does not check the return value of close, so I read the man page for close(2), and it seems it can fail with EINTR, in which case the appropriate behavior would seem to be to call close again with the same argument. Since this code was written by someone with far more experience than I in both C and UNIX, and additionally has stood unchanged in qmail for over a decade, I assume there must be some nuance that I'm missing that makes this code correct. Can anyone explain that nuance to me?

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• overridden styles for flex module

  - by Anand

  Can a flex module have styles different from the main application which loads the modules? Meaning... can I have a main set of styles for the application, and separate styles for each module.. with each of them rendering their own styles without disturbing the other at runtime? My specific case: The main application is developed by me... and the modules are developed by different people who want to contribute to the main application. I want to provide some way for each of the module developers to have their own styles for their modules, without touching the main application or its styles.

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• Which design pattern should I be using?

  - by Gabriel

  Here's briefly what I'm trying to do. The user supplies me with a link to a photo from one of several photo-sharing websites (such as Flickr, Zooomr, et. al). I then do some processing on the photo using their respective APIs. Right now, I'm only implementing one service, but I will most likely add more in the near future. I don't want to have a bunch of if/else or switch statements to define the logic for the different websites (but maybe that's necessary?) I'd rather just call GetImage(url) and have it get me the image from whatever service the url's domain is from. I'm confused how the GetImage function and classes should be designed. Maybe I need the strategy pattern? I'm still reading and trying to understand the various design patterns and how I could make one fit in this case. I'm doing this in C#, but this question is language-agnostic.

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• Why does Rake task enhancement differ between my local environment and when deploying to Heroku Cedar?

  - by John Bachir

  I have this in lib/tasks/foo.rake: Rake::Task["assets:precompile"].enhance do print ">>>>>>>> hello from precompile" end Rake::Task["assets:precompile:nondigest"].enhance do print ">>>>>>>> hello from precompile:nondigest" end When I run rake assets:precompile locally, both messages are printed. When I push to heroku, only the nondigest message is printed. However, according to the buildpack, the push is executing the exact same command as I am locally. Why does the enhancement to the base assets:precompile case not work on heroku but does work locally?

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• What causes my borderless C++/CLI app to crash when overriding WndProc?

  - by Ste

  I use a form with border NONE. I need to override WndProc for resize and move form. However, using this code, my app crashes! static const int WM_NCHITTEST = 0x0084; static const int HTCLIENT = 1; static const int HTCAPTION = 2; protected: virtual void Form1::WndProc(System::Windows::Forms::Message %m) override { switch (m.Msg) { case WM_NCHITTEST: if (m.Result == IntPtr(HTCLIENT)) { m.Result = IntPtr(HTCAPTION); } break; } Form1::WndProc(m); } virtual System::Windows::Forms::CreateParams^ get() override { System::Windows::Forms::CreateParams^ cp = __super::CreateParams; cp->Style |= 0x40000; return cp; } How can I fix my code not to crash but still allow my form to be moved and resized?

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• Mongrel with Ruby 1.9.

  - by JussiR

  When starting the server, I get this strange error after updating to Ruby 1.9: " [BUG] cross-thread violation on rb_gc() ruby 1.8.6 (2008-08-11) [i386-mswin32] This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information. " My mongrel version is 1.1.6, which should be compatible with Ruby 1.9. I also still have the Ruby 1.8.6 installation, so i assume that for some reason mongrel tries to access that and kills ruby? My rails version is 2.3.4, in case it matters.

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• How can I create an .xls file with a readwrite password from Delphi

  - by dummzeuch

  I know that it is possible to create .xls files from Delphi using ADO, OLE automation with Excel and even using several commercial libraries. My requirement now is not just creating a new .xls file and adding data to it but in addition protecting it with a password against editing. I guess this would be possible using OLE automation but that would require an Excel installation on the computer and also add all the potential hassle of OLE automation which I would like to avoid. Does any of the other solutions provide the option of password protecting the file? (Yes, I know this is far from secure, but the customer requests it. Just in case it matters: I am using Delphi 2007.)

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• How do I launch a subprocess in C# with an argv? (Or convert agrv to a legal arg string)

  - by lucas

  I have a C# command-line application that I need to run in windows and under mono in unix. At some point I want to launch a subprocess given a set of arbitrary paramaters passed in via the command line. For instance: Usage: mycommandline [-args] -- [arbitrary program] Unfortunately, System.Diagnostics.ProcessStartInfo only takes a string for args. This is a problem for commands such as: ./my_commandline myarg1 myarg2 -- grep "a b c" foo.txt In this case argv looks like : argv = {"my_commandline", "myarg1", "myarg2", "--", "grep", "a b c", "foo.txt"} Note that the quotes around "a b c" are stripped by the shell so if I simply concatenate the arguments in order to create the arg string for ProcessStartInfo I get: args = "my_commandline myarg1 myarg2 -- grep a b c foo.txt" Which is not what I want. Is there a simple way to either pass an argv to subprocess launch under C# OR to convert an arbitrary argv into a string which is legal for windows and linux shell? Any help would be greatly appreciated.

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• MQ Connection - 2009 error

  - by user171523

  am connectting the MQ with below code. I am able connected to MQ successfully. My case is i place the messages to MQ every 1 min once. After disconnecting the cable i get a ResonCode error but IsConnected property still show true. Is this is the right way to check if the connection is still connected ? Or there any best pratcices around that. I would like to open the connection when applicaiton is started keep it open for ever. public static MQQueueManager ConnectMQ() { if ((queueManager == null) || (!queueManager.IsConnected)||(queueManager.ReasonCode == 2009)) { queueManager = new MQQueueManager(); } return queueManager; }

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• Emacs/xterm color annoyance on Linux

  - by tgamblin

  I'm using emacs in a console window both on my local Linux box and on the login node of a remote cluster. I use emacs regularly, and I've got the foreground color set to white in my .emacs file like so: (set-foreground-color "white") (set-background-color "black") However, when I run emacs, the foreground isn't white; it's grey and very hard to read. On my Mac, emacs in a console window with the same settings shows up as proper white. But on both linux boxes, in konsole and xterm, it's grey. In case it matters, I've got TERM set to xterm-color, the desktop is running RHEL 5, and the cluster node is running RHEL 4 (CentOS). Is this some default with how Linux sets up terminal colors? How do I get white to be white? Note: this is with console emacs, not emacs under X. That's emacs -nw if you have DISPLAY set.

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• Capturing the contents of <select>

  - by joey mueller

  I'm trying to use a regular expression to capture the contents of all option values inside an HTML select element For example, in: <select name="test"> <option value="blah">one</option> <option value="mehh">two</option> <option value="rawr">three</option> </select> I'd like to capture one two and three into an array. My current code is var pages = responseDetails.responseText.match(/<select name="page" .+?>(?:\s*<option .+?>([^<]+)<\/option>)+\s*<\/select>/); for (var c = 0; c<pages.length; c++) { alert(pages[c]); } But it only captures the last value, in this case, "three". How can I modify this to capture all of them? Thanks!

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• MS SQL replace sequence of same characters inside Text Field (TSQL only)

  - by zmische

  I have a text column varchar(4000) with text: 'aaabbaaacbaaaccc' and I need to remove all duplicated chars - so only one from sequence left: 'abacbac' It should not be a function, Procedure or CLR - Regex solution. Only true SQL select. Currently I think about using recursive WITH clause with replace 'aa'-'a', 'bb'-'b', 'cc'-'c'. So recursion should cycle until all duplicated sequences of that chars would be replaced. DO you have another solution, perhaps more Permormant one? PS: I searched through this site about different replace examples - they didnt suit to this case.

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• Passing single attributes to associated factories

  - by lambdabutz

  I'm looking for a way to pass fields into the factories of associated models without having to explicitly call the factory itself. For example, lets say I have some factories like so: Factory.define :person do |person| person.name "Default Bob" person.sex "M" person.house {|p| p.association(:house)} end Factory.define :house do |house| house.color "Red" house.has_ac true house.suburb {|h| h.association(:suburb)} end Factory.define :suburb do |suburb| suburb.name "Little boxes" end This is fine and all, but if I want to use factories to create someone in a specific house in a specific suburb I have do this: sub = Factory(:suburb, :name => "Blue town") house = Factory(:house, :color => "Blue", :suburb => sub) person = Factory(:person, :name => "Bill", :house => house) While this isn't bad in this small case, my actual models sometimes have 7 or 8 associations, and when I want to create an object whose associations I only care about a single attribute, the code for this starts to get really heavy. Is there somewhat I can pass attributes to nested Factories without having to recall the Factory itself?

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• Is NSDictionary key order guaranteed the same as initialized if it never changes?

  - by Thaurin

  I've run into the same problem as found in this question. However, I have a follow-up question. I seem to be in the same situation as the original asker: I have a plist with a hierarchy of dictionaries that define a configuration screen. These are not mutable and will stay the same throughout the application. Since the original discussion seems to focus on problems arising from mutating the dictionary, I must ask for comfirmation: is the order of a dictionary guaranteed the same as they are in the plist, i.e. as it is read (with initWithContentsOfFile)? Can I use allKeys on it in this case to get a correct-order array of keys if the dictionary never changes?

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• Can a 32-bit RHEL4 userland work with a 64-bit kernel?

  - by James

  Is there a way to change an i386 RHEL4 machine to run an amd64 kernel, but ensure that it still builds software into same i386 binaries? On Debian this seems quite straightforward: just install an amd64 kernel (worst case, build one like this guy: http://www.debian-administration.org/users/jonesy/weblog/1) and prefix everything with "linux32". Then everything that considers uname -m will be unchanged, I just need to handle the few cases that consider uname -r. What is the Red Hat equivalent? Is the only way a full 64-bit installation on another disk and then chrooting back to the 32-bit system before anyone builds anything? (Even the best examples of that seem to be Debian-based.) Background: We make a large system that runs on (a variant of) i386 RHEL4. However, some of the larger RHEL build machines now have enough RAM that they might benefit from going 64-bit (for the kernel and maybe some of the bigger build steps). Our build system doesn't support cross-compilation.

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• Initiate a PHP class where class name is a variable

  - by ed209

  I need some help with an error I have not encountered before and can't seem to find anywhere. In a PHP mvc framework (just from a tutorial) I have the following: // Initiate the class $className = 'Controller_' . ucfirst($controller); if (class_exists($className)) { $controller = new $className($this->registry); } $className is showing the correct class name (case is also correct). But when I run it I get this in the apache error log (no php error) [Wed Mar 31 10:34:12 2010] [notice] child pid 987 exit signal Segmentation fault (11) Process id is different on every call. I am running PHP 5.3.0 on os x 10.6. This site seems to work on 5.2.11 on another Mac. Not really sure where to go next to debug it. I guess it could be an apache setting as much as a php bug or a problem with the code... any suggestions on where to look next?

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• What is the best solution to do Reporting on Object data for .NET ?

  - by Peter Fox

  Hi, Our projects are using objects as the data source to reports. Our business layer is returning single objects or IEnumerable. Our reports (quite complex) need to display value-type properties of the object, and its related objects. Typical case would be, from a List, display a master report with category data, then a subreport with data for each Product inside each Category, then a subreport for each Part of each Product, and so on. Reporting from the database is not an option for us. We have tried so far - Reporting Services : works but have to mess around with the XML definition of the report to define the datasource classes, very hard to work with if you use an object datasource, architecturally not too clean - Telerik Reports : quite nice (esp., nice architecture) but seems to have problems with complex reports (master/sub), does not give great paging control, rumored to have performance/crash problems (immature product). Does anyone know a good reporting solution that can be integrated in an ASP.NET application and works well with objects as datasources ?

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• Problem compiling bison & flex program under vc++

  - by Eric

  I'm using bison & flex (downloaded via cygwin) with vc++. When I compile the program I got an error: ...: fatal error C1083: Cannot open include file: 'unistd.h': No such file or directory The corresponding code in the flex-generated file is: #ifndef YY_NO_UNISTD_H /* Special case for "unistd.h", since it is non-ANSI. We include it way * down here because we want the user's section 1 to have been scanned first. * The user has a chance to override it with an option. */ /* %if-c-only */ #include <unistd.h> /* %endif */ /* %if-c++-only */ /* %endif */ #endif If I define YY_NO_UNISTD_H in the flex file(.l) this error will disappear, but I get several other errors: ...: error C2447: '{' : missing function header (old-style formal list?) ...: warning C4018: '<' : signed/unsigned mismatch ...: error C3861: 'isatty': identifier not found How can I fix this problem?

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• What happened to the TMP environment variable?

  - by Mark0978

  I always heard that the proper way to find the temporary folder on a UNIX machine was to look at the TMP environment variable. When writing code that worked on Windows as well as Linux, I would check for TEMP and TMP. Today, I discovered that my Ubuntu install does not have that environment variable at all. I know it seems you can always count on /tmp being there to put your temporary files in, but I understood that TMP was the way the user could tell you to put the temporary files someplace else. Is that still the case?

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• Does anyone have a backup strategy for SQL Azure databases?

  - by Pete

  I'm using SQL Azure on a project and it works great. The problem is that the usual backup features do not exist. I have exported the database a couple of times using SQLAzureMW ( http://sqlazuremw.codeplex.com/ ) but this tool is now choking trying to download the database data with bcp. In any case, it's not as nice a solution as SQL Server backups. Is anyone aware of a commercial or open source tool, or other technique, for making reliable backups of SQL Azure databases? This is really a showstopper.

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• Does the optimizer filter subqueries with outer where clauses

  - by Mongus Pong

  Take the following query: select * from ( select a, b from c UNION select a, b from d ) where a = 'mung' Will the optimizer generally work out that I am filtering a on the value 'mung' and consequently filter mung on each of the queries in the subquery. OR will it run each query within the subquery union and return the results to the outer query for filtering (as the query would perhaps suggest) In which case the following query would perform better : select * from ( select a, b from c where a = 'mung' UNION select a, b from d where a = 'mung' ) Obviously query 1 is best for maintenance, but is it sacrificing much performace for this? Which is best?

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• Efficient calculation of matrix cumulative standard deviation in r

  - by Abiel

  I recently posted this question on the r-help mailing list but got no answers, so I thought I would post it here as well and see if there were any suggestions. I am trying to calculate the cumulative standard deviation of a matrix. I want a function that accepts a matrix and returns a matrix of the same size where output cell (i,j) is set to the standard deviation of input column j between rows 1 and i. NAs should be ignored, unless cell (i,j) of the input matrix itself is NA, in which case cell (i,j) of the output matrix should also be NA. I could not find a built-in function, so I implemented the following code. Unfortunately, this uses a loop that ends up being somewhat slow for large matrices. Is there a faster built-in function or can someone suggest a better approach? cumsd <- function(mat) { retval <- mat*NA for (i in 2:nrow(mat)) retval[i,] <- sd(mat[1:i,], na.rm=T) retval[is.na(mat)] <- NA retval } Thanks.

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