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• Finding recurrence relations of an algorithm

  - by Roarke

  I'm reading my algorithms text book, and I'm reading about recurrence relations and finding the algorithms big O complexity. I run across this line "In the case of the merge-sort algorithm, we get the recurrence equation: t(n) = b if n < 2 = 2t(n/2) +bn if n >= 2 for b > 0 my response was "how the heck did we know that?!?!" So i'm wondering if there is a systematic approach, or just a logical way of getting these recurrence relations from the algorithms can some one explain where the b and the two 2's come from?

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• A question about friend functions

  - by Als

  I faced a problem recently with a 3rd party library which generates classes from a xml. Here is a gist of it: class B; class A { void doSomething(); friend class B; }; class B { void doSomething(); void doSomethingMore() { doSomething(); } }; The compiler flags call to the function doSomething() as ambiguous and flags it as an compiler error. It is easy to understand why it gives the error.Class B being friend of class A, every member of class B has access to all the members of class A. Renaming of the either of functions resolved my problem but it got me thinking that shouldn't in this case the compiler should give a priority to the class's own member function over the function in another class of which it is a friend?

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• Is there a better way to avoid an infinite loop using winforms?

  - by Hamish Grubijan

  I am using .Net 3.5 for now. Right now I am using a using trick to disable and enable events around certain sections of code. The user can change either days, hours, minutes or total minutes, and that should not cause an infinite cascade of events (e.g. minutes changing total, total changing minutes, etc.) While the code does what I want, there might be a better / more straight-forward way. Do you know of any? For brawny points: This control will be used by multiple teams - I do not want to make it embarrassing. I suspect that I do not need to reinvent the wheel when defining hours in a day, days in week, etc. Some other standard .Net library out there must have it. Any other remarks regarding code? This using (EventHacker.DisableEvents(this)) business - that must be a common pattern in .Net ... changing the setting temporarily. What is the name of it? I'd like to be able to refer to it in a comment and also read up more on current implementations. In the general case not only a handle to the thing being changed needs to be remembered, but also the previous state (in this case previous state does not matter - events are turned on and off unconditionally). Then there is also a possibility of multi-threaded hacking. One could also utilize generics to make the code arguably cleaner. Figuring all this out can lead to a multi-page blog post. I'd be happy to hear some of the answers. P.S. Does it seem like I suffer from obsessive compulsive disorder? Some people like to get things finished and move on; I like to keep them open ... there is always a better way. // Corresponding Designer class is omitted. using System; using System.Windows.Forms; namespace XYZ // Real name masked { interface IEventHackable { void EnableEvents(); void DisableEvents(); } public partial class PollingIntervalGroupBox : GroupBox, IEventHackable { private const int DAYS_IN_WEEK = 7; private const int MINUTES_IN_HOUR = 60; private const int HOURS_IN_DAY = 24; private const int MINUTES_IN_DAY = MINUTES_IN_HOUR * HOURS_IN_DAY; private const int MAX_TOTAL_DAYS = 100; private static readonly decimal MIN_TOTAL_NUM_MINUTES = 1; // Anything faster than once per minute can bog down our servers. private static readonly decimal MAX_TOTAL_NUM_MINUTES = (MAX_TOTAL_DAYS * MINUTES_IN_DAY) - 1; // 99 days should be plenty. // The value above was chosen so to not cause an overflow exception. // Watch out for it - numericUpDownControls each have a MaximumValue setting. public PollingIntervalGroupBox() { InitializeComponent(); InitializeComponentCustom(); } private void InitializeComponentCustom() { this.m_upDownDays.Maximum = MAX_TOTAL_DAYS - 1; this.m_upDownHours.Maximum = HOURS_IN_DAY - 1; this.m_upDownMinutes.Maximum = MINUTES_IN_HOUR - 1; this.m_upDownTotalMinutes.Maximum = MAX_TOTAL_NUM_MINUTES; this.m_upDownTotalMinutes.Minimum = MIN_TOTAL_NUM_MINUTES; } private void m_upDownTotalMinutes_ValueChanged(object sender, EventArgs e) { setTotalMinutes(this.m_upDownTotalMinutes.Value); } private void m_upDownDays_ValueChanged(object sender, EventArgs e) { updateTotalMinutes(); } private void m_upDownHours_ValueChanged(object sender, EventArgs e) { updateTotalMinutes(); } private void m_upDownMinutes_ValueChanged(object sender, EventArgs e) { updateTotalMinutes(); } private void updateTotalMinutes() { this.setTotalMinutes( MINUTES_IN_DAY * m_upDownDays.Value + MINUTES_IN_HOUR * m_upDownHours.Value + m_upDownMinutes.Value); } public decimal TotalMinutes { get { return m_upDownTotalMinutes.Value; } set { m_upDownTotalMinutes.Value = value; } } public decimal TotalHours { set { setTotalMinutes(value * MINUTES_IN_HOUR); } } public decimal TotalDays { set { setTotalMinutes(value * MINUTES_IN_DAY); } } public decimal TotalWeeks { set { setTotalMinutes(value * DAYS_IN_WEEK * MINUTES_IN_DAY); } } private void setTotalMinutes(decimal nTotalMinutes) { if (nTotalMinutes < MIN_TOTAL_NUM_MINUTES) { setTotalMinutes(MIN_TOTAL_NUM_MINUTES); return; // Must be carefull with recursion. } if (nTotalMinutes > MAX_TOTAL_NUM_MINUTES) { setTotalMinutes(MAX_TOTAL_NUM_MINUTES); return; // Must be carefull with recursion. } using (EventHacker.DisableEvents(this)) { // First set the total minutes this.m_upDownTotalMinutes.Value = nTotalMinutes; // Then set the rest this.m_upDownDays.Value = (int)(nTotalMinutes / MINUTES_IN_DAY); nTotalMinutes = nTotalMinutes % MINUTES_IN_DAY; // variable reuse. this.m_upDownHours.Value = (int)(nTotalMinutes / MINUTES_IN_HOUR); nTotalMinutes = nTotalMinutes % MINUTES_IN_HOUR; this.m_upDownMinutes.Value = nTotalMinutes; } } // Event magic public void EnableEvents() { this.m_upDownTotalMinutes.ValueChanged += this.m_upDownTotalMinutes_ValueChanged; this.m_upDownDays.ValueChanged += this.m_upDownDays_ValueChanged; this.m_upDownHours.ValueChanged += this.m_upDownHours_ValueChanged; this.m_upDownMinutes.ValueChanged += this.m_upDownMinutes_ValueChanged; } public void DisableEvents() { this.m_upDownTotalMinutes.ValueChanged -= this.m_upDownTotalMinutes_ValueChanged; this.m_upDownDays.ValueChanged -= this.m_upDownDays_ValueChanged; this.m_upDownHours.ValueChanged -= this.m_upDownHours_ValueChanged; this.m_upDownMinutes.ValueChanged -= this.m_upDownMinutes_ValueChanged; } // We give as little info as possible to the 'hacker'. private sealed class EventHacker : IDisposable { IEventHackable _hackableHandle; public static IDisposable DisableEvents(IEventHackable hackableHandle) { return new EventHacker(hackableHandle); } public EventHacker(IEventHackable hackableHandle) { this._hackableHandle = hackableHandle; this._hackableHandle.DisableEvents(); } public void Dispose() { this._hackableHandle.EnableEvents(); } } } }

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• Linux Kernel - Slab Allocator Question

  - by Drex

  I am playing around with the kernel and am looking at the kmem_cache files_cachep belonging to fork.c. It detects the sizeof(files_struct). My question is this: I have altered files_struct and added a rb_root (red/black tree root) using the built-in functionality in linux/rbtree.h. I can properly insert values into this tree. However, at some point, a segfault occurs and GDB backtraces the following information: (gdb) backtrace 0 0x08066ad7 in page_ok (page=) at arch/um/os-Linux/sys-i386/task_size.c:31 1 0x08066bdf in os_get_top_address () at arch/um/os-Linux/sys-i386/task_size.c:100 2 0x0804a216 in linux_main (argc=1, argv=0xbfb05f14) at arch/um/kernel/um_arch.c:277 3 0x0804acdc in main (argc=1, argv=0xbfb05f14, envp=0xbfb05f1c) at arch/um/os-Linux/main.c:150 I have spent many hours trying to figure out why there is a segfault given that the red/black tree inserts properly. I'm thinking it's a memory allocation issue with new processes made by fork() of a parent process. Could this be the case and could it have something to do with kmem_cache files_cachep?

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• Categories & singelton in cocoa

  - by Nava Carmon

  Hi, I have a SingletonClass, which has only one instance. I want to expand it and add to it a category (MoreFeatures). I created a source SingletonClass+MoreFeatures, which interface/implementation looks like that: @interface SingletonClass (MoreFeatures) - (void) feature; @end @implementation SingletonClass (MoreFeatures) - (void) feature() { } @end When I created my SingletonClass i followed the Apple's example of Singleton implementation in cocoa. This singleton resides in a project B, which is a dependency of a bigger project A. I can call for [[SingletonClass sharedInstance] foo] from a source in project A and it works in case that function foo is located in SingletonClass interface/implementation. When I try to call [[SingletonClass sharedInstance] feature] from a source in project A, I get a crash, which says that there is no method feature for class SingletonClass... Why it happens? Thanks a lot, Nava EDIT: The crash happens in a runtime. The category file source resides in project B along with a SingletonClass

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• Resources to learn about engineering aspects of data analytics (OLAP, warehousing, ETL, etc.)

  - by JT

  I'm a math/stats guy, interested in learning more about the engineering aspects of "data analytics" (this may be an overly broad term, this is a case of "I don't know what I don't know", so I'm not sure how to be more specific). I'm fine with manipulating and analyzing the data once it's already stored somewhere and I can access it, and I'm fine with writing scripts and SQL queries (and have a general knowledge of things like normalization). What I don't know is the whole engineering process of capturing and storing the data. For example, terms I've heard thrown about that I only vaguely understand the meaning of include: - OLAP, OLTP - Data warehousing - ETL - ??? What's a good book (or any other resource) to learn about these kinds of things? What are things I should know about database design (normalization seems kinda "obvious" to me, something I would have done even before I knew the term -- is there anything else?)? In other words, for jobs falling under the umbrella term of "analytics engineer", what kinds of things should I know?

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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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• Design Pattern for Server Emulator

  - by adisembiring

  I wanna build server socket emulator, but I want implement some design pattern there. I will described my case study that I have simplified like these: My Server Socket will always listen client socket. While some request message come from the client socket, the server emulator will response the client through the socket. the response is response code. '00' will describe request message processed successfully, and another response code expect '00' will describe there are some error while processing the message request. IN the server there are some UI, this UI contain check response parameter such as. response code timeout interval While the server want to response the client message, the response code taken from input parameter response form UI check the timeout interval, it will create sleep thread and the interval taken from timeout interval input from UI. I have implement the function, but I create it in one class. I feel it so sucks. Can you suggest me what class / interface that I must create to refactor my code.

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• How to get the size of a NSString

  - by camilo

  Hi. A "quicky": how can I get the size (width) of a NSString? I'm trying to see if the string width of a string to see if it is bigger than a given width of screen, case in which I have to "crop" it and append it with "...", getting the usual behavior of a UILabel. string.length won't do the trick since AAAAAAAA and iiiiii have the same length but different sizes (for example). I'm kind of stuck. Thanks a lot.

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• Cannot call scalar-valued CLR UDF from select ... from table statement

  - by Henrik B

  I have created a scalar-valued CLR UDF (user defined function). It takes a timezone id and a datetime and returns the datetime converted to that timezone. I can call it from a simple select without problems: "select dbo.udfConvert('Romance Standard Time', @datetime)" (@datetime is of course a valid datetime variable) But if I call it passing in a datetime from a table it fails: "select dbo.udfConvert('Romance Standard Time', StartTime) from sometable" (column StartTime is of course a column of type datetime) The error message is: "Cannot find either column "dbo" or the user-defined function or aggregate "dbo.udfConvert", or the name is ambiguous." This message is really for beginners that has misspelled something, but as it works in one case and not in the other, I don't think I have done any misspellings. Any ideas?

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• Audio Detection in Matlab

  - by insane-36

  I am writing a matlab code that would be able to read the audio file and then compare it to the another audio and recognize if those audio are the voice of the same person. In both type of the audio, would have the same word utterance and the audio is about 1 minutes long. I have come to know that the approach of sliding windows using hamming window would work best on this approach but have a very little idea on this. The simple code to read an audio file and then display a portion of 10s is as below : [x,fs, nbits]= wavread('01-AudioTrack 01.wav'); subplot(211) plot(x) title('Entire Wave') smallRange = 1:100000; subplot(212) plot(smallRange,x(smallRange)) How do I make Hamming window each of 10ms in this case and what approaches should I take to deal with this problem ?

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• LNK2001: What have I forgotton to set?

  - by graham.reeds

  Following on from my previous question regarding debugging of native code, I decided to create a simple test from a console app as I wasn't getting anywhere with debugging the service directly. So I created a vc6 console app, added the dll project to the workspace and ran it. Instead of executing as expected it spat out the following linker errors: main.obj : error LNK2001: unresolved external symbol "int __stdcall hmDocumentLAdd(char *,char *,long,char *,char *,long,long,long,long *)" (?hmDocumentLAdd@@YGHPAD0J00JJJPAJ@Z) main.obj : error LNK2001: unresolved external symbol "int __stdcall hmGetDocBasePath(char *,long)" (?hmGetDocBasePath@@YGHPADJ@Z) Debug/HazManTest.exe : fatal error LNK1120: 2 unresolved externals This seems to be a simple case of forgetting something in the linker options: However everything seems to be normal, and the lib file, dll and source is available. If I change the lib file to load to nonsense it kicks up the fatal error LNK1104: cannot open file "asdf.lib", so that isn't a problem. I have previously linked to dll and they have just worked, so what I have forgotton to do?

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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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• How to search for "R" materials?

  - by James Lavin

  "The Google" is very helpful... unless your language is called "R," in which case it spits out tons of irrelevant stuff. Anyone have any search engine tricks for "R"? There are some specialized websites, like those below, but how can you tell Google you mean "R" the language? If I'm searching for something specific, I'll use an R-specific term, like "cbind." Are there other such tricks? http://rweb.stat.umn.edu/R/doc/html/search/SearchEngine.html www.rseek.org http://search.r-project.org/ www.dangoldstein.com/search_r.html

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• Android: How to find the position clicked from the context menu

  - by Josemalive

  Hi, I have a list view filled with data. I set up a context menu for the listview using the following code: list.setOnCreateContextMenuListener ( new View.OnCreateContextMenuListener() { public void onCreateContextMenu(ContextMenu menu, View view, ContextMenu.ContextMenuInfo menuInfo) { AdapterContextMenuInfo mi =(AdapterContextMenuInfo) menuInfo; menu.add(0, 0, 0, "Delete item"); } } ); I have the following method override to control de contextmenu menuitem selected: @Override public boolean onContextItemSelected(MenuItem item) { switch(item.getItemId()) { case 0: ShowAlert("hello from delete item"); break; default: return super.onContextItemSelected(item); } return true; } In this overrided method, how could i find the item of the list view that was clicked? Thanks in advance. Best Regards. Jose

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• Strange IE7 behaviors(or not)

  - by c0mrade

  I see no reason why this shouldn't work in all browsers, here is my css for anchor tag : .myButton{ background:none repeat scroll 0 0 #FFFFFF; border:1px solid #D8DFEA !important; color:#3B5998; cursor:pointer; font-size:20px; padding:10px; } Here is how it looks in IE7 : And here is how it looks in other browsers : HTML is nothing unusual as well : <a href="#" class="myButton">Beta</a> All of this is inside table, this anchor html is wrapped around with : <tr> <td><a>...</a></td> <tr> I don't think this has to do it with anything but I mentioned it just in case, so the button is missing border top, any indications what might cause this?

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• Why does an onclick property set with setAttribute fail to work in IE?

  - by Aeon

  Ran into this problem today, posting in case someone else has the same issue. var execBtn = document.createElement('input'); execBtn.setAttribute("type", "button"); execBtn.setAttribute("id", "execBtn"); execBtn.setAttribute("value", "Execute"); execBtn.setAttribute("onclick", "runCommand();"); Turns out to get IE to run an onclick on a dynamically generated element, we can't use setAttribute. Instead, we need to set the onclick property on the object with an anonymous function wrapping the code we want to run. execBtn.onclick = function() { runCommand() }; BAD IDEAS: You can do execBtn.setAttribute("onclick", function() { runCommand() }); but it will break in IE in non-standards mode according to @scunliffe. You can't do this at all execBtn.setAttribute("onclick", runCommand() ); because it executes immediately, and sets the result of runCommand() to be the onClick attribute value, nor can you do execBtn.setAttribute("onclick", runCommand);

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• In Haskell, how can you sort a list of infinite lists of strings?

  - by HaskellNoob

  So basically, if I have a (finite or infinite) list of (finite or infinite) lists of strings, is it possible to sort the list by length first and then by lexicographic order, excluding duplicates? A sample input/output would be: Input: [["a", "b",...], ["a", "aa", "aaa"], ["b", "bb", "bbb",...], ...] Output: ["a", "b", "aa", "bb", "aaa", "bbb", ...] I know that the input list is not a valid haskell expression but suppose that there is an input like that. I tried using merge algorithm but it tends to hang on the inputs that I give it. Can somebody explain and show a decent sorting function that can do this? If there isn't any function like that, can you explain why? In case somebody didn't understand what I meant by the sorting order, I meant that shortest length strings are sorted first AND if one or more strings are of same length then they are sorted using < operator. Thanks!

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• RDF Usage Rates for Syndication

  - by David in Dakota

  Is RDF still used widely for content syndication? Specifically, I know only of Slashdot as a large scale website syndicating content in that format (say versus RSS). Understandably this might seem vague to answer so more specifically: Can anyone list any larger sites similar in scale to Amazon or CNN using it? Any web based publishing platforms (Wordpress, Joomla, etc...) that generate syndication feeds with this xml vocabulary. Any other more quantifiable evidence that it is used for syndication online. I understand that RDF may be a parent specification but in this case I'm talking about sites that syndicate content using <rdf as a root element and heavily leveraging elements from the RDF namespace: http://www.w3.org/1999/02/22-rdf-syntax-ns#

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• How to remove one instance of one string in PHP?

  - by Jane

  I have a open source editor on the cms that I am making that automatically inserts a <br /> tag at the beginning of the post it submits to the database. This makes validation a pain, since even though there is no real text being submitted, the form still accepts the break tag as input and prevents the "Please enter some text" error from showing. So I tried to remove the opening break tag by filtering my input like this: substr($_POST['content'], 6); This works as long as the user doesn't press the backspace a couple of times which removes the break tag in which case the first 8 characters of the post gets removed even if they are not a break tag. So how can I remove the first 6 characters of the input ONLY if those first 6 characters are composed of the break tag. Also I don't want to remove all break tags, only the one at the very beginning of the post.

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• C++ and Scripting.Dictionary from scrrun.dll

  - by MaxFX

  Hello. I have some trouble with Scripting.Dictionary in C++. I'm trying to use interface IDictionary via smart pointer but methods of creating object don't work and I can't understand why. CoInitialize(NULL); IDictionaryPtr dict; dict.CreateInstance(__uuidof(Dictionary)); _variant_t num1 = 1; _variant_t num2 = 2; dict->Add(&num1, &num2); long i; dict->get_Count(&i); cout << i << "\n"; But method Add does not work and cout of elements in dictionary is always 0. How correct to use Scripting.Dictionary in that case. PS.: I'm getting Scripting interfaces by #import "scrrun.dll"

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• How to change a Datasource's username/password at runtime in a J2EE app?

  - by Toto

  I've deployed a web-module which connects to the database via a datasource configured in the J2EE application server. Currently, the user/password for the database connection is set in the proper J2EE application server's datasources configuration file. I want to change during runtime the datasource's user/password. (e.g.: implement a new web form in which the user is asked to enter de user/password to be used in the database connection). Is there a standard way to do that in J2EE applications or it depends on the J2EE application server? In this case I'm using Orion application server.

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• pitchbend (varispeed) audio with iPhone SDK's AudioUnit

  - by fetzig

  hi, I'm trying to manipulate the speed (and pitch) of a sound while playing. so i played around with iphone sdk's AudioUnit. downloaded iPhoneMultichannelMixerTest and tried to add an AUComponent to the graph (in this case a formatconverter). but i get (pretty soon) following error when building: #import <AudioToolbox/AudioToolbox.h> #import <AudioUnit/AudioUnit.h> ... AUComponentDescription varispeed_desc(kAudioUnitType_FormatConverter, kAudioUnitSubType_Varispeed, kAudioUnitManufacturer_Apple); ^^ error: 'kAudioUnitSubType_Varispeed' was not declared in this scope. any ideas why? the documentation on this topic doesn't help me at all (just api doc isn't very helpful when having no clue about the concept behind). there are no examples on how to wire these effects together and manipulating there properties...so maybe i'm totally wrong, anyway any hint is great. thx for help.

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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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• 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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