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• where on disk is space allocated for new files inside LVM lv with ext4 file system?

  - by Jost

  I run a multi-disk server with LVM2. Several large disks serve as LVM2 physical volumes for one volume group, containing one logical volume formatted with ext4. Nothing fancy, just your standard linear setup. Recently an additional, very small disk was added as physical volume to that volume group and I expanded both the logical volume, and the ext4 file system therein onto that disk. This lv is used to store incremental backups using rsync and is only about 30% full, there have rarely been any files deleted from it, only incremental writes. Now this new HDD I added to the pre-existing volume group has unexpectedly died on me, and the volume group won't come up because it is missing one physical volume. As fate will have it, this WAS the "in an event of catastrophic failure on the primary server"-backup, the event happened, the boss is not happy, so this kinda has to work... According to this (Part 3): http://www.novell.com/coolsolutions/appnote/19386.html it is possible to trick LVM into starting anyway by creating a new pv with identical metadata to the failed disk, which will make the volume accessible, but of course leave giant holes in the file system. I have'n tried it yet, because it involves repairing (writing to) the file system which eliminates the possibility of trying other things if it fails. Now my question is: How does this setup actually allocate disk space for new data? Is it allocated linearly from beginning to end of PVs, in the order they were added to the vg? Is it striped somehow in order to increase performance/balance load? since this defective disk was added only later to an existing lvm2 vg and lv, containing a half-empty ext4, what are the chances that there was never any data written to the defective disk? In other words: what are the chances of recovering all my data, even without the defective disk, by just starting the volume group as-is? Am I about to go spend $1500 on having 250GB of empty space recovered when I send the defective disk in for repair? Is there a way to check without mounting the file system and opening the files, hoping they contain something other than zeros? (comparing addresses of used data blocks inside ext4 to address ranges that were on the missing pv, something like that, preferably easy to automate) I know bitwise-copying the entire lv into an image file before trying to repair the ext4 would probably be a good idea, but since this lv is very large and I just suffered major file system failure on several systems it is probably a luxury I don't have... Any suggestions?

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• what in/out bound mail system to use ? hosted or not ?

  - by rick moss

  hi all I have a ruby / rails application that integrates in and outgoing email directly into the app. The app is going to be running on multiple domains each with posible many users sending and recieving email. I have looked into sendgrid, mailchimp and mad mimi as hosted services and also looked to create my own email server. There are advantages and disadvantages of both solutions and i am not sure which one to go down and am hoping someone can give me advice ?? Any help will be great. I know email is a hassle to manage but once set up correctly cant be that bad ?? Thanks in advance Rick

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• Proper way in Python to raise errors while setting variables

  - by ensnare

  What is the proper way to do error-checking in a class? Raising exceptions? Setting an instance variable dictionary "errors" that contains all the errors and returning it? Is it bad to print errors from a class? Do I have to return False if I'm raising an exception? Just want to make sure that I'm doing things right. Below is some sample code: @property def password(self): return self._password @password.setter def password(self,password): # Check that password has been completed try: # Check that password has a length of 6 characters if (len(password) < 6): raise NameError('Your password must be greater \ than 6 characters') except NameError: print 'Please choose a password' return False except TypeError: print 'Please choose a password' return False #Set the password self._password = password #Encrypt the password password_md5 = md5.new() password_md5.update(password) self._password_md5 = password_md5.hexdigest()

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• Heuristic algorithm for load balancing among threads.

  - by Il-Bhima

  I'm working on a multithreaded program where I have a number of worker threads performing tasks of unequal length. I want to load-balance the tasks to ensure that they do roughly the same amount of work. For task T_i I have a number c_i which provides a good approximation to the amount of work that is required for that task. I'm looking for an efficient (O(N) N = num tasks or better) algorithm which will give me "roughly" a good load balance given the values of c_i. It doesn't have to be optimal, but I would like to be able to have some theoretical bounds on how bad the resulting allocations are. Any ideas?

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• Why don't purely functional languages use reference counting?

  - by Zifre

  In purely functional languages, data is immutable. With reference counting, creating a reference cycle requires changing already created data. It seems like purely functional languages could use reference counting without worrying about the possibility of cycles. Am is right? If so, why don't they? I understand that reference counting is slower than GC in many cases, but at least it reduces pause times. It would be nice to have the option to use reference counting in cases where pause times are bad.

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• CA1034: Nested types should not be visible

  - by George

  Here's an explanation of the rule that that I am trying to understand. Here's the simplified code that the Code Analyzer was complaining about: Public Class CustomerSpeed Public Enum ProfitTypeEnum As Integer NotSpecified = 0 FlatAmount = 1 PercentOfProfit = 2 End Enum Private _ProfitTypeEnum As ProfitTypeEnum Public Sub New(ByVal profitType As ProfitTypeEnum) _ProfitTypeEnum = profitType End Sub End Class If the enum pertains only to the class, why is it a bad thing to make it a contained type within the class? Seems neater to me... Does anyone know what is meant by the following line?: Nested types include the notion of member accessibility, which some programmers do not understand clearly Using Namespaces to group the Class and Enum doesn't seem like a useful way to resolve this warning, since I would like both the enum to belong to the same parent level as the class name.

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• Form input validation with JAX-RS

  - by deamon

  I want to use JAX-RS REST services as a back-end for a web application used directly by humans with browsers. Since humans make mistakes from time to time I want to validate the form input and redisplay the form with validation message, if something wrong was entered. By default JAX-RS sends a 400 or 404 status code if not all or wrong values were send. Say for example the user entered a "xyz" in the form field "count": @POST public void create(@FormParam("count") int count) { ... } JAX-RS could not convert "xyz" to int and returns "400 Bad Request". How can I tell the user that he entered an illegal value into the field "count"? Is there something more convenient than using Strings everywhere and perform conversation by hand?

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• Secure ajax form POST

  - by user194630

  I was wondering how to develop a secure form post through AJAX. For example, i have: My HTML form. My JavaScript handling the submit. The submit url is "post_data.php" The posted data is: id=8&name=Denis The PHP verifies if variables id and name are POSTED and their data type. If this is ok it proceed to do some stuff on a database. My question is, how can i prevent someone from creating his own html form, outside my web site, or whatever, and posting false data to my PHP script? Imagine that data realy exists on my database, this could be bad. Thanks

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• Quartz in Webapplication

  - by JKV

  I have a question in scheduling jobs in web application. If we have to schedule jobs in web application we can either use java util Timer/TimerTask or Quartz(there are also other scheduling mechanism, but I considered Quartz). I was considering which one to use, when i hit the site http://oreilly.com/pub/a/java/archive/quartz.html?page=1 which says using timer has a bad effect as it creates a thread that is out of containers control in the last line. The other pages discuss Quartz and its capabilities, but I can read that Quartz also uses thread and/or threadpool to schedule tasks. My guess is that these threads are also not under the containers control Can anybody clarify this to me Is it safe to use Quartz in my web applications without creating hanging threads or thread locking issues? Thanks in advance

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• Should I match the curly brace usage of the previous author?

  - by Error 454

  When working on code from multiple authors, I often encounter the issue of curly-brace preference (same line vs new line). Is it good/bad practice or even a non-issue when it comes to matching the existing style vs using your own preference? Does the situation change if you are adding new code to a Class vs modifying existing code? Finally, if style should be matched, how far should the match propagate? i.e. the file, the class, subclasses etc. Example: if(this) { doThat(); } Vs. if(this){ doThat(); }

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• How to change id value when using Html.DropDownListFor helper in asp.net mvc 2.0?

  - by chobo2

  Hi I have a partial view that has something like this <%= Html.DropDownListFor(m => m.SelectedProductName, Model.ProductList, "Select a Product") %> Now you can create a new product and edit a existing product. Both editing and creating use the same form. The create is on the main page on load up. Edit popus up in a jquery u.i model dialog and renders a new partial view. So as far as the page is concerned is that I have 2 dropdown boxes with the same "id" which is bad since they should be unique. So how do I change the id? So when the edit loads it might have a id of "editSelectedProductName"? I tried to do this in the view model public string SelectedProductName{ get; set; } ViewModelConstructor() { SelectedProductName = "EditSelectedProductName"; } But it seems to not care and keeps using "SelectedProductName" as the product name. Thanks

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• Using CSS Classes for indivdual effects - opinions?

  - by Cool Hand Luke UK

  Hey, Just trying to canvas some opinions here. I was wondering how people go about adding individual effects to html elements. Take this example: you have three types of h1 titles all the same size but some are black some are gold and some are white. Some have a text-shadow etc. Would you create separate CSS classes and add them do the h1 tag or would you create a new single class for each different h1 title type (with grouped CSS elements)? With singular class for each effect you can build up combos of classes in html class="gold shadow" but also how would you name them. For example its bad practice to give classes and id names associated to colours, because it doesn't define what it does well. However is this ok with textual CSS classes? Just wondering what others do, I know there are no hard and fast rules. Cheers.

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• Memory mapped files causes low physical memory

  - by harik

  I have a 2GB RAM and running a memory intensive application and going to low available physical memory state and system is not responding to user actions, like opening any application or menu invocation etc. How do I trigger or tell the system to swap the memory to pagefile and free physical memory? I'm using Windows XP. If I run the same application on 4GB RAM machine it is not the case, system response is good. After getting choked of available physical memory system automatically swaps to pagefile and free physical memory, not that bad as 2GB system. To overcome this problem (on 2GB machine) attempted to use memory mapped files for large dataset which are allocated by application. In this case virtual memory of the application(process) is fine but system cache is high and same problem as above that physical memory is less. Even though memory mapped file is not mapped to process virtual memory system cache is high. why???!!! :( Any help is appreciated. Thanks.

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• How to stop worker threads in a multithreaded Windows service on service stop

  - by RobW

  I have a Windows service that uses the producer/consumer queue model with multiple worker threads processing tasks off a queue. These tasks can be very long running, in the order of many minutes if not hours, and do not involve loops. My question is about the best way to handle the service stop to gracefully end processing on these worker threads. I have read in another SO question that using thread.Abort() is a sign of bad design, but it seems that the service OnStop() method is only given a limited amount of time to finish before the service is terminated. I can do sufficient clean-up in the catch for ThreadAbortException (there is no danger of inconsistent state) so calling thread.Abort() on the worker threads seems OK to me. Is it? What are the alternatives?

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• Is there a rake task for advancing or retreating your schema version by exactly one?

  - by user30997

  Back when migration version numbers were simply incremented as you created migrations, it was easy enough to do: rake migrate VERSION=097 rake migrate VERSION=098 rake migrate VERSION=099 rake migrate VERSION=100 ...but we now have migration numbers that are something like YYYYMMDDtimeofday. Not that this is a bad thing - it keeps the migration version collisions to a minimum - but when I have 50 migrations and want to step through them one-at-a-time, it is a hassle: rake migrate VERSION=20090129215142 rake migrate VERSION=20090129219783 ...etc. I have to have a list of all the migrations open in front of me, typing out the version numbers to advance by one. Is there anything that would have an easier syntax, like: rake migrate VERSION=NEXT or rake migrate VERSION=PREV ?

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• Is it proper to get and especially set Perl module's global variables directly?

  - by DVK

  I was wondering what the best practice in Perl is regarding getting - or, more importantly, setting - a global variable of some module by directly accessing $Module::varName in case the module didn't provide getter/setter method for it. The reason it smells bad to me is the fact that it sort of circumvents encapsulation. Just because I can do it in Perl, I'm not entirely certain I should (assuming there actually is an alternative such as adding a getter/setter to the module). I'm asking this because I'm about to request an addition of a getter/setter for a global variable in one of the core Perl modules, and I would like to avoid it soundly and unanimously rejected on the grounds of "Why the heck do you need one when you can access the variable in the package directly?" - in case doing the latter is actually considered perfectly OK by the community.

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• Windows Network Programming

  - by bdhar

  I am planning to get some good book for Windows Socket Programming in VC++. I have 2+ years of experience in working with VC++/ATL/COM/MFC; but not in the networking domain. I have been doing some search in Google for "Windows network programming" books. There are few but they have both good and bad comments scattered all over; and I am not able to decide anything. Please recommend some good book with Pros and Cons. The books I found are below. Windows Sockets Network programming Network Programming for Microsoft Windows Thanks.

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• Are there any worse sorting algorithms than Bogosort (a.k.a Monkey Sort)?

  - by womp

  My co-workers took me back in time to my University days with a discussion of sorting algorithms this morning. We reminisced about our favorites like StupidSort, and one of us was sure we had seen a sort algorithm that was O(n!). That got me started looking around for the "worst" sorting algorithms I could find. We postulated that a completely random sort would be pretty bad (i.e. randomize the elements - is it in order? no? randomize again), and I looked around and found out that it's apparently called BogoSort, or Monkey Sort, or sometimes just Random Sort. Monkey Sort appears to have a worst case performance of O(∞), a best case performance of O(n), and an average performance of O(n * n!). Are there any named algorithms that have worse average performance than O(n * n!)? Or are just sillier than Monkey Sort in general?

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• MYSQL - Group by limit

  - by jono2010

  Hello Is there a simple way to LIMIT the GROUP BY results to the top 2. The following query returns all the results. Using 'LIMIT 2' reduces the overall list to the top 2 entries only. select distinct(rating_name), id_markets, sum(rating_good) 'good', sum(rating_neutral)'neutral', sum(rating_bad) 'bad' from ratings where rating_year=year(curdate()) and rating_week= week(curdate(),1) group by rating_name,id_markets order by rating_name, sum(rating_good) desc Results in the following :- poland 78 48 24 12 <- keep poland 1 15 5 0 <- keep poland 23 12 6 3 poland 2 5 0 0 poland 3 0 5 0 poland 4 0 0 5 ireland 1 9 3 0 <- keep ireland 2 3 0 0 <- keep ireland 3 0 3 0 ireland 4 0 0 3 france 12 24 12 6 <- keep france 1 3 1 0 <- keep france 231 1 0 0 france 2 1 0 0 france 4 0 0 1 france 3 0 1 0 Thanks Jon

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• Block IP Address including ICMP using UFW

  - by dr jimbob

  I prefer ufw to iptables for configuring my software firewall. After reading about this vulnerability also on askubuntu, I decided to block the fixed IP of the control server: 212.7.208.65. I don't think I'm vulnerable to this particular worm (and understand the IP could easily change), but wanted to answer this particular comment about how you would configure a firewall to block it. I planned on using: # sudo ufw deny to 212.7.208.65 # sudo ufw deny from 212.7.208.65 However as a test that the rules were working, I tried pinging after I setup the rules and saw that my default ufw settings let ICMP through even from an IP address set to REJECT or DENY. # ping 212.7.208.65 PING 212.7.208.65 (212.7.208.65) 56(84) bytes of data. 64 bytes from 212.7.208.65: icmp_seq=1 ttl=52 time=79.6 ms ^C --- 212.7.208.65 ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 79.630/79.630/79.630/0.000 ms Now, I'm worried that my ICMP settings are too generous (conceivably this or a future worm could setup an ICMP tunnel to bypass my firewall rules). I believe this is the relevant part of my iptables rules is given below (and even though grep doesn't show it; the rules are associated with the chains shown): # sudo iptables -L -n | grep -E '(INPUT|user-input|before-input|icmp |212.7.208.65)' Chain INPUT (policy DROP) ufw-before-input all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-before-input (1 references) ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 3 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 4 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 11 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 12 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 8 ufw-user-input all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-user-input (1 references) DROP all -- 0.0.0.0/0 212.7.208.65 DROP all -- 212.7.208.65 0.0.0.0/0 How should I go about making it so ufw blocks ICMP when I specifically attempt to block an IP address? My /etc/ufw/before.rules has in part: # ok icmp codes -A ufw-before-input -p icmp --icmp-type destination-unreachable -j ACCEPT -A ufw-before-input -p icmp --icmp-type source-quench -j ACCEPT -A ufw-before-input -p icmp --icmp-type time-exceeded -j ACCEPT -A ufw-before-input -p icmp --icmp-type parameter-problem -j ACCEPT -A ufw-before-input -p icmp --icmp-type echo-request -j ACCEPT I'm tried changing ACCEPT above to ufw-user-input: # ok icmp codes -A ufw-before-input -p icmp --icmp-type destination-unreachable -j ufw-user-input -A ufw-before-input -p icmp --icmp-type source-quench -j ufw-user-input -A ufw-before-input -p icmp --icmp-type time-exceeded -j ufw-user-input -A ufw-before-input -p icmp --icmp-type parameter-problem -j ufw-user-input -A ufw-before-input -p icmp --icmp-type echo-request -j ufw-user-input But ufw wouldn't restart after that. I'm not sure why (still troubleshooting) and also not sure if this is sensible? Will there be any negative effects (besides forcing the software firewall to force ICMP through a few more rules)?

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• Does ActiveRecord make Ruby on Rails code hard to test?

  - by Erik Öjebo

  I've spent most of my time in statically typed languages (primarily C#). I have some bad experiences with the Active Record pattern and unit testing, because of the static methods and the mix of entities and data access code. Since the Ruby community probably is the most test driven of the communities out there, and the Rails ActiveRecord seems popular, there must be some way of combining TDD and ActiveRecord based code in Ruby on Rails. I would guess that the problem goes away in dynamic languages, somehow, but I don't see how. So, what's the trick?

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• Metaprograming - self explanatory code - tutorials, articles, books

  - by elena

  Hello everybody, I am looking into improving my programming skils (actually I try to do my best to suck less each year, as our Jeff Atwood put it), so I was thinking into reading stuff about metaprogramming and self explanatory code. I am looking for something like an idiot's guide to this (free books for download, online resources). Also I want more than your average wiki page and also something language agnostic or preferably with Java examples. Do you know of such resources that will allow to efficiently put all of it into prectice (I know experience has a lot to say in all of this but i kind of want to build experience avoiding the flow bad decitions - experience - good decitions)? Thank you!

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• TDD, DDD and the No-getters principle

  - by Justin

  Hi all, After several years of following the bad practice handed down from 'architects' at my place of work and thinking that there must be a better way, I've recently been reading up around TDD and DDD and I think the principles and practices would be a great fit for the complexity of the software we write. However, many of the TDD samples I have seen call a method on the domain object and then test properties of the object to ensure the behaviour executed correctly. On the other hand, several respected people in the industry (Greg Young most noticeably so) advocate the "no-getters" principle on our domain objects. My question therefore is: How does one test the functionality of a domain object if it is forbidden to retrieve its state? I believe I am missing something fundamental so please feel free to call me an idiot and enlighten me - any guidance would be greatly appreciated.

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• Thoughts on moving to Maven in an enterprise environment

  - by Josh Kerr

  I'm interested in hearing from those who either A) use Maven in an enterprise environment or B) tried to use Maven in an enterprise environment. I work for a large company that is contemplating bringing in Maven into our environment. Currently we use OpenMake to build/merge and home-grown software to deploy code to 100+ servers running various platforms (eg. WAS and JBoss). OpenMake works fine for us however Maven does have some ideal features, most importantly being dependency management, but is it viable in a large environment? Also what headaches have/did you incur, if any, in maintaining a Maven environment. Side note, I've read http://stackoverflow.com/questions/861382/why-does-maven-have-such-a-bad-rep, http://stackoverflow.com/questions/303853/what-are-your-impressions-of-maven, and a few other posts. It's interesting seeing the split between developers.

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• Why does calling glMatrixMode(GL_PROJECTION) give me EXC_BAD_ACCESS in an iPhone app?

  - by MrDatabase

  I have an iphone app where I call these three functions in appDidFinishLaunching: glMatrixMode(GL_PROJECTION); glOrthof(0, rect.size.width, 0, rect.size.height, -1, 1); glMatrixMode(GL_MODELVIEW); When stepping through with the debugger I get EXC BAD ACCESS when I execute the first line. Any ideas why this is happening? Btw I have another application where I do the same thing and it works fine. So I've tried to duplicate everything in that app (#imports, adding OpenGLES framework, etc) but now I'm just stuck.

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