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• Why is memory management so visible in Java VM?

  - by Emil

  I'm playing around with writing some simple Spring-based web apps and deploying them to Tomcat. Almost immediately, I run into the need to customize the Tomcat's JVM settings with -XX:MaxPermSize (and -Xmx and -Xms); without this, the server easily runs out of PermGen space. Why is this such an issue for Java VMs compared to other garbage collected languages? Comparing counts of "tune X memory usage" for X in Java, Ruby, Perl and Python, shows that Java has easily an order of magnitude more hits in Google than the other languages combined. I'd also be interested in references to technical papers/blog-posts/etc explaining design choices behind JVM GC implementations, across different JVMs or compared to other interpreted language VMs (e.g. comparing Sun or IBM JVM to Parrot). Are there technical reasons why JVM users still have to deal with non-auto-tuning heap/permgen sizes?

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• How to design Models the correct way: Object-oriented or "Package"-oriented?

  - by ajsie

  I know that in OOP you want every object (from a class) to be a "thing", eg. user, validator etc. I know the basics about MVC, how they different parts interact with each other. However, i wonder if the models in MVC should be designed according to the traditional OOP design, that is to say, should every model be a database/table/row (solution 2)? Or is the intention more like to collect methods that are affecting the same table or a bunch of related tables (solution 1). example for an Address book module in CodeIgniter, where i want be able to "CRUD" a Contact and add/remove it to/from a CRUD-able Contact Group. Models solution 1: bunching all related methods together (not real object, rather a "package") class Contacts extends Model { function create_contact() {) function read_contact() {} function update_contact() {} function delete_contact() {} function add_contact_to_group() {} function delete_contact_from_group() {} function create_group() {} function read_group() {} function update_group() {} function delete_group() {} } Models solution 2: the OOP way (one class per file) class Contact extends Model { private $name = ''; private $id = ''; function create_contact() {) function read_contact() {} function update_contact() {} function delete_contact() {} } class ContactGroup extends Model { private $name = ''; private $id = ''; function add_contact_to_group() {} function delete_contact_from_group() {} function create_group() {} function read_group() {} function update_group() {} function delete_group() {} } i dont know how to think when i want to create the models. and the above examples are my real tasks for creating an Address book. Should i just bunch all functions together in one class. then the class contains different logic (contact and group), so it can not hold properties that are specific for either one of them. the solution 2 works according to the OOP. but i dont know why i should make such a dividing. what would the benefits be to have a Contact object for example. Its surely not a User object, so why should a Contact "live" with its own state (properties and methods). you experienced guys with OOP/MVC, please shed a light on how one should think here in this very concrete task.

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• MQ EOL Data conversion

  - by lemotdit

  we are sending data trough MQ from a z/OS/CICS system to an AS400. Original encoding of the message is CCSID 500 with a MQSTR Format. The client application is getting the message with the CONVERT option and CCSID 819. Data is almost converted correctly except for the end of line caracter. Any idea? The z/OS is sending 0D (CR) as end of line caracter. If they had 0D+0A (CR+LF), CCSID automatically change from 500 to 437, and the end of line still ain't right on the client side.

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• Put text input inside label for radio button?

  - by Martijn

  I'm trying to make a radio group specifying a bunch of options, and an extra option "other" with a text input to specify. The code for this particular radio button I'm using is <input type='radio' name='RadioInput' value='Other' id='RadioInput_Other' /> <label for='RadioInput_Other'>Ohter: <input type='text' name='RadioInput_Other_Value' id='RadioInput_Other_Value' value='' /> </label> The idea is that if you give focus to the text input, the radio button corresponding to it is selected. The code above almost does this (since the text input is inside the label). However, it also shifts focus to the radio button (which is annoying, since whatever you type next is lost). Is there any way to prevent this using XHTML1.0 / CSS2? Preferably without using javascript.

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• Using string.Format for simple things?

  - by Gerrie Schenck

  In my early .Net programming days, I used string.Format() only for complex string concatenations, for example to compile strings as Problem with customer order 234 of date 2/2/2002 and payment id 55543. But now I use string.Format for almost every string concatenation I have to do, also simple ones such as prefixing a string with something. Console.WriteLine(string.Format("\t\t{0}", myString)); Is there any possible overhead on this? Maybe I should use the regular + operator to do these simple operations? What's your opinion on this?

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• Why packets injected with libpcap are duplicated?

  - by r0u1i

  I'm using sharppcap in order to send packets as part of a monitoring system. Usually it works well but I've encountered the strangest bug on a hosted vista machine and I would like your help. On that virtual vista machine, injected packets are duplicated. That is, if I send a ping request using libpcap, it somehow gets duplicated and I get two requests on the destination machine. The two requests are almost identical byte-wise, and the only difference between them is that the second packet's TTL field is one minus the original packet's value. Using wireshark I can see the packet gets duplicated before it (and its clone) leave the vista machine. The problem is manifested even when using other tools for injecting packets using libpcap (namely PlayCap). Any ideas?

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• How to reference a sql server with a slash (\) in its name?

  - by Bill Paetzke

  Givens: One SQL Server is named: DevServerA Another is named: DevServerB\2K5 Problem: From DevServerA, how can I write a query that references DevServerB\2K5? I tried a sample, dummy query (running it from DevServerA): SELECT TOP 1 * FROM DevServerB\2K5.master.sys.tables And I get the error: Msg 102, Level 15, State 1, Line 2 Incorrect syntax near '\.'. However, I know my syntax is almost correct, since the other way around works (running this query from DevServerB\2K5): SELECT TOP 1 * FROM DevServerA.master.sys.tables Please help me figure out how to reference DevServerB\2K5 from DevServerA. Thanks.

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• Access block level storage via kernel

  - by N 1.1

  How to access block level storage via the kernel (w/o using scsi libraries)? My intent is to implement a block level storage protocol over network for learning purpose, almost the same way SCSI works. Requests will be generated by initiator and sent to target (both userspace program) which makes call to kernel module and returns the data using TCP protocol to initiator. So far, I have managed to build a simple "Hello" module and run it (I am new at kernel programming), but unable to proceed with block access. After searching a lot, I found struct buffer_head * bread(int dev,int block) in linux/fs.h, but the compiler throws error. error: implicit declaration of function ‘bread’ Please help, also feel free to advice on starting with kernel programming. Thank you!

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• HTTP: can GET and POST requests from a same machine come from different IPs?

  - by NoozNooz42

  I'm pretty sure I remember reading --but cannot find back the links anymore-- about this: on some ISP (including at least one big ISP in the U.S.) it is possible to have a user's GET and POST request appearing to come from different IPs. (note that this is totally programming related, and I'll give an example below) I'm not talking about having your IP adress dynamically change between two requests. I'm talking about this: IP 1: 123.45.67.89 IP 2: 101.22.33.44 The same user makes a GET, then a POST, then a GET again, then a POST again and the servers see this: - GET from IP 1 - POST from IP 2 - GET from IP 1 - POST from IP 2 So altough it's the same user, the webserver sees different IPs for the GET and the POSTs. Surely seen that HTTP is a stateless protocol this is perfectly legit right? I'd like to find back the explanation as to how/why certain ISP have their networks configured such that this may happen. I'm asking because someone asked me to implement the following IP filter and I'm pretty sure it is fundamentally broken code (breaking havoc for at least one major american ISP users). Here's a Java servlet filter that is supposed to protect against some attacks. The reasoning is that: "For any session filter checks that IP address in the request is the same that was used when session was created. So in this case session ID could not be stolen for forming fake sessions." http://www.servletsuite.com/servlets/protectsessionsflt.htm However I'm pretty sure this is inherently broken because there are ISPs where you may see GET and POST coming from different IPs. Any info on this subject is very welcome.

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• Correct initialization sequence for Linux serial port

  - by whitequark

  I wrote an application that must use serial ports on Linux, especially ttyUSB ones. Reading and writing operations are performed with standard select()/read() loop and write(), and there is probably nothing wrong in them, but initialization code (or absence of some part of it) damages something in the tty subsystem. Here it is: vuxboot(string filename, unsigned baud = B115200) : _debug(false) { _fd = open(filename.c_str(), O_RDWR | O_NOCTTY); if(!_fd) throw new io_error("cannot open port"); // Serial initialization was written with FTDI USB-to-serial converters // in mind. Anyway, who wants to use non-8n1 protocol? tcgetattr(_fd, &_termios); termios tio = {0}; tio.c_iflag = IGNPAR; tio.c_oflag = 0; tio.c_cflag = baud | CLOCAL | CREAD | CS8; tio.c_lflag = 0; tcflush(_fd, TCIFLUSH); tcsetattr(_fd, TCSANOW, &tio); } Another tcsetattr(_fd, TCSANOW, &_termios) sits in the destructor, but it is irrelevant. With or without this termios initialization, strange things happen in system after the application exits. Sometimes plain cat (or hd) exits immediately printing nothing or same stuff each time, sometimes it is waiting and not displaying any of the data that is surely sent onto the port; and close() (read() too, but not every time) emits a strange WARNING to dmesg referring to usb-serial.c. I checked the hardware and firmware tens of times (even on different machines) and I am sure it is working as intended; moreover, I stripped the firmware to just print same message over and over. How can I use serial port without destroying anything? Thanks.

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• Scrapy Could not find spider Error

  - by Nacari

  I have been trying to get a simple spider to run with scrapy, but keep getting the error: Could not find spider for domain:stackexchange.com when I run the code with the expression scrapy-ctl.py crawl stackexchange.com. The spider is as follow: from scrapy.spider import BaseSpider from __future__ import absolute_import class StackExchangeSpider(BaseSpider): domain_name = "stackexchange.com" start_urls = [ "http://www.stackexchange.com/", ] def parse(self, response): filename = response.url.split("/")[-2] open(filename, 'wb').write(response.body) SPIDER = StackExchangeSpider()` Another person posted almost the exact same problem months ago but did not say how they fixed it, http://stackoverflow.com/questions/1806990/scrapy-spider-is-not-working I have been following the turtorial exactly at http://doc.scrapy.org/intro/tutorial.html, and cannot figure out why it is not working.

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• Do minidump files contain the timestamp of the crash?

  - by Roger Lipscombe

  The MiscInfoStream in a minidump file contains the process create time. I'd like to find out how long the process has been running for before the crash. Does a minidump file contain the exception timestamp anywhere? WinDbg on this dump file displays the following, which implies that it's in there somewhere... Debug session time: Tue Dec 29 15:49:20.000 2009 (GMT+0) System Uptime: not available Process Uptime: 0 days 0:33:03.000 Note that today's Mar 15, so this is almost certainly the timestamp of the crash. I'd like a programmatic way to retrieve that value and the "Process Uptime" value. I found the MINIDUMP_MISC_INFO_3 structure, which contains some timezone information, but it doesn't seem to contain the exception time.

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• When to best implement a I2C driver module in Linux

  - by stefangachter

  I am currently dealing with two devices connected to the I2C bus within an embedded system running Linux. I am using an exisiting driver for the first device, a camera. For the second device, I have successfully implemented a userspace program with which I can communicate with the second device. So far, both devices seem to coexist happily. However, almost all I2C devices have their own driver module. Thus, I am wondering what the advantages of a driver module are. I had a look at the following thread... http://stackoverflow.com/questions/149032/when-should-i-write-a-linux-kernel-module ... but without conclusion. Thus, what would be the advantage of writing a I2C driver module over a userspace implementation? Regards, Stefan

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• Clustered index dilemma - ID or sort?

  - by richardtallent

  I have a table with two very important fields: id INT identity(1,1) PRIMARY KEY identifiersortcode VARCHAR(900) My app always sorts and pages search results in the UI based on identifiersortcode, but all table joins (and they are legion) are on the id field. (Aside: yes, the sort code really is that long. There's a strong BL reason.) Also, due to O/RM use, most SELECT statements are going to pull almost every column. Currently, the clustered index is on id, but I'm wondering if the TOP / ORDER BY portion of most queries would make identifiersortcode a more attractive option as the clustered key, even considering all of the table joins going on. Inserts on the table and changes to the identifiersortcode are limited enough that changing my clustered index would be a problem for insert/update operations. Trying to make the sort code's non-clustered index a covering index (using INCLUDE) is not a good option. There are a number of large columns, and some of them have a lot of update activity.

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• Measuring device drivers CPU/IO utilization caused by my program

  - by Lior Kogan

  Sometimes code can utilize device drivers up to the point where the system is unresponsive. Lately I've optimized a WIN32/VC++ code which made the system almost unresponsive. The CPU usage, however, was very low. The reason was 1000's of creations and destruction of GDI objects (pens, brushes, etc.). Once I refactored the code to create all objects only once - the system became responsive again. This leads me to the question: Is there a way to measure CPU/IO usage of device drivers (GPU/disk/etc) for a given program / function / line of code?

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• Determine Click-thru Percentage With PHP

  - by Lea

  Hi all, I am currently working on a small sponsorship application(PHP/MySql) for my personal blog, and am almost finish, but I am stuck on how to calculate the click-thru rate of my sponsors campaigns. I was always terrible with working out percentages, so any practical help would be appreciated. The data is stored in the DB as simple numbers.. So as expected, when a page refreshes, or a sponsors ad is clicked, the data updates with an incrementation of 1. So using these values...say $clicks and $impressions, how would I determine the click-thru rate? What would be the sum I would use to calculate? An example function would really be appreciated. Kind Regards, Lea

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• NHibernate Validator - how to validate enum type

  - by Herr W.

  I'm using nhibernate validator in my current solution. Everythings is almost fine but... My view model has a property of type Gender (see example below) public virtual Gender Gender { get; set; } public enum Gender { Female = 1, Male = 2 } Now i like to have some validation to ensure that the gender property ist set. But neither the NotEmpty nor the NotNull Attribute fulfil the requirement. Is there a kind of a generic solution or best practice to handle enum validations. Thanks in advance.

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• Background image of table cell

  - by Shuaib

  Hey guys, Trying to set a background image for a table view cell, tried almost everything but failing. Hoping someone would notice what I am doing wrong. Here is how my current code looks like: static NSString *CustomCellIdentifier = @"listCustomCell"; listCustomCell *cell = (listCustomCell *)[tableView dequeueReusableCellWithIdentifier: CustomCellIdentifier]; if (cell == nil) { NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"listCustomCell" owner:self options:nil]; for (id oneObject in nib) if ([oneObject isKindOfClass:[listCustomCell class]]) cell = (listCustomCell *)oneObject; } cell.backgroundColor = [UIColor clearColor]; UIImageView *backgroundImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"list_selected.png"]]; //[cell setBackgroundView:backgroundImageView]; cell.backgroundView = backgroundImageView; The image won't show up in the background of the cell. All I see is plain white background. Thanks for help.

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• Very slow Eclipse 4.2, how to make it more responsive?

  - by Laurent

  I'm using Eclipse PDT on a rather large PHP project and the IDE is almost unusable. It takes nearly 30 seconds to open a file, and other actions, like selecting a folder in the file explorer, editing some text, etc. are equally slow. I followed various instructions to speed it up but nothing seems to work. This is my current eclipse.ini file. Any idea how I can improve it? -startup plugins/org.eclipse.equinox.launcher_1.3.0.v20120522-1813.jar --launcher.library plugins/org.eclipse.equinox.launcher.win32.win32.x86_1.1.200.v20120522-1813 -showsplash org.eclipse.platform --launcher.XXMaxPermSize 256m --launcher.defaultAction openFile -vmargs -server -Dosgi.requiredJavaVersion=1.7 -Xmn128m -Xms1024m -Xmx1024m -Xss2m -XX:PermSize=128m -XX:MaxPermSize=128m -XX:+UseParallelGC System: Eclipse 4.2.0, Windows 7, 4 GB RAM

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• Twitter - Get users live tweets on my website instantly

  - by Gublooo

  Hello guys, I was checking out the stocktwits.com website. While signing up I provided them with my twitter username. Now whenever I tweet and if my tweet contains $ and a stock ticker symbol - it instantly appears on Stocktwits.com I am interested in implementing something similar in my website. Just wanted an understanding of how this would work. This is how I'm assuming it would work at a high level: 1) On my website - require users to provide their twitter usernames 2) Run a cron job every few minutes to pull the latest tweets for each of the usernames provided using something like http://twitter.com/statuses/user_timeline/username.xml I've tried Stocktwits and they updates are almost instantaneous - so it does not appear like they are checking for updates every few minutes. What are the best ways to implement this solution Thanks

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• Choosing a plotting library for web/browser application

  - by Goro

  Hello, I am looking for a plotting/graphing library (mostly to do line plots) for my application. I have been looking at JavaScript APIs (like Google's) but I found them to be slowing down things at client side (I am plotting a quite large number of points). I also found that with client-side libraries, the performance was quite varied depending on the user's computer. With moving to a server-side library I would cut down on this variance, and would have more control over data flow (my data is in a MySQL database). I have then looked at some PHP-based plotting libraries, but a lot of them seem to be "forgotten" (no new version for years). I have been eying pChart, but it has not had an update in almost two years. First, what would you recommend: server-side or client-side approach? Second, what library would you recommend. Paid libraries are definitely an option, as I don't mind paying for quality software that would cut down on my development time. Thanks,

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• How to deal with presence or not of xml namespaces using xslt.

  - by Mycol

  I have some XML/TEI documents, and i'm writing an XSLT 2.0 to extract their content. Almost all TEI documents has no namespace, but one has the default namespace (xmlns="http://www.tei-c.org/ns/1.0"). So all documents has the same aspect, with unqulified tags like <TEI> or <teiHeader>, but if I try to extract the content, all works with "non-namespaced-documents", but nothing (of course) is extracted from the namespaced-document. So i used the attribute xpath-default-namespace="http://www.tei-c.org/ns/1.0" and now (of course) the only document working is the namespaced one. I can't edit documents at all, so what I'm asking is if there's a way to change dynamically the xpath-default-namespace in order to make work xpaths like //teiHeader both with namespaced and non-namespaced documents

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• DB Design Question

  - by hazimdikenli

  I am designing an Org Chart, model is almost ready and simplified a bit for clarity here. OrgUnit (OrgUnitId, Name, ReportsToOrgUnitId, ...) OrgUnitJobs (OrgUnitJobId, OrgUnitId, JobName, ReportsToOrgUnitJobId, ... ,IsJobGroup) Employee (EmployeeId, ........) OrgUnitJobEmployee (OrgUnitJobId, EmployeeId, AssignedDate, .....,) so I want to know every OrgUnit's ManagerEmployee (should have one), and Employees can have more than one job, but one of them has to be the main job, so I know whats his manager and other stuff. This is going to support a little workflow behind the scnese, so that is why it is not a very simple Org chart Model. so what would you do, would you add properties like (IsManager property to OrgUnitJobs model) or add ManagerOrgUnitJobId to OrgUnitModel. and why? Likewise, for employees would you add IsPrimaryJob property to OrgUnitJobEmployee model, or add PrimaryJobId to Employee Model.

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• Using * in SELECT Query

  - by libregeek

  I am currently porting an application written in MySQL3 and PHP4 to MySQL5 and PHP5. On analysis I found several SQL queries which uses "select * from tablename" even if only one column(field) is processed in PHP. The table has almost 60 columns and it has a primary key. In most cases, the only column used is id which is the primary key. Will there be any performance boost if I use queries in which the column names are explicitly mentioned instead of * ? (In this application there is only one method which we need all the columns and all other methods return only a subset of the columns)

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• Stack trace in website project, when debug = false

  - by chandmk

  We have a website project. We are logging unhanded exceptions via a appdomain level exception handler. When we set debug= true in web.config, the exception log is showing the offending line numbers in the stack trace. But when we set debug = false, in web.config, log is not displaying the line numbers. We are not in a position to convert the website project in to webapplication project type at this time. Its legacy application and almost all the code is in aspx pages. We also need to leave the project in 'updatable' mode. i.e. We can't user pre-compile option. We are generating pdb files. Is there anyway to tell this kind of website projects to generate the pdb files, and show the line numbers in the stack trace?

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