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• Staggering java linux process startup to prevent OOM

  - by ctennis

  I am running a number of java processes on a single Linux machine. From a memory and computing standpoint, everything is fine when things are static. However, periodically we use a configuration management package up upgrade the jar or war files, and restart the java process. The problem is, that is restarts them all relatively quickly, and so we get 10 or so java VMs restarting all at the same time (we use daemontools for the service stops/starts), which wreaks havoc on the machine, in terms of OOMs or just really slow. This is because it's spawning the JVM 10x at the same time. Other than trying to stagger the startups, is there a smarter way of handling this? Maybe a sysctl tuning performance parameters, or a JVM parameter?

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• What are performance limits of a database?

  - by Tommy

  What are some rough performance limits (read/s, write/s) for a single database server (no master-slave architecture), assuming storage on disk? How many read/s, write/s, depending on the kind of disk? (SSD vs non-SSD) , assuming simple operations (select one row by primary key, update one row, correctly indexed). I assume this limit is dependent on disk seek/write. EDIT: My question is more about getting rough metrics of the number of operations a database supports: to be able to know for example, if a new feature triggering 300 inserts/s can be supported without scaling out with additional servers.

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• Connecting a USB laptop to a RJ45 serial port

  - by Jon

  We are about to get our first managed switch at work (Procurve 2520G-24-PoE), and this lowly programmer gets to put on his admin hat and try to configure it. The switch has an RJ45 serial port for console access. My laptop has USB ports but no serial port. In fact, there isn't a single computer in the office with a serial port. I've seen USB-to-DB9 adapters, but I need to go from USB to RJ45 (serial). How would I go about accomplishing this? Do I need two adapters? Will USB-to-DB9 and then DB9-to-RJ45 work? Thanks in advance.

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• How to make a vm scale when demand for resource increases

  - by Cray XT3

  i am having a server with 16 virtual core and 24G RAM,using Xen virtualization and ubuntu as dom0 Created 4 VMs (in para mode),each with different applications. CPU Load vary on each vm,somtimes first vm reaches nearly 100% CPU and others under 25% or even less. So is there a way in which vm can get cpu from other vms when they are not actually using it or utilization is under 25%.Same in the case of RAM also. I am not sure whether i am mentioning Cloud here. Initially i would like to give every vm a single VCPU,but can scale up to 8 or more by taking cpu from other vms if they are not using it. Is there any kind of tool that makes vm to scale its resources when demand increases. Is cloudstack and openstack designed for these kind of purpose or is that just a GUI to manage VMs.

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• One-Way Backup Service? [closed]

  - by Jon Rodriguez

  Up until a month ago, my girlfriend has used MobileMe to backup all the files on her MacBook. This turned out terribly when a quirk of MobileMe caused it to erase all of her files on MobileMe, and then sync the newly-erased MobileMe down to her computer, erasing everything. A week's worth of college essays and CS homework were gone. Now, I am terrified of any commercial cloud-backup solutions because of the possibility of this happening. Going off the list provided in these answers, could you please help me find a good backup service that is completely one-way? I want a service where there is literally not a single line of code that has the possibility of writing to my computer's drive. I want a pure one-way backup service.

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• capture nimbuzz traffic

  - by lurscher

  I need to capture all the traffic, specially during login, between nimbuzz pc client and nimbuzz server. The reason is that i need to debug outgoing packets at login that mark the user visibility status in order to reproduce them in a in-house XMPP client application I've tried doing this with wireshark, but i seem to be pretty helpless with this tool. Also, the packets i've been able to see are all before the SASL negotiation happens, after that, i cannot see the xml packets being exchanged any help for how to achieve this task is greatly appreciated (preferably on Windows, since there is no nimbuzz client for linux, in any case i can install one in a VM and monitor the traffic between the VM instance in the linux host)

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• nfs server on cygwin slow

  - by Weltenwanderer

  The setup: We run an instance of cygwin nfsd on a Windows 2008 Server (Xeon 3,2 GHz). There are several Sun Solaris and SunOS machines accessing the shares. This is the exports file: /disk3 (rw,all_squash) /disk2 (rw,all_squash) Those paths are soft linked to the relevant cygdrive/d/path/to/dir paths. Some of the folders contain up to 10k files. The Problem: ls -la on the mounted folder on the sun boxes takes 2 - 3 minutes and the general read performance is really bad. cat filename displays the file in slow bursts and this hurts performance on tasks that access those shared files heavily. Processor load is not the issue, the nfs server idles most of the time, the cygwin tasks never get over 1% load.

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• How do I backup my customer's data?

  - by marcamillion

  If you run a SaaS app, or work on one, I would love to hear from you. Where the safety and security of your customer's data is paramount, how do you secure it and back it up? I would love to know your main host (e.g. Heroku, Engine Yard, Rackspace, MediaTemple, etc.) and who you use for your backup. Be as detailed as possible - e.g. a quick overview of your service and the data you store (images for instance), what happens with the images when the user uploads them (e.g. they go to your Linode VPS, and posted to the site for them to see - then they are automatically sent to AWS or wherever, then once a week they are backed up to tape by the managed hosting provider, and you also back them up to your house/office). If you could also give some idea as to what the unit cost (per GB/per user/per month) of storage is - on average, I would really appreciate that. Getting ready to launch my app, and I would love to get some more perspective on the nitty gritty details involved. Thanks!

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• What technical test should I give to a job candidate

  - by Romain Braun

  I'm not sure if this is the right stackexhange website, but : I have three candidates coming in tomorrow. One has 15 years of experience in PHP, and the two others have about 1 year of experience in PHP/ frontend development. For the last ones I was thinking about a test where they would have to develop a web app allowing users to manage other users, as in : Display a list of users, display a single user, modify an user, and add extended properties to an user. This way it would feature html, css, js, ajax, php and SQL. Do you think this would be a good test? What test should I give to the first one? He needs something much more difficult, I guess. I'm also listening, if you have any advice/ideas about what makes a good developer, and what I should pay attention to in the guys' codes. I was also considering thinking outside of the box, more algorithm-related, and asked him to make the fastest function to tell if a number is a prime number, because there are a lot of optimizations you can apply to such a function. They have one day to do it.

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• Open Source Visualization and Dashboard Software

  - by helios

  I am working on an open source Application Performance Monitoring (APM) software and looking for a visualization tool with dashboard capabilities. I came across Graphite which looks pretty good but wondering if there is anything better out there before I settle down with that tool. Here's the list of features I am interested in: Must-Have Open Source license API to submit real time data Web-based visualization interface Persistence - file or database Nice-To-Have Dashboard Capabilities: Allow users to select a few metrics (CPU, Heap Usage, # of Active Users etc.) and place them on a single page for easier monitoring. Any suggestions?

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• How can I remove the DRM from books I have purchased for my Kindle? [closed]

  - by Jeremy Banks

  How can I the remove DRM from books I have purchased for my Kindle? A solution that works on Mac OS X and/or Linux would be ideal, but a Windows-only solution is also acceptable. Moral aside: I do not plan to share or pirate books; I am very happy with the Amazon Kindle store and have purchased more books from there since getting my Kindle a month ago than I had in the previous two years. However, I do not feel comfortable keeping them in an encrypted format that only a single company's software will allow me to access. I may also want to convert them into a format for other readers in the future, which is not possible without first removing the DRM.

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• script Disk Management configuration

  - by Joseph

  I have 10 workstations with large monitors that have USB slots and several card readers built in. The card readers cannot be disabled and will map to drive letters when I image the computers. I go into Disk Management and delete the drive mappings and add mappings to a single folder in C:\ with a folder for each slot. I have to do this because of scripts that run that are expecting specific letter drive mappings to network resources. Is there a way to script the deleting and adding of drive mappings instead of having to use the Disk Management GUI manually on each workstation? The workstations are running XP Professional.

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• Mac sees mangled filenames from Linux SAMBA share

  - by me2

  Certain filenames in my SAMBA shares from Linux are not getting transmitted properly. It's certain files in certain folders and it doesn't affect all folders or all files within a single folder. I can find no discerning pattern to the mangling but hoping that this is a known problem. No amount of reboot, restart, etc. will fix this problem. The filenames, when they get mangled, all end up in this form: 0JY4B3~H.M4V 0MBS1O~M.M4V 0NKDX9~R.M4V 0O0ZTA~A.M4V These are MPEG4 files. The extension remains intact. Any ideas?

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• What's the best way to manage error logging for exceptions?

  - by Peter Boughton

  Introduction If an error occurs on a website or system, it is of course useful to log it, and show the user a polite message with a reference code for the error. And if you have lots of systems, you don't want this information dotted around - it is good to have a single centralised place for it. At the simplest level, all that's needed is an incrementing id and a serialized dump of the error details. (And possibly the "centralised place" being an email inbox.) At the other end of the spectrum is perhaps a fully normalised database that also allows you to press a button and see a graph of errors per day, or identifying what the most common type of error on system X is, whether server A has more database connection errors than server B, and so on. What I'm referring to here is logging code-level errors/exceptions by a remote system - not "human-based" issue tracking, such as done with Jira,Trac,etc. Questions I'm looking for thoughts from developers who have used this type of system, specifically with regards to: What are essential features you couldn't do without? What are good to have features that really save you time? What features might seem a good idea, but aren't actually that useful? For example, I'd say a "show duplicates" function that identifies multiple occurrence of an error (without worrying about 'unimportant' details that might differ) is pretty essential. A button to "create an issue in [Jira/etc] for this error" sounds like a good time-saver. Just to re-iterate, what I'm after is practical experiences from people that have used such systems, preferably backed-up with why a feature is awesome/terrible. (If you're going to theorise anyway, at the very least mark your answer as such.)

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• Apache does not serve non-locally

  - by yodaj007

  I have a freshly installed instance of Fedora Core 16 inside VirtualBox using bridged networking. On it, as root I typed in: yum -y install httpd service httpd start ifconfig Inside the VM, I can open a web browser to 'localhost' and I get the Apache test page. It works. But in Windows (the machine hosting the VM), I point my browser to the IP address returned by ifconfig (192.168.2.122). The connection times out. I can go to a command prompt and ping the VM. Is there a firewall or something that comes with Fedora by default? Or is there something I need to change in a config file?

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• Why do Cisco IOS routers hang in the middle of large downloads?

  - by cjavapro

  After a few years in use. We have seen Cisco 871 and 851 routers that would hang if you had a single download that was more than 100M large. It is intermittent. Sometimes the problem goes away, sometimes it happens on very small downloads (just a 10KB web page). It seems that the just about all the downloads eventually finish, but the bigger the download the longer the hang. Is there a way to resolve this? (short of router replacement which is what we have been doing)

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• a load balancing scenario using HAProxy and keepalived shows no performance advantage

  - by chakoshi

  Hi, I am trying to setup a load balanced web server scenario, using two HAproxy load balancers and two debian web servers following this guide http://www.howtoforge.com/setting-up-a-high-availability-load-balancer-with-haproxy-keepalived-on-debian-lenny. the setup is working but the results of simple performance benchmarking is not what I expected. I tried apache benchmark tool to send lots of requests to servers (one time directly testing one of the web servers and the other time testing through the load balancer) using the command "ab -n 1000000 -c 500 http://IP/index.html", but the test results shows better performance for the single server without load balancer. can any one tell me if I'm going wrong on some thing?

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• Rename outlook2007 categories not working

  - by Bob Rivers

  Hi, I'm new to outlook 2007 and I'm trying to rename a category. Acordingly to MS, I can achieve it by just renaming it: http://office.microsoft.com/en-us/outlook/HA012316361033.aspx But as soon as I click the OK button, confirming the change, it returns to it's original value. For instance, if I rename the "Blue Category" to "Home" it will accept without erros. But, when I click again in the Categorize icon, I'll see that the "Blue Category" is still there, and my "Home" category does not exist. Has someone experienced this kind of problem? TIA, Bob

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• Configuring BitLocker on existing Windows Server 2008

  - by neildeadman

  On our file server, we want to enable BitLocker so that we can encrypt a single drive and I know that we have to also encrypt the drive the system is installed on. In my tests with VMs, I have to create a partition on the same disk as Windows is installed either before I install Windows or after (I can use the BitLocker Drive Preparation Tool). This tool shrinks the C: drive to make way for a 1.5GB partition. I'm a little concerned about doing this with a live system so wanted to see if it was possible to get BitLocker to use a partition on another drive?

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• Make sniqt recognize all tray abilities (or create a working indicator in Qt)

  - by hakermania

  There is this old thread of mine: How do I create a working indicator with Qt/C++? where I was suggested to use the QSystemTray library for making a tray icon in Ubuntu for my application. Sniqt is a program that takes care of the rest. As known, Ubuntu has got rid of tray icons. Instead, it now uses indicators and only indicators. Sniqt converts the Qt tray icons into working indicators. The problem is that it doesn't do a very decent convertion. Actions like single click, middle click etc do not work, while they do in systems that support tray icons. Is there a way to have these actions back? Can I use QSystemTray icon and still have these interesting (and very helpful, in my occasion) actions in Ubuntu? I would be glad to know the answer to the other thread I talked about earlier (how to make a working indicator using the GTK libraries and prevent the crash), as well. Link for Sniqt bug: https://bugs.launchpad.net/sni-qt/+bug/1027652

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• Are the only types of data "sources" static and dynamic?

  - by blunders

  Thinking that there might be others, but not sure -- but before getting into that, let me explain what I mean by static and dynamic data sources. Static (or datastore) - Meaning that the data's state is non-changing, and if was changed, that would be a new state, and the old data would be considered stateless; meaning it no longer is known to exist, or not exist. Another way of possibly looking at a static data source might be that if read and written back without modification, the checksum for before and after should be exactly the same regardless of the duration of time between the reading and rewriting of the data. Examples: Photos, Files, Database Record, Dynamic (or datastream) - Meaning that the data's state is known to be in flux, and never expected to be the same per input. Example: Live video/audio feed, Stock Market feed, First let me say, the above is a very loose mapping of the concepts, and I'd welcome any feedback. Next, onto the core of the question, that being are these the only two types of data sources. My guess, is that yes, they are -- but that there are hybrid versions of the two. That being, streaming data that has a fixed state. For example, the data being streamed has a checksum given and each unique checksum is known to be a single instance of static data. On the flip side, static data could be chained via say a version control system; when played back, each version might be viewed as a segment of a stream; thing is, the very fact that it can be played back makes the data source static. Another type might be that the data source is being organically discovered, and it's simply unknown what the state is. Questions, feedback, requests -- just comment, thanks!!

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• Is it possible to add hardware on a remote machine and use it as if it was installed on the local machine?

  - by that0th3rGuy

  Probably a silly question. We have two computers in the apartment running Windows 7 and Windows Vista. 99% of the time we use headphones but every now and then we have a desire for some ambiance so we got a set of 2.1 speakers. But now only one of us has access to the speakers unless we move them around every now and then. So I was wondering if it's possible to add the other computer's sound card as a hardware device on my computer so that I can configure, for instance, Winamp to play through the other computer's sound card, hence the speakers connected to the other computer.

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• Approach to retrieve files from server

  - by Aerus

  I'm in the process of making a Java application with a corresponding update application. At any given time the user may want to update the application and the updater will ask for a list of files of the latest release. Based on this list, the updater can determine which files need to be downloaded to complete the update. I now have 2 approaches to solve this, but i would like to know what approach will put the least stress on my application and server. I could send a list of files i want to download to my server and the server zips the files and simply returns this compressed file to the application. The updater sents a request for each seperate file to the server, which simply returns the file The application will be used mainly in Belgium and The Netherlands and connections/bandwidth tend to be pretty decent in here. The average size of a single file should be around 100Kb and at most 1Mb. I expect an update to have anywhere between 10 to 50 new files. I expect at most 100 persons/day to update the application, i.e. in the week when a new version is released. I hope this is enough information to sketch my problem and any advice is welcome. If there is another common way to tackle this, i'd be glad to hear it.

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• How to create multiple OS on same DVD [duplicate]

  - by learner

  This question already has an answer here: How to make a multiboot CD that will start a user-chosen ISO file 7 answers I searched this forum but there are only general answers which doesn't give me desired output. Here is what I want to do. I have (1). Windows 7 ISO (2). Windows 8.1 previews ISO and (3). Ubuntu 12.10 ISO files. Using which I want to create single bootable DVD, so that after creating DVD it should ask to choose to install between 3 OS. Is it possible? If so please help me.

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• Canonical representation of a class object containing a list element in XML

  - by dendini

  I see that most implementations of JAX-RS represent a class object containing a list of elements as follows (assume a class House containing a list of People) <houses> <house> <person> <name>Adam</name> </person> <person> <name>Blake</name> </person> </house> <house> </house> </houses> The result above is obtained for instance from Jersey 2 JAX-RS implementation, notice Jersey creates a wrapper class "houses" around each house, however strangely it doesn't create a wrapper class around each person! I don't feel this is a correct mapping of a list, in other words I'd feel more confortable with something like this: <houses> <house> <persons> <person> <name>Adam</name> </person> <person> <name>Blake</name> </person> </persons> </house> <house> </house> </houses> Is there any document explaining how an object should be correctly mapped apart from any opninion?

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