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• Cloud Based Load Testing Using TF Service &amp; VS 2013

  - by Tarun Arora [Microsoft MVP]

  Originally posted on: http://geekswithblogs.net/TarunArora/archive/2013/06/30/cloud-based-load-testing-using-tf-service-amp-vs-2013.aspx One of the new features announced as part of the Visual Studio 2013 Ultimate Preview is ‘Cloud Based Load Testing’. In this blog post I’ll walk you through, What is Cloud Based Load Testing? How have I been using this feature? – Success story! Where can you find more resources on this feature? What is Cloud Based Load Testing? It goes without saying that performance testing your application not only gives you the confidence that the application will work under heavy levels of stress but also gives you the ability to test how scalable the architecture of your application is. It is important to know how much is too much for your application! Working with various clients in the industry I have realized that the biggest barriers in Load Testing & Performance Testing adoption are, High infrastructure and administration cost that comes with this phase of testing Time taken to procure & set up the test infrastructure Finding use for this infrastructure investment after completion of testing Is cloud the answer? 100% Visual Studio Compatible Scalable and Realistic Start testing in < 2 minutes Intuitive Pay only for what you need Use existing on premise tests on cloud There are a lot of vendors out there offering Cloud Based Load Testing, to name a few, Load Storm Soasta Blaze Meter Blitz And others… The question you may want to ask is, why should you go with Microsoft’s Cloud based Load Test offering. If you are a Microsoft shop or already have investments in Microsoft technologies, you’ll see great benefit in the natural integration this offers with existing Microsoft products such as Visual Studio and Windows Azure. For example, your existing Web tests authored in Visual Studio 2010 or Visual Studio 2012 will run on the cloud without requiring any modifications what so ever. Microsoft’s cloud test rig also supports API based testing, for example, if you are building a WPF application which consumes WCF services, you can write unit tests to invoke the WCF service, these tests can be run on the cloud test rig and loaded with ‘N’ concurrent users for performance testing. If you have your assets already hosted in the Azure and possibly in the same data centre as the Cloud test rig, your Azure app will not incur a usage cost because of the generated traffic since the traffic is coming from the same data centre. The licensing or pricing information on Microsoft’s cloud based Load test service is yet to be announced, but I would expect this to be priced attractively to match the market competition.   The only additional configuration required for running load tests on Microsoft Cloud based Load Tests service is to select the Test run location as Run tests using Visual Studio Team Foundation Service, How have I been using Microsoft’s Cloud based Load Test Service? I have been part of the Microsoft Cloud Based Load Test Service advisory council for the last 7 months. This gave the opportunity to see the product shape up from concept to working solution. I was also the first person outside of Microsoft to try this offering out. This gave me the opportunity to test real world application at various clients using the Microsoft Load Test Service and provide real world feedback to the Microsoft product team. One of the most recent systems I tested using the Load Test Service has been an insurance quote generation engine. This insurance quote generation engine is,   hosted in Windows Azure expected to get quote requests from across the globe expected to handle 5 Million quote requests in a day (not clear how this load will be distributed across the day) There was no way, I could simulate such kind of load from on premise without standing up additional hardware. But Microsoft’s Cloud based Load Test service allowed me to test my key performance testing scenarios, i.e. Simulate expected Load, Endurance Testing, Threshold Testing and Testing for Latency. Simulating expected load: approach to devising a load pattern My approach to devising a load test pattern has been to run the test scenario with 1 user to figure out the response time. Then work out how many users are required to reach the target load. So, for example, to invoke 1 quote from the quote engine software takes 0.5 seconds. Now if you do the math,   1 quote request by 1 user = 0.5 seconds   quotes generated by 1 user in 24 hour = 1 * (((2 * 60) * 60) * 24) = 172,800   quotes generated by 30 users in 24 hours = 172,800 * 30 =  5,184,000 This was a very simple example, if your application requires more concurrent users to test scenario’s such as caching, etc then you can devise your own load pattern, some examples of load test patterns can be found here.  Endurance Testing To test for endurance, I loaded the quote generation engine with an expected fixed user load and ran the test for very long duration such as over 48 hours and observed the affect of the long running test on the Azure infrastructure. Currently Microsoft Load Test service does not support metrics from the machine under test. I used Azure diagnostics to begin with, but later started using Cerebrata Azure Diagnostics Manager to capture the metrics of the machine under test. Threshold Testing To figure out how much user load the application could cope with before falling on its belly, I opted to step load the quote generation engine by incrementing user load with different variations of incremental user load per minute till the application crashed out and forced an IIS reset. Testing for Latency Currently the Microsoft Load Test service does not support generating geographically distributed load, I however, deployed the insurance quote generation engine in different Azure data centres and ran the same set of performance tests to measure for latency. Because I could compare load test results from different runs by exporting the results to excel (this feature is provided out of the box right from Visual Studio 2010) I could see the different in response times. More resources on Microsoft Cloud based Load Test Service A few important links to get you started, Download Visual Studio Ultimate 2013 Preview Getting started guide for load testing using Team Foundation Service Troubleshooting guide for FAQs and known issues Team Foundation Service forum for questions and support Detailed demo and presentation (link to Tech-Ed session recording) Detailed demo and presentation (link to Build session recording) There a few limits on the usage of Microsoft Cloud based Load Test service that you can read about here. If you have any feedback on Microsoft Cloud based Load Test service, feel free to share it with the product team via the Visual Studio User Voice forum. I hope you found this useful. Thank you for taking the time out and reading this blog post. If you enjoyed the post, remember to subscribe to http://feeds.feedburner.com/TarunArora. Stay tuned!

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• General monitoring for SQL Server Analysis Services using Performance Monitor

  - by Testas

  A recent customer engagement required a setup of a monitoring solution for SSAS, due to the time restrictions placed upon this, native Windows Performance Monitor (Perfmon) and SQL Server Profiler Monitoring Tools was used as using a third party tool would have meant the customer providing an additional monitoring server that was not available.I wanted to outline the performance monitoring counters that was used to monitor the system on which SSAS was running. Due to the slow query performance that was occurring during certain scenarios, perfmon was used to establish if any pressure was being placed on the Disk, CPU or Memory subsystem when concurrent connections access the same query, and Profiler to pinpoint how the query was being managed within SSAS, profiler I will leave for another blogThis guide is not designed to provide a definitive list of what should be used when monitoring SSAS, different situations may require the addition or removal of counters as presented by the situation. However I hope that it serves as a good basis for starting your monitoring of SSAS. I would also like to acknowledge Chris Webb’s awesome chapters from “Expert Cube Development” that also helped shape my monitoring strategy:http://cwebbbi.spaces.live.com/blog/cns!7B84B0F2C239489A!6657.entrySimulating ConnectionsTo simulate the additional connections to the SSAS server whilst monitoring, I used ascmd to simulate multiple connections to the typical and worse performing queries that were identified by the customer. A similar sript can be downloaded from codeplex at http://www.codeplex.com/SQLSrvAnalysisSrvcs.     File name: ASCMD_StressTestingScripts.zip. Performance MonitorWithin performance monitor,  a counter log was created that contained the list of counters below. The important point to note when running the counter log is that the RUN AS property within the counter log properties should be changed to an account that has rights to the SSAS instance when monitoring MSAS counters. Failure to do so means that the counter log runs under the system account, no errors or warning are given while running the counter log, and it is not until you need to view the MSAS counters that they will not be displayed if run under the default account that has no right to SSAS. If your connection simulation takes hours, this could prove quite frustrating if not done beforehand JThe counters used……  Object Counter Instance Justification System Processor Queue legnth N/A Indicates how many threads are waiting for execution against the processor. If this counter is consistently higher than around 5 when processor utilization approaches 100%, then this is a good indication that there is more work (active threads) available (ready for execution) than the machine's processors are able to handle. System Context Switches/sec N/A Measures how frequently the processor has to switch from user- to kernel-mode to handle a request from a thread running in user mode. The heavier the workload running on your machine, the higher this counter will generally be, but over long term the value of this counter should remain fairly constant. If this counter suddenly starts increasing however, it may be an indicating of a malfunctioning device, especially if the Processor\Interrupts/sec\(_Total) counter on your machine shows a similar unexplained increase Process % Processor Time sqlservr Definately should be used if Processor\% Processor Time\(_Total) is maxing at 100% to assess the effect of the SQL Server process on the processor Process % Processor Time msmdsrv Definately should be used if Processor\% Processor Time\(_Total) is maxing at 100% to assess the effect of the SQL Server process on the processor Process Working Set sqlservr If the Memory\Available bytes counter is decreaing this counter can be run to indicate if the process is consuming larger and larger amounts of RAM. Process(instance)\Working Set measures the size of the working set for each process, which indicates the number of allocated pages the process can address without generating a page fault. Process Working Set msmdsrv If the Memory\Available bytes counter is decreaing this counter can be run to indicate if the process is consuming larger and larger amounts of RAM. Process(instance)\Working Set measures the size of the working set for each process, which indicates the number of allocated pages the process can address without generating a page fault. Processor % Processor Time _Total and individual cores measures the total utilization of your processor by all running processes. If multi-proc then be mindful only an average is provided Processor % Privileged Time _Total To see how the OS is handling basic IO requests. If kernel mode utilization is high, your machine is likely underpowered as it's too busy handling basic OS housekeeping functions to be able to effectively run other applications. Processor % User Time _Total To see how the applications is interacting from a processor perspective, a high percentage utilisation determine that the server is dealing with too many apps and may require increasing thje hardware or scaling out Processor Interrupts/sec _Total  The average rate, in incidents per second, at which the processor received and serviced hardware interrupts. Shoulr be consistant over time but a sudden unexplained increase could indicate a device malfunction which can be confirmed using the System\Context Switches/sec counter Memory Pages/sec N/A Indicates the rate at which pages are read from or written to disk to resolve hard page faults. This counter is a primary indicator of the kinds of faults that cause system-wide delays, this is the primary counter to watch for indication of possible insufficient RAM to meet your server's needs. A good idea here is to configure a perfmon alert that triggers when the number of pages per second exceeds 50 per paging disk on your system. May also want to see the configuration of the page file on the Server Memory Available Mbytes N/A is the amount of physical memory, in bytes, available to processes running on the computer. if this counter is greater than 10% of the actual RAM in your machine then you probably have more than enough RAM. monitor it regularly to see if any downward trend develops, and set an alert to trigger if it drops below 2% of the installed RAM. Physical Disk Disk Transfers/sec for each physical disk If it goes above 10 disk I/Os per second then you've got poor response time for your disk. Physical Disk Idle Time _total If Disk Transfers/sec is above  25 disk I/Os per second use this counter. which measures the percent time that your hard disk is idle during the measurement interval, and if you see this counter fall below 20% then you've likely got read/write requests queuing up for your disk which is unable to service these requests in a timely fashion. Physical Disk Disk queue legnth For the OLAP and SQL physical disk A value that is consistently less than 2 means that the disk system is handling the IO requests against the physical disk Network Interface Bytes Total/sec For the NIC Should be monitored over a period of time to see if there is anb increase/decrease in network utilisation Network Interface Current Bandwidth For the NIC is an estimate of the current bandwidth of the network interface in bits per second (BPS). MSAS 2005: Memory Memory Limit High KB N/A Shows (as a percentage) the high memory limit configured for SSAS in C:\Program Files\Microsoft SQL Server\MSAS10.MSSQLSERVER\OLAP\Config\msmdsrv.ini MSAS 2005: Memory Memory Limit Low KB N/A Shows (as a percentage) the low memory limit configured for SSAS in C:\Program Files\Microsoft SQL Server\MSAS10.MSSQLSERVER\OLAP\Config\msmdsrv.ini MSAS 2005: Memory Memory Usage KB N/A Displays the memory usage of the server process. MSAS 2005: Memory File Store KB N/A Displays the amount of memory that is reserved for the Cache. Note if total memory limit in the msmdsrv.ini is set to 0, no memory is reserved for the cache MSAS 2005: Storage Engine Query Queries from Cache Direct / sec N/A Displays the rate of queries answered from the cache directly MSAS 2005: Storage Engine Query Queries from Cache Filtered / Sec N/A Displays the Rate of queries answered by filtering existing cache entry. MSAS 2005: Storage Engine Query Queries from File / Sec N/A Displays the Rate of queries answered from files. MSAS 2005: Storage Engine Query Average time /query N/A Displays the average time of a query MSAS 2005: Connection Current connections N/A Displays the number of connections against the SSAS instance MSAS 2005: Connection Requests / sec N/A Displays the rate of query requests per second MSAS 2005: Locks Current Lock Waits N/A Displays thhe number of connections waiting on a lock MSAS 2005: Threads Query Pool job queue Length N/A The number of queries in the job queue MSAS 2005:Proc Aggregations Temp file bytes written/sec N/A Shows the number of bytes of data processed in a temporary file MSAS 2005:Proc Aggregations Temp file rows written/sec N/A Shows the number of bytes of data processed in a temporary file 

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• Logs show failed password for invalid user root from <IP Address> port 2924 ssh2

  - by Chris Hanson

  I'm getting a constant flow of these messages in my logs. The port is variable (seemingly between 1024 and 65535). I can simulate it myself by running sftp root@<my ip> I've commented out the sftp subsystem line in my sshd_config. These ports should be closed by provider's firewall. I don't understand: Why sftp would be selecting a random port like that. It seems to be behaving like FTP in passive mode, but I can't make any sense of why that would be. Why it can even hit my server in the first place if these ports are closed.

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• Dichroic Glass in Blender

  - by KalAurum

  I am trying to use blender to simulate the Lycurgus Cup. The cup is an example of dichroic (two-color) glass, and appears green when a light source is on the outside of the cup, and appears red when a light source is inside the cup. Here is an image of when light is outside and it appears green: Here is an image of when light is inside and it appears red: I have created a glass cup in blender. I have made the glass a red color, and then used the colorbands under the Object-Material/Shading-Ramps tab to add green specular and diffuse color. However, this makes the glass appear the same mix of red and green whether I put the light source on the inside or outside the cup. An example can be seen here: According to the second post here, someone was able to to fake the effect of a dichroic glass in blender rather easily through the use of a magic procedural texture but they provide no clues on how to do this (in blender). Does anyone know how to achieve this effect in blender?

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• How to create a shared lock blocking an intent exclusive lock

  - by FremenFreedom

  As I understand it, a SELECT statement will place a shared lock on the rows that it will return. While that SELECT is running, if an UPDATE statement comes along and needs to grab an intent exclusive lock then that UPDATE statement will need to wait until the SELECT statement releases its shared locks. I am trying to test this SELECT shared lock thing by doing a BEGIN TRAN and then running a SELECT, not COMMITing, and then running an UPDATE in another session on the exact same row. The UPDATE worked fine -- no lock, no wait. So this must not be a valid way to simulate a shared lock blocking an intent exclusive lock? Can you give me a scenario where I can create a lock with a SELECT that would force an UPDATE to wait? I'm working with SQL Server 2000 and 2005 across a linked server: the table is on the 2005 instance, the select is happening on 2000, and the update is executed from 2005. All in SSMS 2005.

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• Best Linux distro for load-balancers?

  - by Vimvq1987

  I wanted to try HAProxy/Linux Virtual Server like front-end load-balancers, but as far I know, they're Linux-based software. I don't have any experiences with Linux yet. so there're quite many questions to ask: What is the best Linux distro(s) for load-balancing? I plan to use VirtualPC to run some virtual machines. How much RAM is the best for each machine run that distro? I want to simulate a load-balancer with can handle about 100 hits/second, is it possible? Thank you very much!

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• Red Hat cluster: Failure of one of two services sharing the same virtual IP tears down IP

  - by js01

  I'm creating a 2+1 failover cluster under Red Hat 5.5 with 4 services of which 2 have to run on the same node, sharing the same virtual IP address. One of the services on each node needs a (SAN) disk, the other doesn't. I'm using HA-LVM. When I shut down (via ifdown) the two interfaces connected to the SAN to simulate SAN failure, the service needing the disk is disabled, the other keeps running, as expected. Surprisingly (and unfortunately), the virtual IP address shared by the two services on the same machine is also removed, rendering the still-running service useless. How can I configure the cluster to keep the IP address up?

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• How to test TempDB performance?

  - by Matt Penner

  I'm getting some conflicting advice on how to best configure our SQL storage with our current SAN. I would like to do some of my own performance testing with a few different configurations. I looked at using SQLIOSim but it doesn't seem to simulate TempDB. Can anyone recommend a way to test data, log and TempDB performance? What about using a SQL profiler trace file from our production system? How would I use This to run against my test server? Thanks, Matt

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• Timing issue with autohotscript, fails to dump or open destination file

  - by learnerforever

  I've created a autohotscript to quickly dump selected text into my jot file on the Desktop and I think I'm facing a timing error. The script works like thus: Select text when reading a text file, browsing internet, reading PDF, etc. Hit Ctrl + J Contents of selected text is dumped into my jot file. When I press Ctrl + J very quickly, it sometimes doesn't come up in my jot file and sometimes when I keep pressing Ctrl + J for a long time, many instances of the text appear. Could somebody please point out what's wrong with this script and how I can improve it. ^j:: Clipboard := "" ; clear Send, ^c ; simulate Ctrl+C (=selection in clipboard) selection = %Clipboard% ; save the content of the clipboard FileAppend, `n%selection%`n,C:\Users\jagrati\Desktop\jots.txt return

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• Help me a routing server on Windows XP

  - by Lu Lu

  I am developing client/server applications and need to test them on Internet environment. However, I only have one PC without connecting the public internet, so I have a plan to simulate a virtual internet environment on my PC. I think I will install the virtual machines for my purpose, but I can install only one machine because of my slowly PC. At the moment, my PC has 2 machines: the host machine (use Windows XP) & the virtual machine (use Windows Server 2003 Ent). Each machine will have 2 network adapter (host-only & internal), and in 2 network adapters, the internal adapter is private on each machine, and host-only adapters are connected together. With Windows 2003, routing server is ok, but I wonder on Windows XP, are there any routing server product? Please help me. Thanks.

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• Prepare bootable Mac OS install usb on Windows

  - by Dave

  Hello, Is there any software out there that can simulate Disk Utility (Mac app) for Windows? I need to reinstall leopard on my Mac because I screwed something up on the current OS. The thing is, the DVD drive is broken on there, so I need to prepare a bootable USB drive from my Leopard DMG file. This is easily done with the Disk Utility app on the Mac. But seeing how my cannot even log on to my Mac right now, I don't know how to prepare that USB stick. The only other machine I have is a PC with Windows 7. If anyone has any suggestion, please help me out! Thanks so much!

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• Load balance between two virtual directories on a single machine running IIS6

  - by Emil Lerch

  I'm trying to simulate a production environment using a single VM. The production environment will have 3 servers behind a load balancer with sticky sessions. Production will be using IIS6. For development, I have no need to distribute load, but I want to make sure the team does not write code that relies on a single-server module. I have been hoping to set up two virtual directories and find some isapi filter to perform some rudimentary software load balancing, but I've been unable to locate anything suitable. isapi_rewrite comes close but there's no ability for a random rewrite. I don't even need sticky sessions since the application does not (in theory) rely on them. Is there something easy/free to do this, or am I stuck with multiple VMs and a NLB setup (which seems like total overkill)?

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• dialup connection script

  - by BParker

  I've just started working for a company who produce a specialist modem. In the test department they simulate actual use with a bunch of pc's acting as clients connecting over this modem. As such each needs to dial a set of dial-up connections. Each of these has to be created manually, and currently takes quite a while on each machine, so i was hoping to be able to automate the creation process. Back in the early days of the internet i remember getting CD's from ISP's where the dial-up connection was configured automatically, and i was wondering if anyone lknew how to do this, or if they could point me in the direction of a tutorial about it. To be clear, i don't want to automate actually dialing the connection, but i do want to run a script which creates the icons in the networking applet that allows us to dial these connection. Thanks in advance!!!

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• Changing IP every sec with Firefox

  - by Carol

  I looking for ip changer what is faster than PROXY (i tried Elite Proxy Switcher + Firefox add-on, but it's too slow. I set automatic switching to 4 sec and yes he change the ip every 4 sec however it's not enough because it loads pages very slowly.) Secondly I tried the TOR Project but this is not good..because the TOR would be nice and working good however he needs more than 10 seconds, a new identity and it's not to good for me because i want to change my ip lass than 10 sec. So I find the solution. This is IPfucker alias ipFlood (https://addons.mozilla.org/en-us/firefox.../ipflood/) But it does not work on all sites unfortunately...because this is just simulation "Simulate the use of a series of proxy changing at each new connection.". Anyone knows a solution to the problem? Is there an alternative (VPS, Proxy, TOR)? Thanks in advice.

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• Simulating an UNC path with a leading dot

  - by Uwe Keim

  Being a C# .NET Windows Forms developer, some customers are running our applications on an Apple OS X Mac inside a Parallels virtual machine. Parallels presents host folders to the guest Windows as UNC paths with a leading dot like \\.psf\Home\Some\More\Folders Now an application of us cannot handle the leading dot correctly when accessing files from these kind of shares ("Invalid URI, cannot analyze host name" exception). I want to debug and fix this issue, unfortunately I do have no Mac and Parallels around here to test it. My question is: Is there a way to "simulate" this kind of share on a normal Windows server or client so that I'll be able to debug my application with Visual Studio? What I tried so far: I already tried to edit my HOSTS file to contain an entry like # ... 127.0.0.1 .psf # ... but Windows just seems to not recognize the share at all.

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• Simulating a low-bandwidth, high-latency network connection on Linux

  - by Justin L.

  I'd like to simulate a high-latency, low-bandwidth network connection on my Linux machine. Limiting bandwidth has been discussed before, e.g. here, but I can't find any posts which address limiting both bandwidth and latency. I can get either high latency or low bandwidth using tc. But I haven't been able to combine these into a single connection. In particular, the example rate control script here doesn't work for me: # tc qdisc add dev lo root handle 1:0 netem delay 100ms # tc qdisc add dev lo parent 1:1 handle 10: tbf rate 256kbit buffer 1600 limit 3000 RTNETLINK answers: Operation not supported How can I create a low-bandwidth, high-latency connection, using tc or any other readily-available tool?

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• Connection timed out exception, why?

  - by Dheeraj Kumar Aggarwal

  I am developing an application which uses embedded tomcat server 7, and deploys a web application on embedded server. My application accesses the embedded webapp through Rest APIs, but my clients are getting Connection Timed Out exceptions and port is also not blocked. I never gets this exception when I install this application on my local machine. Some points: IP address is used in the host name part (They are able to access this IP address on other port) Port is not blocked We are using Apache HttpClient library to access the URL Timeout interval seems not to be an issue. What are the possible reasons for this exception Connection Timed Out? or How can I simulate this problem on my local machine? Any pointers would be helpful.

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• How can Firefox masquerade as Chrome?

  - by Christos Jonathan Hayward

  I have access to Firefox but not Chrome under XP. I would like extensions to make it more Chrome-like: in particular, 1: A tabbed theme that works like Chrome. 2: One address/search bar that will go to URLs and submit search queries appropriately. (I have already installed "Download Statusbar.") I am looking on a relatively superficial level; I'm not hoping to simulate V8 or Chrome's screaming render times. But I would like a setup that minimally breaks the illusion for someone accustomed to Chrome.

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• Is FreeBSD better than CentOS for firing 40k concurrent connections (for Jmeter)?

  - by blacklotus

  Hi, I am trying to run Jmeter to simulate 40k concurrent users and stress test a particular system. Putting aside the possibility that Jmeter may not be able to push such a high number (although I have read that it is at least possible to handle 10k concurrent threads on a very powerful machine), is FreeBSD a better OS as compare to CentOS to be used for my Jmeter machine? Reason for asking this is that, I have found articles on FreeBSD for tuning and optimizing for maximum outbound connections, but seem to have little luck with CentOS. Personally however, I am more familiar with CentOS and would like to stick with it if possible. Any input is greatly appreciated!

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• Is FreeBSD more suitable than CentOS for firing 40k concurrent connections (for Jmeter)?

  - by blacklotus

  Hi, I am trying to run Jmeter to simulate 40k concurrent users and stress test a particular system. Putting aside the possibility that Jmeter may not be able to push such a high number (although I have read that it is at least possible to handle 10k concurrent threads on a very powerful machine), is FreeBSD a more suitable OS as compare to CentOS to be used for my Jmeter machine for handling 40k (or as high as possible) of concurrent outbound connections? Reason for asking this is that, I have found articles on FreeBSD for tuning and optimizing for maximum outbound connections, but seem to have little luck with CentOS. It makes me wonder if for some specific reasons, people don't use CentOS for such high number of outbound connections. Personally however, I am more familiar with CentOS and would like to stick with it if possible. Any input is greatly appreciated!

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• How can I calculate the sum of all positive integers less than n?

  - by Adrian Godong

  I have the following function: f(n) = f(n - 1) + (n - 1) f(0) = 0 n >= 0 I have n declared on column A, and need the result of f(n) on column B. I'm trying to find the Excel formula equivalent for this function. Sample Result: A | B --+-- 0 | 0 or: A | B --+-- 1 | 0 or: A | B --+-- 4 | 6 but never: A | B --+-- 0 | 0 1 | 0 2 | 1 ... The biggest problem is, I can't simulate the value of f(n - 1). So referencing the previous row like the above example is invalid. I'm almost sure the answer is trivial, I just can't find it.

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• Map mouse xbuttons to keypress?

  - by Will

  Hi, the utilities that come with my HP vector mouse are fairly basic. My old logitech G9, the best mouse ever made (except when it gets senile and starts having 'gaps') had a utility to map each of the buttons to a keypress, which I use in games, such as xbutton1 and 2 for run, etc. is there a utility, or a way, that I can map the 2 xbuttons on my new mouse so that they generate/simulate a keypress? I'm wondering if there are built in mappings in Windows that do this already, and its just a case of finding out what the keypresses are? thanks, Will

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• How to synchronize two folders on two remote Linux virtual machines

  - by Manoj Agarwal

  I have two virtual machines, Host OS is ESXi 3.5 and guest OS is Centos 4.6. There are two ESXi servers remotely located, each containing a Centos 4.6 virtual machine. I wish, whatever change I make in any file/folder in one virtual machine should be automatically synchronized on other remote virtual machine. The synchronization process should be automatic. It should only sync differentials, not simulate entire copy with overwrite operation. Sync should be intelligent enough to look for what has changed and what not, and should only update the changed files/folders. Further, there should be some sort of overview and selection for syncing, for example, if it shows 4 files have changed, It should be possible to sync only two files and leave other two for the time being. So, some intelligent syncing mechanism for Linux is needed.

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• Is there any software or hardware which lets you stop, slow down, speed up or even reverse time?

  - by tjrobinson

  Obviously I'm talking about time in terms of the PC clock rather than real time. We were testing an application we've developed at work by setting the clock forward and back to simulate different scenarios and I started thinking how useful it would be if you could adjust the rate(?) of the system clock with finer control. So you could make a minute pass in a second or a day pass in 30 seconds and watch how the program you're developing copes with changes in date and time. I'd be interested to hear if anyone knows of any software or hardware which can let you do some or all of the above.

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• Likeliness of obtaining same IP address after restarting a router

  - by ?affael

  My actual objective is to simulate logged IPs of web-site users who are all assumed to use dynamically assigned IPs. There will be two kinds of users: good users who only change IP when the ISP assignes a new one bad users who will restart their router to obtain a new IP So what I would like to understand is what assignment mechanics are usually at work here deciding from what pool of IPs one is chosen and whether the probability is uniformly distributed. I know there is no definite and global answer as this process can be adjusted be the ISP but maybe there is something like a technological frame and common process that allows some plausible assumptions. UPDATE: A bad user will restart the router as often as possible if necessary. So here the central question is how many IP changes on average are necessary to end up with a previously used IP.

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