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  • What is good usage scenario for Rackspace Cloud Files CDN (powered by AKAMAI) [closed]

    - by Andrew Smith
    I have just setup my website as static page via Rackspace CDN / Akamai. www.example.co.uk is an alias for d9771e6f24423091aebc-345678991111238fabcdef6114258d0e1.r61.cf3.rackcdn.com. d9771e6f24423091aebc-345678991111238fabcdef6114258d0e1.r61.cf3.rackcdn.com is an alias for a61.rackcdn.com. a61.rackcdn.com is an alias for a61.rackcdn.com.mdc.edgesuite.net. a61.rackcdn.com.mdc.edgesuite.net is an alias for a63.dscg10.akamai.net. a63.dscg10.akamai.net has address 63.166.98.41 a63.dscg10.akamai.net has address 63.166.98.40 a63.dscg10.akamai.net has IPv6 address 2001:428:4c02::cda8:ecb9 a63.dscg10.akamai.net has IPv6 address 2001:428:4c02::cda8:ed09 The HTTP header: HTTP/1.0 200 OK Last-Modified: Fri, 19 Oct 2012 23:27:41 GMT ETag: fdf9e14b77def799e09e8ce815a521da X-Timestamp: 1350689261.23382 Content-Type: text/html X-Trans-Id: tx457979be3bd746c2b4e5403a1189cdbc Cache-Control: public, max-age=900 Expires: Sat, 27 Oct 2012 22:18:56 GMT Date: Sat, 27 Oct 2012 22:03:56 GMT Content-Length: 7124 Connection: keep-alive I am wondering, if it's really the fastest solution to power the website? By investigating it thru http://www.just-ping.com/ it seems, that from many places the ping is very high, and during quick investigation I found that they use GeoIP to resolve addresses based on WHOIS, which is not accurate and because of that from many places the ping is above 300ms (for example, if ISP is in balgladore and request is routed to bangladore even if it's 300ms, for period of 1 month), while by just using Amazon Web Services and Route 53 Anycast DNS servers and only 4 EC2 instances it seems that for example India is always below 100ms, while using Akamai it goes above 300ms in some cases, and this is because Route 53 is using BGP. By quickly checking the Akamai, it seems that they are not getting feedback from the traffic - the high ping stays constant even if I keep downloading large files and videos, which is opposite to what they say on their website. They state, that they optimize the performance by taking feedback from the requests, while it seems they just use GeoIP with per City resolution (which are mostly big cities). Because of this, AWS with Route 53 / Anycast DNS seems to be much more reliable, as well EdgeCast which is using BGP, but I dont know how much does it cost to deploy static website. Actually, I dont know if EdgeCast is not a lie, because from isolated places there are many errors - so their performance is at the cost of quality of delivery, because of BGP switching the routes during transfer of large files. So I was wondering, what is really Akamai good for, because they dont seem to pose any strength in any field in what I do understand now, except they offer some software based WAF on their website, but what I really care about is the core distribiution, so the question is? Is really Akamai good for Videos? For static websites? ??? I found so far AWS most usable with most consistent ping and stable transfers.

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  • Ubuntu server loses exactly 5 minutes once in a while

    - by Harold Smith
    I noticed that my server, an Ubuntu server 12.04, was losing time. I figured the hardware clock was off or maybe dying due to a faulty CMOS battery. I installed NTP to ensure the drift would be corrected, but to no avail. During a day it would lose 20 minutes or so. To debug, I created a small cron job to check against a remote servers time, which I knew to be correct. The script calculates the difference in seconds between local and remote time. The result was interesting. It seems to be losing exactly 5 minutes several times during the day. Look at this log (difference from remote server noted in seconds): Tue Oct 23 03:30:02 CEST 2012: 284 Tue Oct 23 03:35:02 CEST 2012: 284 Tue Oct 23 03:40:01 CEST 2012: 285 Tue Oct 23 03:45:02 CEST 2012: 285 Tue Oct 23 03:50:02 CEST 2012: 285 Tue Oct 23 03:55:02 CEST 2012: 284 Tue Oct 23 04:00:02 CEST 2012: 284 Tue Oct 23 04:05:01 CEST 2012: 285 Tue Oct 23 04:10:01 CEST 2012: 285 Tue Oct 23 04:15:02 CEST 2012: 585 Tue Oct 23 04:20:02 CEST 2012: 584 Tue Oct 23 04:25:02 CEST 2012: 584 Tue Oct 23 04:30:02 CEST 2012: 584 Tue Oct 23 04:35:01 CEST 2012: 585 Tue Oct 23 04:40:01 CEST 2012: 585 Tue Oct 23 04:45:02 CEST 2012: 585 Tue Oct 23 04:50:02 CEST 2012: 584 Tue Oct 23 04:55:02 CEST 2012: 584 Tue Oct 23 05:00:02 CEST 2012: 584 Tue Oct 23 05:05:01 CEST 2012: 585 Tue Oct 23 05:10:01 CEST 2012: 585 Tue Oct 23 05:15:02 CEST 2012: 585 Tue Oct 23 05:20:02 CEST 2012: 584 Tue Oct 23 05:25:02 CEST 2012: 584 Tue Oct 23 05:30:02 CEST 2012: 584 Tue Oct 23 05:35:01 CEST 2012: 585 Tue Oct 23 05:40:01 CEST 2012: 585 Tue Oct 23 05:45:02 CEST 2012: 584 Tue Oct 23 05:50:02 CEST 2012: 584 Tue Oct 23 05:55:02 CEST 2012: 584 Tue Oct 23 06:00:02 CEST 2012: 584 Tue Oct 23 06:05:03 CEST 2012: 584 Tue Oct 23 06:10:02 CEST 2012: 584 Tue Oct 23 06:15:01 CEST 2012: 585 Tue Oct 23 06:20:02 CEST 2012: 584 Tue Oct 23 06:25:02 CEST 2012: 584 Tue Oct 23 06:30:02 CEST 2012: 584 Tue Oct 23 06:35:02 CEST 2012: 584 Tue Oct 23 06:40:02 CEST 2012: 584 Tue Oct 23 06:45:01 CEST 2012: 585 Tue Oct 23 06:50:02 CEST 2012: 584 Tue Oct 23 06:55:01 CEST 2012: 585 Tue Oct 23 07:00:02 CEST 2012: 584 Tue Oct 23 07:05:02 CEST 2012: 584 Tue Oct 23 07:10:02 CEST 2012: 584 Tue Oct 23 07:15:02 CEST 2012: 584 Tue Oct 23 07:20:02 CEST 2012: 584 Tue Oct 23 07:25:02 CEST 2012: 584 Tue Oct 23 07:30:01 CEST 2012: 585 Tue Oct 23 07:35:02 CEST 2012: 584 Tue Oct 23 07:40:02 CEST 2012: 584 Tue Oct 23 07:45:02 CEST 2012: 584 Tue Oct 23 07:50:02 CEST 2012: 584 Tue Oct 23 07:55:02 CEST 2012: 584 Tue Oct 23 08:00:01 CEST 2012: 585 Tue Oct 23 08:05:02 CEST 2012: 584 Tue Oct 23 08:10:02 CEST 2012: 584 Tue Oct 23 08:15:02 CEST 2012: 584 Tue Oct 23 08:20:02 CEST 2012: 584 Tue Oct 23 08:25:02 CEST 2012: 584 Tue Oct 23 08:30:01 CEST 2012: 585 Tue Oct 23 08:35:02 CEST 2012: 584 Tue Oct 23 08:40:02 CEST 2012: 584 Tue Oct 23 08:45:02 CEST 2012: 584 Tue Oct 23 08:50:02 CEST 2012: 584 Tue Oct 23 08:55:02 CEST 2012: 584 Tue Oct 23 09:00:02 CEST 2012: 584 Tue Oct 23 09:05:03 CEST 2012: 584 Tue Oct 23 09:10:02 CEST 2012: 584 Tue Oct 23 09:15:02 CEST 2012: 584 Tue Oct 23 09:20:02 CEST 2012: 584 Tue Oct 23 09:25:02 CEST 2012: 584 Tue Oct 23 09:30:01 CEST 2012: 584 Tue Oct 23 09:35:02 CEST 2012: 584 Tue Oct 23 09:40:02 CEST 2012: 584 Tue Oct 23 09:45:02 CEST 2012: 584 Tue Oct 23 09:50:02 CEST 2012: 584 Tue Oct 23 09:55:02 CEST 2012: 584 Tue Oct 23 10:00:01 CEST 2012: 584 Tue Oct 23 10:05:02 CEST 2012: 584 Tue Oct 23 10:10:07 CEST 2012: 584 Tue Oct 23 10:15:02 CEST 2012: 584 Tue Oct 23 10:20:02 CEST 2012: 884 Tue Oct 23 10:25:02 CEST 2012: 884 Tue Oct 23 10:30:02 CEST 2012: 883 Tue Oct 23 10:35:01 CEST 2012: 884 Tue Oct 23 10:40:02 CEST 2012: 884 Tue Oct 23 10:45:02 CEST 2012: 884 Tue Oct 23 10:50:02 CEST 2012: 884 Tue Oct 23 10:55:02 CEST 2012: 1184 Tue Oct 23 11:00:02 CEST 2012: 1183 Tue Oct 23 11:05:01 CEST 2012: 1184 Tue Oct 23 11:10:02 CEST 2012: 1184 Tue Oct 23 11:15:02 CEST 2012: 1184 Tue Oct 23 11:20:02 CEST 2012: 1184 This does not seem to be faulty CMOS battery in my opinion. But what do you think?

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  • PS/2 vs USB keyboards: performance and energy consumption

    - by Mister Smith
    As far as I know, PS/2 keyboards are interrupt driven, while USB are polled. Typically a PS/2 keyboard was assigned IRQ_1 on Windows. I'm no hardware expert, but at a first glance seems like the PS/2 keyboards are more efficient. So here are my questions: On modern day computers, are PS/2 keyboard better (or faster), and if so, would it be noticeable at all? (e.g.: in gaming) Since they don't need polling, do PS/2 keyboards save energy compared to USB? (notice I'm not talking only about the peripheral here, but about the overall computer energy consumption). In case PS/2 had any advantage over USB, would adding a PS/2 adapter to my USB keyboard make the device as good as an actual PS/2 keyboard? Conversely, would adding a USB adapter to a PS/2 make it as bad as a USB KB? Thanks in advance.

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  • XP User account cannot write to USB

    - by Quick Joe Smith
    Is there a local security policy setting or somesuch to allow limited user accounts to modify the contents of USB drives? Currently I get an "Access denied" error, further saying "Make sure the disk is not full or write-protected and that the file is not currently in use." The Administrator account has no such obstacles. Update: The problem is at least solvable by altering NTFS permissions (granting Full Control to Users), and therefore I'm losing hope that there is a more global solution.

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  • Setting up phpMemCacheAdmin on CentOS 5.5

    - by Bill Smith
    I have been able to setup phpMemCacheAdmin (http://code.google.com/p/phpmemcacheadmin/) on CentOS and am able to view the localhost MemCache statistics however whenever I add other MemCached nodes the config is never changed. I am fairly certain it has something to do with permissions however I am unable to track down what exactly needs to be done, or how to do it. The install was pretty straightforward: wget http://phpmemcacheadmin.googlecode.com/files/phpMemCacheAdmin-1.1.3r161.tar.gz tar xvzf phpMemCacheAdmin-1.1.3r161.tar.gz chmod +w Config/Memcache.ini But, it also states that Apache has rw right in the temp file folder (default : Temp/) and the entire config directory (Config/) -- that is the part I am unsure of. Help!

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  • Wacom tablet or Evoluvent Vertical Mouse

    - by Bob Smith
    Having tried a number of mice that didn't help with wrist pain, I am contemplating buying a Wacom tablet or Evoluvent Vertical Mouse. I have heard great things about both of them. What do you recommend for someone with wrist pain in both hands that seems to be getting worse by the day? PS: I work mostly in Windows and Visual Studio environment. I currently have the MS natural ergonomic keyboard. I have started taking regular breaks and am also planning to see a doctor.

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  • 2d & 3d CAD software on the MAC [closed]

    - by Mark Smith
    Hey I was wondering what 2d & 3d CAD softwares people use on the mac? There are a couple of other questions like this on the site but they're over a year old and knowing how fast paced the software game is I thought i'd repost! I use MacDraft for my 2d drafting and the same companies Interiors Pro for my 3d work, have done for a while. I used Rhino 4.0 at uni but being a student I had to find software that wasn't thousands of £$£$!! thus stumbling onto the Microspot products. Anybody using the software or found any other bargains out there?

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  • Create Virtual Image of Laptop before Formatting

    - by Simon Mark Smith
    I have a 3 year old laptop running Windows XP that I used for business. Although I have not used the laptop in over a year, I now want to re-commission it with Windows 7 and a fresh install. Before I do the fresh install I want to create a Virtual Image of the laptop that I can keep and potentially run on my desktop machine should I ever need to access any of the old files/projects that it contains currently. I know that most people will say just copy the files over to your desktop, but my concern is the configuration of the laptop. I used to use it for development and it has older versions of Visual Studio, SQL Server, Active X controls etc, etc than I currently use so I really want to preserve the environment not just the files. So really I am asking what is the best tool-set/method to achieve this? I understand there are free VM tools available but I have never done this before and would appreciate any help.

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  • Can't create a new HomeGroup in Windows 8

    - by Ian Smith
    I'm trying to create a new HomeGroup in Windows 8 for 2 new PCs with Windows 8 installed so that I can share printers etc. Both PCs use Microsoft Account to log in - a Microsoft Account I set up about a year ago with one of the early beta's with a PC that's since been repaved with the RTM of Windows 8 When I click on "HomeGroup" in the "Metro" control panel the "Create" option is not there. Instead I'm told that "HomeGroup" already exists on the PC I've since repaved and renamed and I can join it by entering the password. I have no recollection of what the password might have been and in any event that PC doesn't exist, but there is no way to say "That group doesn't exist anymore just create me a new one dammit". Even using the old Control Panel the "HomeGroup" nonsense persists with the only option being "Join" that needs a password. How do I "start afresh" and create a new HomeGroup that I can use to connect my Windows 8 and Windows 7 PCs and use common printers, network drives etc.

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  • What is causing sudden freezing during running real-time program?

    - by Trevor Boyd Smith
    So I run a high intensive (CPU/GPU) real-time program. During normal execution suddenly everything freezes for 1-4 seconds. I opened "Process Explorer" in the background to help gain insight and maybe identify something. Here is what the CPU/GPU graphs looks like when I align them in time: Notice the 4 distinct drops in both the CPU/GPU. You can see that it goes from some sort of positive CPU/GPU usage to almost zero. These drops in the graph align with when the real-time program suddenly freezes. How do I find what is causing these sudden drops? NOTE: When you put your mouse over the graph it tells you the time, accurate to the second, for where your cursor is. Maybe this mouse over feature could be helpful in some way (e.g. what if you had a log of all processes every 100ms). EDIT: The real-time program is a video game and so I can't watch some sort of instrumentation while the video game is running. I need a solution that let's you look back in time somehow to see what was happening when the slow down occurred. EDIT: RE - Recording Data vs using real-time monitor: So the windows performance recorder is for some reason not recording what I expect it to record. So I switched to using "perfmon" and then opening it's "resource monitor". RE - Setting it up so I can view real-time monitor: In the video game I set it to spectate and then put the video game in "windowed" mode so that I can view the real time display that Resource Monitor has. Now that I can get semi-real time (only once per second... how do you get more than once per second?) I started looking at the various real time data readouts. Getting to the cause: I noticed a strong correlation in high disk IO and low CPU usage (which is also seen by having in-game freezing). How do you use resource monitor to find out who is doing all this offending disk IO?

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  • phpredis + pconnect

    - by john smith
    I am using phpredis on my php based website. The webserver I am using is a the simplest apache apt-get installation, no configuration involved, as this is only a development environment. The issue I am facing is that basically, while using phpredis, there is no difference between "connect" and "pconnect" commands: they both create a new connection everytime, as I can see from the "info" command on redis-cli. Now, I am pretty sure it is because of the apache configuration and the fact that it probably (most likely) is a multi-threaded env, therefore can't enstablish a single connection. My question is basically for when I will turn into production: what would the best choice of a webserver be to avoid this problem? I remember using lighttpd with thousands of users and still get only a very few (like 2 or 3) connections on mongoDB. Any ideas? Thanks in advance.

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  • How do I create an ISO image from a directory structure on CentOS?

    - by tom smith
    I'm trying to figure out the exact mkisofs cmd to create the ISO with the following directory and file structure. I've tried different commands, but when I mount the ISO that is created the directory tree has not been reproduced. The initial directory tree is: master.iso:: mount -o loop /apps/vmware/master.iso /mnt/vmtest ls /mnt/vmtest isolinux ks.cfg upgra32 upgra64 upgrade.sh ls /mnt/vmtest/isolinux boot.cat initrd.img isolinux.bin isolinux.cfg vmlinuz I've used different variations of the following mkisofs command without success: mkisofs -o '/foo/test.iso' -b 'isolinux.bin' -c 'boot.cat' -no-emul-boot -boot-load-size 4 -boot-info-table 'isolinux' How do I make an ISO that captures a directory's exact structure?

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  • Organization: Ways to link/group documents with emails?

    - by Scott Smith
    I like keeping my stuff organized, but short of printing everything out and keeping it in an actual file cabinet, I've never figured out a good way to link/group document files with related emails. This means that when I'm looking for something, I often have to search in my email program, and then through the documents stored in some filesystem folder. Has anyone out there come up with a neat way to group related stuff like this for searching, archiving, etc?

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  • Tools to monitor guest OS performance in vSphere

    - by Quick Joe Smith
    I am looking for some tool or way to retrieve performance data from guest VMs running under vSphere 4.1. I am currently interested in the 4 basic metrics: CPU(%), Memory(%), Disk availability(%) & Network utilisation(Kb/s). The issue I have is that all of vSphere's performance data is from a ESXi host perspective (active, shared, consumed, overhead, swapped etc.) which is far removed from the data from the VM's own perspective. For instance, I have a Windows server VM idling, using around 410MB (~25% of its allocated 2GB) as reported by Task Manager, and this is the value I'm after. vSphere's metrics seem unable to arrive at this figure by any reliable and repeatable means. Is anyone aware of tools that can obtain this kind of data? The simpler, the better.

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  • Server 2008 Task Scheduler and a CMD file

    - by Mark Smith
    Task Scheduler - I have a .cmd file I'm trying to execute on a regular basis through Task Scheduler. I've set the task so that it points to the cmd file. I want the task to execute even when no one is logged in. I've set the credentials associated with the task to the local service account. When I execute the task, nothing happens. The Last Run Result shows 0x1, this means it didn't execute properly. When I run the file from a command prompt it executes just fine. Any help out there would be appreciated. I would post the code but it has sensitive information in it and I'm not allowed to let the code outside. Thanks

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  • Windows 7 - Opening files from Windows Explorer with Elevated Permissions?

    - by Martin Smith
    I've just started using Windows 7 and am instantly finding one aspect pretty annoying. When I open certain files from Windows Explorer / Windows Search results etc then I then cannot save them as it throws up the following message box. C:\Windows\System32\drivers\etc\hosts You don’t have permission to save in this location. Contact the administrator to obtain permission. Would you like to save in the My Documents folder instead? [Yes] [No] However I can't see any way of opening the file with elevated permissions. Is the only workflow to first open the application with elevated permissions then open the file?

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  • Configure ubuntu 12.10 to share internet through second NIC with subnetwork

    - by Dan Smith
    I have an Ubuntu 12.10 box with 2 NICs. eth0 is connected to my 192.168.1.X network, which is connected to my home router and out to the internet. I want the other interface, eth1,to support 10.0.0.x and allow devices on that network to access the internet through my ubuntu box. I do not need dhcp on the 10.0.0.x network. Here's a schematic: Internet --- home router ---- ubuntu[eth0:192.168.1.x, eth1:10.0.0.x] --- [10.0.0.x device] How do I configure the ubuntu box to share the internet with devices on that subnetwork? Thanks!

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  • Kill xserver from command line (init 3/5 does not work)

    - by John Smith
    Hi, I'm running Linux Mint 10, although I've had this same issue with other variants of Linux. I've been told/found while researching that if the X server hangs or otherwise errors, one can drop to a root prompt, usually at another tty, and execute init 3 (to drop to single user mode) and then init 5 to return to the default, graphical session. Needless to say, I've tried this before in multiple configurations on multiple machines to no avail. The only feedback I receive form executing those two commands is a listing of VMWare services (from a kernel module) that are stopped and then restarted. Note: If I run startx (either before or after init 3), then I am told that the xserver is still running and that I should remove /tmp/.X0-lock. Having tried that, it removes that error message, but claims that the xserver cannot be attached as another instance is running. How do I kill the xserver completely? Can I killall some process name?

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  • Stress test a server for simultaneous connection

    - by weston smith
    I am trying to figure out a practical way to stress test a server for 300 to 600 simultaneous connections. Any advice? Thank you everyone for the help. To be more specific (sorry I wasn't before) this is a Flash Media Server on AWS that will be streaming live video. I've been having problems with the video freezing/buffering for everyone and I need to verify if its on the user end, upload end, or server end. I mainly need help with stress testing the server with 300-600 multiple request before going live.

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  • Squid - Selective reverse proxy and forward proxy

    - by Dean Smith
    I'd like to setup a squid instance to do selective reverse proxy for a configured list of URLs whilst acting as a normal forward proxy for everything else. We are building new infrastructure, parallel live as it where, and I want to have a proxy that people can use that will force selective traffic into the new platform whilst just acting as a forward proxy for anything else. This makes it very easy for people/systems to test the portions of the new platform we want without having to change too much, just use a proxy address. Is such a setup possible ?

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  • My new favourite traceflag

    - by Dave Ballantyne
    As we are all aware, there are a number of traceflags.  Some documented, some semi-documented and some completely undocumented.  Here is one that is undocumented that Paul White(b|t) mentioned almost as an aside in one of his excellent blog posts. Much has been written about residual predicates and how a predicate can be pushed into a seek/scan operation.  This is a good thing to happen,  it does save a lot of processing from having to be done.  For the uninitiated though: If we have a simple SELECT statement such as : the process that SQL Server goes through to resolve this is : The index IX_Person_LastName_FirstName_MiddleName is navigated to find the first “Smith” For each “Smith” the middle name is checked for being a null. Two operations!, and the execution plan doesnt fully represent all the work that is being undertaken. As you can see there is only a single seek operation, the work undertaken to resolve the condition “MiddleName is not null” has been pushed into it.  This can be seen in the properties. “Seek predicate” is how the index has been navigated, and “Predicate” is the condition run over every row,  a scan inside a seek!. So the question is:  How many rows have been resolved by the seek and how many by the scan ?  How many rows did the filter remove ? Wouldn’t it be nice if this operation could be split ?  That exactly what traceflag 9130 does. Executing the query: That changes the plan rather dramatically, and should be changing how we think about the index seek itself.  The Filter operator has been added and, unsurprisingly, the condition in this is “MiddleName is not null” So it is now evident that the seek operation found 103 Smiths and 60 of those Smiths had a non-null MiddleName. This traceflag has no place on a production system,  dont even think about it

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  • Evaluate cron expression

    - by Jake A. Smith
    Is there a command line tool that will simply evaluate a cron expression and return a bool response if it is supposed to be running right now? I'm looking for something I can use as a utility in another bash script. Something like so: run_script=$(/tools/evaluate-cron-expression "02 4 * * *") if [ "$run_script" -eq "1" ] # etc etc I know, I know, I could just setup a real cron job, but I'm playing with the idea of wrapping all of my scheduled scripts inside of another script.

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  • How to reliably recieve message from AWS that my instance was rebooted / terminated / stopped?

    - by Andrew Smith
    I have Nagios, and I want it to stop monitoring instances when they are stopped from the console. The requirements are: The message passed from AWS is 100R% reliable, e.g. when Nagios is down, and the message cannot be delivered, it will be re-delivered promptly when Nagios is up The message will pass quickly There is no need to scan status of all instances via EC2 API all the time, but only once a while Many thanks!

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  • Should I use "Raid 5 + spare" or "Raid 6"?

    - by Trevor Boyd Smith
    What is "Raid 5 + Spare" (excerpt from User Manual, Sect 4.17.2, P.54): RAID5+Spare: RAID 5+Spare is a RAID 5 array in which one disk is used as spare to rebuild the system as soon as a disk fails (Fig. 79). At least four disks are required. If one physical disk fails, the data remains available because it is read from the parity blocks. Data from a failed disk is rebuilt onto the hot spare disk. When a failed disk is replaced, the replacement becomes the new hot spare. No data is lost in the case of a single disk failure, but if a second disk fails before the system can rebuild data to the hot spare, all data in the array will be lost. What is "Raid 6" (excerpt from User Manual, Sect 4.17.2, P.54): RAID6: In RAID 6, data is striped across all disks (minimum of four) and a two parity blocks for each data block (p and q in Fig. 80) is written on the same stripe. If one physical disk fails, the data from the failed disk can be rebuilt onto a replacement disk. This Raid mode can support up to two disk failures with no data loss. RAID 6 provides for faster rebuilding of data from a failed disk. Both "Raid 5 + spare" and "Raid 6" are SO similar ... I can't tell the difference. When would "Raid 5 + Spare" be optimal? And when would "Raid 6" be optimal"? The manual dumbs down the different raid with 5 star ratings. "Raid 5 + Spare" only gets 4 stars but "Raid 6" gets 5 stars. If I were to blindly trust the manual I would conclude that "Raid 6" is always better. Is "Raid 6" always better?

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