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• Why change net.inet.tcp.tcbhashsize in FreeBSD?

  - by sh-beta

  In virtually every FreeBSD network tuning document I can find: # /boot/loader.conf net.inet.tcp.tcbhashsize=4096 This is usually paired with some unhelpful statement like "TCP control-block hash table tuning" or "Set this to a reasonable value." man 4 tcp isn't much help either: tcbhashsize Size of the TCP control-block hash table (read-only). This may be tuned using the kernel option TCBHASHSIZE or by setting net.inet.tcp.tcbhashsize in the loader(8). The only document I can find that touches on this mysterious thing is the Protocol Control Block Lookup subsection beneath Transport Layer in Optimizing the FreeBSD IP and TCP Stack, but its description is more about potential bottlenecks in using it. It seems tied to matching new TCP segments to their listening sockets, but I'm not sure how. What exactly is the TCP Control Block used for? Why would you want to set its hash size to 4096 or any other particular number?

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• MySQL Locking Up

  - by Ian

  I've got a innodb table that gets a lot of reads and almost no writes (like, 1 write for every 400,000 reads approx). I'm running into a pretty big problem though when I do INSERT into the table. MySQL completely locks up. It uses 100% cpu, and every single other table (in other databases even) have their statuses set to "Locked" until the INSERT is done. This is a big problem because MySQL stays locked up for up to 4 minutes. I'm using version 5.1.47 (rpm from mysql.com). Any ideas?

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• Identify Long Running or Slow PHP Scripts

  - by Kirk

  I have web server that is getting around 25K visits a day up at yougetsignal.com. Sometimes the site feels a bit sluggish. I am hosting it on nginx with php5-fpm. Is there a way for me to see a list of all of the long running requests that are coming to the site? I'd love to have a real-time list of all of the active requests that PHP is handling and how long they have been running. Kind of like top, but just for the web server. This would let me know how long requests are taking and which script is the culprit. Anyone have any ideas on how I can do this?

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• SQL Profiler Through StreamInsight Sample Solution

  In this postI show how you can use StreamInsight to take events coming from SQL Server Profiler in real-time and do some analytics whilst the data is in flight.  Here is the solution for that post.  The download contains Project that reads events from a previously recorded trace file Project that starts a trace and captures events in real-time from a custom trace definition file (Included) It is a very simple solution and could be extended.  Whilst this example traces against SQL Server it would be trivial to change this so it profiles events in Analysis Services.       Enjoy.

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• Using wildcard domains to serve images without http blocking

  - by iopener

  I read that browsers sometimes block waiting for multiple images from the same host, and I'm trying to do everything I can to speed up page load times. One caveat: I need to serve files over HTTPS. Any opinions about whether this is feasible: Setup a wildcard cert for *.domain.com. Whenever I need an image, generate an number based on a hash mod 5 of the filename, and append it to an 'img' subdomain (eg img1.domain.com, img4.domain.com, img3.domain.com, etc.); the hash will make any filename always use the same subdomain, and therefore the browser should be able to cache the images Configure a dynamic virtualhost record to point all img#. subdomains to /var/www/img I am looking for feedback about this plan. My concerns are: Will I get warnings when my page has https:// links to multiple subdomains? Is the dynamic virtualhost record I'm talking about even possible? Considering the amount of processing this would require, is it likely to even produce any kind of overall benefit? I'm probably averaging a half-dozen images per page, with only half being changed on each page refresh. Thanks in advance for you feedback.

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• windows 2000 freezing during large disk write

  - by robert

  We have a windows 2000 sp4 server which freezes up for about 1 minutes while its web-app does a ~500mb write operation. I can see the webapp start to do I/O activity (through process explorer) then the RDP session becomes unresponsive, you can click on windows and buttons but nothing happens. When the disk write finally finishes the session 'catches up' on all the mouse clicks you did during the freeze in a mad flurry of window activity and the server returns to normal. During the freeze the web-app stops as well. The same behaviour happens on the console of the server. (so I know its not a network thing) Nothing appears in the Event logs. Its like nothing happened. I have upgraded all the HP hardware drivers to the latest proliant support pack. And also run a HP hardware diagnostics which found nothing wrong. What would cause a disk write to lock the rest of the OS?

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• Email server for huge number of subscriber

  - by bogha

  My question is that my company is thinking of providing a free email account for each of its customers. As a new company we will assume that our corporate email system will be MS Exchange server which will support about 1000 employees. They are asking why not adding the customer list to be a part of Exchange users. My suggestion was to separate the two systems, for the corporate we can use Exchange but for customers (around 30000) we have to use a Linux based system. My only argument was that Linux can be used for enterprise services like this and Microsoft may fail. What do you suggest? And if you are with me on choosing Linux as the server platform, what do you suggest to use as an alternative for Exchange in Linux? Thank you.

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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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• Where do vendors publish internal transfer rates of HDDs?

  - by red888

  So I've started to dig into storage fundamentals and found that in order to calculate the IOPS of a HDD you need to know the internal transfer rate of the drive (time it takes data to move from the platters to internal disk's cache). I went on newegg and even a few vendor sites and could not find this info published for any HDDs. Is it sometimes called something else? Take this link to a seagate HDD for instance. Nowhere do I see "internal transfer rate", but I do see something called "Sustained Data Rate OD"- is that the same thing? Just so you know where I'm getting this info (Book: "Information Storage and Management Storing, Managing..."): Consider an example with the following specifications provided for a disk: The average seek time is 5 ms in a random I/O environment; therefore, T = 5 ms. Disk rotation speed of 15,000 revolutions per minute or 250 revolutions per second — from which rotational latency (L) can be determined, which is one-half of the time taken for a full rotation or L = (0.5/250 rps expressed in ms). 40 MB/s internal data transfer rate, from which the internal transfer time (X) is derived based on the block size of the I/O — for example, an I/O with a block size of 32 KB; therefore X = 32 KB/40 MB. Consequently, the time taken by the I/O controller to serve an I/O of block size 32 KB is (TS) = 5 ms + (0.5/250) + 32 KB/40 MB = 7.8 ms. Therefore, the maximum number of I/Os serviced per second or IOPS is (1/TS) = 1/(7.8 × 10^-3) = 128 IOPS.

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• MySQL maintenance - how to clear the buffer?

  - by Dougal

  We have a server running our web app (PHP / MySQL) which is SLOW. My predecessor says that: "We use to do database maintenance, which use to clear the buffer, cached and unwanted variables." And I wonder what on earth he means with that statement? Does he mean a simple optimize of the tables? Or the query cache? I understand MySQL but don't really know what he is describing. I would appreciate any pointers. Thanks.

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• What is the effect on LVM snapshot size when a file block is rewritten with it's original contents?

  - by NevilleDNZ

  I'm exploring using LVM snapshot's to off site incremental archives from a snapshot "master" file system. In essence: simply copy across only the files on the "master" that have changed since the last incremental copy to the "archive". Then snapshot the "archive" to retain the incremental. I am a bit puzzled as to the block usage behaviour of the archive's own incremental snapshot. I'm expecting that LVM is not smart enough to know that the "file block" is actually unchanged, and the a new copy will be allocated and written for the fresh "archive" file system. Can anyone confirm this, or point me to a document/page that gives some hints? BTW: the OS hard disk cache, hard disk physical cache and hard disk itself also doesn't need to do any actual "disk writes" as the "disk block" likewise is unnecessary. Any pointers to discussion of this style of optimisation would also be ineresting.

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• Encrypt shared files on AD Domain.

  - by Walter

  Can I encrypt shared files on windows server and allow only authenticated domain users have access to these files? The scenario as follows: I have a software development company, and I would like to protect my source code from being copied by my programmers. One problem is that some programmers use their own laptops to developing the company's software. In this scenario it's impossible to prevent developers from copying the source code for their laptops. In this case I thought about the following solution, but i don't know if it's possible to implement. The idea is to encrypt the source code and they are accessible (decrypted) only when developers are logged into the AD domain, ie if they are not logged into the AD domain, the source code would be encrypted be useless. How can be implemented this using EFS?

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• Brand new Seagate HDD has high raw read error rate

  - by kpax

  I've just purchased a brand new Seagate ST31000524AS 1TB HDD. Manufacture date shows as January 2012 (yes that's as new as new can get), so must be one of the new batches from the post-flood Thailand. Anyway, I downloaded a copy of Active Hard Disk Monitor tool to check the S.M.A.R.T. parameters and I find the parameter Raw Read Error Rate is very low. Should I be worried? Will this rectify over time? This hdd is just 7 hours old; what gives? Edit: I meant high raw read error rate - Title updated accordingly

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• Google déploie Android 4.2 et publie son code source ainsi que son SDK

  Fuite des fonctionnalités d'Android 4.2 : nouveau Google Play, gestion du multi-utilisateur et contrôle parental Google a récemment envoyé des invitations à la presse pour un évènement Android le 29 octobre prochain à New York. Au cours de cet évènement, l'éditeur pourrait dévoiler Android 4.2, une mise à jour mineure de la version 4.1, Jelly Bean. Cette nouvelle a laissé place à des rumeurs qui viennent dévoiler quelques-unes des nouvelles fonctionnalités et améliorations qu'apportera cette version d'Android. Selon le site spécialisé Android Police, la prochaine mise à jour de l'OS mobile de Google apportera une nouvelle version de la galerie d'applications...

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• Is having 'Util' classes a cause for concern? [closed]

  - by Matt Fenwick

  I sometimes create 'Util' classes which primarily serve to hold methods and values that don't really seem to belong elsewhere. But every time I create one of these classes, I think "uh-oh, I'm gonna regret this later ...", because I read somewhere that it's bad. But on the other hand, there seem to be two compelling (at least for me) cases for them: implementation secrets that are used in multiple classes within a package providing useful functionality to augment a class, without cluttering its interface Am I on the way to destruction? What you say !! Should I refactor?

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• How to camel-case where consecutive words have numbers?

  - by Rob I

  Just wondering if anybody has a good convention to follow in this corner-corner-corner case. I really use Java but figured the C# folks might have some good insight too. Say I am trying to name a class where two consecutive words in the class name are numeric (note that the same question could asked about identifier names). Can't get a great example, but think of something like "IEEE 802 16 bit value". Combining consecutive acronyms is doable if you accept classnames such as HttpUrlConnection. But it seriously makes me throw up a little to think of naming the class IEEE80216BitValue. If I had to pick, I'd say that's even worse than IEEE802_16BitValue which looks like a bad mistake. For small numbers, I'd consider IEEE802SixteenBitValue but that doesn't scale that well. Anyone out there have a convention? Seems like Microsoft's naming guidelines are the only ones that describe acronym naming in enough detail to get the job done, but nobody has addressed numbers in classnames.

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• linux: accessing thousands of files in hash of directories

  - by 130490868091234

  I would like to know what is the most efficient way of concurrently accessing thousands of files of a similar size in a modern Linux cluster of computers. I am carrying an indexing operation in each of these files, so the 4 index files, about 5-10x smaller than the data file, are produced next to the file to index. Right now I am using a hierarchy of directories from ./00/00/00 to ./99/99/99 and I place 1 file at the end of each directory, like ./00/00/00/file000000.ext to ./00/00/00/file999999.ext. It seems to work better than having thousands of files in the same directory but I would like to know if there is a better way of laying out the files to improve access.

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• What significant progress have we made in Rapid Application Development?

  - by Frank Computer

  Since the introduction of OOPL's and event-driven programming, I feel like developing an application has become harder and more tedious, when it should have been the other way around! We should have development tools which can generate prototype apps which can be quickly and easily customized into sophisticated applications, even by novice users! We really need new ideas in this area of software development and I would like to know of any good ideas. If we can't really find them, then we should ask "Where did we miss the boat?.. Why?.. and What should we be doing?"

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• Multiple servers vs 1 big server performace

  - by pistacchio

  Hi to all! My team of developers has suggested a server structure for an upcoming project we are developing. Our structure is "logical", meaning that the various logical components of the application (it is a distributed one) relies on different servers. Some components are more critical than others and will be subjected to more load. Our proposal was to have 1 server per component but the hardware guys suggested to replace the various machines with a single, bigger one with virtual servers. They're gonna use Blade Servers. Now, I'm not an expert at all, but my question to the guys was: so if we need, for example, 3 2GHz CPU / 2GB RAM machines and you give me 1 machine with 3 2GHz CPUs and 6 GB of RAM it is the same? They told me it is. Is this accurate? What are the advantages or disadvantages of both the solutions? What are the generally accepted best practices? Could you point out some URL reference dealing with the problem? Thank you in advance! EDIT: Some more info. The (internet / intranet) application is already layered. We have some servers on the DMZ that will expose pages to the internet and the databases are on their own machines. What we want to split (and they want to join) are some webservers that mainly expose webservices. One is a DAL that communicates with the database layer, one is our Single Sign On / User Profile application that gets called once per page and one is a clone of what seen on the Internet to be used on our lan.

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• Why Can't I Pre-Zip Server Files?

  - by ThinkBohemian

  It's just good common sense to have your server gzip your files before they send them to users (I use Nginx) Is there anyway to save the server some overhead and pre-zip those files for the server, and if not why? For instance rather than giving the server an myscript.js and having the server zip the file and send it to the user, is there a way to create myscript.js.zip so the server doesn't have to?

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• Flash stream makes my internet slow and cpu rush

  - by user1225840

  When I try to watch a live Flash stream, my CPU usage goes up to 75% and my Internet speed goes down. If I run a test before the video-stream, my speed is ~40/10Mbps and during the stream it drops to 0.1-0.5Mbps. The stream is laggy and I can only watch one to two seconds at a time, start/stop/start/stop. I have cleared my history, cache, cookies, temp files, and so on. I have searched for malware and took care of that. I have updated my drivers, reinstalled Flash and everything else I can think of, but it remains slow. I had this problem before and it just started working normally from one day to another. Could it be a hardware problem?

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• Configuring Site Policy in SharePoint 2013 using server code

  - by panjkov

  When you create Site Policy in SharePoint, you can configure its options using browser, which is particularly convenient when you have that policy configured for publishing in Content Type Hub. But, when you need to configure multiple sites with same policy, and you for any reason have to deploy multiple instances of same site policy, this browser-based editing process is not something that you would want to use. In that case, some way of configuring policy options automatically would be helpful...(read more)

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• Code execution time out occationally

  - by Athul k Surendran

  I am working on an e-commerce website. There is a case where I need to fetch the whole data in database through third-party API and send it to an indexing engine. This third-party API has many functions like getproducts, getproductprice, etc., and each of that functions will return the data in XML format. From there I will take charge, I will use various API calls and will handle the XML data with XSLT. And will write to a CSV file. This file will be uploaded to an Indexing engine. Right now I have details of 8000 products to feed the engine, and almost all time the this process takes about 15 min to complete, and sometimes fails. I can't find a better solution for this. I am thinking about handling the XML data in C# itself and get rid of XSLT. As I think, XSLT is far slower than C#. Is it a good Idea? Or what else I can do to solve this issue?

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• What is the computer "doing" when it is running slow and task manager is not showing any CPU activity?

  - by Joakim Tall

  Typical example is when shutting down a memoryintensive application. It can take quite a while before the computer gets back up to speed. Is there some inherent cost in releasing memory? Or is it throttled by some kind of harddrive activity, and if so is there any good way to track that? I usually bring up task manager when a computer is running slow, and usually sorting by cpu activity can show what process is causing the problem, but sometimes there is no activity showing. And yes I "show processes from all users", I have been wondering this since the days win2k :)

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• How can I setup a Proxy I can sniff traffic from using an ESX vswitch in promiscuous mode?

  - by sandroid

  I have a pretty specific requirement, detailed below. Here's what I'm not looking for help for, to keep things tidy and on topic: How to configure a standard proxy Any ESX setup required to facilitate traffic sniffing How to sniff traffic Any changes in design (my scope limits me) I need to setup a test environment for a network-sniffing based HTTP app monitoring tool, and I need to troubleshoot a client issue but he only has a prod network, so making changes to the config on client's system "just to try" is costly. The goal here is to create a similar system in my lab, and hit the client's webapp and redirect my traffic - using a proxy - into the lab environment. The reason I want to use a proxy is so that only this specific traffic is redirected for all to see, and not all my web traffic (like my visits to serverfault :P). Everything will run inside an ESX 4.1 machine. In there, there is a traffic collection vswitch in promiscuous mode that is not on the local network for security reasons. The VM containing our listening agent is connected to this vswitch. On the same ESX host, I will setup a basic linux server and install a proxy (either apache + mod_proxy or squid, doesn't matter). I'm looking for ideas on how to deploy this for my needs so I can then figure out how to set it up accordingly. Some ideas I've had were to setup two proxies, and have them talk to eachother through this vswitch in promiscuous mode, but it seems like alot of work. Another idea is a dual-homed proxy, but I've never seen/done that before so I'm not sure how doable it is for what I'd like. I am OK with setting up a second vswitch in promiscuous mode to facilitate this if need be, but I cannot put the vswitch on the lan (which is used so my browser would communicate with the proxy) in promiscuous mode. Any ideas are welcome.

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