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  • Writing at the end of file

    - by user342534
    Hi, I'm working on a system that requires high file I/O performance (with C#). Basically, I'm filling up large files (~100MB) from the start of the file until the end of the file. Every ~5 seconds I'm adding ~5MB to the file (sequentially from the start of the file), on every bulk I'm flushing the stream. Every few minutes I need to update a structure which I write at the end of the file (some kind of metadata). When flushing each one of the bulks I have no performance issue. However, when updating the metadata at the end of the file I get really low performance. My guess is that when creating the file (which also should be done extra fast), the file doesn't really allocates the entire 100MB on the disk and when I flush the metadata it must allocates all space until the end of file. Guys/Girls, any Idea how I can overcome this problem? Thanks a lot!

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  • Accessing Java Connector Architecture (JCA) from a Non-Managed environment

    - by Paul Kuykendall
    Hi, We have been using a JCA to interface with a low-level network resource from within WebSphere, however we have a requirement to be able to access the same network resource externally from Tomcat (i.e. not in a managed environment). The network communication and protocol layouts is very verbose, so we would rather not copy/paste several thousand lines of code (and then have to maintain them separately). From reading the JCA spec, there is supposedly some support to execute the code in a non-managed environment (such as Tomcat). Unfortunately, I have no idea what the interfaces are supposed to do, or how to call them from outside a managed environment (the spec is pretty vague). Are there any implementation examples out there that show how to modify a JCA to be usable in a non-managed environment? Thanks!

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  • php web based portal authentication through IP.

    - by user434885
    i have a web portal running which involves basic data entry. The issue being that this is highly sensitive data. And the credibility of the data entry personel is very low. Therefore i have implemented recording of IP when an entry is made. The Problem i am facing is if this if this person starts forwarding his IP from a proxy server then i am unable to track authenticity of the data. How do i detect if the IP forwarding is happening/ get the real ip address of the person.

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  • Conversion of Single to two UInt16 values in .net

    - by Gio
    In the good old days of C. I could cast a float to an int (assuming 32 bit system), do some bit manipluation ( bitwise and, right shift, ect ), and get the upper and lower 16 bit hex representations of the floating point number, which I could then store in two short values. I'm not seeing an easy way of doing this in C#. System.Convert.ToUInt16 just does a float to int convert (even after I shift right), which leaves a vlaue of 0 if the float is less than 0, which is not the desired effect. //useless leaves me witg a value 0f 0 UIN16 s1 = (UInt16)((System.Convert.ToUInt32(d2) & 0xffff0000) >> 16); //capture the high word UInt16 s2 = (UInt16)(System.Convert.ToUInt32(d2) & 0xffff); //capture the low word A basic cast (UInt32) doesn't work either.

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  • TCP Scanner Python MultiThreaded

    - by user1473508
    I'm trying to build a small tcp scanner for a netmask. The code is as follow: import socket,sys,re,struct from socket import * host = sys.argv[1] def RunScanner(host): s = socket(AF_INET, SOCK_STREAM) s.connect((host,80)) s.settimeout(0.1) String = "GET / HTTP/1.0" s.send(String) data = s.recv(1024) if data: print "host: %s have port 80 open"%(host) Slash = re.search("/", str(host)) if Slash : netR,_,Wholemask = host.partition('/') Wholemask = int(Wholemask) netR = struct.unpack("!L",inet_aton(netR))[0] for host in (inet_ntoa(struct.pack("!L", netR+n)) for n in range(0, 1<<32-Wholemask)): try: print "Doing host",host RunScanner(host) except: pass else: RunScanner(host) To launch : python script.py 10.50.23.0/24 The problem I'm having is that even with a ridiculous low settimeout value set, it takes ages to cover the 255 ip addresses since most of them are not assigned to a machine. How can i make a way faster scanner that wont get stuck if the port is close.MultiThreading ? Thanks !

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  • Is this data set in third normal form?

    - by user2980802
    UNF: (Customer-name, Customer-id, Customer-address, (Unit-price, Order-id, Quantity, Product-id, Delivery-date) (Supplier-name, Supplier-id, Supplier-Address) 3NF: CUSTOMER (Customer-id, Order-id, Customer-name, Customer-address) ORDER (Order-id, Customer-id) ORDER/PRODUCT (Order-id, Quantity, Product-id) PRODUCT (Order-id, Product-id, Delivery-date, Supplier-id, Unit-price,) SUPPLIER (Supplier-name, Supplier-id, Supplier-Address, Product-id) Basically, the UNF is the un-normalised form. The information should have EXACTLY five tables, it's a hint we were given. The tables listed are the definite table names. We were told to make assumptions based on this information: Customer Invoice is generated from customer orders (Order & Order/Product entities) Supplier Order is generated for products that are low in stock (Product entity) Assumptions A customer can place many orders but an order is placed by only one customer An order can be for many products and a product can be ordered many times A product is supplied by only one supplier, a supplier may supply many products This is one of my modules in university and my lecturer is all but useful, I'm really struggling so any help is really appreciated.

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  • Number guessing game (3+- guessed result)

    - by Nick Waring
    I've been assigned a task to create a game that generates 4 digits and the user has to guess the digits one at a time to get the correct result. If the number is correct a Y is displayed and if not, a N. This was easy, now the next step was to implement another two responses. If the answer is too high, a H is displayed and too low, an N. Again, was easy - now the third is to use the same design as game 2 but if the number is 3 higher than a H is displayed and same if it's 3 lower than a L is displayed - otherwise an X is displayed. I can't figure out how to do this. Here's my test code for game 2 for just one of the digits - any help is appreciated. (5 was used just for a test.) def guess(): x = 5 g= int(input("Guess the number: ")) if g == x: print("Y") elif g < x: print("L") else: print("H")

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  • What is a better way to sort by a 5 star rating?

    - by Vizjerai
    I'm trying to sort a bunch of products by customer ratings using a 5 star system. The site I'm setting this up for does not have a lot of ratings and continue to add new products so it will usually have a few products with a low number of ratings. I tried using average star rating but that algorithm fails when there is a small number of ratings. Example a product that has 3x 5 star ratings would show up better than a product that has 100x 5 star ratings and 2x 2 star ratings. Shouldn't the second product show up higher because it is statistically more trustworthy because of the larger number of ratings?

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  • Will Haskell be a good choice for my task?

    - by Narzanka
    I'm starting a new project and don't know which language to use. My 'must have' requirements are: Be able to run on Windows/LinuxMacOs natively (native executable) - user should be able to just run the exe (when on Windows for example) and see the results. No runtimes/interpreters (no jvm, clr, etc) - one file download should be enough to run the application. Full unicode support. Be able to manipulate OS threads (create them, run multiple tasks in parallel on multi-core CPUs, etc). Be reasonably fast (Python level performance and better). To have some kind of standard library that does low-level, mundane tasks. Not very niche and have some community behind it to be able to ask questions. My 'nice to have' requirements are: Language should be functional It should have good string manipulation capabilities (not necessarily regex) Not extremely hard to learn I'm thinking about Haskell now but keeping in mind OCaml as well. Please advice if my choice is correct.

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  • php vs python django or something else for CMS module

    - by Michael
    We're looking to develop a CMS module for our website and I need some help in choosing the language/framework for this project. Basically we need to develop a "help' module like this one from ebay http://pages.ebay.com/help/index.html which will contain a lot of static pages with nice URLs for SEO. The application must run fast using low computer resources. We have been looking to use php on a custom made mvc framework but we received advice from other sources that py/django is the exactly language/framework that we need in terms of maintainability and development speed because it was developed for exactly this kind of projects so I need an expert advice on this matter with pro and cons for each choice.

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  • Outputting audio stream into microphone

    - by Brap
    Hey everyone. Is there a way of outputting audio from my program and redirecting that stream to the system's microphone input 'layer'? I understand this might require some low-level calls being 'Pinvoked', but are there any articles that might help me. For example, if I was to run the output audio stream of my application into Window's Sound Recorder program, it would think that the audio is coming from a microphone and thus record that. I don't want to record a stream, just output it to the device's micrphone input. Thanks for any ideas.

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  • Understanding behaviour of read() and write()

    - by neo730
    hi i am a student and just start learning low level c programming.i tried to understand read() and write() methods with this program. #include <unistd.h> #include <stdlib.h> main() { char *st; st=calloc(sizeof(char),2);//allocate memory for 2 char read(0,st,2); write(1,st,2); } i was expecting that it would give segmentation fault when i would try to input more than 2 input characters.but when i execute program and enter " asdf " after giving " as " as output it executes "df" command. i want to know why it doesn't give segmentation fault when we assign more than 2 char to a string of size 2.and why is it executing rest(after 2 char)of input as command instead of giving it as output only? also reading man page of read() i found read() should give EFAULT error,but it doesn't. I am using linux.

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  • Eclipse 3.5 (Cocoa) slowing down irregularly after some time

    - by chris_l
    Hi, I'd like to hear, if anyone else encounters the same problems, and doesn't use Google's GWT (2.0) plugins: Sometimes, my Eclipse 3.5 (Cocoa) slows down after some time of usage (=30 minutes), so that things like maximizing an editor or moving the splitters becomes unbearably slow (reacting only after several seconds). After an Eclipse restart, everything's fine again. I'm not running low on memory (neither free RAM, nor memory available to Eclipse - Heap/Stack/PermGenSpace), and my system specs are not too bad. I know exactly one other person so far, who sees the same problem - but he also uses the GWT plugins. Since these issues appear irregularly, they're hard to track. Before creating an issue on the GWT bug tracker, I'd like to find out, if this also happens for somebody without Google's plugins. Thanks, Chris Edit: I'm running Snow Leopard 10.6.2

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  • Using a database with C#

    - by Mike
    I have been trying to do something that I think would be really easy but have never used C# before and am having trouble with the details. I simple want to use a sql database with Visual C# Express 2008. For testing purposes I have a datagrid on my form that can reflect changes to the db. If i use this: codesTableAdapter.Fill(dataSet1.codes); The datagrid(dataset) will fill with the info from the sql database. If i then do something like this: codesTableAdapter.InsertQuery(txtCode.Text,txtName.Text); codesTableAdapter.Fill(dataSet1.codes); codesTableAdapter.Update(dataSet1); dataSet1.AcceptChanges(); The datagrid reflects the changes but if close the program and go to the database the changes are not there. When I open the program again the changes are not there. I have a feeling this isn't too clear as my understanding here is very low so please let me know what other info is needed. Thanks

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  • Converting byte[] of binary fixed point to floating point value?

    - by Sean Donohue
    I'm reading some data over a socket. The integral data types are no trouble, the System.BitConverter methods are correctly handling the conversion. (So there are no Endian issues to worry about, I think?) However, BitConverter.ToDouble isn't working for the floating point parts of the data...the source specification is a bit low level for me, but talks about a binary fixed point representation with a positive byte offset in the more significant direction and negative byte offset in the less significant direction. Most of the research I've done has been aimed at C++ or a full fixed-point library handling sines and cosines, which sounds like overkill for this problem. Could someone please help me with a C# function to produce a float from 8 bytes of a byte array with, say, a -3 byte offset?

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  • Showing a loading page in a google chrome extension

    - by user1092042
    I have searched high and low for this but whatever i do this simply does not seem to work. I have a google chrome extension which send an XHR request using a background.js file. Now my requirement is that i need to show a small loading icon while the xhr request is proceeding. Are there any tutorials out there which explains how to do this. I have tried an iframe but it looks ugly when it expands as the entire popup.html expands. Is jquery my only option here because that would mean adding a lot of size to my current project just for a simple animation.

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  • How do I select the item with the highest value using LINQ?

    - by mafutrct
    Imagine you got a class like this: class Foo { string key; int value; } How would you select the Foo with the highest value from an IEnumeralbe<Foo>? A basic problem is to keep the number of iterations low (i.e. at 1), but that affects readability. After all, the best I could find was something along the lines of this: IEnumerable<Foo> list; Foo max = list.Aggregate ((l, r) => l.value > r.value ? l : r); Can you think of a more better way?

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  • Inventory Management OOP design

    - by rgamber
    This was an OOP design and implementation interview question, which I came across on glassdoor.com. Design and implement a inventory management system to minimize the number of missed delivery dates while keeping costs to the company low. Of course there is no right answer to this, but I am not sure I understand the question correctly and am wondering what would be a good answer. Is this as simple as creating an undirected graph with nodes as the delivery points, and edges having weights as the cost of the delivery, and then use a single-source-shortest-path algorithm (like Dijkstras, or Bellman-Ford) on the graph? Not sure if this type of question should be asked here,so let me know and I will delete it.

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  • Detecting when Javascript is performing poorly

    - by what-the-crap
    I'm working on a webapp in jquery that, on older machines or machines without much resources, may perform poorly. To get around this I'd like to make a degraded version that disables some of the features, particularly those that rely on large images. How can I tell if my app is running poorly on the user's computer in jquery or javascript in general? I just need a way to call a function that will degrade the app. (especially when the user may run low on system memory) The only way I can think of is for manual user intervention, but the option would add clutter for users that don't need it and users that do need it may not notice it. Thanks!

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  • Action(Of T) in Visual Basic in List(Of T).ForEach

    - by Jason
    I have searched high and low for documentation on how to use this feature. While the loop I could write would be simple and take no time, I really would like to learn how to use this. Basically I have a class, say, Widget, with a Save() sub that returns nothing. So: Dim w as New Widget() w.Save() basically saves the widget. Now let's say I have a generic collection List(Of Widget) name widgetList(Of Widget) and I want to run a Save() on each item in that list. It says I can do a widgetList.ForEach([enter Action(Of T) here]) ....but how in the F does this work??? There is no documentation anywhere on the intrablags. Help would be much much appreciated.

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  • SElinux process killed while trying to set boolean

    - by Antonio
    I've got a strange problem. I can not allow apache to connect to database at my CentOC 6.4 box: [root@centos6 ~]# setsebool -P httpd_can_network_connect on Killed [root@centos6 ~]# sestatus -b | grep httpd_can_network_connect httpd_can_network_connect off httpd_can_network_connect_cobbler off httpd_can_network_connect_db off I watched log file, but there was no log messages: tail -f /var/log/audit/audit.log UPDATE: There are some information in /var/log/messages: Nov 9 19:07:16 vs302 kernel: setsebool invoked oom-killer: gfp_mask=0x280da, order=0, oom_adj=0, oom_score_adj=0 Nov 9 19:07:16 vs302 kernel: setsebool cpuset=/ mems_allowed=0 Nov 9 19:07:16 vs302 kernel: Pid: 1660, comm: setsebool Not tainted 2.6.32-358.23.2.el6.x86_64 #1 Nov 9 19:07:16 vs302 kernel: Call Trace: Nov 9 19:07:16 vs302 kernel: [<ffffffff810cb641>] ? cpuset_print_task_mems_allowed+0x91/0xb0 Nov 9 19:07:16 vs302 kernel: [<ffffffff8111ce40>] ? dump_header+0x90/0x1b0 Nov 9 19:07:16 vs302 kernel: [<ffffffff8111d2c2>] ? oom_kill_process+0x82/0x2a0 Nov 9 19:07:16 vs302 kernel: [<ffffffff8111d201>] ? select_bad_process+0xe1/0x120 Nov 9 19:07:16 vs302 kernel: [<ffffffff8111d700>] ? out_of_memory+0x220/0x3c0 Nov 9 19:07:16 vs302 kernel: [<ffffffff8112c3dc>] ? __alloc_pages_nodemask+0x8ac/0x8d0 Nov 9 19:07:16 vs302 kernel: [<ffffffff81160d6a>] ? alloc_pages_vma+0x9a/0x150 Nov 9 19:07:16 vs302 kernel: [<ffffffff81143f0b>] ? handle_pte_fault+0x76b/0xb50 Nov 9 19:07:16 vs302 kernel: [<ffffffff81228664>] ? task_has_capability+0xb4/0x110 Nov 9 19:07:16 vs302 kernel: [<ffffffff81004a49>] ? __raw_callee_save_xen_pmd_val+0x11/0x1e Nov 9 19:07:16 vs302 kernel: [<ffffffff8114452a>] ? handle_mm_fault+0x23a/0x310 Nov 9 19:07:16 vs302 kernel: [<ffffffff811485b6>] ? vma_adjust+0x556/0x5e0 Nov 9 19:07:16 vs302 kernel: [<ffffffff810474e9>] ? __do_page_fault+0x139/0x480 Nov 9 19:07:16 vs302 kernel: [<ffffffff81148b8a>] ? vma_merge+0x29a/0x3e0 Nov 9 19:07:16 vs302 kernel: [<ffffffff81149fdc>] ? do_brk+0x26c/0x350 Nov 9 19:07:16 vs302 kernel: [<ffffffff8100ba1d>] ? retint_restore_args+0x5/0x6 Nov 9 19:07:16 vs302 kernel: [<ffffffff81513bfe>] ? do_page_fault+0x3e/0xa0 Nov 9 19:07:16 vs302 kernel: [<ffffffff81510fb5>] ? page_fault+0x25/0x30 Nov 9 19:07:16 vs302 kernel: Mem-Info: Nov 9 19:07:16 vs302 kernel: Node 0 DMA per-cpu: Nov 9 19:07:16 vs302 kernel: CPU 0: hi: 0, btch: 1 usd: 0 Nov 9 19:07:16 vs302 kernel: Node 0 DMA32 per-cpu: Nov 9 19:07:16 vs302 kernel: CPU 0: hi: 186, btch: 31 usd: 30 Nov 9 19:07:16 vs302 kernel: active_anon:132249 inactive_anon:46 isolated_anon:0 Nov 9 19:07:16 vs302 kernel: active_file:56 inactive_file:59 isolated_file:0 Nov 9 19:07:16 vs302 kernel: unevictable:0 dirty:2 writeback:0 unstable:0 Nov 9 19:07:16 vs302 kernel: free:1369 slab_reclaimable:1774 slab_unreclaimable:11588 Nov 9 19:07:16 vs302 kernel: mapped:54 shmem:48 pagetables:1211 bounce:0 Nov 9 19:07:16 vs302 kernel: Node 0 DMA free:2440kB min:72kB low:88kB high:108kB active_anon:12156kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:14648kB mlocked:0kB dirty:0kB writeback:0kB mapped:0kB shmem:0kB slab_reclaimable:24kB slab_unreclaimable:8kB kernel_stack:0kB pagetables:16kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? yes Nov 9 19:07:16 vs302 kernel: lowmem_reserve[]: 0 590 590 590 Nov 9 19:07:16 vs302 kernel: Node 0 DMA32 free:3036kB min:3072kB low:3840kB high:4608kB active_anon:516840kB inactive_anon:184kB active_file:224kB inactive_file:236kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:604988kB mlocked:0kB dirty:8kB writeback:0kB mapped:216kB shmem:192kB slab_reclaimable:7072kB slab_unreclaimable:46344kB kernel_stack:880kB pagetables:4828kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:128 all_unreclaimable? no Nov 9 19:07:16 vs302 kernel: lowmem_reserve[]: 0 0 0 0 Nov 9 19:07:16 vs302 kernel: Node 0 DMA: 0*4kB 1*8kB 0*16kB 0*32kB 0*64kB 1*128kB 1*256kB 0*512kB 0*1024kB 1*2048kB 0*4096kB = 2440kB Nov 9 19:07:16 vs302 kernel: Node 0 DMA32: 129*4kB 67*8kB 30*16kB 19*32kB 6*64kB 2*128kB 1*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 3036kB Nov 9 19:07:16 vs302 kernel: 182 total pagecache pages Nov 9 19:07:16 vs302 kernel: 0 pages in swap cache Nov 9 19:07:16 vs302 kernel: Swap cache stats: add 0, delete 0, find 0/0 Nov 9 19:07:16 vs302 kernel: Free swap = 0kB Nov 9 19:07:16 vs302 kernel: Total swap = 0kB Nov 9 19:07:16 vs302 kernel: 157439 pages RAM Nov 9 19:07:16 vs302 kernel: 6271 pages reserved Nov 9 19:07:16 vs302 kernel: 2686 pages shared Nov 9 19:07:16 vs302 kernel: 146395 pages non-shared Nov 9 19:07:16 vs302 kernel: [ pid ] uid tgid total_vm rss cpu oom_adj oom_score_adj name Nov 9 19:07:16 vs302 kernel: [ 271] 0 271 2798 231 0 -17 -1000 udevd Nov 9 19:07:16 vs302 kernel: [ 476] 0 476 2797 230 0 -17 -1000 udevd Nov 9 19:07:16 vs302 kernel: [ 718] 0 718 2279 122 0 0 0 dhclient Nov 9 19:07:16 vs302 kernel: [ 762] 0 762 6909 58 0 -17 -1000 auditd Nov 9 19:07:16 vs302 kernel: [ 787] 0 787 62270 147 0 0 0 rsyslogd Nov 9 19:07:16 vs302 kernel: [ 801] 25 801 40326 2655 0 0 0 named Nov 9 19:07:16 vs302 kernel: [ 850] 0 850 16563 172 0 -17 -1000 sshd Nov 9 19:07:16 vs302 kernel: [ 875] 0 875 23451 240 0 0 0 sshd Nov 9 19:07:16 vs302 kernel: [ 966] 498 966 4780 44 0 0 0 wrapper Nov 9 19:07:16 vs302 kernel: [ 968] 498 968 497404 40812 0 0 0 java Nov 9 19:07:16 vs302 kernel: [ 1057] 0 1057 20216 225 0 0 0 master Nov 9 19:07:16 vs302 kernel: [ 1064] 89 1064 20278 209 0 0 0 qmgr Nov 9 19:07:16 vs302 kernel: [ 1071] 0 1071 27075 121 0 0 0 bash Nov 9 19:07:16 vs302 kernel: [ 1111] 0 1111 24880 350 0 0 0 httpd Nov 9 19:07:16 vs302 kernel: [ 1117] 48 1117 24913 351 0 0 0 httpd Nov 9 19:07:16 vs302 kernel: [ 1118] 48 1118 24880 337 0 0 0 httpd Nov 9 19:07:16 vs302 kernel: [ 1119] 48 1119 24880 337 0 0 0 httpd Nov 9 19:07:16 vs302 kernel: [ 1120] 48 1120 24880 337 0 0 0 httpd Nov 9 19:07:16 vs302 kernel: [ 1121] 48 1121 24880 337 0 0 0 httpd Nov 9 19:07:16 vs302 kernel: [ 1122] 48 1122 24880 337 0 0 0 httpd Nov 9 19:07:16 vs302 kernel: [ 1124] 48 1124 24880 337 0 0 0 httpd Nov 9 19:07:16 vs302 kernel: [ 1125] 48 1125 24880 337 0 0 0 httpd Nov 9 19:07:16 vs302 kernel: [ 1129] 0 1129 29313 151 0 0 0 crond Nov 9 19:07:16 vs302 kernel: [ 1143] 0 1143 1018 22 0 0 0 agetty Nov 9 19:07:16 vs302 kernel: [ 1146] 0 1146 1015 22 0 0 0 mingetty Nov 9 19:07:16 vs302 kernel: [ 1514] 0 1514 23451 237 0 0 0 sshd Nov 9 19:07:16 vs302 kernel: [ 1517] 0 1517 27075 113 0 0 0 bash Nov 9 19:07:16 vs302 kernel: [ 1641] 89 1641 20236 218 0 0 0 pickup Nov 9 19:07:16 vs302 kernel: [ 1659] 0 1659 25234 39 0 0 0 tail Nov 9 19:07:16 vs302 kernel: [ 1660] 0 1660 89903 85712 0 0 0 setsebool Nov 9 19:07:16 vs302 kernel: Out of memory: Kill process 1660 (setsebool) score 568 or sacrifice child Nov 9 19:07:16 vs302 kernel: Killed process 1660, UID 0, (setsebool) total-vm:359612kB, anon-rss:342708kB, file-rss:140kB

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  • Network throughput issue (ARP-related)

    - by Joel Coel
    The small college where I work is having some very strange network issues. I'm looking for any advice or ideas here. We were fine over the summer, but the trouble began few days after students returned to campus in force for the fall term. Symptoms The main symptom is that internet access will work, but it's very slow... often to the point of timeouts. As an example, a typical result from Speedtest.net will return .4Mbps download, but allow 3 to 8 Mbps upload speed. Lesser symptoms may include severely limited performance transferring data to and from our file server, or even in some cases the inability to log in to the computer (cannot reach the domain controller). The issue crosses multiple vlans, and has effected devices on nearly every vlan we operate. The issue does not impact all machines on the network. An unaffected machine will typically see at least 11Mbps download from speedtest.net, and perhaps much more depending on larger campus traffic patterns at the time. There is one variation on the larger issue. We have one vlan where users were unable to log into nearly all of the machines at all. IT staff would log in using a local administrator account (or in some cases cached credentials), and from there a release/renew or pinging the gateway would allow the machine to work... for a while. Complicating this issue is that this vlan covers our computer labs, which use software called Deep Freeze to completely reset the hard drives after a reboot. It could just the same issue manifesting differently because of stale data on machines that have not permanently altered low-level info for weeks. We were able to solve this, however, by creating a new vlan and moving the labs over to the new vlan wholesale. Instigations Eventually we noticed that the effected machines all had recent dhcp leases. We can predict when a machine will become "slow" by watching when a dhcp lease comes up for renewal. We played with setting the lease time very short for a test vlan, but all that did was remove our ability to predict when the machine would become slow. Machines with static IPs have pretty much always worked normally. Manually releasing/renewing an address will never cause a machine to become slow. In fact, in some cases this process has fixed a machine in that state. Most of the time, though, it doesn't help. We also noticed that mobile machines like laptops are likely to become slow when they cross to new vlans. Wireless on campus is divided up into "zones", where each zone maps to a small set of buildings. Moving to a new building can place you in a zone, thereby causing you to get a new address. A machine resuming from sleep mode is also very likely to be slow. Mitigations Sometimes, but not always, clearing the arp cache on an effected machine will allow it to work normally again. As already mentioned, releasing/renewing a local machine's IP address can fix that machine, but it's not guaranteed. Pinging the default gateway can also sometimes help with a slow machine. What seems to help most to mitigate the issue is clearing the arp cache on our core layer-3 switch. This switch is used for our dhcp system as the default gateway on all vlans, and it handles inter-vlan routing. The model is a 3Com 4900SX. To try to mitigate the issue, we have the cache timeout set on the switch all the way down to the lowest possible time, but it hasn't helped. I also put together a script that runs every few minutes to automatically connect to the switch and reset the cache. Unfortunately, this does not always work, and can even cause some machines to end up in the slow state for a short time (though these seem to correct themselves after a few minutes). We currently have a scheduled job that runs every 10 minutes to force the core switch to clear it's ARP cache, but this is far from perfect or desirable. Reproduction We now have a test machine that we can force into the slow state at will. It is connected to a switch with ports set up for each of our vlans. We make the machine slow by connecting to different vlans, and after a new connection or two it will be slow. It's also worth noting in this section that this has happened before at the start of prior terms, but in the past the problem has gone away on it's own after a few days. It solved itself before we had a chance to do much diagnostic work... hence why we've allowed it to drag so long into the term this time 'round; the expectation was this would be a short-lived situation. Other Factors It's worth mentioning that we have had about half a dozen switches just outright fail over the last year. These are mainly 2003/2004-era 3Coms (mostly 4200's) that were all put in at about the same time. They should still be covered under warranty, buy HP has made getting service somewhat difficult. Mostly in power supplies that have failed, but in a couple cases we have used a power supply from a switch with a failed mainboard to bring a switch with a failed power supply back to life. We do have UPS devices on all but three of four switches now, but that was not the case when I started two and a half years ago. Severe budget constraints (we were on the Dept. of Ed's financially challenged institutions list a couple years back) have forced me to look to the likes of Netgear and TrendNet for replacements, but so far these low-end models seem to be holding their own. It's also worth mentioning that the big change on our network this summer was migrating from a single cross-campus wireless SSID to the zoned approach mentioned earlier. I don't think this is the source of the issue, as like I've said: we've seen this before. However, it's possible this is exacerbating the issue, and may be much of the reason it's been so hard to isolate. Diagnosis At first it seemed clear to us, given the timing and persistent nature of the problem, that the source of the issue was an infected (or malicious) student machine doing ARP cache poisoning. However, repeated attempts to isolate the source have failed. Those attempts include numerous wireshark packet traces, and even taking entire buildings offline for brief periods. We have not been able even to find a smoking gun bad ARP entry. My current best guess is an overloaded or failing core switch, but I'm not sure on how to test for this, and the cost of replacing it blindly is steep. Again, any ideas appreciated.

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  • Company Review: Google Products

    Google, Inc offers an array of products and services to all of its end-users. However their search capabilities are the foundation for Google’s current success and their primary business focus. Currently, Google offers over twenty different search applications that allow users to search the internet for books, maps, videos, images, products and much more. Their product decisions have allowed users demands to be met while focusing on the free based model. This allows users to access Google data free of charge and indirectly gives Google a strong competitive advantage of other competitors along with the accuracy of the search results. According to Google, Inc, they offer the following types of searching capabilities: Alerts Get email updates on the topics of your choice Blog Search Find blogs on your favorite topics  Books Search the full text of books  Custom Search Create a customized search experience for your community  Desktop Search and personalize your computer  Dictionary Search for definitions of words and phrases Directory Search the web, organized by topic or category Earth Explore the world from your computer Finance Business info, news and interactive charts GOOG-411 Find and connect for free with businesses from your phone  Images Search for images on the web Maps View maps and directions News Search thousands of news stories Patent Search Search the full text of US Patents Product Search Search for stuff to buy Scholar Search scholarly papers Toolbar Add a search box to your browser Trends Explore past and present search trends Videos Search for videos on the web Web Search Search billions of web pages Web Search Features Find movies, music, stocks, books and more mapping Google’s free based business model is only one way it differentiates itself from its competition. There is also a strong focus on the accuracy of search results and the speed in which they are returned to the end-user. Quality function deployment (QFD) is a structured method used to help connect user needs to the design features of a project proposed to address those needs. This method is particularly useful in accounting for needs that are not easily articulated or precisely defined according to the U. S. Department of Transportation Federal Highway Administration. Due to the fact that QFD is so customer driven Google is always in a constant state of change in attempt to reengineer its search algorithms, and other dependant systems so that end-users requirements are constantly being met. Value engineering is a key example of this, Google is constantly trying to improve all aspects of its products, improve system maintainability, and system interoperability. Bridgefield Group defines value engineering as an organized methodology that identifies and selects the lowest lifecycle cost options in design, materials and processes that achieves the desired level of performance, reliability and customer satisfaction. In addition, it seeks to remove unnecessary costs in the above areas and is often a joint effort with cross-functional internal teams and relevant suppliers. Common issues that appear when developing large scale systems like Google’s search applications include modular design of a product and/or service and providing accurate value analysis. A design approach that adheres to four fundamental tenets of cohesiveness, encapsulation, self-containment, and high binding to design a system component as an independently operable unit subject to change is how the Open System Joint Task Force defines modular design. More specifically M. S. Schmaltz defines modular software design as having a large collection of statements strung together in one partition of in-line code; we segment or divide the statements into logical groups called modules. Each module performs one or two tasks, and then passes control to another module. By breaking up the code into "bite-sized chunks", so to speak, we are able to better control the flow of data and control. This is especially true in large software systems. Value analysis is a process to evaluate products and services based on effectiveness, safety, and cost. Value analysis involves assessing the quality as well as the cost of a product or service as defined by the Healthcare Financial Management Association.  “Operations Management deals with the design and management of products, processes, services and supply chains. It considers the acquisition, development, and utilization of resources that firms need to deliver the goods and services their clients want.” (MIT,2010) Google, Inc encourages an open environment between all employees, also known as Googlers. This is reinforced by a cross-section team or cross-functional teams comprised from multiple departments assigned to every project so that every department like marketing, finance, and quality assurance has input on every project. In addition, Google is known for their openness to new ideas regardless of the status or seniority of an employee. In fact, Google allows for 20% of an employee’s time can be devoted to developing new ideas and/or pet projects. HumTech.com defines a cross-functional team as a collection of people with varied levels of skills and experience brought together to accomplish a task. As the name implies, Cross-Functional Team members come from different organizational units. Cross-Functional Teams may be permanent or ad hoc. Google’s search application product strategy primarily focuses on mass customization. This is allows Google to create a base search application and allows results to be returned to the end-users quickly based on specific parameters and search settings. In addition, they also store the data that is returned in case other desire the same results based on other end-users supplying the same customized settings. This allows Google to appear to render search results in virtually real-time to the user while allowing for complete customization of the searching criteria. Greg Vogl, a professor at Uganda Martyrs University, defines mass customization as when a business gives its customers the opportunity to tailor its products or services to the customer's specifications. The IT staff at Google play a key role in ensuring that the search application’s product strategy is maintained simply because the IT staff designs, develops, and maintains all of their proprietary applications. In fact, they also maintain all network infrastructure to ensure that it is available to all end-users. References: http://www.google.com/intl/en/options/ http://ops.fhwa.dot.gov/freight/publications/ftat_user_guide/sec5.htm http://www.bridgefieldgroup.com/bridgefieldgroup/glos9.htm#V http://www.acq.osd.mil/osjtf/termsdef.html http://www.cise.ufl.edu/~mssz/Pascal-CGS2462/prog-dsn.html http://www.hfma.org/publications/business_caring_newsletter/exclusives/Supply+and+Inventory+Terms+Defined.htm http://mitsloan.mit.edu/omg/om-definition.php http://www.humtech.com/opm/grtl/ols/ols3.cfm http://www.gregvogl.net/courses/mis1/glossary.htm

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  • SQL Sentry First Impressions

    - by AjarnMark
    After struggling to defend my SQL Servers from a political attack recently, I realized that I needed better tools to back me up, and SQL Sentry is the leading candidate. A couple of weeks ago, seemingly from out of nowhere, complaints from the business users started coming in that one of the core internal applications was running dramatically slower than normal, and fingers were being pointed at the SQL Server.  Unfortunately, we don’t have a production DBA whose entire job is to monitor and maintain our SQL Servers.  The responsibility falls to me to do the best I can, investing only a small portion of my time, because there are so many other responsibilities to take care of, and our industry is still deep in recession.  I inherited these SQL Servers and have made significant improvements in process and procedure, but I had not yet made the time to take real baseline measurements or keep a really close eye on the performance.  Like many DBAs, I wrote several of my own tools and used the “built-in tools” like Profiler, PerfMon, and sp_who2 (did I mention most of our instances are SQL Server 2000?).  These have all served me well for in-the-moment troubleshooting and maintenance, but they really fell down on the job when I was called upon to “prove” that SQL Server performance was acceptable and more importantly had not degraded recently (i.e. historical comparisons).  I really didn’t have anything from a historical comparison perspective, but I was able to show that current performance was acceptable, and deflect attention back onto other components (which in fact turned out to be the real culprit). That experience dramatically illustrated the need for better monitoring tools.  Coincidentally, I had been talking recently to my boss about the mini nightmare of monitoring several critical and interdependent overnight jobs that operate on separate instances of SQL Server.  Among other tools, I had been using Idera’s SQL Job Manager which is a free tool and did a nice job of showing me job schedules and histories in a nice calendar view.  This worked fairly well, and for the money (did I mention it was free?) it couldn’t be beat.  But it is based on the stored job history in MSDB, and there were other performance problems that we ran into when we started changing the settings for how much job history to retain, in order to be able to look back a month or more in the calendar view.  Another coincidence (if you believe in such things) was that when we had some of those performance challenges, I posted a couple of questions to the #sqlhelp hashtag on Twitter and Greg Gonzalez (@SQLSensei) suggested I check out SQL Sentry’s Event Manager.  At the time, I just thought he worked there, but later found out that he founded the company.  When I took a quick look at the features & benefits, the one that really jumped out at me is Chaining and Queueing which sounded like it would really help with our “interdependent jobs on different servers” issue. I know that is a lot of background story and coincidences, but hopefully you have stuck with me so far, and now we have arrived at the point where last week I downloaded and installed the 30-day trial of the SQL Sentry Power Suite, which is Event Manager plus Performance Advisor.  And I must say that I really like what I see so far.  Here are a few highlights: Great Support.  I had two issues getting the trial setup and monitoring a handful of our servers.  One of which was entirely my fault (missed a security setting in SQL 2008) and the other was mostly my fault (late change to some config settings that were apparently cached and did not get refreshed properly).  In both cases, the support staff at SQL Sentry were very responsive and rather quickly figured out what the cause and fix was for each of them.  This left me with a great impression of the company.  Kudos to them! Chaining and Queueing.  While I have not yet activated this feature, I am very excited about the possibilities.  We have jobs on three different instances of SQL Server that have to be run in a certain order, and each has to finish before the next can successfully begin, and I believe this feature will ensure just that.  It has been a real pain in the backside when one of those jobs runs just a little too long and does not finish before the job on another instance starts, thus triggering a chain reaction of either outright job failures, or worse, successful completion of completely invalid processing. Calendar View.  I really, really like the Event Manager calendar view where I can see all jobs and events across all instances and identify potential resource contention as well as windows of opportunity for maintenance activity.  Very well done, and based on Event Manager’s own database of accumulated historical information rather than querying the source instances every time. Performance Advisor Dashboard History View.  This view let’s me quickly select a date and time range and it displays graphs of key SQL Server and Windows metrics.  This is exactly the thing I needed to answer the “has performance changed recently” question at the beginning of this post. Reporting Services Subscription Jobs with Report Name.  This was a big and VERY pleasant surprise.  If you have ever looked at the list of SQL Server jobs that SQL Server Reporting Services creates when you make a Subscription, you will notice that they all have some sort of GUID as the name of the job.  This is really ugly, and really annoying because when you are just looking at the SQL Agent and Job Activity Monitor, if you see that Job X failed, you really do not have any indication in the name or the properties of the Job itself, as to what Report that was for.  But with SQL Sentry Event Manager you do.  The Jobs list in the Navigator pane in SQL Sentry, amazingly, displays the name of the Report that the Subscription Job is for.  And when you open it to see more details, it shows you the full Reporting Services path to that Report, so you can immediately track it down in the Report Manager in case you want to identify/notify the owner or edit the Subscription information.  I did not expect this at all, but I sure do like it.  HOORAY! That is just my first impressions from using the tools for a few days.  And I haven’t even gotten into how it showed me where I was completely mistaken about one aspect of my SQL Server disk configurations.  I’ll share that lesson in another blog entry.  But I have to say it again, the combination of Event Manager and Performance Advisor working together have really made me a fan.

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  • VS 2010 JavaScript editor – matching braces highlighting – is it so difficult to implement?

    - by AGS777
    I do not know. Just curious. But first things first. As a web developer I spend about 80% of my work-time editing JavaScript code. And since my server-side platform is .NET then it would be very convenient to have decent JavaScript text editor within Visual Studio IDE. So, Visual Studio 2010 is out. Downloaded and installed. What were my expectations regarding JavaScript editor? Pretty low, actually.  I just wanted to have matching braces highlighted eventually. That’s all. Yes, I know about Ctrl + ] shortcut but it is not event remotely close to convenience. And the result? Alas. Without further ado, just look at some real-world fragment of code from jQuery Templates Proposal experimental plugin as I see it in Notepad++, Notepad2 and Visual Studio 2010 editors respectively: Notepad++ Notepad2 Visual Studio 2010 Look at the highlighted parentheses, regular expression literals, numbers. Do you have a feeling that the last screenshot is not very informative in comparison with the other ones? If yes, then my question is why? Instead I was given an IntelliSense. Sorry, but I do not need it to rot my mind. Especially the one which does not always work properly (try to use it with base2 library for example). With all the expressive power of the language I have to know what I am doing. Instead I still have the same plain old Notepad with some of the JavaScript keywords colorized, plus partially functional/useful IntelliSense. What I do need, is just a little help to make less errors when I type the code – some essential text editor facilities that I really need. Give me that and only then feel free to improve on something else. Maybe I am wrong. Then, sorry. Just cannot believe that I have to wait for another couple of years to get very basic code editor feature.  

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