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  • Can I use memcpy in C++ to copy classes that have no pointers or virtual functions

    - by Shane MacLaughlin
    Say I have a class, something like the following; class MyClass { public: MyClass(); int a,b,c; double x,y,z; }; #define PageSize 1000000 MyClass Array1[PageSize],Array2[PageSize]; If my class has not pointers or virtual methods, is it safe to use the following? memcpy(Array1,Array2,PageSize*sizeof(MyClass)); The reason I ask, is that I'm dealing with very large collections of paged data, as decribed here, where performance is critical, and memcpy offers significant performance advantages over iterative assignment. I suspect it should be ok, as the 'this' pointer is an implicit parameter rather than anything stored, but are there any other hidden nasties I should be aware of?

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  • Inserting asyncronously into Oracle, any benefits?

    - by Karl Trumstedt
    I am using ODP.NET for loading data into Oracle. I am bulking inserts into groups of a 1000 rows each call. Is there any performance benefits in calling my load method asynchronously? So say I want to insert 10000 rows, instead of making 10 calls synchronously I make 10 calls asynchronously. My database is using ASSM right now but otherwise plenty of freelists are used of course. The database server has several cores as well. My initial tests seem to point to a performance increase, but maybe there is something I cannot see? Potential deadlock or contention issues? Of course, there is added complexity in handling transactions and such doing my load this way.

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  • In what circumstances can large pages produce a speedup ?

    - by timday
    Modern x86 CPUs have the ability to support larger page sizes than the legacy 4K (ie 2MB or 4MB), and there are OS facilities (Linux, Windows) to access this functionality. The Microsoft link above states large pages "increase the efficiency of the translation buffer, which can increase performance for frequently accessed memory". Which isn't very helpful in predicting whether large pages will improve any given situation. I'm interested in concrete, preferably quantified, examples of where moving some program logic (or a whole application) to use huge pages has resulted in some performance improvement. Anyone got any success stories ? There's one particular case I know of myself: using huge pages can dramatically reduce the time needed to fork a large process (presumably as the number of TLB records needing copying is reduced by a factor on the order of 1000). I'm interested in whether huge pages can also benefit more mundane applications though.

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  • CXF code first service, WSDL generation; soap:address changes?

    - by jcalvert
    I have a simple Java interface/implementation I am exposing via CXF. I have a jaxws element in my Spring configuration file like this: <jaxws:endpoint id="managementServiceJaxws" implementor="#managementService" address="/jaxws/ManagementService" > </jaxws:endpoint> It generates the WSDL from my annotated interface and exposes the service. Then when I hit http://myhostname/cxf/jaxws/ManagementService?wsdl I get a lovely WSDL. At the bottom in the wsdl:service element, I'll see <soap:address location="http://myhostname/cxf/jaxws/ManagementService"/> However, some time a day or so later, with no application restart, hitting that same url produces: This causes a number of problems, but what I really want is to fix it. Right now, there's a particular client to the webservice that sets the endpoint to localhost; because it runs on the same machine. Is it possible the wsdl is getting regenerated and cached and then exposing the 'localhost' version? In part I don't know the exact mechanism by which one goes from a ?wsdl request in CXF to the response. It seems almost certain that it's retrieving some cached version, given that it's supposed to be determining the address by asking the servletcontainer (Jetty). For reference I know a stopgap solution is using the hostname on the client and making sure an alias in place so that it goes over the loopback. EDIT: For reference, I confirmed that if I bring my application up and first hit it over localhost, then querying for the wsdl via the hostname shows the address as localhost. Conversely, first hitting it over the hostname causes localhost requests to show the hostname. So obviously something is getting cached here.

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  • VS2008 intellisense performance issue with large number of partial static classes

    - by scebula
    My question is a follow-up to the issue posted here regarding the Intellisense performance issue when building a large solution in VS2008 that has many partial static classes. Since Microsoft does not seem to be addressing the issue for VS2008, I would like to know if there are other ways around the problem? Waiting for VS2010 is not an option at this time. The proposed solution in the previous post is not practical as some of the partial classes may be regenerated and this would be a maintenance headache.

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  • Is there a preferred method of including the source code(s) of other software you've used in your ap

    - by Adam S
    I've used a few F/OSS libraries in my commercial application. As per their licenses, I am obligated to include their source codes along with my VS2008 application. This is my first time making a "real" commercial application, and I would appreciate some advice on how best to go about including their source codes. I don't want to package them as zip files alongside my installed. I still want my installer to be a single file.

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  • When I use WinForms (C#) designer in VS2010, it still generates code that StyleCop complains about.

    - by Hamish Grubijan
    Some problems that I recall (there may be more): Includes regions Does not use this. prefix for member variables and methods Includes comments like the one below ( having // by itself catches the eye of StyleCop) // // fileNameTextBox // If I make a change to the text, and then open the designer again, and screws up my previously perfected fruits of hard labor. How did / would you solve this problem? I heard but did not personally experience a similar problem with WPF. How did / would you fix that? Thanks.

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  • Can I optimize this at all?

    - by Moshe
    I'm working on an iOS app and I'm using the following code for one of my tables to return the number of rows in a particular section: return [[kSettings arrayForKey:@"views"] count]; Is there any other way to write that line of code so that it is more memory efficient? EDIT: kSettings = NSUserDefaults standardUserDefaults. Is there any way to rewrite my line of code so that whatever memory it occupies is released sooner than it is released now?

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  • How to copy and paste code with retaining the format

    - by Sab
    This question may have been asked before but I was unable to find any solution. So here goes: When I browse and see some code that I would like to copy I simply use ctrl+c and ctrl+v. Most of the time this works fine. But in some cases (websites like stackoverflow and others ) when I copy the code and paste it , it only comes on one line in eclipse. I have tried pasting this code into eclipse and select all and hitting auto format but this doesnt help either. I have also pasted the code into komodo and word. But to no avail. The code simply refuses to align itself. Does anyone know any solution to this?

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  • Propor usage of double and single quotes?

    - by Phox
    I'm talking about the performance increase here. From all I know you can echo variables in double quotes ("), like so: <?php echo "You are $yourAge years old"; ?> But single quotes will just return You are $yourAge years old. But what about performance differences? I've always gone by the rule that single quotes are faster because the PHP interpreter doesn't have to search through the string for variables. But I'm seeing more and more blog and forum posts on the web saying differently. Does anyone actually have any information on this subject? Perhaps benchmark tests or something? Cheers.

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  • Why would Linux VM in vSphere ESXi 5.5 show dramatically increased disk i/o latency?

    - by mhucka
    I'm stumped and I hope someone else will recognize the symptoms of this problem. Hardware: new Dell T110 II, dual-core Pentium G860 2.9 GHz, onboard SATA controller, one new 500 GB 7200 RPM cabled hard drive inside the box, other drives inside but not mounted yet. No RAID. Software: fresh CentOS 6.5 virtual machine under VMware ESXi 5.5.0 (build 174 + vSphere Client). 2.5 GB RAM allocated. The disk is how CentOS offered to set it up, namely as a volume inside an LVM Volume Group, except that I skipped having a separate /home and simply have / and /boot. CentOS is patched up, ESXi patched up, latest VMware tools installed in the VM. No users on the system, no services running, no files on the disk but the OS installation. I'm interacting with the VM via the VM virtual console in vSphere Client. Before going further, I wanted to check that I configured things more or less reasonably. I ran the following command as root in a shell on the VM: for i in 1 2 3 4 5 6 7 8 9 10; do dd if=/dev/zero of=/test.img bs=8k count=256k conv=fdatasync done I.e., just repeat the dd command 10 times, which results in printing the transfer rate each time. The results are disturbing. It starts off well: 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GB) copied, 20.451 s, 105 MB/s 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GB) copied, 20.4202 s, 105 MB/s ... but after 7-8 of these, it then prints 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GG) copied, 82.9779 s, 25.9 MB/s 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GB) copied, 84.0396 s, 25.6 MB/s 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GB) copied, 103.42 s, 20.8 MB/s If I wait a significant amount of time, say 30-45 minutes, and run it again, it again goes back to 105 MB/s, and after several rounds (sometimes a few, sometimes 10+), it drops to ~20-25 MB/s again. Plotting the disk latency in vSphere's interface, it shows periods of high disk latency hitting 1.2-1.5 seconds during the times that dd reports the low throughput. (And yes, things get pretty unresponsive while that's happening.) What could be causing this? I'm comfortable that it is not due to the disk failing, because I also had configured two other disks as an additional volume in the same system. At first I thought I did something wrong with that volume, but after commenting the volume out from /etc/fstab and rebooting, and trying the tests on / as shown above, it became clear that the problem is elsewhere. It is probably an ESXi configuration problem, but I'm not very experienced with ESXi. It's probably something stupid, but after trying to figure this out for many hours over multiple days, I can't find the problem, so I hope someone can point me in the right direction. (P.S.: yes, I know this hardware combo won't win any speed awards as a server, and I have reasons for using this low-end hardware and running a single VM, but I think that's besides the point for this question [unless it's actually a hardware problem].) ADDENDUM #1: Reading other answers such as this one made me try adding oflag=direct to dd. However, it makes no difference in the pattern of results: initially the numbers are higher for many rounds, then they drop to 20-25 MB/s. (The initial absolute numbers are in the 50 MB/s range.) ADDENDUM #2: Adding sync ; echo 3 > /proc/sys/vm/drop_caches into the loop does not make a difference at all. ADDENDUM #3: To take out further variables, I now run dd such that the file it creates is larger than the amount of RAM on the system. The new command is dd if=/dev/zero of=/test.img bs=16k count=256k conv=fdatasync oflag=direct. Initial throughput numbers with this version of the command are ~50 MB/s. They drop to 20-25 MB/s when things go south. ADDENDUM #4: Here is the output of iostat -d -m -x 1 running in another terminal window while performance is "good" and then again when it's "bad". (While this is going on, I'm running dd if=/dev/zero of=/test.img bs=16k count=256k conv=fdatasync oflag=direct.) First, when things are "good", it shows this: When things go "bad", iostat -d -m -x 1 shows this:

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  • Proper usage of double and single quotes?

    - by Phox
    I'm talking about the performance increase here. From all I know you can echo variables in double quotes ("), like so: <?php echo "You are $yourAge years old"; ?> But single quotes will just return You are $yourAge years old. But what about performance differences? I've always gone by the rule that single quotes are faster because the PHP interpreter doesn't have to search through the string for variables. But I'm seeing more and more blog and forum posts on the web saying differently. Does anyone actually have any information on this subject? Perhaps benchmark tests or something?

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  • Elegantly Handle Repetitive Property Code in C#

    - by Eric J.
    The language shortcut public string Code { get; set; } saves a bit of typing when defining trivial properties in C#. However, I find myself writing highly repetitive, not-quite-as-trivial property code that still follows a clear pattern e.g. public string Code { get { return code; } set { if (code != value) { code = value; NotifyPropertyChanged("Code"); } } } I can certainly define a Visual Studio snippet to reduce typing. However, if I need to add something to my pattern, I have to go back and change quite a bit of existing code. Is there a more elegant approach? Is a snippet the best way to go?

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  • Even lighter than SQLite

    - by Richard Fabian
    I've been looking for a C++ SQL library implementation that is simple to hook in like SQLite, but faster and smaller. My projects are in games development and there's definitely a cutoff point between needing to pass the ACID test and wanting some extreme performance. I'm willing to move away from SQL string style queries, allowing it to be code driven, but I haven't found anything out there that provides SQL like flexibility while also preferring performance over the ACID test. I don't want to go reinventing the wheel, and the idea of implementing an SQL library on my own is quite daunting, even if it's only going to be simple subset of all the calls you could make. I need the basic commands (SELECT, MODIFY, DELETE, INSERT, with JOIN, and WHERE), not data operations (like sorting, min, max, count) and don't need the database to be atomic, or even enforce consistency (I can use a real SQL service while I'm testing and debugging).

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