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• Difference between Cloud and Virtualization

  - by Akash Kava

  Ops: This does not belong to ServerFault because it focuses on Programing Architecture. I have following questions regarding differences between Cloud and Virtualization.. How Cloud is different then Virtualization? Currently I tried to find out pricing of Rackspace, Amazone and all similar cloud providers, I found that our current 6 dedicated servers came cheaper then their pricing. So how one can claim cloud is cheaper? Is it cheaper only in comparison of normal hosting? We re organized our infrastructure in virtual environment to reduce or configuration overhead at time of failure, we did not have to rewrite any peice of code that is already written for earlier setup. So moving to virtualization does not require any re programming. But cloud is absoltely different and it will require entire reprogramming right? Is it really worth to recode when our current IT costs are 3-4 times lower then cloud hosting including raid backups and all sort of clustering for high availability? New programming architecture means new overheads of training staff, new methods of testing and new deployment schemes, does it justify over "on demand resource usage" words of cloud? We are having current development architecture with simple Server side ASP.NET WebServices with no local context and on client side Flex/Silverlight which offers pretty good REST architecture and its highly scalable. How does cloud differs from REST model of deployment? On storage, SQL Server or MySQL offers pretty good replication and high availibility then what is advantage in cloud? Data guarantee, one of our vendor hosting some other customer's app on cloud (one of most used), lost Entire Hard Disk (the virtual) and entire module in first 6 months. Second provider said its your duty to take backup, fine I agree, but no provider gives SLA for data guarantee, they give 99% uptime. However in most business apps, uptime is less important then data integrity. In our 10 years of dedicated hosting experience we had only one hard disk crash. This makes me little skeptical to go for cloud and loosing control over data. And I feel its just a big marketing buzz to sell virtulization in different form. Size of data, currently all providers charge very heavy for large data, if you are hosting only below 100GB cloud can be good alternative, but I think virtual servers and dedicated servers above 100GB to few TBs are still cheaper. Why would want to pay so high on cloud when there is no data guarentee as well as it doesnt say anything about redundancy. (I wish SO had something for spell check for Internet Explorer, sorry for wrong spellings in my post)

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• Type Declaration - Pointer Asterisk Position

  - by sahs

  Hello, in C++, the following means "allocate memory for an int pointer": int* number; So, the asterisk is part of the variable type; without it, that would mean something else (that's why I usually don't separate the asterisk from the variable type). Then what is the reason the asterisk is considered something else, instead of being part of the type? For example, it seems better, if the following meant "allocate memory for two int pointers": int* number1, number2; Am I wrong?

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• C++'s std::string pools, debug builds? std::string and valgrind problems

  - by Den.Jekk

  Hello, I have a problem with many valgrind warnings about possible memory leaks in std::string, like this one: 120 bytes in 4 blocks are possibly lost in loss record 4,192 of 4,687 at 0x4A06819: operator new(unsigned long) (vg_replace_malloc.c:230) by 0x383B89B8B0: std::string::_Rep::_S_create(unsigned long, unsigned long, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.8) by 0x383B89C3B4: (within /usr/lib64/libstdc++.so.6.0.8) by 0x383B89C4A9: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, unsigned long, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.8) I'm wondering: does std::string (GCC 4.1.2) use any memory pools? if so, is there any way to disable the pools (in form of a debug build etc.)? Regards, Den

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• c++ std::ostringstream vs std::string::append

  - by NickSoft

  In all examples that use some kind of buffering I see they use stream instead of string. How is std::ostringstream and << operator different than using string.append. Which one is faster and which one uses less resourses (memory). One difference I know is that you can output different types into output stream (like integer) rather than the limited types that string::append accepts. Here is an example: std::ostringstream os; os << "Content-Type: " << contentType << ";charset=" << charset << "\r\n"; std::string header = os.str(); vs std::string header("Content-Type: "); header.append(contentType); header.append(";charset="); header.append(charset); header.append("\r\n"); Obviously using stream is shorter, but I think append returns reference to the string so it can be written like this: std::string header("Content-Type: "); header.append(contentType) .append(";charset=") .append(charset) .append("\r\n"); And with output stream you can do: std::string content; ... os << "Content-Length: " << content.length() << "\r\n"; But what about memory usage and speed? Especially when used in a big loop. Update: To be more clear the question is: Which one should I use and why? Is there situations when one is preferred or the other? For performance and memory ... well I think benchmark is the only way since every implementation could be different. Update 2: Well I don't get clear idea what should I use from the answers which means that any of them will do the job, plus vector. Cubbi did nice benchmark with the addition of Dietmar Kühl that the biggest difference is construction of those objects. If you are looking for an answer you should check that too. I'll wait a bit more for other answers (look previous update) and if I don't get one I think I'll accept Tolga's answer because his suggestion to use vector is already done before which means vector should be less resource hungry.

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• data structure for counting frequencies in a database table-like format

  - by user373312

  i was wondering if there is a data structure optimized to count frequencies against data that is stored in a database table-like format. for example, the data comes in a (comma) delimited format below. col1, col2, col3 x, a, green x, b, blue ... y, c, green now i simply want to count the frequency of col1=x or col1=x and col2=green. i have been storing the data in a database table, but in my profiling and from empirical observation, database connection is the bottle-neck. i have tried using in-memory database solutions too, and that works quite well; the only problem is memory requirements and quirky init/destroy calls. also, i work mainly with java, but have experience with .net, and was wondering if there was any api to work with "tabular" data in a linq way using java. any help is appreciated.

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• C++ conditional compilation

  - by Shaown

  I have the following code snippet #ifdef DO_LOG #define log(p) record(p) #else #define log(p) #endif void record(char *data){ ..... ..... } Now if I call log("hello world") in my code and DO_LOG isn't defined, will the line be compiled, in other words will it eat up the memory for the string "hello world"? P.S. There are a lot of record calls in the program and it is memory sensitive, so is there any other way to conditionally compile so that it only depends on the #define DO_LOG? Thanks in advance.

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• What is faster: multiple `send`s or using buffering?

  - by dauerbaustelle

  I'm playing around with sockets in C/Python and I wonder what is the most efficient way to send headers from a Python dictionary to the client socket. My ideas: use a send call for every header. Pros: No memory allocation needed. Cons: many send calls -- probably error prone; error management should be rather complicated use a buffer. Pros: one send call, error checking a lot easier. Cons: Need a buffer :-) malloc/realloc should be rather slow and using a (too) big buffer to avoid realloc calls wastes memory. Any tips for me? Thanks :-)

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• NHibernate and objects with value-semantics

  - by Groo

  Problem: If I pass a class with value semantics (Equals method overridden) to NHibernate, NHibernate tries to save it to db even though it just saved an entity equal by value (but not by reference) to the database. What am I doing wrong? Here is a simplified example model for my problem: Let's say I have a Person entity and a City entity. One thread (producer) is creating new Person objects which belong to a specific existing City, and another thread (consumer) is saving them to a repository (using NHibernate as DAL). Since there is lot of objects being flushed at a time, I am using Guid.Comb id's to ensure that each insert is made using a single SQL command. City is an object with value-type semantics (equal by name only -- for this example purposes only): public class City : IEquatable<City> { public virtual Guid Id { get; private set; } public virtual string Name { get; set; } public virtual bool Equals(City other) { if (other == null) return false; return this.Name == other.Name; } public override bool Equals(object obj) { return Equals(obj as City); } public override int GetHashCode() { return this.Name.GetHashCode(); } } Fluent NH mapping is something like: public class PersonMap : ClassMap<Person> { public PersonMap() { Id(x => x.Id) .GeneratedBy.GuidComb(); References(x => x.City) .Cascade.SaveUpdate(); } } public class CityMap : ClassMap<City> { public CityMap() { Id(x => x.Id) .GeneratedBy.GuidComb(); Map(x => x.Name); } } Right now (with my current NHibernate mapping config), my consumer thread maintains a dictionary of cities and replaces their references in incoming person objects (otherwise NHibernate will see a new, non-cached City object and try to save it as well), and I need to do it for every produced Person object. Since I have implemented City class to behave like a value type, I hoped that NHibernate would compare Cities by value and not try to save them each time -- i.e. I would only need to do a lookup once per session and not care about them anymore. Is this possible, and if yes, what am I doing wrong here?

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• How can I detect endianness on a system where all primitive integer sizes are the same?

  - by Joe Wreschnig

  (This question came out of explaining the details of CHAR_BIT, sizeof, and endianness to someone yesterday. It's entirely hypothetical.) Let's say I'm on a platform where CHAR_BIT is 32, so sizeof(char) == sizeof(short) == sizeof(int) == sizeof(long). I believe this is still a standards-conformant environment. The usual way to detect endianness at runtime (because there is no reliable way to do it at compile time) is to make a union { int i, char c[sizeof(int)] } x; x.i = 1 and see whether x.c[0] or x.c[sizeof(int)-1] got set. But that doesn't work on this platform, as I end up with a char[1]. Is there a way to detect whether such a platform is big-endian or little-endian, at runtime? Obviously it doesn't matter inside this hypothetical system, but one can imagine it is writing to a file, or some kind of memory-mapped area, which another machine reads and reconstructs it according to its (saner) memory model.

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• Can my app arrange a gdb breakpoint or watch?

  - by Larry Gritz

  Is there a way for my code to be instrumented to insert a break point or watch on a memory location that will be honored by gdb? (And presumably have no effect when gdb is not attached.) I know how to do such things as gdb commands within the gdb session, but for certain types of debugging it would be really handy to do it "programmatically", if you know what I mean -- for example, the bug only happens with a particular circumstance, not any of the first 11,024 times the crashing routine is called, or the first 43,028,503 times that memory location is modified, so setting a simple break point on the routine or watch point on the variable is not helpful -- it's all false positives. I'm concerned mostly about Linux, but curious about if similar solutions exist for OS X (or Windows, though obviously not with gdb).

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• Using the windows api and C++, how could I load an exe from the hard drive and run it in its own thread?

  - by returneax

  For the sake of learning I'm trying to do what the OS does when launching a program ie. parsing a PE file and giving it a thread of execution. If I have two exe's one called foo.exe and the other bar.exe, how could I have foo.exe load the contents of bar.exe into memory then have it execute from there in its own thread? I know how to get it into memory using MapViewOfFile or by simple loading the contents on the hard drive into a buffer. I'm assuming simply copying the contents of bar.exe on disk into its own suspended thread and running it wouldn't work. I am semi-familiar with PE file internals. All help is very much appreciated, of course :)

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• What is the effect on record size of reordering columns in PostgreSQL?

  - by Summer

  Since Postgres can only add columns at the end of tables, I end up re-ordering by adding new columns at the end of the table, setting them equal to existing columns, and then dropping the original columns. So, what does PostgreSQL do with the memory that's freed by dropped columns? Does it automatically re-use the memory, so a single record consumes the same amount of space as it did before? But that would require a re-write of the whole table, so to avoid that, does it just keep a bunch of blank space around in each record? Thanks! ~S

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• Sound Manager Classes for Windows (C# or C++ .Net 2.0)

  - by Yakov

  Hi guys! I need some classes for playing short wav sounds, this classes would load this wav files into memory when an instance created, play sounds in background when needed, release this wav files from memory when an instance disposed. How can I do this on C# for windows (.Net 2.0)? (Win API's sndPlaySound, OpenAL or may be any wrapper) Ideally I would love to find an exist solution that simple and able to solve my task. Do you know any solutions for this issue? Thankx for your time.

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• removing dependancy of a private function inside a public function using Rhino Mocks

  - by L G

  Hi All, I am new to mocking, and have started with Rhino Mocks. My scenario is like this..in my class library i have a public function and inside it i have a private function call, which gets output from a service.I want to remove the private function dependency. public class Employee { public virtual string GetFullName(string firstName, string lastName) { string middleName = GetMiddleName(); return string.Format("{0} {2} {1}", firstName, lastName,middleName ); } private virtual string GetMiddleName() { // Some call to Service return "George"; } } This is not my real scenario though, i just wanted to know how to remove dependency of GetMiddleName() function and i need to return some default value while unit testing. Note : I won't be able to change the private function here..or include Interface..Keeping the functions as such, is there any way to mock this.Thank

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• C++ design with static methods

  - by user231536

  I would like to define as class X with a static method: class X { static string get_type () {return "X";} //other virtual methods } I would like to force classes which inherit from X to redefine the get_type() method and return strings different from "X" (I am happy if they just redefine get_type for now). How do I do this? I know that I cannot have virtual static methods. Edit: The question is not about the type_id, but in general about a static method that should be overriden. For example class X { static int getid() {return 1;} }

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• MVC DropDownListFor not populating the selected value

  - by user2254436

  I'm really having troubles with MVC, in another project I've done the same thing and it worked fine but in this project I just don't understand why the selected item in the dropdown is not populating the class correctly with EF. I have 2 classes: public partial class License { public License() { this.Customers = new HashSet<Customer>(); } public int LicenseID { get; set; } public int Lic_LicenseTypeID { get; set; } public int Lic_LicenseStatusID { get; set; } public string Lic_LicenseComments { get; set; } public virtual EntitiesList LicenseStatus { get; set; } public virtual EntitiesList LicenseType { get; set; } } public partial class EntitiesList { public EntitiesList() { this.LicensesStatus = new HashSet<License>(); this.LicensesType = new HashSet<License>(); } public int ListID { get; set; } public string List_EntityValue { get; set; } public string List_Comments { get; set; } public string List_EntityName { get; set; } public virtual ICollection<License> LicensesStatus { get; set; } public virtual ICollection<License> LicensesType { get; set; } public string List_DisplayName { get { return Regex.Replace(List_EntityName, "([a-z])([A-Z])", "$1 $2"); ; } } public string List_DisplayValue { get { return Regex.Replace(List_EntityValue, "([a-z])([A-Z])", "$1 $2"); } } } The EntitiesList is table in db that have all my "enum" lists. For example: ListID - 0 List_EntityValue - Activate List_EntityName - LicenseStatus ListID - 1 List_EntityValue - Basic List_EntityName - LicenseType This is my model: public class LicenseModel { public License License { get; set; } public SelectList LicenseStatuses { get; set; } public int SelectedStatus { get; set; } public SelectList LicenseTypes { get; set; } public int SelectedType { get; set; } } My controller for create: public ActionResult Create() { LicenseModel model = new LicenseModel(); model.License = new License(); model.LicenseStatuses = new SelectList(managerLists.GetAllLicenseStatuses(), "ListID", "List_DisplayValue"); model.LicenseTypes = new SelectList(managerLists.GetAllLicenseTypes(), "ListID", "List_DisplayValue"); return View(model); } [HttpPost] [ValidateAntiForgeryToken] public ActionResult Create(LicenseModel model) { if (ModelState.IsValid) { model.License.Lic_LicenseTypeID = model.SelectedType; model.License.Lic_LicenseStatusID = model.SelectedStatus; managerLicense.AddNewObject(model.License); return RedirectToAction("Index"); } return View(model); } managerLists and managerLicense are the managers that connect between the entities in db and the MVC UI, nothing special... they contains queries for adding new objects, getting the lists, editing and so on. And the view for creating the License: @using (Html.BeginForm()) { @Html.AntiForgeryToken() @Html.ValidationSummary(true) <fieldset> <legend>License</legend> <div class="form-group"> @Html.LabelFor(model => model.License.Lic_LicenseTypeID) @Html.DropDownListFor(model => model.SelectedType, Model.LicenseTypes, new { @class = "form-control" }) <p class="help-block">@Html.ValidationMessageFor(model => model.License.Lic_LicenseTypeID)</p> </div> <div class="form-group"> @Html.LabelFor(model => model.License.Lic_LicenseStatusID) @Html.DropDownListFor(model => model.SelectedStatus, Model.LicenseStatuses, new { @class = "form-control" }) <p class="help-block">@Html.ValidationMessageFor(model => model.License.Lic_LicenseStatusID)</p> </div> <div class="form-group"> @Html.LabelFor(model => model.License.Lic_LicenseComments) @Html.TextAreaFor(model => model.License.Lic_LicenseComments, new { @class = "form-control", rows = "3" }) <p class="help-block">@Html.ValidationMessageFor(model => model.License.Lic_LicenseComments)</p> </div> <p> <input type="submit" value="Create" /> </p> </fieldset> } Now, when I'm trying to save the new license, when it gets to the db.SaveChanges() in the manager I'm getting: "Validation failed for one or more entities. See 'EntityValidationErrors' property for more details." In breakpoint, the Lic_LicenseTypeID and Lic_LicenseStatusID are getting correctly the ID's from the selected item in the dropdown but the LicenseStatus and LicenseStatus properties are null. What an I missing?

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• Multimap Space Issue: Guava

  - by Arpssss

  In my Java code, I am using Guavas Multimap (com.google.common.collect.Multimap) by using this: Multimap< Integer, Integer Index = HashMultimap.create() Here, Multimap key is some portion of URL and value is another portion of URL (converted into integer). Now, I assign my JVM 2560 Mb (2.5 GB) heap space (by using Xmx and Xms). However, it can only store 9 millions of such (key,value) pairs of integers (approx 10 million). But, theoretically (according to memory occupied by int) it should store more. Can anybody help me, 1) Why is this happening (means Multimap is taking lots of space) ? I checked my code with out inserting pairs in Multimap, it takes only 1/2 MB space. 2) Is there any other way or home-baked solution to solve this space issue ? More clearly, how to solve this memory issue ? Thanks in advance and any idea is perfectly OK for me.

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• C++: Why don't I need to check if references are invalid/null?

  - by jbu

  Hi all, Reading http://www.cprogramming.com/tutorial/references.html, it says: In general, references should always be valid because you must always initialize a reference. This means that barring some bizarre circumstances (see below), you can be certain that using a reference is just like using a plain old non-reference variable. You don't need to check to make sure that a reference isn't pointing to NULL, and you won't get bitten by an uninitialized reference that you forgot to allocate memory for. My question is how do I know that the object's memory hasn't been freed/deleted AFTER you've initialized the reference. What it comes down to is that I can't take this advice on faith and I need a better explanation. Can anyone shed some light? Thanks, jbu

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• SQL Stored Procedure

  - by Nathan

  I am trying to run a stored procedure with a while loop in it using Aqua Data Studio 6.5 and as soon as the SP starts Aqua Data starts consuming an increasing amount of my CPU's memory which makes absolutely no sense to me because everything should be off on the Sybase server I am working with. I have commented out and tested every piece of the SP and narrowed the issue down to the while loop. Can anyone explain to me what is going on? create procedure sp_check_stuff as begin declare @counter numeric (9), @max_id numeric (9), @exists numeric (1), @rows numeric (1) select @max_id = max(id) from my_table set @counter = 0 set @exists = 0 set @rows = 0 while @count <= @max_id begin //More logic which doesn't affect memory usage based //on commenting it out and running the SP set @counter = @counter + 1 set @exists = 0 set @rows = 0 end end return

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• What the best approach to iterate and "store" files over a directory in C (Linux) ?

  - by Andrei Ciobanu

  I have written a function that checks if to files are duplicates or not. This function signature is: int check_dup_memmap(char *f1_name, char *f2_name) It returns: (-1) - If something went wrong; (0) - If the two files are similar; (+1) - If the two files are different; The next step is to write a function that iterates through all the files in a certain directory,apply the previous function, and gives a report on every existing duplicates. Initially I've thought to write a function that generates a file with all the filenames in a certain directory and then, read that file again and gain and compare every two files. Here is that version of the function, that gets all the filenames in a certain directory. void *build_dir_tree(char *dirname, FILE *f) { DIR *cdir = NULL; struct dirent *ent = NULL; struct stat buf; if(f == NULL){ fprintf(stderr, "NULL file submitted. [build_dir_tree].\n"); exit(-1); } if(dirname == NULL){ fprintf(stderr, "NULL dirname submitted. [build_dir_tree].\n"); exit(-1); } if((cdir = opendir(dirname)) == NULL){ char emsg[MFILE_LEN]; sprintf(emsg, "Cannot open dir: %s [build_dir_tree]\t",dirname); perror(emsg); } chdir(dirname); while ((ent = readdir(cdir)) != NULL) { lstat(ent->d_name, &buf); if (S_ISDIR(buf.st_mode)) { if (strcmp(".", ent->d_name) == 0 || strcmp("..", ent->d_name) == 0) { continue; } build_dir_tree(ent->d_name, f); } else{ fprintf(f, "/%s/%s\n",util_get_cwd(),ent->d_name); } } chdir(".."); closedir(cdir); } Still I consider this approach a little inefficient, as I have to parse the file again and again. In your opinion what are other approaches should I follow: Write a datastructure and hold the files instead of writing them in the file ? I think for a directory with a lot of files, the memory will become very fragmented. Hold all the filenames in auto-expanding array, so that I can easy access every file by their index, because they will in a contiguous memory location. Map this file in memory using mmap() ? But mmap may fail, as the file gets to big. Any opinions on this. I want to choose the most efficient path, and access as few resources as possible. This is the requirement of the program... EDIT: Is there a way to get the numbers of files in a certain directory, without iterating through it ?

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• python dictionary with constant value-type

  - by s.kap

  hi there, I bumped into a case where I need a big (=huge) python dictionary, which turned to be quite memory-consuming. However, since all of the values are of a single type (long) - as well as the keys, I figured I can use python (or numpy, doesn't really matter) array for the values ; and wrap the needed interface (in: x ; out: d[x]) with an object which actually uses these arrays for the keys and values storage. I can use a index-conversion object (input -- index, of 1..n, where n is the different-values counter), and return array[index]. I can elaborate on some techniques of how to implement such an indexing-methods with reasonable memory requirement, it works and even pretty good. However, I wonder if there is such a data-structure-object already exists (in python, or wrapped to python from C/++), in any package (I checked collections, and some Google searches). Any comment will be welcome, thanks.

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• What is the best way to "override" enums?

  - by Tyler

  I have a number of classes which extend an abstract class. The abstract parent class defines an enum with a set of values. Some of the subclasses inherit the parent class's enum values, but some of the subclasses need the enum values to be different. Is there any way to somehow override the enum for these particular subclasses, and if not, what is a good way to achieve what I'm describing? class ParentClass { private MyEnum m_EnumVal; public virtual MyEnum EnumVal { get { return m_EnumVal; } set { m_EnumVal = value; } } public enum MyEnum { a, b, c }; } class ChildClass : ParentClass { private MyEnum m_EnumVal; public virtual MyEnum EnumVal { get { return m_EnumVal; } set { m_EnumVal = value; } } public enum MyEnum { d, e, f }; }

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• How to deal with large result sets with Linq to Entities?

  - by user169867

  I have a fairly complex linq to entities query that I display on a website. It uses paging so I never pull down more than 50 records at a time for display. But I also want to give the user the option to export the full results to Excel or some other file format. My concern is that there could potentially be a large # of records all being loaded into memory at one time to do this. Is there a way to process a linq result set 1 record at a time like you could w/ a datareader so only 1 record is really being kept in memory at a time? I'd appreciate any help. Thanks

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• are runtime linking library globals shared among plugins loaded with dlopen?

  - by conejoroy

  I've a C++ program that links at runtime with, lets say, mylib.so. then, the same program uses dlopen()/dlsym() to load a function from myplugin.so, dynamic library that in turn has dependencies to mylib.so. My question is: will the program AND the function in the plugin access the same globals defined in mydlib.so in the same memory area reserved for the program, or each will be assigned different, unrelated copies in its own memory space? if the latter is the default behaviour, is it possible to change that? Thanks in advance =)!

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• Speed-up of readonly MyISAM table

  - by Ozzy

  We have a large MyISAM table that is used to archive old data. This archiving is performed every month, and except from these occasions data is never written to the table. Is there anyway to "tell" MySQL that this table is read-only, so that MySQL might optimize the performance of reads from this table? I've looked at the MEMORY storage engine, but the problem is that this table is so large that it would take a large portion of the servers memory, which I don't want. Hope my question is clear enough, I'm a novice when it comes to db administration so any input or suggestions are welcome.

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