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  • Python Sets vs Lists

    - by mvid
    In Python, which data structure is more efficient/speedy? Assuming that order is not important to me and I would be checking for duplicates anyway, is a Python set slower than a Python list?

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  • How well do zippers perform in practice, and when should they be used?

    - by Rob
    I think that the zipper is a beautiful idea; it elegantly provides a way to walk a list or tree and make what appear to be local updates in a functional way. Asymptotically, the costs appear to be reasonable. But traversing the data structure requires memory allocation at each iteration, where a normal list or tree traversal is just pointer chasing. This seems expensive (please correct me if I am wrong). Are the costs prohibitive? And what under what circumstances would it be reasonable to use a zipper?

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  • Cache of Objects or OutPut in View ? Wich is better ?

    - by Felipe
    Hi everybody, I have an ecommerce working in ASP.Net MVC. i'm using Caching to improve more performace in my pages and it's working fine. I'd link to know what is more performative, for example, I can set OutPutCache in my views and and use this cache for all page OR I could get my List of Products in controller, put it on cache (like the code below) and send it to View to render for the user??? private IEnumerable<Products> GetProductsCache(string key, ProductType type) { if (HttpContext.Cache[key] == null) HttpContext.Cache.Insert(key, ProductRepository.GetProducts(type), null, DateTime.Now.AddMinutes(10), Cache.NoSlidingExpiration); return (IEnumerable<Products>)HttpContext.Cache[key]; } public ActionResult Index() { var home = new HomeViewModel() { Products = GetProductsCache("ProductHomeCache", ProductType.Product) Services = GetProductsCache("ServiceHomeCache", ProductType.Service) }; return View(home); } Both works fine, but I'd like to know what is suggested to improve more performace ? Or is there others way to do it better ? PS: sorry for my english! thanks all... Cheers

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  • Practical approach to concurrency control

    - by Industrial
    Hi everyone, I'd read this article recently and are very interested on how to make a practical approach to Concurrency control on a web server. The server will run CentOS + PHP + mySQL with Memcached. How would you set it up to work? http://saasinterrupted.com/2010/02/05/high-availability-principle-concurrency-control/ Thanks!

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  • Speeding Up Slow, CPU-Intensive Scrolling in WinForms

    - by S B
    How can I speed up the scrolling of UserControls in a WinForms app.? My main form has trouble scrolling quickly on slow machines--painting for each of the small scroll increments is CPU intensive. My form has roughly fifty UserControls (with multiple fields) positioned one below the other. I’ve tried intercepting OnScroll and UserPaint in order to eliminate some of the unnecessary re-paints for very small scroll events, but the underlying Paint gets called anyway. How can I streamline scrolling on slower machines?

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  • Of these 3 methods for reading linked lists from shared memory, why is the 3rd fastest?

    - by Joseph Garvin
    I have a 'server' program that updates many linked lists in shared memory in response to external events. I want client programs to notice an update on any of the lists as quickly as possible (lowest latency). The server marks a linked list's node's state_ as FILLED once its data is filled in and its next pointer has been set to a valid location. Until then, its state_ is NOT_FILLED_YET. I am using memory barriers to make sure that clients don't see the state_ as FILLED before the data within is actually ready (and it seems to work, I never see corrupt data). Also, state_ is volatile to be sure the compiler doesn't lift the client's checking of it out of loops. Keeping the server code exactly the same, I've come up with 3 different methods for the client to scan the linked lists for changes. The question is: Why is the 3rd method fastest? Method 1: Round robin over all the linked lists (called 'channels') continuously, looking to see if any nodes have changed to 'FILLED': void method_one() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } while(true) { for(std::size_t i = 0; i < channel_list.size(); ++i) { Data* current_item = channel_cursors[i]; ACQUIRE_MEMORY_BARRIER; if(current_item->state_ == NOT_FILLED_YET) { continue; } log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[i] = static_cast<Data*>(current_item->next_.get(segment)); } } } Method 1 gave very low latency when then number of channels was small. But when the number of channels grew (250K+) it became very slow because of looping over all the channels. So I tried... Method 2: Give each linked list an ID. Keep a separate 'update list' to the side. Every time one of the linked lists is updated, push its ID on to the update list. Now we just need to monitor the single update list, and check the IDs we get from it. void method_two() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } UpdateID* update_cursor = static_cast<UpdateID*>(update_channel.tail_.get(segment)); while(true) { if(update_cursor->state_ == NOT_FILLED_YET) { continue; } ::uint32_t update_id = update_cursor->list_id_; Data* current_item = channel_cursors[update_id]; if(current_item->state_ == NOT_FILLED_YET) { std::cerr << "This should never print." << std::endl; // it doesn't continue; } log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[update_id] = static_cast<Data*>(current_item->next_.get(segment)); update_cursor = static_cast<UpdateID*>(update_cursor->next_.get(segment)); } } Method 2 gave TERRIBLE latency. Whereas Method 1 might give under 10us latency, Method 2 would inexplicably often given 8ms latency! Using gettimeofday it appears that the change in update_cursor-state_ was very slow to propogate from the server's view to the client's (I'm on a multicore box, so I assume the delay is due to cache). So I tried a hybrid approach... Method 3: Keep the update list. But loop over all the channels continuously, and within each iteration check if the update list has updated. If it has, go with the number pushed onto it. If it hasn't, check the channel we've currently iterated to. void method_three() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } UpdateID* update_cursor = static_cast<UpdateID*>(update_channel.tail_.get(segment)); while(true) { for(std::size_t i = 0; i < channel_list.size(); ++i) { std::size_t idx = i; ACQUIRE_MEMORY_BARRIER; if(update_cursor->state_ != NOT_FILLED_YET) { //std::cerr << "Found via update" << std::endl; i--; idx = update_cursor->list_id_; update_cursor = static_cast<UpdateID*>(update_cursor->next_.get(segment)); } Data* current_item = channel_cursors[idx]; ACQUIRE_MEMORY_BARRIER; if(current_item->state_ == NOT_FILLED_YET) { continue; } found_an_update = true; log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[idx] = static_cast<Data*>(current_item->next_.get(segment)); } } } The latency of this method was as good as Method 1, but scaled to large numbers of channels. The problem is, I have no clue why. Just to throw a wrench in things: if I uncomment the 'found via update' part, it prints between EVERY LATENCY LOG MESSAGE. Which means things are only ever found on the update list! So I don't understand how this method can be faster than method 2. The full, compilable code (requires GCC and boost-1.41) that generates random strings as test data is at: http://pastebin.com/e3HuL0nr

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  • atomic operation cost

    - by osgx
    Hello What is the cost of the atomic operation? How much cycles does it consume? Will it pause other processors on SMP or NUMA, or will it block memory accesses? Will it flush reorder buffer in out-of-order CPU? What effects will be on the cache? Thanks.

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  • Scalable Ticketing / Festival Website

    - by Luke Lowrey
    I've noticed major music festivals (at least in Australia) and other events that experience a peak in traffic when tickets go on sale have huge problems keeping their websites running well. I've seen a few different techniques used to try combat this such as short sessions and virtual queues but they dont seem to have much effect. If you were to design a website to sell a lot of tickets in a short amount of time how would you handle scalability? What technologies and programming techniques would you use?

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  • Lazy/deferred loading of a CollectionViewSource?

    - by Shimmy
    When you create a CollectionViewSource in the Resources section, is the set Source loaded when the resources are initalized (i.e. when the Resources holder is inited) or when data is bound? Is there a xamly way to make a CollectionViewSource lazy-load? deferred-load? explicit-load?

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  • One large file or multiple small files?

    - by Dan
    I have an application (currently written in Python as we iron out the specifics but eventually it will be written in C) that makes use of individual records stored in plain text files. We can't use a database and new records will need to be manually added regularly. My question is this: would it be faster to have a single file (500k-1Mb) and have my application open, loop through, find and close a file OR would it be faster to have the records separated and named using some appropriate convention so that the application could simply loop over filenames to find the data it needs? I know my question is quite general so direction to any good articles on the topic are as appreciated as much as suggestions. Thanks very much in advance for your time, Dan

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  • Are these tables too big for SQL Server or Oracle

    - by Jeffrey Cameron
    Hey all, I'm not much of a database guru so I would like some advice. Background We have 4 tables that are currently stored in Sybase IQ. We don't currently have any choice over this, we're basically stuck with what someone else decided for us. Sybase IQ is a column-oriented database that is perfect for a data warehouse. Unfortunately, my project needs to do a lot of transactional updating (we're more of an operational database) so I'm looking for more mainstream alternatives. Question Given these tables' dimensions, would anyone consider SQL Server or Oracle to be a viable alternative? Table 1 : 172 columns * 32 million rows Table 2 : 453 columns * 7 million rows Table 3 : 112 columns * 13 million rows Table 4 : 147 columns * 2.5 million rows Given the size of data what are the things I should be concerned about in terms of database choice, server configuration, memory, platform, etc.?

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  • clarification on yslow rules

    - by ooo
    i ran yslow and i got a bad score on expires header: Here was the message: Grade F on Add Expires headers There are 45 static components without a far-future expiration date. i am using IIS on a hosted environment. what do i need to do on my css or js files to fix this issue ?

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  • HTML Chrome Audit Specify Image Dimensions

    - by AKRamkumar
    I just started using the chrome developer tools for some basic html websites and I used the audit tool. I had two identical images, one with the height and width attribute, and one without. On the Resources section, both the latency and the download time were identical. However, the Audit showed Specify image dimensions (1) A width and height should be specified for all images in order to speed up page display. Does this actually help? And are there any other ways to speed up page time? This is only a splash page for the website I am building and as such it is only html, no css or javascript or anything. I have already compressed the images but I want to speed up load time even more. Is there a way?

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  • C++: how to truncate the double in efficient way?

    - by Arman
    Hello, I would like to truncate the float to 4 digits. Are there some efficient way to do that? My current solution is: double roundDBL(double d,unsigned int p=4) { unsigned int fac=pow(10,p); double facinv=1.0/static_cast<double>(fac); double x=static_cast<unsigned int>(x*fac)/facinv; return x; } but using pow and delete seems to me not so efficient. kind regards Arman.

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  • Optimizing Haskell code

    - by Masse
    I'm trying to learn Haskell and after an article in reddit about Markov text chains, I decided to implement Markov text generation first in Python and now in Haskell. However I noticed that my python implementation is way faster than the Haskell version, even Haskell is compiled to native code. I am wondering what I should do to make the Haskell code run faster and for now I believe it's so much slower because of using Data.Map instead of hashmaps, but I'm not sure I'll post the Python code and Haskell as well. With the same data, Python takes around 3 seconds and Haskell is closer to 16 seconds. It comes without saying that I'll take any constructive criticism :). import random import re import cPickle class Markov: def __init__(self, filenames): self.filenames = filenames self.cache = self.train(self.readfiles()) picklefd = open("dump", "w") cPickle.dump(self.cache, picklefd) picklefd.close() def train(self, text): splitted = re.findall(r"(\w+|[.!?',])", text) print "Total of %d splitted words" % (len(splitted)) cache = {} for i in xrange(len(splitted)-2): pair = (splitted[i], splitted[i+1]) followup = splitted[i+2] if pair in cache: if followup not in cache[pair]: cache[pair][followup] = 1 else: cache[pair][followup] += 1 else: cache[pair] = {followup: 1} return cache def readfiles(self): data = "" for filename in self.filenames: fd = open(filename) data += fd.read() fd.close() return data def concat(self, words): sentence = "" for word in words: if word in "'\",?!:;.": sentence = sentence[0:-1] + word + " " else: sentence += word + " " return sentence def pickword(self, words): temp = [(k, words[k]) for k in words] results = [] for (word, n) in temp: results.append(word) if n > 1: for i in xrange(n-1): results.append(word) return random.choice(results) def gentext(self, words): allwords = [k for k in self.cache] (first, second) = random.choice(filter(lambda (a,b): a.istitle(), [k for k in self.cache])) sentence = [first, second] while len(sentence) < words or sentence[-1] is not ".": current = (sentence[-2], sentence[-1]) if current in self.cache: followup = self.pickword(self.cache[current]) sentence.append(followup) else: print "Wasn't able to. Breaking" break print self.concat(sentence) Markov(["76.txt"]) -- module Markov ( train , fox ) where import Debug.Trace import qualified Data.Map as M import qualified System.Random as R import qualified Data.ByteString.Char8 as B type Database = M.Map (B.ByteString, B.ByteString) (M.Map B.ByteString Int) train :: [B.ByteString] -> Database train (x:y:[]) = M.empty train (x:y:z:xs) = let l = train (y:z:xs) in M.insertWith' (\new old -> M.insertWith' (+) z 1 old) (x, y) (M.singleton z 1) `seq` l main = do contents <- B.readFile "76.txt" print $ train $ B.words contents fox="The quick brown fox jumps over the brown fox who is slow jumps over the brown fox who is dead."

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  • mysql partitioning

    - by Yang
    just want to verify that database partition is implemented only at the database level, when we query a partitioned table, we still do our normal query, nothing special with our queries, the optimization is performed automatically when parsing the query, is that correct? e.g. we have a table called 'address' with a column called 'country_code' and 'city'. so if i want to get all the addresses in New York, US, normally i wound do something like this: select * from address where country_code = 'US' and city = 'New York' if now the table is partitioned by 'country_code', and i know that now the query will only be executed on the partition which contains country_code = US. My question is do I need to explicitly specify the partition to query in my sql statement? or i still use the previous statement and the db server will optimize it automatically? Thanks in advance!

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  • Javascript Running slow in IE

    - by SharePoint Newbie
    Hi, Javascript is running extremely slow on IE on some pages in our site. Profiling seems to show that the following methods are taking the most time: (Method, count, inclusive time, exclusive time) JScript - window script block 2,332 237.98 184.98 getDimensions 4 33 33 eh 213 32 32 extend 446 30 30 tt_HideSrcTagsRecurs 1,362 26 26 String.split 794 18 18 $ 717 49 17 findElements 104 184.98 14 What does "JScript - window script block" do? We are using jquery and prototype. Thanks,

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  • The fastest way to do a collection subtraction

    - by Tony
    I have two Sets. Set<B> b is the subset of Set<A> a. they're both very huge Sets. I want to subtract b from a , what's the best practice to do this common operation ? I've written to many codes like this , and I don't think it's efficient. what's your idea ? for(int i = 0 ; i < a.size(); i++) { for (int j=0 ; j < b.size() ;j++) { // do comparison , if found equals ,remove from a break; } } And I want to find an algorithm , not only applies to Sets, also works for Array.

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  • PHP website Optimization

    - by ana
    I have a high traffic website and I need make sure my site is fast enough to display my pages to everyone rapidly. I searched on Google many articles about speed and optimization and here's what I found: Cache the page Save it to the disk Caching the page in memory: This is very fast but if I need to change the content of my page I have to remove it from cache and then re-save the file on the disk. Save it to disk This is very easy to maintain but every time the page is accessed I have to read on the disk. Which method should I go with? Thanks

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  • Advantage of using a static member function instead of an equivalent non-static member function?

    - by jonathanasdf
    I was wondering whether there's any advantages to using a static member function when there is a non-static equivalent. Will it result in faster execution (because of not having to care about all of the member variables), or maybe less use of memory (because of not being included in all instances)? Basically, the function I'm looking at is an utility function to rotate an integer array representing pixel colours an arbitrary number of degrees around an arbitrary centre point. It is placed in my abstract Bullet base class, since only the bullets will be using it and I didn't want the overhead of calling it in some utility class. It's a bit too long and used in every single derived bullet class, making it probably not a good idea to inline. How would you suggest I define this function? As a static member function of Bullet, of a non-static member function of Bullet, or maybe not as a member of Bullet but defined outside of the class in Bullet.h? What are the advantages and disadvantages of each?

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  • Oracle EXECUTE IMMEDIATE changes explain plan of query.

    - by Gunny
    I have a stored procedure that I am calling using EXECUTE IMMEDIATE. The issue that I am facing is that the explain plan is different when I call the procedure directly vs when I use EXECUTE IMMEDIATE to call the procedure. This is causing the execution time to increase 5x. The main difference between the plans is that when I use execute immediate the optimizer isn't unnesting the subquery (I'm using a NOT EXISTS condition). We are using Rule Based Optimizer here at work. Example: Fast: begin package.procedure; end; / Slow: begin execute immediate 'begin package.' || proc_name || '; end;'; end; /

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  • Optimizing MySql query to avoid using "Using filesort"

    - by usef_ksa
    I need your help to optimize the query to avoid using "Using filesort".The job of the query is to select all the articles that belongs to specific tag. The query is: "select title from tag,article where tag='Riyad' AND tag.article_id=article.id order by tag.article_id". the tables structure are the following: Tag table CREATE TABLE `tag` ( `tag` VARCHAR( 30 ) NOT NULL , `article_id` INT NOT NULL , INDEX ( `tag` ) ) ENGINE = MYISAM ; Article table CREATE TABLE `article` ( `id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY , `title` VARCHAR( 60 ) NOT NULL ) ENGINE = MYISAM Sample data INSERT INTO `article` VALUES (1, 'About Riyad'); INSERT INTO `article` VALUES (2, 'About Newyork'); INSERT INTO `article` VALUES (3, 'About Paris'); INSERT INTO `article` VALUES (4, 'About London'); INSERT INTO `tag` VALUES ('Riyad', 1); INSERT INTO `tag` VALUES ('Saudia', 1); INSERT INTO `tag` VALUES ('Newyork', 2); INSERT INTO `tag` VALUES ('USA', 2); INSERT INTO `tag` VALUES ('Paris', 3); INSERT INTO `tag` VALUES ('France', 3);

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