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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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  • How to fire server-side methods with jQuery

    - by Nasser Hajloo
    I have a large application and I'm going to enabling short-cut key for it. I'd find 2 JQuery plug-ins (demo plug-in 1 - Demo plug-in 2) that do this for me. you can find both of them in this post in StackOverFlow My application is a completed one and I'm goining to add some functionality to it so I don't want towrite code again. So as a short-cut is just catching a key combination, I'm wonder how can I call the server methods which a short-cut key should fire? So How to use either of these plug-ins, by just calling the methods I'd written before? Actually How to fire Server methods with Jquery? You can also find a good article here, by Dave Ward Update: here is the scenario. When User press CTRL+Del the GridView1_OnDeleteCommand so I have this protected void grdDocumentRows_DeleteCommand(object source, System.Web.UI.WebControls.DataGridCommandEventArgs e) { try { DeleteRow(grdDocumentRows.DataKeys[e.Item.ItemIndex].ToString()); clearControls(); cmdSaveTrans.Text = Hajloo.Portal.Common.Constants.Accounting.Documents.InsertClickText; btnDelete.Visible = false; grdDocumentRows.EditItemIndex = -1; BindGrid(); } catch (Exception ex) { Page.AddMessage(GetLocalResourceObject("AProblemAccuredTryAgain").ToString(), MessageControl.TypeEnum.Error); } } private void BindGrid() { RefreshPage(); grdDocumentRows.DataSource = ((DataSet)Session[Hajloo.Portal.Common.Constants.Accounting.Session.AccDocument]).Tables[AccDocument.TRANSACTIONS_TABLE]; grdDocumentRows.DataBind(); } private void RefreshPage() { Creditors = (decimal)((AccDocument)Session[Hajloo.Portal.Common.Constants.Accounting.Session.AccDocument]).Tables[AccDocument.ACCDOCUMENT_TABLE].Rows[0][AccDocument.ACCDOCUMENT_CREDITORS_SUM_FIELD]; Debtors = (decimal)((AccDocument)Session[Hajloo.Portal.Common.Constants.Accounting.Session.AccDocument]).Tables[AccDocument.ACCDOCUMENT_TABLE].Rows[0][AccDocument.ACCDOCUMENT_DEBTORS_SUM_FIELD]; if ((Creditors - Debtors) != 0) labBalance.InnerText = GetLocalResourceObject("Differentiate").ToString() + "?" + (Creditors - Debtors).ToString(Hajloo.Portal.Common.Constants.Common.Documents.CF) + "?"; else labBalance.InnerText = GetLocalResourceObject("Balance").ToString(); lblSumDebit.Text = Debtors.ToString(Hajloo.Portal.Common.Constants.Common.Documents.CF); lblSumCredit.Text = Creditors.ToString(Hajloo.Portal.Common.Constants.Common.Documents.CF); if (grdDocumentRows.EditItemIndex == -1) clearControls(); } Th other scenario are the same. How to enable short-cut for these kind of code (using session , NHibernate, etc)

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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 many SQL Server DBAs does an organization need?

    - by RickHeiges
    "How many SQL Server DBAs do we need?" - This is a question that often comes up in conversations with customers. Essentially, customers want to know if they have enough DBAs or too many. This is not a trivial question. If you do some research online via your favorite search engine, you will most likely come across numbers such as 40-65 DBs per DBA (for SQL Server). I remember finding another number relating to storage space instead of the number of DBs; the range was 3-5TB per DBA. I have had custoemrs...(read more)

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • appending to cursor in oracle

    - by Omnipresent
    I asked a question yesterday which got answers but didnt answer the main point. I wanted to reduce amount of time it took to do a MINUS operation. Now, I'm thinking about doing MINUS operation in blocks of 5000, appending each iterations results to the cursor and finally returning the cursor. I have following: V_CNT NUMBER :=0; V_INTERVAL NUMBER := 5000; begin select count(1) into v_cnt from TABLE_1 while (v_cnt > 0) loop open cv_1 for SELECT A.HEAD,A.EFFECTIVE_DATE, FROM TABLE_1 A WHERE A.TYPE_OF_ACTION='6' AND A.EFFECTIVE_DATE >= ADD_MONTHS(SYSDATE,-15) AND A.ROWNUM <= V_INTERVAL MINUS SELECT B.head,B.EFFECTIVE_DATE, FROM TABLE_2 B AND B.ROWNUM <= V_INTERVAL V_CNT := V_CNT - V_INTERVAL; END LOOP; end; However, as you see...in each iteration the cursor is overwritten. How can I change the code so that in each iteration it appends to cv_1 cursor rather than overwriting?

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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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  • 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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  • Field specific errors for ETL

    - by AaronLS
    I am creating a ETL process in MS SQL Server and I would like to have errors specific to a particular column of a particular row. For example, the data is initially loaded from excel files into a table(we'll call the Initial table) where all columns are varchar(2000) and then I stage the data to another table(the DataTypedTable) that contains more specific data types (datetime,int, etc.) or more tightly constrained varchar lengths. I need to be able to create error messages for a specific field such as: "Jan. 13th" is not a valid date format for the submission date. Please use a format of MM/DD/YYYY These error messages would need to be stored in some way such that later in the process a automated process can create reports with the error messages such that each message references a specific row and field(someone will need to go back and correct the data in the source system and resubmit the excel file). So ideally it would be inserted into a Failures tables of some sort and contain the primary key of the failed row, the column name, and the error message. Question: So I am wondering if this can be accomplished with SSIS, or some open source tool like Talend, and if so, what would be your general approach? Or what hand coded approach you would take? Couple approaches I've thought of using SQL(up until no I have done ETL by hand in SQL procs, but I want to consider other approaches. Possible C# even.): Use a cursor to read through the Initial table, and for each row insert a blank record with only the primary key into the DataTyped table, then use a single update statement for each column, such that if that update fails I can insert a very specific error message specific to that column in the error messages table. Insert all the data as is into the DataTyped table, but have duplicate columns like SubmissionDate and SubmissionDateOld. After the initial insert the *Old columns have data, the rest are blank, and I have a single update for each column that sets the SubmissionDate based on the SubmissionDateOld. In addition to suggesting an approach, I'd like to know if you are using that approach or something similar already in the work you do.

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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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  • Showing response time in a rails app.

    - by anshul
    I want to display a This page took x seconds widget at the bottom of every page in my rails application. I would like x to reflect the approximate amount of time the request spent on my server. What is the usual way this is done in Rails?

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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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  • 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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  • "Priming" a whole database in MSSQL for first-hit speed

    - by David Spillett
    For a particular apps I have a set of queries that I run each time the database has been restarted for any reason (server reboot usually). These "prime" SQL Server's page cache with the common core working set of the data so that the app is not unusually slow the first time a user logs in afterwards. One instance of the app is running on an over-specced arrangement where the SQL box has more RAM than the size of the database (4Gb in the machine, the DB is under 1.5Gb currently and unlikely to grow too much relative to that in the near future). Is there a neat/easy way of telling SQL Server to go away and load everything into RAM? It could be done the hard way by having a script scan sysobjects & sysindexes and running SELECT * FROM <table> WITH(INDEX(<index_name>)) ORDER BY <index_fields> for every key and index found, which should cause every used page to be read at least once and so be in RAM, but is there a cleaner or more efficient way? All planned instances where the database server is stopped are out-of-normal-working-hours (all the users are at most one timezone away and unlike me none of them work at silly hours) so such a process (until complete) slowing down users more than the working set not being primed at all would is not an issue.

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