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• A map and set which uses contiguous memory and has a reserve function

  - by edA-qa mort-ora-y

  I use several maps and sets. The lack of contiguous memory, and high number of (de)allocations, is a performance bottleneck. I need a mainly STL-compatbile map and set class which can use a contiguous block of memory for internal objects (or multiple blocks). It also needs to have a reserve function so that I can preallocate for expected sizes. Before I write my own I'd like to check what is available first. Is there something in Boost which does this? Does somebody know of an available implementation elsewhere? Intrusive collection types are not usable here as the same objects need to exist in several collections. As far as I know STL memory pools are per-type, not per instance. These global pools are not efficient with respect to memory locality in mutli-cpu/core processing. Object pools don't work as the types will be shared between instance but their pool should not. In many cases a hash map may be an option in some cases.

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• Remove undesired indexed keywords from Sql Server FTS Index

  - by Scott

  Could anyone tell me if SQL Server 2008 has a way to prevent keywords from being indexed that aren't really relevant to the types of searches that will be performed? For example, we have the IFilters for PDF and Word hooked in and our documents are being indexed properly as far as I can tell. These documents, however, have lots of numeric values in them that people won't really be searching for or bring back meaningful results. These are still being indexed and creating lots of entries in the full text catalog. Basically we are trying to optimize our search engine in any way we can and assumed all these unnecessary entries couldn't be helping performance. I want my catalog to consist of alphabetic keywords only. The current iFilters work better than I would be able to write in the time I have but it just has more than I need. This is an example of some of the terms from sys.dm_fts_index_keywords_by_document that I want out: $1,000, $100, $250, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 129, 13.1, 14, 14.12, 145, 15, 16.2, 16.4, 18, 18.1, 18.2, 18.3, 18.4, 18.5 These are some examples from the same management view that I think are desirable for keeping and searching on: above, accordingly, accounts, add, addition, additional, additive Any help would be greatly appreciated!

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• How does PHP PDO work internally ?

  - by Rachel

  I want to use pdo in my application, but before that I want to understand how internally PDOStatement->fetch and PDOStatement->fetchAll. For my application, I want to do something like "SELECT * FROM myTable" and insert into csv file and it has around 90000 rows of data. My question is, if I use PDOStatement->fetch as I am using it here: // First, prepare the statement, using placeholders $query = "SELECT * FROM tableName"; $stmt = $this->connection->prepare($query); // Execute the statement $stmt->execute(); var_dump($stmt->fetch(PDO::FETCH_ASSOC)); while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) { echo "Hi"; // Export every row to a file fputcsv($data, $row); } Will after every fetch from database, result for that fetch would be store in memory ? Meaning when I do second fetch, memory would have data of first fetch as well as data for second fetch. And so if I have 90000 rows of data and if am doing fetch every time than memory is being updated to take new fetch result without removing results from previous fetch and so for the last fetch memory would already have 89999 rows of data. Is this how PDOStatement::fetch works ? Performance wise how does this stack up against PDOStatement::fetchAll ?

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• C# Execute Method (with Parameters) with ThreadPool

  - by washtik

  We have the following piece of code (idea for this code was found on this website) which will spawn new threads for the method "Do_SomeWork()". This enables us to run the method multiple times asynchronously. The code is: var numThreads = 20; var toProcess = numThreads; var resetEvent = new ManualResetEvent(false); for (var i = 0; i < numThreads; i++) { new Thread(delegate() { Do_SomeWork(Parameter1, Parameter2, Parameter3); if (Interlocked.Decrement(ref toProcess) == 0) resetEvent.Set(); }).Start(); } resetEvent.WaitOne(); However we would like to make use of ThreadPool rather than create our own new threads which can be detrimental to performance. The question is how can we modify the above code to make use of ThreadPool keeping in mind that the method "Do_SomeWork" takes multiple parameters and also has a return type (i.e. method is not void). Also, this is C# 2.0.

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• In .NET, What Is Fastest Way to Initialize Multi-Dimensional Array to Non-Default Value

  - by AMissico

  How do I initialize a multi-dimensional array of a primitive type as fast as possible? I am stuck with using multi-dimensional arrays. My problem is performance. The following routine initializes a 100x100 array in approx. 500 ticks. Removing the int.MaxValue initialization results in approx. 180 ticks just for the looping. Approximately 100 ticks to create the array without looping and without initializing to int.MaxValue. Routines similiar to this are called a few tens-of-thousands to several million times. I am open to suggestions on how to optimize this non-default initialization of an array. One idea I had is to use a smaller primitive type when available. For instance, using byte instead of int, saves 100 ticks. I would be happy with this, but I am hoping that I don't have to change the primitive data type. public int[,] CreateArray(Size size) { int[,] array = new int[size.Width, size.Height]; for (int x = 0; x < size.Width; x++) { for (int y = 0; y < size.Height; y++) { array[x, y] = int.MaxValue; } } return array; }

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• How can I factor out repeated expressions in an SQL Query? Column aliases don't seem to be the ticke

  - by Weston C

  So, I've got a query that looks something like this: SELECT id, DATE_FORMAT(CONVERT_TZ(callTime,'+0:00','-7:00'),'%b %d %Y') as callDate, DATE_FORMAT(CONVERT_TZ(callTime,'+0:00','-7:00'),'%H:%i') as callTimeOfDay, SEC_TO_TIME(callLength) as callLength FROM cs_calldata WHERE customerCode='999999-abc-blahblahblah' AND CONVERT_TZ(callTime,'+0:00','-7:00') >= '2010-04-25' AND CONVERT_TZ(callTime,'+0:00','-7:00') <= '2010-05-25' If you're like me, you probably start thinking that maybe it would improve readability and possibly the performance of this query if I wasn't asking it to compute CONVERT_TZ(callTime,'+0:00','-7:00') four separate times. So I try to create a column alias for that expression and replace further occurances with that alias: SELECT id, CONVERT_TZ(callTime,'+0:00','-7:00') as callTimeZoned, DATE_FORMAT(callTimeZoned,'%b %d %Y') as callDate, DATE_FORMAT(callTimeZoned,'%H:%i') as callTimeOfDay, SEC_TO_TIME(callLength) as callLength FROM cs_calldata WHERE customerCode='5999999-abc-blahblahblah' AND callTimeZoned >= '2010-04-25' AND callTimeZoned <= '2010-05-25' This is when I learned, to quote the MySQL manual: Standard SQL disallows references to column aliases in a WHERE clause. This restriction is imposed because when the WHERE clause is evaluated, the column value may not yet have been determined. So, that approach would seem to be dead in the water. How is someone writing queries with recurring expressions like this supposed to deal with it?

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• Best way to replace mass emails sent from Entourage with a proper mailing list solution?

  - by aaandre

  I am helping a Los Angeles choreographer to transition away from sending her announcements via Entourage. Here's the situation: She has multiple conact groups, and sends classes and performance announcements several times a month, to different groups. She manages the contact groups manually. The group size is between 1500 and 2500 people. Recently verizon blocked her outgoing port 25, presumably for spam activity. Again, her contacts are interested in the content. She is aware of mailchimp, constantcontact etc. but would like to be able to send the email via her email software and not have to create a newsletter for every single mailing. Also, she's very short on $$. So, what would be the best way to set up a system allowing her to send announcements from Entourage, with attached images, to her lists, without having Entourage send every single email? I am thinking of setting up a set of mailing lists, each corresponding to one of her groups. I have never set up a mailing list before and am wondering if it's possible to have a list accept emails from only one person (Admin) and distribute them to the group? Recipients should be able to unsubscribe easily, and by default reply to her but not the list. She should be the only one able to use the list for distribution, and should be able to send messages (with attachments) directly from her email client without modification. Is this possible? Where can I find step-by-step instructions? What are best practices to avoid her domain being blacklisted? What's the easiest way to convert her contact groups to mailing list subscribers? I am helping her for free, so the simpler the better :) Thank you! UPDATE: She has a standard linux hosting account allowing her to run php etc. And, ideally, the emails would come from her personally or at least from her domain name.

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• From ASPX to WCF

  - by Barguast

  I'm hoping someone can advise me on how to solve my networking scenario. Both the client and server are to be C# / .NET based. I basically want to invoke some kind of web service from my client in order to retrieve both binary data (e.g. files) and serialised objects and lists of objects (e.g. database query results). At the moment, I'm using ASPX pages, using the query string to provide parameters and I get back either the binary data, or the binary data of the serialised messages. This affords me a lot of flexbility, and I can choose how to transmit the data, perform simulatanous requests, cancel ongoing requests, etc. Since I can control the serialised format, I can also deserialise lists of objects as they are received which is crucial. My problem isn't a problem as such, but this feels a little hack-ish and I can't help but wonder if there are better ways to go about it. I'm considering moving on to WCF or perhaps another technology to see if it helps. However, I need to know if it helps with my scenarios above that is; Can a WCF method return a list of objects, and can the client receive the items of this list as they arrive as opposed to getting the entire list on completion (i.e. streaming). Does anyone know of any examples of this? Am I likely to get any performance benefits from this? I don't know how well ASPX pages are tuned for this, as it surely isn't their primary purpose. Are there any other approaches I should consider? Thanks for your time spent reading this. I hope you can help.

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• deepcopy and python - tips to avoid using it?

  - by blackkettle

  Hi, I have a very simple python routine that involves cycling through a list of roughly 20,000 latitude,longitude coordinates and calculating the distance of each point to a reference point. def compute_nearest_points( lat, lon, nPoints=5 ): """Find the nearest N points, given the input coordinates.""" points = session.query(PointIndex).all() oldNearest = [] newNearest = [] for n in xrange(nPoints): oldNearest.append(PointDistance(None,None,None,99999.0,99999.0)) newNearest.append(obj2) #This is almost certainly an inappropriate use of deepcopy # but how SHOULD I be doing this?!?! for point in points: distance = compute_spherical_law_of_cosines( lat, lon, point.avg_lat, point.avg_lon ) k = 0 for p in oldNearest: if distance < p.distance: newNearest[k] = PointDistance( point.point, point.kana, point.english, point.avg_lat, point.avg_lon, distance=distance ) break else: newNearest[k] = deepcopy(oldNearest[k]) k += 1 for j in range(k,nPoints-1): newNearest[j+1] = deepcopy(oldNearest[j]) oldNearest = deepcopy(newNearest) #We're done, now print the result for point in oldNearest: print point.station, point.english, point.distance return I initially wrote this in C, using the exact same approach, and it works fine there, and is basically instantaneous for nPoints<=100. So I decided to port it to python because I wanted to use SqlAlchemy to do some other stuff. I first ported it without the deepcopy statements that now pepper the method, and this caused the results to be 'odd', or partially incorrect, because some of the points were just getting copied as references(I guess? I think?) -- but it was still pretty nearly as fast as the C version. Now with the deepcopy calls added, the routine does it's job correctly, but it has incurred an extreme performance penalty, and now takes several seconds to do the same job. This seems like a pretty common job, but I'm clearly not doing it the pythonic way. How should I be doing this so that I still get the correct results but don't have to include deepcopy everywhere?

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• Using variables inside macros in SQL

  - by Tim

  Hello I'm wanting to use variables inside my macro SQL on Teradata. I thought I could do something like the following: REPLACE MACRO DbName.MyMacro ( MacroNm VARCHAR(50) ) AS ( /* Variable to store last time the macro was run */ DECLARE V_LAST_RUN_DATE TIMESTAMP; /* Get last run date and store in V_LAST_RUN_DATE */ SELECT LastDate INTO V_LAST_RUN_DATE FROM DbName.RunLog WHERE MacroNm = :MacroNm; /* Update the last run date to now and save the old date in history */ EXECUTE MACRO DbName.RunLogUpdater( :MacroNm ,V_LAST_RUN_DATE ,CURRENT_TIMESTAMP ); ); However, that didn't work, so I thought of this instead: REPLACE MACRO DbName.MyMacro ( MacroNm VARCHAR(50) ) AS ( /* Variable to store last time the macro was run */ CREATE VOLATILE TABLE MacroVars AS ( SELECT LastDate AS V_LAST_RUN_DATE FROM DbName.RunLog WHERE MacroNm = :MacroNm; ) WITH DATA ON COMMIT PRESERVE ROWS; /* Update the last run date to now and save the old date in history */ EXECUTE MACRO DbName.RunLogUpdater( :MacroNm ,SELECT V_LAST_RUN_DATE FROM MacroVars ,CURRENT_TIMESTAMP ); ); I can do what I'm looking for with a Stored Procedure, however I want to avoid for performance. Do you have any ideas about this? Is there anything else I can try? Cheers Tim

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• SQL to get list of dates as well as days before and after without duplicates

  - by Nathan Koop

  I need to display a list of dates, which I have in a table SELECT mydate AS MyDate, 1 AS DateType FROM myTable WHERE myTable.fkId = @MyFkId; Jan 1, 2010 - 1 Jan 2, 2010 - 1 Jan 10, 2010 - 1 No problem. However, I now need to display the date before and the date after as well with a different DateType. Dec 31, 2009 - 2 Jan 1, 2010 - 1 Jan 2, 2010 - 1 Jan 3, 2010 - 2 Jan 9, 2010 - 2 Jan 10, 2010 - 1 Jan 11, 2010 - 2 I thought I could use a union SELECT MyDate, DateType FROM ( SELECT mydate - 1 AS MyDate, 2 AS DateType FROM myTable WHERE myTable.fkId = @MyFkId; UNION SELECT mydate + 1 AS MyDate, 2 AS DateType FROM myTable WHERE myTable.fkId = @MyFkId; UNION SELECT mydate AS MyDate, 1 AS DateType FROM myTable WHERE myTable.fkId = @MyFkId; ) AS myCombinedDateTable This however includes duplicates of the original dates. Dec 31, 2009 - 2 Jan 1, 2009 - 2 Jan 1, 2010 - 1 Jan 2, 2010 - 2 Jan 2, 2010 - 1 Jan 3, 2010 - 2 Jan 9, 2010 - 2 Jan 10, 2010 - 1 Jan 11, 2010 - 2 How can I best remove these duplicates? I am considering a temporary table, but am unsure if that is the best way to do it. This also appears to me that it may provide performance issues as I am running the same query three separate times. What would be the best way to handle this request?

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• MYSQL fetch 10 posts, each w/ vote count, sorted by vote count, limited by where clause on posts

  - by nibblebot

  I want to fetch a set of Posts w/ vote count listed, sorted by vote count (e.g.) Post 1 - Post Body blah blah - Votes: 500 Post 2 - Post Body blah blah - Votes: 400 Post 3 - Post Body blah blah - Votes: 300 Post 4 - Post Body blah blah - Votes: 200 I have 2 tables: Posts - columns - id, body, is_hidden Votes - columns - id, post_id, vote_type_id Here is the query I've tried: SELECT p.*, v.yes_count FROM posts p LEFT JOIN (SELECT post_id, vote_type_id, COUNT(1) AS yes_count FROM votes WHERE (vote_type_id = 1) GROUP BY post_id ORDER BY yes_count DESC LIMIT 0, 10) v ON v.post_id = p.id WHERE (p.is_hidden = 0) ORDER BY yes_count DESC LIMIT 0, 10 Correctness: The above query almost works. The subselect is including votes for posts that have is_hidden = 1, so when I left join it to posts, if a hidden post is in the top 10 (ranked by votes), I can end up with records with NULL on the yes_count field. Performance: I have ~50k posts and ~500k votes. On my dev machine, the above query is running in .4sec. I'd like to stay at or below this execution time. Indexes: I have an index on the Votes table that covers the fields: vote_type_id and post_id EXPLAIN id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY p ALL NULL NULL NULL NULL 45985 Using where; Using temporary; Using filesort 1 PRIMARY <derived2> ALL NULL NULL NULL NULL 10 2 DERIVED votes ref VotingPost VotingPost 4 319881 Using where; Using index; Using temporary; Using filesort

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• iPhone OS: Strategies for high density image work

  - by Jasconius

  I have a project that is coming around the bend this summer that is going to involve, potentially, an extremely high volume of image data for display. We are talking hundreds of 640x480-ish images in a given application session (scaled to a smaller resolution when displayed), and handfuls of very large (1280x1024 or higher) images at a time. I've already done some preliminary work and I've found that the typical 640x480ish image is just a shade under 1MB in memory when placed into a UIImageView and displayed... but the very large images can be a whopping 5+ MB's in some cases. This project is actually be targeted at the iPad, which, in my Instruments tests seems to cap out at about 80-100MB's of addressable physical memory. Details aside, I need to start thinking of how to move huge volumes of image data between virtual and physical memory while preserving the fluidity and responsiveness of the application, which will be high visibility. I'm probably on the higher ends of intermediate at Objective-C... so I am looking for some solid articles and advice on the following: 1) Responsible management of UIImage and UIImageView in the name of conserving physical RAM 2) Merits of using CGImage over UIImage, particularly for the huge images, and if there will be any performance gain 3) Anything dealing with memory paging particularly as it pertains to images I will epilogue by saying that the numbers I have above maybe off by about 10 or 15%. Images may or may not end up being bundled into the actual app itself as opposed to being loaded in from an external server.

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• 301 Redirecting URLs based on GET variables in .htaccess

  - by technicalbloke

  I have a few messy old URLs like... http://www.example.com/bunch.of/unneeded/crap?opendocument&part=1 http://www.example.com/bunch.of/unneeded/crap?opendocument&part=2 ...that I want to redirect to the newer, cleaner form... http://www.example.com/page.php/welcome http://www.example.com/page.php/prices I understand I can redirect one page to another with a simple redirect i.e. Redirect 301 /bunch.of/unneeded/crap http://www.example.com/page.php But the source page doesn't change, only it's GET vars. I can't figure out how to base the redirect on the value of these GET variables. Can anybody help pls!? I'm fairly handy with the old regexes so I can have a pop at using mod-rewrite if I have to but I'm not clear on the syntax for rewriting GET vars and I'd prefer to avoid the performance hit and use the cleaner Redirect directive. Is there a way? and if not can anyone clue me in as to the right mod-rewrite syntax pls? Cheers, Roger.

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• PHP autoloader: ignoring non-existing include

  - by Bart van Heukelom

  I have a problem with my autoloader: public function loadClass($className) { $file = str_replace(array('_', '\\'), '/', $className) . '.php'; include_once $file; } As you can see, it's quite simple. I just deduce the filename of the class and try to include it. I have a problem though; I get an exception when trying to load a non-existing class (because I have an error handler which throws exceptions). This is inconvenient, because it's also fired when you use class_exists() on a non-existing class. You don't want an exception there, just a "false" returned. I fixed this earlier by putting an @ before the include (supressing all errors). The big drawback with this, though, is that any parser/compiler errors (that are fatal) in this include won't show up (not even in the logs), resulting in a hard to find bug. What would be the best way to solve both problems at once? The easiest way would be to include something like this in the autoloader (pseudocode): foreach (path in the include_path) { if (is_readable(the path + the class name)) readable = true; } if (!readable) return; But I worry about the performance there. Would it hurt a lot? (Solved) Made it like this: public function loadClass($className) { $file = str_replace(array('_', '\\'), '/', $className) . '.php'; $paths = explode(PATH_SEPARATOR, get_include_path()); foreach ($paths as $path) { if (is_readable($path . '/' . $file)) { include_once $file; return; } } }

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• Why use bin2hex when inserting binary data from PHP into MySQL?

  - by Atli

  I heard a rumor that when inserting binary data (files and such) into MySQL, you should use the bin2hex() function and send it as a HEX-coded value, rather than just use mysql_real_escape_string on the binary string and use that. // That you should do $hex = bin2hex($raw_bin); $sql = "INSERT INTO `table`(`file`) VALUES (X'{$hex}')"; // Rather than $bin = mysql_real_escape_string($raw_bin); $sql = "INSERT INTO `table`(`file`) VALUES ('{$bin}')"; It is supposedly for performance reasons. Something to do with how MySQL handles large strings vs. how it handles HEX-coded values However, I am having a hard time confirming this. All my tests indicate the exact oposite; that the bin2hex method is ~85% slower and uses ~24% more memory. (I am testing this on PHP 5.3, MySQL 5.1, Win7 x64 - Using a farily simple insert loop.) For instance, this graph shows the private memory usage of the mysqld process while the test code was running: Does anybody have any explainations or reasources that would clarify this? Thanks.

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• Query on object id in VQL

  - by Banang

  I'm currently working with the versant object database (using jvi), and have a case where I need to query the database based on an object id. What I'm trying to achieve is something along the lines of Employee employee = new Employee("Mr. Pickles"); session.commit(); FundVQLQuery q = new FundVQLQuery(session, "select * from Employee employee where employee = $1"); q.bind(employee); q.execute(); However, I'm finding out the hard way (I get an EVJ_NOT_A_VALID_KEY_TYPE error thrown at me) that this is infact not the way to do it. Anyone got any experience in working with VQL? Your help is much apreciated! A small clarification: The problem is I'm running some performance tests on the database using the pole position framework, and one of the tests in that framework requires me to fetch an object from the database using either an object reference or a low level object id. Thus, I'm not allowed to reference specific fields in the employee object, but must perform the query on the object in its entirety. So, it's not allowed for me to go "select * from Employee e where e.id = 4", I need it to use the entire object. Accepted answer: Since there is some sort of lunacy magic built into SO that prevents me to mark an accepted answer after a bounty has run out, readers should know that the answer posted by Chris Holmes solves this issue. Readers are encouraged to up-vote his post to further signalize the correctness of his answer to any future readers of this thread.

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• Asp.Net tree view in SharePoint webpart- Input string error

  - by Faiz

  Hi All, I am facing a very strange issue. I have a SharePoint webpart that displays an asp.net tree view. It takes tree depth from a drop down. To improve performance of the tree view, i am setting the PopulateOnDemand property to true for the last level of the tree depth. For example, if i have a total of 10 levels in the data and the user selects tree depth as 3, then the third level data i set PopulateOnDemand to true. Now comes the strange part. When i click on the + image on the third level, and if there are children under that particular node then call back happens and node gets expanded. But if there no children for that particular node, then click + throws "Input string was not in the correct format" error. I have made sure that there is no server side error. Some things looks to be fishy when internet explorer is trying to bind construct the expanded node. Please let me know if any one faced similar issue or the resolution for the same? Thanks in advance

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• Fastest way to generate delimited string from 1d numpy array

  - by Abiel

  I have a program which needs to turn many large one-dimensional numpy arrays of floats into delimited strings. I am finding this operation quite slow relative to the mathematical operations in my program and am wondering if there is a way to speed it up. For example, consider the following loop, which takes 100,000 random numbers in a numpy array and joins each array into a comma-delimited string. import numpy as np x = np.random.randn(100000) for i in range(100): ",".join(map(str, x)) This loop takes about 20 seconds to complete (total, not each cycle). In contrast, consider that 100 cycles of something like elementwise multiplication (x*x) would take than one 1/10 of a second to complete. Clearly the string join operation creates a large performance bottleneck; in my actual application it will dominate total runtime. This makes me wonder, is there a faster way than ",".join(map(str, x))? Since map() is where almost all the processing time occurs, this comes down to the question of whether there a faster to way convert a very large number of numbers to strings.

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• how do i work bool!

  - by user350217

  HI! im a beginner and im really getting frustrated with this whole concept. i dont understand how to exactly use the bool function. i know what it is but i cantfigure out how to make it work in my program. Im trying to say that if my variable "selection" is any letter beween 'A' and 'I' then it is valid and can continue on to the next function which is called calcExchangeAmt(amtExchanged, selection). if it is false i want it to ask the user if they want to repeat the program and if they agree to repeat i want it to clear the screen and restart to the main function. please help edit my work! this is my bool function: bool isSelectionValid(char selection, char yesNo, double amtExchanged) { bool validData; validData = true; if((selection >= 'a' && selection <= 'i') || (selection >= 'A' && selection <= 'I')) { validData = calcExchangeAmt (amtExchanged, selection); } else(validData == false); { cout<<"Do you wish to continue? (Y for Yes / N for No)"; cin>>yesNo; } do { main(); } while ((yesNo =='y')||(yesNo == 'Y')); { system("cls"); } return 0; } this is the warning that im gettng: warning C4800: 'double' : forcing value to bool 'true' or 'false' (performance warning)

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• Does this mimic perfectly a function template specialization?

  - by zeroes00

  Since the function template in the following code is a member of a class template, it can't be specialized without specializing the enclosing class. But if the compiler's full optimizations are on (assume Visual Studio 2010), will the if-else-statement in the following code get optimized out? And if it does, wouldn't it mean that for all practical purposes this IS a function template specialization without any performance cost? template<typename T> struct Holder { T data; template<int Number> void saveReciprocalOf(); }; template<typename T> template<int Number> void Holder<T>::saveReciprocalOf() { //Will this if-else-statement get completely optimized out if(Number == 0) data = (T)0; else data = (T)1 / Number; } //----------------------------------- void main() { Holder<float> holder; holder.saveReciprocalOf<2>(); cout << holder.data << endl; }

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• Model login constraints based on time

  - by DaDaDom

  Good morning, for an existing web application I need to implement "time based login constraints". It means that for each user, later maybe each group, I can define timeslots when they are (not) allowed to log in into the system. As all data for the application is stored in database tables, I need to somehow create a way to model this idea in that way. My first approach, I will try to explain it here: Create a tree of login constraints (called "timeslots") with the main "categories", like "workday", "weekend", "public holiday", etc. on the top level, which are in a "sorted" order (meaning "public holiday" has a higher priority than "weekday") for each top level node create subnodes, which have a finer timespan, like "monday", "tuesday", ... below that, create an "hour" level: 0, 1, 2, ..., 23. No further details are necessary. set every member to "allowed" by default For every member of the system create a 1:n relationship member:timeslots which defines constraints, e.g. a member A may have A:monday-forbidden and A:tuesday-forbidden Do a depth-first search at every login and check if the member has a constraint. Why a depth first search? Well, I thought that it may be that a member has the rules: A:monday->forbidden, A:monday-10->allowed, A:mondey-11->allowed So a login on monday at 12:30 would fail, but one at 10:30 succeed. For performance reasons I could break the relational database paradigm and set a flag for every entry in the member-to-timeslots-table which is set to true if the member has information set for "finer" timeslots, but that's a second step. Is this model in principle a good idea? Are there existing models? Thanks.

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• Question about creating device-compatible bitmaps in C#

  - by MusiGenesis

  I am storing bitmap-like data in a two-dimensional int array. To convert this array into a GDI-compatible bitmap (for use with BitBlt), I am using this function: public IntPtr GetGDIBitmap(int[,] data) { int w = data.GetLength(0); int h = data.GetLength(1); IntPtr ret = IntPtr.Zero; using (Bitmap bmp = new Bitmap(w, h)) { for (int x = 0; x < w; x++) { for (int y = 0; y < h; y++) { Color color = Color.FromArgb(data[x, y]); bmp.SetPixel(x, y, color); } } ret = bmp.GetHbitmap(); } return ret; } This works as expected, but the call to bmp.GetHbitmap() has to allocate memory for the returned bitmap. I'd like to modify this method in two (probably related) ways: I'd like to remove the intermediate Bitmap from the above code entirely, and go directly from my int[,] array to the device-compatible bitmap (i.e. the IntPtr). I presume this would involve calling CreateCompatibleBitmap, but I don't know how to go from that call to actually manipulating the pixel values. This should logically follow from the answer to the first, but I'd also like my method to re-use existing GDI bitmap handles (instead of creating a new bitmap each time). How can I do this? NOTE: I don't really use Bitmap.SetPixel(), as its performance could best be described as "glacial". The code is just for illustration.

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• Mysql Server Optimization

  - by Ish Kumar

  Hi Geeks, We are having serious MySQL(InnoDB) performance issues at a moment when we do: (10-20) insertions on TABLE1 (10-20) updates on TABLE2 Note: Both above operations happens within fraction of a second. And this occurs every few (10-15) minutes. And all online users (approx 400-600) doing read operation on join of TABLE1 & TABLE2 every 1 second. Here is our mysql configuration info: http://docs.google.com/View?id=dfrswh7c_117fmgcmb44 Issues: Lot queries wait and expire later (saw it from phpmyadmin / processes). My poor MySQL server crashes sometimes Questions Q1: Any suggestions to optimize at MySQL level? Q2: I thinking to use persistent connections at application level, is it right? Info Added Later: Database Engine: InnoDB TABLE1 : 400,000 rows (inserting 8,000 daily) & TABLE2: 8,000 rows 1 second query: SELECT b.id, b.user_id, b.description, b.debit, b.created, b.price, u.username, u.email, u.mobile FROM TABLE1 b, TABLE2 u WHERE b.credit = 0 AND b.user_id = u.id AND b.auction_id = "12345" ORDER BY b.id DESC LIMIT 10; // there are few more but they are not so critical. Indexing is good, we are using them wisely. In above query all id's are indexed And TABLE1 has frequent insertions and TABLE2 has frequent updates.

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• is mysql index useful on column 'state' when only doing bit-operations on the column?

  - by Geert-Jan

  I have a lot of domain entities (stored in mysql) which undergo lots of different operations. Each operation is executed from a different program. I need to keep (flow)-state for these entities which I implemented in as a long field 'flowstate' used as a bitset. to query mysql for entities which have undergone a certain operation I do something like: select * from entities where state >> 7 & 1 = 1 Indicating bit 7 (cooresponding to operation 7) has run. (<-- simplified) Anyway, I really didn't pay attention to the performance implications of this setup in the beginning, and I think I'm in a bit of trouble since queries as the above run pretty slow. What I'd like to know: Does an mysql index on 'flowstate' help at all? After all it's not a single value Mysql can quickly find using a binary sort or whatever. If it doesn't, are there any other things I could do to speed things up? . Are there special 'mask-indices' for fields with use-cases as the above? TIA, Geert-jan

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