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  • Quickest algorithm for finding sets with high intersection

    - by conradlee
    I have a large number of user IDs (integers), potentially millions. These users all belong to various groups (sets of integers), such that there are on the order of 10 million groups. To simplify my example and get to the essence of it, let's assume that all groups contain 20 user IDs (i.e., all integer sets have a cardinality of 100). I want to find all pairs of integer sets that have an intersection of 15 or greater. Should I compare every pair of sets? (If I keep a data structure that maps userIDs to set membership, this would not be necessary.) What is the quickest way to do this? That is, what should my underlying data structure be for representing the integer sets? Sorted sets, unsorted---can hashing somehow help? And what algorithm should I use to compute set intersection)? I prefer answers that relate C/C++ (especially STL), but also any more general, algorithmic insights are welcome. Update Also, note that I will be running this in parallel in a shared memory environment, so ideas that cleanly extend to a parallel solution are preferred.

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  • Improving the speed of php

    - by cast01
    I'm currently working on a website in PHP, and I'm wondering what the best practices/methods are to reduce the time requests take. I've build the site in a modular way, so a page would consist of a number of modules, and each of these would need to request information. For example, I have a cart module, that (if a cart is set) will fetch the cart with the id (stored in a session variable) from the database and return its contents. I have another module that lists categories and this needs to fetch the categories from the database. My system is built with models, and each model might also make a request, for example a category model will make a request to get products in that category.

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  • ColdFusion speed cost of FileExists

    - by davidosomething
    I want to: on every page, check if a file exists include that file if TRUE i.e.: <cfset variables.includes.header = ExpandPath("_inc_header.cfm")> <cfif FileExists(variables.includes.header)> <cfinclude template = "#variables.includes.header#"> </cfif> Is this a good idea?

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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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  • Storing high precision latitude/longitude numbers in iOS Core Data

    - by Bryan
    I'm trying to store Latitude/Longitudes in core data. These end up being anywhere from 6-20 digit precision. And for whatever reason, i had them as floats in Core Data, its rounding them and not giving me the exact values back. I tried "decimal" type, with no luck either. Are NSStrings my only other option? EDIT NSManagedObject: @interface Event : NSManagedObject { } @property (nonatomic, retain) NSDecimalNumber * dec; @property (nonatomic, retain) NSDate * timeStamp; @property (nonatomic, retain) NSNumber * flo; @property (nonatomic, retain) NSNumber * doub; Here's the code for a sample number that I store into core data: NSNumber *n = [NSDecimalNumber decimalNumberWithString:@"-97.12345678901234567890123456789"]; Code to access it again: NSNumber *n = [managedObject valueForKey:@"dec"]; NSNumber *f = [managedObject valueForKey:@"flo"]; NSNumber *d = [managedObject valueForKey:@"doub"]; Printed values: Printing description of n: -97.1234567890124 Printing description of f: <CFNumber 0x603f250 [0xfef3e0]>{value = -97.12345678901235146441, type = kCFNumberFloat64Type} Printing description of d: <CFNumber 0x6040310 [0xfef3e0]>{value = -97.12345678901235146441, type = kCFNumberFloat64Type}

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  • IPC speed and compare

    - by Lily
    I am trying to implement a real-time application which involves IPC across different modules. The modules are doing some data intensive processing. I am using message queue as the backbone(Activemq) for IPC in the prototype, which is easy(considering I am a totally IPC newbie), but it's very very slow. Here is my situation: I have isolated the IPC part so that I could change it other ways in future. I have 3 weeks to implement another faster version. ;-( IPC should be fast, but also comparatively easy to pick up I have been looking into different IPC approaches: socket, pipe, shared memory. However, I have no experience in IPC, and there is definitely no way I could fail this demo in 3 weeks... Which IPC will be the safe way to start with? Thanks. Lily

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  • Important question about linq to SQL performance on high loaded web applications

    - by Alex
    I started working with linq to SQL several weeks ago. I got really tired of working with SQL server directly through the SQL queries (sqldatareader, sqlcommand and all this good stuff).  After hearing about linq to SQL and mvc I quickly moved all my projects to these technologies. I expected linq to SQL work slower but it suprisongly turned out to be pretty fast, primarily because I always forgot to close my connections when using datareaders. Now I don't have to worry about it. But there's one problem that really bothers me. There's one page that's requested thousands of times a day. The system gets data in the beginning, works with it and updates it. Primarily the updates are ++ @ -- (increase and decrease values). I used to do it like this UPDATE table SET value=value+1 WHERE ID=@I'd It worked with no problems obviously. But with linq to SQL the data is taken in the beginning, moved to the class, changed and then saved. Stats.registeredusers++; Db.submitchanges(); Let's say there were 100 000 users. Linq will say "let it be 100 001" instead of "let it be increased by 1". But if there value of users has already been increased (that happens in my site all the time) then linq will be like oops, this value is already 100 001. Whatever I'll throw an exception" You can change this behavior so that it won't throw an exception but it still will not set the value to 100 002. Like I said, it happened with me all the time. The stas value was increased twice a second on average. I simply had to rewrite this chunk of code with classic ado net. So my question is how can you solve the problem with linq

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  • Recommendations of a high volume log event viewer in a Java enviroment

    - by Thorbjørn Ravn Andersen
    I am in a situation where I would like to accept a LOT of log events controlled by me - notably the logging agent I am preparing for slf4j - and then analyze them interactively. I am not as such interested in a facility that presents formatted log files, but one that can accept log events as objects and allow me to sort and display on e.g. threads and timelines etc. Chainsaw could maybe be an option but is currently not compatible with logback which I use for technical reasons. Is there any project with stand alone viewers or embedded in an IDE which would be suitable for this kind of log handling. I am aware that I am approaching what might be suitable for a profiler, so if there is a profiler projekt suitable for this kind of data acquisition and display where I can feed the event pipe, I would like to hear about it). Thanks for all feedback Update 2009-03-19: I have found that there is not a log viewer which allows me to see what I would like (a visual display of events with coordinates determined by day and time, etc), so I have decided to create a very terse XML format derived from the log4j XMLLayout adapted to be as readable as possible while still being valid XML-snippets, and then use the Microsoft LogParser to extract the information I need for postprocessing in other tools.

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  • Threading cost - minimum execution time when threads would add speed

    - by Lukas
    I am working on a C# application that works with an array. It walks through it (meaning that at one time only a narrow part of the array is used). I am considering adding threads in it to make it perform faster (it runs on a dualcore computer). The problem is that I do not know if it would actually help, because threads cost something and this cost could easily be more than the parallel gain... So how do I determine if threading would help?

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  • speed up wamp server + drupal on windows vista

    - by Andrew Welch
    Hi, My localhost performance with drupal six is pretty slow. I found a solution to add a # before the :: localhost line of the system32/etc/hosts file but this was something I had already done and didn't help much. does anyone know of any other optimisations that might work? tHanks Andy

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  • Large Y-axis tickInterval in high charts does not work

    - by ckovacs
    I have a chart at this JSFiddle to demonstrate a problem where our charts are not respecting the y-axis tick interval for large values: http://jsfiddle.net/z2cDu/1/ var plots = {"usBytePlots":[[1362009600000,143663192997],[1362096000000,110184848742],[1362182400000,97694974247],[1362268800000,90764690805],[1362355200000,112436517747],[1362441600000,113563368701],[1362528000000,139579327454],[1362614400000,118406594506],[1362700800000,125366899935],[1362787200000,134189435596],[1362873600000,132873135854],[1362960000000,121002328604],[1363046400000,123138222001],[1363132800000,115667785553],[1363219200000,103746172138],[1363305600000,108602633473],[1363392000000,89133998142],[1363478400000,92170701458],[1363564800000,86696922873],[1363651200000,80980159054],[1363737600000,97604615694],[1363824000000,108011666339],[1363910400000,124419138381],[1363996800000,121704988344],[1364083200000,124337959109],[1364169600000,137495512348],[1364256000000,136017103319],[1364342400000,60867510427]],"dsBytePlots":[[1362009600000,1734982247336],[1362096000000,1471928923201],[1362182400000,1453869593201],[1362268800000,1411787942581],[1362355200000,1460252447519],[1362441600000,1595590020177],[1362528000000,1658007074783],[1362614400000,1411941908699],[1362700800000,1447659369450],[1362787200000,1643008799861],[1362873600000,1792357973023],[1362960000000,1575173242169],[1363046400000,1565139003978],[1363132800000,1549211975554],[1363219200000,1438411448469],[1363305600000,1380445413578],[1363392000000,1298319283929],[1363478400000,1194578344720],[1363564800000,1211409679299],[1363651200000,1142416351471],[1363737600000,1223822672626],[1363824000000,1267692136487],[1363910400000,1384335759541],[1363996800000,1577205919828],[1364083200000,1675715948928],[1364169600000,1517593781592],[1364256000000,1562183018457],[1364342400000,681007264598]],"aggregatedTotalBytes":43476367948896,"aggregatedUsBytes":3150320403841,"aggregatedDsBytes":40326047545055,"maxTotalBytes":328186292129,"maxTotalBitsPerSecond":30387619.641574074} ; $('#container').highcharts({ yAxis: { tickInterval: 53687091200 // 500 gigabytes. Maximum y-axis value is approx 1.8TB }, series : [ { color: 'rgba(80, 180, 77, 0.7)', type: 'areaspline', name : 'Downstream', data : plots.dsBytePlots, total: plots.aggregatedDsBytes }, { color: 'rgba(33, 143, 197, 0.7)', type: 'areaspline', name : 'Upstream', data : plots.usBytePlots, total: plots.aggregatedUsBytes }] }); In this example we are charting bandwidth utilization in bytes. The chart has a maximum value of about 1.8TB. We set the y-axis tick interval to exactly 500GB but the rendered y-axis ticks don't make any sense for the given interval.

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  • php curl upload speed

    - by zanatic
    hey i made a script that uploads files to different servers using php curl and the problem is that it eats all my upload bandwith and my apache does not respond as i would like. the call is made from the php-cli and can not use any apache bandwith limiting bandwith thanks in advance

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  • PostgreSQL, Foreign Keys, Insert speed & Django

    - by Miles
    A few days ago, I ran into an unexpected performance problem with a pretty standard Django setup. For an upcoming feature, we have to regenerate a table hourly, containing about 100k rows of data, 9M on the disk, 10M indexes according to pgAdmin. The problem is that inserting them by whatever method literally takes ages, up to 3 minutes of 100% disk busy time. That's not something you want on a production site. It doesn't matter if the inserts were in a transaction, issued via plain insert, multi-row insert, COPY FROM or even INSERT INTO t1 SELECT * FROM t2. After noticing this isn't Django's fault, I followed a trial and error route, and hey, the problem disappeared after dropping all foreign keys! Instead of 3 minutes, the INSERT INTO SELECT FROM took less than a second to execute, which isn't too surprising for a table <= 20M on the disk. What is weird is that PostgreSQL manages to slow down inserts by 180x just by using 3 foreign keys. Oh, disk activity was pure writing, as everything is cached in RAM; only writes go to the disks. It looks like PostgreSQL is working very hard to touch every row in the referred tables, as 3MB/sec * 180s is way more data than the 20MB this new table takes on disk. No WAL for the 180s case, I was testing in psql directly, in Django, add ~50% overhead for WAL logging. Tried @commit_on_success, same slowness, I had even implemented multi row insert and COPY FROM with psycopg2. That's another weird thing, how can 10M worth of inserts generate 10x 16M log segments? Table layout: id serial primary, a bunch of int32, 3 foreign keys to small table, 198 rows, 16k on disk large table, 1.2M rows, 59 data + 89 index MB on disk large table, 2.2M rows, 198 + 210MB So, am I doomed to either drop the foreign keys manually or use the table in a very un-Django way by defining saving bla_id x3 and skip using models.ForeignKey? I'd love to hear about some magical antidote / pg setting to fix this.

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  • OpenGL: Textured Primitives + High Framerate

    - by James D
    Short version: What's the best practice going forward for efficiently rendering large numbers of independent texture-mapped, lighted 2D/3D primitives (circles, rects, etc.) in OpenGL? For example: a typical particle system using billboarded quads/triangles, point sprites, or whatever other technique, with blending. Because after reading this thread on the messiness of OpenGL versioning/deprecation I'm starting to have my doubts. My specific question is not the ABCs of displaying primitives in OpenGL, but rather how to do so efficiently in post-deprecation (or pre-deprecation) OpenGL, in a way that's going to be compatible with a wide range of commodity hardware and in a way that's not going to break or itself get deprecated, five years down the line. Thanks!

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  • memory usage in C# (.NET) app is very high, until I call System.GC.Collect()

    - by Chris Gray
    I've written an app that spins a few threads each of which read several MB of memory. Each thread then connects to the Internet and uploads the data. this occurs thousands of times and each upload takes some time I'm seeing a situation where (verified with windbg/sos and !dumpheap) that the Byte[] are not getting collected automatically, causing 100/150MB of memory to be reported in task manager if I call System.GC.Collect() i'm seeing a huge drop in memory, a drop of over 100MB I dont like calling System.GC.Collect() and my PC has tons of free memory. however if anyone looks at TaskManager they're going to be concerned, thinking my app is leaking horribly. tips?

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  • streaming speed for video content on iphone

    - by Jim
    My application was rejected from Apple today.Apple says that the video stream should be not more than at 64kbps. what should i will have to do get my application approve on App Store?? Should i have to make changes on video content that i am streaming from my iPhone or should i have to change in code? Please suggest. Thanks, Jim.

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  • CSS font-size causing the last line to be too high

    - by tster
    OK, I have a list (<ul>) then inside each <li> element I have an <a...> Here are all the applicable CSS items to the <a> tag .search_area li a { font-size:11px; } sResCntr li { list-style-type:none; } body { font-family:Arial; } Everything looked great, until I put that font-size:11px in there. The problem is that the hyperlinks wrap to multiple lines within the list (which is fine). But when I decrease the font-size, the last line of the hyperlink always has a larger gap between it and the line above it than the other lines. All the other lines look good, but the last line looks like it is 1.5 spaced or something. I have adjusted the line-height property, but always the last line is larger than the rest. If you need a demo to look at to see what I mean, I can arrange it when I get home.

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  • linq: SQL performance on high loaded web applications

    - by Alex
    I started working with linq to SQL several weeks ago. I got really tired of working with SQL server directly through the SQL queries (sqldatareader, sqlcommand and all this good stuff).  After hearing about linq to SQL and mvc I quickly moved all my projects to these technologies. I expected linq to SQL work slower but it suprisongly turned out to be pretty fast, primarily because I always forgot to close my connections when using datareaders. Now I don't have to worry about it. But there's one problem that really bothers me. There's one page that's requested thousands of times a day. The system gets data in the beginning, works with it and updates it. Primarily the updates are ++ @ -- (increase and decrease values). I used to do it like this UPDATE table SET value=value+1 WHERE ID=@I'd It worked with no problems obviously. But with linq to SQL the data is taken in the beginning, moved to the class, changed and then saved. Stats.registeredusers++; Db.submitchanges(); Let's say there were 100 000 users. Linq will say "let it be 100 001" instead of "let it be increased by 1". But if there value of users has already been increased (that happens in my site all the time) then linq will be like oops, this value is already 100 001. Whatever I'll throw an exception" You can change this behavior so that it won't throw an exception but it still will not set the value to 100 002. Like I said, it happened with me all the time. The stas value was increased twice a second on average. I simply had to rewrite this chunk of code with classic ado net. So my question is how can you solve the problem with linq

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  • php parsing speed optimization

    - by Arnaud
    I would like to add tooltip or generate link according to the element available in the database, for exemple if the html page printed is: to reboot your linux host in single-user mode you can ... I will use explode(" ", $row[page]) and the idea is now to lookup for every single word in the page to find out if they have a related referance in this exemple let's say i've got a table referance an one entry for reboot and one for linux reboot: restart a computeur linux: operating system now my output will look like (replaced < and by @) to @a href="ref/reboot"@reboot@/a@ your @a href="ref/linux"@linux@/a@ host in single-user mode you can ... Instead of have a static list generated when I saved the content, if I add more keyword in the future, then the text will become more interactive. My main concerne and question is how can I create a efficient enough process to do it ? Should I store all the db entry in an array and compare them ? Do an sql query for each word (seems to be crazy) Dump the table in a file and use a very long regex or a "grep -f pattern data" way of doing it? Or or or or I'm sure it must be a better way of doing it, just don't have a clue about it, or maybe this will be far too resource un-friendly and I should avoid doing such things. Cheers!

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  • Why is this code's execution speed so different?

    - by Steve Watkins
    In Internet Explorer 7, this code executes consistently in 47 ms: function updateObjectValues() { $('.objects').html(12345678); // ~500 DIVs } however, this code executes consistently in 157 ms: function updateObjectValues() { $('.objects').html('12345678'); // ~500 DIVs } Passing a number is over 3x faster than a string. Why are these results so dramatically different? And, is there any way to help the performance of the string?

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  • c# - SQL - speed up code to DB

    - by user228058
    I have a page with 26 sections - one for each letter of the alphabet. I'm retrieving a list of manufacturers from the database, and for each one, creating a link - using a different field in the Database. So currently, I leave the connection open, then do a new SELECT by each letter, WHERE the Name LIKE that letter. It's very slow, though. What's a better way to do this? TIA

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