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  • mySQL & Relational databases: How to handle sharding/splitting on application level?

    - by Industrial
    Hi everybody, I have thought a bit about sharding tables, since partitioning cannot be done with foreign keys in a mySQL table. Maybe there's an option to switch to a different relational database that features both, but I don't see that as an option right now. So, the sharding idea seems like a pretty decent thing. But, what's a good approach to do this on a application level? I am guessing that a take-off point would be to prefix tables with a max value for the primary key in each table. Something like products_4000000 , products_8000000 and products_12000000. Then the application would have to check with a simple if-statement the size of the id (PK) that will be requested is smaller then four, eight or twelve million before doing any actual database calls. So, is this a step in the right direction or are we doing something really stupid?

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  • Are Conditional subquery

    - by Tobias Schulte
    I have a table foo and a table bar, where each foo might have a bar (and a bar might belong to multiple foos). Now I need to select all foos with a bar. My sql looks like this SELECT * FROM foo f WHERE [...] AND ($param IS NULL OR (SELECT ((COUNT(*))>0) FROM bar b WHERE f.bar = b.id)) with $param being replaced at runtime. The question is: Will the subquery be executed even if param is null, or will the dbms optimize the subquery out?

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  • How to profile object creation in Java?

    - by gooli
    The system I work with is creating a whole lot of objects and garbage collecting them all the time which results in a very steeply jagged graph of heap consumption. I would like to know which objects are being generated to tune the code, but I can't figure out a way to dump the heap at the moment the garbage collection starts. When I tried to initiate dumpHeap via JConsole manually at random times, I always got results after GC finished its run, and didn't get any useful data. Any notes on how to track down excessive temporary object creation are welcome.

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  • Better to combine & minify javascript or use Google CDN?

    - by jessegavin
    I am building a site which currently uses javascript from several sources: Group 1: Google Maps API v3 (hosted by Google) Group 2: jQuery & swfobject (hosted on Google CDN) Group 3: Several jQuery plugins and non-jquery javascript files (hosted on my server) I am using Justin Etheredge's tool SquishIt to combine and minify all the javascript files that are hosted on my server (group 3). I am wondering if the site would 'feel' faster to users if I were to host the files in (group 2) locally so that they can be combined with all the other files in (group 3) and requiring only one HTTP request for groups 2 & 3. This would mean that I don't get the benefits of the Google CDN however. Does anyone have any advice on this matter?

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  • How to speed this kind of for-loop?

    - by wok
    I would like to compute the maximum of translated images along the direction of a given axis. I know about ordfilt2, however I would like to avoid using the Image Processing Toolbox. So here is the code I have so far: imInput = imread('tire.tif'); n = 10; imMax = imInput(:, n:end); for i = 1:(n-1) imMax = max(imMax, imInput(:, i:end-(n-i))); end Is it possible to avoid using a for-loop in order to speed the computation up, and, if so, how?

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  • Scalable way of doing self join with many to many table

    - by johnathan
    I have a table structure like the following: user id name profile_stat id name profile_stat_value id name user_profile user_id profile_stat_id profile_stat_value_id My question is: How do I evaluate a query where I want to find all users with profile_stat_id and profile_stat_value_id for many stats? I've tried doing an inner self join, but that quickly gets crazy when searching for many stats. I've also tried doing a count on the actual user_profile table, and that's much better, but still slow. Is there some magic I'm missing? I have about 10 million rows in the user_profile table and want the query to take no longer than a few seconds. Is that possible?

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  • About the String#substring() method

    - by alain.janinm
    If we take a look at the String#substring method implementation : new String(offset + beginIndex, endIndex - beginIndex, value); We see that a new String is created with the same original content (parameter char [] value). So the workaround is to use new String(toto.substring(...)) to drop the reference to the original char[] value and make it eligible for GC (if no more references exist). I would like to know if there is a special reason that explain this implementation. Why the method doesn't create herself the new shorter String and why she keeps the full original value instead? The other related question is : should we always use new String(...) when dealing with substring?

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  • Quickest way to compare a bunch of array or list of values.

    - by zapping
    Can you please let me know on the quickest and efficient way to compare a large set of values. Its like there are a list of parent codes(string) and each code has a series of child values(string). The child lists have to be compared with each other and find out duplicates and count how many times they repeat. code1(code1_value1, code1_value2, code3_value3, ..., code1_valueN); code2(code2_value1, code1_value2, code2_value3, ..., code2_valueN); code3(code2_value1, code3_value2, code3_value3, ..., code3_valueN); . . . codeN(codeN_value1, codeN_value2, codeN_value3, ..., codeN_valueN); The lists are huge say like there are 100 parent codes and each has about 250 values in them. There will not be duplicates within a code list. Doing it in java and the solution i could figure out is. Store the values of first set of code in as codeMap.put(codeValue, duplicateCount). The count initialized to 0. Then compare the rest of the values with this. If its in the map then increment the count otherwise append it to the map. The downfall of this is to get the duplicates. Another iteration needs to be performed on a very large list. An alternative is to maintain another hashmap for duplicates like duplicateCodeMap.put(codeValue, duplicateCount) and change the initial hashmap to codeMap.put(codeValue, codeValue). Speed is what is requirement. Hope one of you can help me with it.

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  • MySQL Single Query Benchmarking Strategies

    - by Pepper
    Hello, I have a slow mySQL query in my application that I need to re-write. The problem is, it's only slow on my production server and only when it's not cached. The first time I run it, it will take 12 seconds, then anytime after that it'll be 500 milliseconds. Is there an easy way to test this query without it hitting the query cache so I can see the results of my refactoring? Thanks!

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  • Is Java serialization a tool to shrink the memory footprint?

    - by Pentius
    Hey folks, does serialization in Java always have to shrink the memory that is used to hold an object structure? Or is it likely that serialization will have higher costs? In other words: Is serialization a tool to shrink the memory footprint of object structures in Java? Edit I'm totally aware of what serialization was intended for, but thanks anyway :-) But you know, tools can be misused. My question is, whether it is a good tool to decrease the memory usage. So what reasons can you imagine, why memory usage should increase/decrease? What will happen in most cases?

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  • Generated images fail to load in browser

    - by notJim
    I've got a page on a webapp that has about 13 images that are generated by my application, which is written in the Kohana PHP framework. The images are actually graphs. They are cached so they are only generated once, but the first time the user visits the page, and the images all have to be generated, about half of the images don't load in the browser. Once the page has been requested once and images are cached, they all load successfully. Doing some ad-hoc testing, if I load an individual image in the browser, it takes from 450-700 ms to load with an empty cache (I checked this using Google Chrome's resource tracking feature). For reference, it takes around 90-150 ms to load a cached image. Even if the image cache is empty, I have the data and some of the application's startup tasks cached, so that after the first request, none of that data needs to be fetched. My questions are: Why are the images failing to load? It seems like the browser just decides not to download the image after a certain point, rather than waiting for them all to finish loading. What can I do to get them to load the first time, with an empty cache? Obviously one option is to decrease the load times, and I could figure out how to do that by profiling the app, but are there other options? As I mentioned, the app is in the Kohana PHP framework, and it's running on Apache. As an aside, I've solved this problem for now by fetching the page as soon as the data is available (it comes from a batch process), so that the images are always cached by the time the user sees them. That feels like a kludgey solution to me, though, and I'm curious about what's actually going on.

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  • How to set up a load/stress test for a web site?

    - by Ryan
    I've been tasked with stress/load testing our company web site out of the blue and know nothing about doing so. Every search I make on google for "how to load test a web site" just comes back with various companies and software to physically do the load testing. For now I'm more interested in how to actually go about setting up a load test like what I should take into account prior to load testing, what pages within my site I should be testing load against and what things I'm going to want to monitor when doing the test. Our web site is on a multi-tier system complete with a separate database server (IIS 7 Web Server, SQL Server 2000 db). I imagine I'd want to monitor both the web server and the database server for testing load however when setting up scenarios to load test the web server I'd have to use pages that query the database to see any load on the database server at the same time. Are web servers and database servers generally tested simultaneously or are they done as separate tests? As you can see I'm pretty clueless as to the whole operation so any incite as to how to go about this would be very helpful. FYI I have been tinkering with Pylot and was able to create and run a scenario against our site but I'm not sure what I should be looking for in the results or if the scenario I created is even a scenario worth measuring for our site. Thanks in advance.

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  • Cuboid inside generic polyhedron

    - by DOFHandler
    I am searching for an efficient algorithm to find if a cuboid is completely inside or completely outside or (not-inside and not-outside) a generic (concave or convex) polyhedron. The polyhedron is defined by a list of 3D points and a list of facets. Each facet is defined by the subset of the contour points ordinated such as the right-hand normal points outward the solid. Any suggestion? Thank you

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  • How do you share pre-calculated data between calls to a Rails web service?

    - by Nigel Thorne
    I have a Rails app that allows users to build up a network structure and then ask questions about how to navigate around it. When adding nodes and connections these are just saved to the database. At the point you make a query of the network I calculate the shortest path from any node to any other node. Constructing this in memory takes a while (something I need to fix), but once it is there, you can instantly get the answer to any of these path questions. The question is... How do I share this network between calls to the website, so each request doesn't regenerate the paths network each time? Note: I am hosting this on apache server using passenger (mod ruby) Thoughts?

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  • C++ code which is slower than its C equivalent?

    - by user997112
    Are there any aspects to the C++ programming language where the code is known to be slower than the equivalent C language? Obviously this would be excluding the OO features like virtual functions and vtable features etc. I am wondering whether, when you are programming in a latency-critical area (and you aren't worried about OO features) whether you could stick with basic C++ or would C be better?

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  • Cache layer for MVC - Model or controller?

    - by Industrial
    Hi everyone, I am having some second thoughts about where to implement the caching part. Where is the most appropriate place to implement it, you think? Inside every model, or in the controller? Approach 1 (psuedo-code): // mycontroller.php MyController extends Controller_class { function index () { $data = $this->model->getData(); echo $data; } } // myModel.php MyModel extends Model_Class{ function getData() { $data = memcached->get('data'); if (!$data) { $query->SQL_QUERY("Do query!"); } return $data; } } Approach 2: // mycontroller.php MyController extends Controller_class { function index () { $dataArray = $this->memcached->getMulti('data','data2'); foreach ($dataArray as $key) { if (!$key) { $data = $this->model->getData(); $this->memcached->set($key, $data); } } echo $data; } } // myModel.php MyModel extends Model_Class{ function getData() { $query->SQL_QUERY("Do query!"); return $data; } } Thoughts: Approach 1: No multiget/multi-set. If a high number of keys would be returned, overhead would be caused. Easier to maintain, all database/cache handling is in each model Approach 2: Better performancewise - multiset/multiget is used More code required Harder to maintain Tell me what you think!

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  • Does variable = null set it for garbage collection

    - by manyxcxi
    Help me settle a dispute with a coworker: Does setting a variable or collection to null in Java aid in garbage collection and reducing memory usage? If I have a long running program and each function may be iteratively called (potentially thousands of times): Does setting all the variables in it to null before returning a value to the parent function help reduce heap size/memory usage?

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  • MySQL left outer join is slow

    - by Ryan Doherty
    Hi, hoping to get some help with this query, I've worked at it for a while now and can't get it any faster: SELECT date, count(id) as 'visits' FROM dates LEFT OUTER JOIN visits ON (dates.date = DATE(visits.start) and account_id = 40 ) WHERE date >= '2010-12-13' AND date <= '2011-1-13' GROUP BY date ORDER BY date ASC That query takes about 8 seconds to run. I've added indexes on dates.date, visits.start, visits.account_id and visits.start+visits.account_id and can't get it to run any faster. Table structure (only showing relevant columns in visit table): create table visits ( `id` int(11) NOT NULL AUTO_INCREMENT, `account_id` int(11) NOT NULL, `start` DATETIME NOT NULL, `end` DATETIME NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; CREATE TABLE `dates` ( `date` date NOT NULL, PRIMARY KEY (`date`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1; dates table contains all days from 2010-1-1 to 2020-1-1 (~3k rows). visits table contains about 400k rows dating from 2010-6-1 to yesterday. I'm using the date table so the join will return 0 visits for days there were no visits. Results I want for reference: +------------+--------+ | date | visits | +------------+--------+ | 2010-12-13 | 301 | | 2010-12-14 | 356 | | 2010-12-15 | 423 | | 2010-12-16 | 332 | | 2010-12-17 | 346 | | 2010-12-18 | 226 | | 2010-12-19 | 213 | | 2010-12-20 | 311 | | 2010-12-21 | 273 | | 2010-12-22 | 286 | | 2010-12-23 | 241 | | 2010-12-24 | 149 | | 2010-12-25 | 102 | | 2010-12-26 | 174 | | 2010-12-27 | 258 | | 2010-12-28 | 348 | | 2010-12-29 | 392 | | 2010-12-30 | 395 | | 2010-12-31 | 278 | | 2011-01-01 | 241 | | 2011-01-02 | 295 | | 2011-01-03 | 369 | | 2011-01-04 | 438 | | 2011-01-05 | 393 | | 2011-01-06 | 368 | | 2011-01-07 | 435 | | 2011-01-08 | 313 | | 2011-01-09 | 250 | | 2011-01-10 | 345 | | 2011-01-11 | 387 | | 2011-01-12 | 0 | | 2011-01-13 | 0 | +------------+--------+ Thanks in advance for any help!

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  • Syncing Data to Remote Services, Best Practices for Caching?

    - by viatropos
    I want to be able to publish events to Eventbrite, Eventful, and Google Calendar for my Google Apps. Each service has slightly different properties for events... I will be syncing many other things too, such as users with Google Contacts and MailChimp, Documents with Google Docs and some other services, etc... So I'm wondering, what is the recommended way of retrieving the data for the end user so that it's reasonably maintainable and optimized? Here are the things I'm thinking that I'm having trouble with: My App keeps a central database of all the models (Event, Document, User, Form, etc.), and whenever Admin creates an object (e.g. create through Eventbrite or through our Admin panel), we sync them and store a copy in our local database. When User goes to the site /events, App retrieves the events from the database. Read Events from a target feed, such as the Eventbrite or Eventful feed, and scrap the local database. Basically, I'm wondering, if we're storing all of the data on a remote service, do we really need to have a local database copy of the data? When would we need to have a local database, when wouldn't we?

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