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  • Design review for application facing memory issues

    - by Mr Moose
    I apologise in advance for the length of this post, but I want to paint an accurate picture of the problems my app is facing and then pose some questions below; I am trying to address some self inflicted design pain that is now leading to my application crashing due to out of memory errors. An abridged description of the problem domain is as follows; The application takes in a “dataset” that consists of numerous text files containing related data An individual text file within the dataset usually contains approx 20 “headers” that contain metadata about the data it contains. It also contains a large tab delimited section containing data that is related to data in one of the other text files contained within the dataset. The number of columns per file is very variable from 2 to 256+ columns. The original application was written to allow users to load a dataset, map certain columns of each of the files which basically indicating key information on the files to show how they are related as well as identify a few expected column names. Once this is done, a validation process takes place to enforce various rules and ensure that all the relationships between the files are valid. Once that is done, the data is imported into a SQL Server database. The database design is an EAV (Entity-Attribute-Value) model used to cater for the variable columns per file. I know EAV has its detractors, but in this case, I feel it was a reasonable choice given the disparate data and variable number of columns submitted in each dataset. The memory problem Given the fact the combined size of all text files was at most about 5 megs, and in an effort to reduce the database transaction time, it was decided to read ALL the data from files into memory and then perform the following; perform all the validation whilst the data was in memory relate it using an object model Start DB transaction and write the key columns row by row, noting the Id of the written row (all tables in the database utilise identity columns), then the Id of the newly written row is applied to all related data Once all related data had been updated with the key information to which it relates, these records are written using SqlBulkCopy. Due to our EAV model, we essentially have; x columns by y rows to write, where x can by 256+ and rows are often into the tens of thousands. Once all the data is written without error (can take several minutes for large datasets), Commit the transaction. The problem now comes from the fact we are now receiving individual files containing over 30 megs of data. In a dataset, we can receive any number of files. We’ve started seen datasets of around 100 megs coming in and I expect it is only going to get bigger from here on in. With files of this size, data can’t even be read into memory without the app falling over, let alone be validated and imported. I anticipate having to modify large chunks of the code to allow validation to occur by parsing files line by line and am not exactly decided on how to handle the import and transactions. Potential improvements I’ve wondered about using GUIDs to relate the data rather than relying on identity fields. This would allow data to be related prior to writing to the database. This would certainly increase the storage required though. Especially in an EAV design. Would you think this is a reasonable thing to try, or do I simply persist with identity fields (natural keys can’t be trusted to be unique across all submitters). Use of staging tables to get data into the database and only performing the transaction to copy data from staging area to actual destination tables. Questions For systems like this that import large quantities of data, how to you go about keeping transactions small. I’ve kept them as small as possible in the current design, but they are still active for several minutes and write hundreds of thousands of records in one transaction. Is there a better solution? The tab delimited data section is read into a DataTable to be viewed in a grid. I don’t need the full functionality of a DataTable, so I suspect it is overkill. Is there anyway to turn off various features of DataTables to make them more lightweight? Are there any other obvious things you would do in this situation to minimise the memory footprint of the application described above? Thanks for your kind attention.

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  • Should a domain expert make class diagrams?

    - by Matthieu
    The domain expert in our team uses UML class diagrams to model the domain model. As a result, the class diagrams are more of technical models rather than domain models (it serves of some sort of technical specifications for developpers because they don't have to do any conception, they just have to implement the model). In the end, the domain expert ends up doing the job of the architect/technical expert right? Is it normal for a domain expert (not a developer or technical profile) to do class diagrams? If not, what kind of modeling should he be using?

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  • Why are PHP function signatures so inconsistent?

    - by Shamim Hafiz
    I was going through some PHP functions and I could not help notice the following: <?php function foo(&$var) { } foo($a); // $a is "created" and assigned to null $b = array(); foo($b['b']); var_dump(array_key_exists('b', $b)); // bool(true) $c = new StdClass; foo($c->d); var_dump(property_exists($c, 'd')); // bool(true) ?> Notice the array_key_exists() and property_exists() function. In the first one, the property name(key for an array) is the first parameter while in the second one it is the second parameter. By intuition, one would expect them to have similar signature. This can lead to confusion and the development time may be wasted by making corrections of this type. Shouldn't PHP, or any language for that matter, consider making the signatures of related functions consistent?

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  • Variable naming conventions?

    - by Ziv
    I've just started using ReSharper (for C#) and I kind of like its code smells finder, it shows me some things about my writing that I meant to fix a long time ago (mainly variable naming conventions). It caused me to reconsider some of my naming conventions for methods and instance variables. ReSharper suggests that instance variable be lower camel case and begin with an underscore. For a while I meant to make all my local variables lower camel case but is the underscore necessary? Do you find it comfortable? I don't like this convention but I also haven't tried it yet, what is you opinion of it? The second thing it prompted me to re-evaluate is my naming conventions for GUI event handlers. I usually use the VS standard of ControlName_Action and my controls usually use hungarian notation (as a suffix, to help clarify in code what is visible to the user and what isn't when dealing with similarly named variable) so I end up with OK_btn_Click(), what is your opinion of that? Should I succumb to the ReSharper convention or there are other equally valid options?

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  • Implementing separation of concerns via MVC

    - by user2368481
    I'm creating a question to see if my understanding of MVC separation is correct, I haven't been able to find a clear answer anywhere online. So is this the right way to implement it (in Java): I would have 3 .java files, one each for Model, Controller, View. I would put all the classes related to Model in the Model.java like so: //Model.java { public class Model //class fields public Model(); public ModelClassA(); public ModelClassB(); public ModelClassC(); } With the ModelClasses being any class that I consider belonging to the Model. Is it correct to have the classes within the Model Class, as I have read that nested classes should be avoided where possible.

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  • Are there any companies using BDD in a .NET environment?

    - by Nick
    I've seen BDD in action (in this case using SpecFlow and Selenium in a .NET environment) for a small test project. I was very impressed - mainly due to the fact that the language used to specify the acceptance tests meant they engaged with the product owner much more easily. I'm now keen to bring this into my current organisation. However I'm asked 'who else uses this?' and 'show me some case-studies'. Unfortunately I cannot find any 'big names' (or even 'small names' for that matter!) of companies who are actively using BDD. I have two questions really: Is BDD adopted by companies out there? Who are they? How can BDD be implemented in an agile .NET environment and are there any significant drawbacks to doing it?

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  • Programming by dictation?

    - by Andrew M
    ie. you speak out the code, and someone else across the room types it in Anyone tried this? Obviously the person taking the dictation would need to be a coder too, so you didn't have to explain everything and go into tedious detail (not 'open bracket, new line...' but more like 'create a new class called myParser that takes three arguments, first one is...'). I thought of it because sometimes I'm too easily distracted at my computer. Surrounded by buttons, instant gratification a click away, the world at my fingertips. To get stuff done, I want to get away, write my code on paper. But that would mean losing access to necessary resources, and necessitate tedious typing-up later on. The solution? Dictate. Pros: no chance to check reddit, stackexchange, gmail, etc. code while you pace the room, lie down, play billiards, whatever train your brain to think more abstractedly (have to visualize things if you can't just see the screen) skip the tedious details (closing brackets etc.) the typist gets to shadow a more experienced programmer and learn how they work the typist can provide assistance/suggestions external pressure of typist expecting instructions, urging you to stay focussed Cons might be too hard might not work any better rather inefficient use of assisting programmer need to find/pay someone to do this

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  • Who is Configuration Manager?

    - by altern
    I would like to ask members of the community about the role of Configuration Manager, as you see it. I'm not asking what Configuration Management is, as long it had been asked before. What I need to know is: What tasks do you think Configuration Manager should perform (or performs) in your team? What is primary responsibility of Configuration Manager? What are secondary/auxiliary responsibilities of Configuration Manager? Does Configuration Manager need to be in charge of development processes on the project/company or he should be told what to do? What are relations between Configuration Manager, Build Manager, Release Manager, Deployment Engineer, CI Engineer roles? Aren't they all the same - Configuration Management? Maybe term Configuration Management is redundant and Technical/Team Lead should do all the related work instead? It would be really great if you could share your vision and experience.

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  • Confusion related to sigwait in multiprocess system

    - by user34790
    I am having difficulty in understanding IPC in multiprocess system. I have this system where there are three child processes that send two types of signals to their process group. There are four types of signal handling processes responsible for a particular type of signal. There is this monitoring process which waits for both the signals and then processes accordingly. When I run this program for a while, the monitoring process doesn't seem to pick up the signal as well as the signal handling process. I could see in the log that the signal is only being generated but not handled at all. My code is given below #include <cstdlib> #include <iostream> #include <iomanip> #include <unistd.h> #include <sys/types.h> #include <sys/wait.h> #include <sys/time.h> #include <signal.h> #include <unistd.h> #include <fcntl.h> #include <cstdio> #include <stdlib.h> #include <stdio.h> #include <pthread.h> using namespace std; double timestamp() { struct timeval tp; gettimeofday(&tp, NULL); return (double)tp.tv_sec + tp.tv_usec / 1000000.; } double getinterval() { srand(time(NULL)); int r = rand()%10 + 1; double s = (double)r/100; } int count; int count_1; int count_2; double time_1[10]; double time_2[10]; pid_t senders[1]; pid_t handlers[4]; pid_t reporter; void catcher(int sig) { printf("Signal catcher called for %d",sig); } int main(int argc, char *argv[]) { void signal_catcher_int(int); pid_t pid,w; int status; if(signal(SIGUSR1, SIG_IGN) == SIG_ERR) { perror("1"); return 1; } if(signal(SIGUSR2 ,SIG_IGN) == SIG_ERR) { perror("2"); return 2; } if(signal(SIGINT,signal_catcher_int) == SIG_ERR) { perror("3"); return 2; } //Registering the signal handler for(int i=0; i<4; i++) { if((pid = fork()) == 0) { cout << i << endl; //struct sigaction sigact; sigset_t sigset; int sig; int result = 0; sigemptyset(&sigset); if(i%2 == 0) { if(signal(SIGUSR2, SIG_IGN) == SIG_ERR) { perror("2"); return 2; } sigaddset(&sigset, SIGUSR1); sigprocmask(SIG_BLOCK, &sigset, NULL); } else { if(signal(SIGUSR1, SIG_IGN) == SIG_ERR) { perror("2"); return 2; } sigaddset(&sigset, SIGUSR2); sigprocmask(SIG_BLOCK, &sigset, NULL); } while(true) { int result = sigwait(&sigset, &sig); if(result == 0) { cout << "The caught signal is " << sig << endl; } } exit(0); } else { cout << "Registerd the handler " << pid << endl; handlers[i] = pid; } } //Registering the monitoring process if((pid = fork()) == 0) { sigset_t sigset; int sig; int result = 0; sigemptyset(&sigset); sigaddset(&sigset, SIGUSR1); sigaddset(&sigset, SIGUSR2); sigprocmask(SIG_BLOCK, &sigset, NULL); while(true) { int result = sigwait(&sigset, &sig); if(result == 0) { cout << "The monitored signal is " << sig << endl; } else { cout << "error" << endl; } } } else { reporter = pid; } sleep(3); //Registering the signal generator for(int i=0; i<1; i++) { if((pid = fork()) == 0) { if(signal(SIGUSR1, SIG_IGN) == SIG_ERR) { perror("1"); return 1; } if(signal(SIGUSR2, SIG_IGN) == SIG_ERR) { perror("2"); return 2; } srand(time(0)); while(true) { volatile int signal_id = rand()%2 + 1; cout << "Generating the signal " << signal_id << endl; if(signal_id == 1) { killpg(getpgid(getpid()), SIGUSR1); } else { killpg(getpgid(getpid()), SIGUSR2); } int r = rand()%10 + 1; double s = (double)r/100; sleep(s); } exit(0); } else { cout << "Registered the sender " << pid << endl; senders[i] = pid; } } while(w = wait(&status)) { cout << "Wait on PID " << w << endl; } } void signal_catcher_int(int the_sig) { //cout << "Handling the Ctrl C signal " << endl; for(int i=0; i<1; i++) { kill(senders[i],SIGKILL); } for(int i=0; i<4; i++) { kill(handlers[i],SIGKILL); } kill(reporter,SIGKILL); exit(3); } Any suggestions? Here is a sample of the output as well In the beginning Registerd the handler 9544 Registerd the handler 9545 1 Registerd the handler 9546 Registerd the handler 9547 2 3 0 Registered the sender 9550 Generating the signal 1 The caught signal is 10 The monitored signal is 10 The caught signal is 10 Generating the signal 1 The caught signal is 10 The monitored signal is 10 The caught signal is 10 Generating the signal 1 The caught signal is 10 The monitored signal is 10 The caught signal is 10 Generating the signal 1 The caught signal is 10 The monitored signal is 10 The caught signal is 10 Generating the signal 2 The caught signal is 12 The caught signal is 12 The monitored signal is 12 Generating the signal 2 Generating the signal 2 The caught signal is 12 The caught signal is 12 Generating the signal 1 The caught signal is 12 The monitored signal is 10 The monitored signal is 12 Generating the signal 1 Generating the signal 2 The caught signal is 12 Generating the signal 1 Generating the signal 2 10 The monitored signal is 10 The caught signal is 12 Generating the signal 1 The caught signal is 12 The monitored signal is GenThe caught signal is TheThe caught signal is 10 Generating the signal 2 Later on The monitored signal is GenThe monitored signal is 10 Generating the signal 1 Generating the signal 2 The caught signal is 10 The caught signal is 10 The caught signal is 10 The caught signal is 12 Generating the signal 1 Generating the signal 2 Generating the signal 1 Generating the signal 1 Generating the signal 2 Generating the signal 2 Generating the signal 2 Generating the signal 2 Generating the signal 2 Generating the signal 1 The caught signal is 12 The caught signal is 10 The caught signal is 10 Generating the signal 2 Generating the signal 1 Generating the signal 1 Generating the signal 2 Generating the signal 1 Generating the signal 2 Generating the signal 2 Generating the signal 2 Generating the signal 1 Generating the signal 2 Generating the signal 1 Generating the signal 2 Generating the signal 2 The caught signal is 10 Generating the signal 2 Generating the signal 1 Generating the signal 1 As you can see initially, the signal was generated and handled both by my signal handlers and monitoring processes. But later on the signal was generated a lot, but it was not quite processes in the same magnitude as before. Further I could see very less signal processing by the monitoring process Can anyone please provide some insights. What's going on?

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  • Questions to ask a 3rd party API provider

    - by Jarede
    I'm due to meet with a developer/sales person from a new 3rd party resource we're about to start using. The main topic I'll be interested in, is their API as I will be the developer making use of it and explaining it to the rest of the team. What questions would you recommend asking? Things I'm already thinking about are: What happens and how will I be notified when they depreciate a method? Is there ever any downtime? Who will I deal with first when I have API issues?

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  • Does TDD lead to the good design?

    - by Eugen Martynov
    I'm in transition from "writing unit tests" state to TDD. I saw as Johannes Brodwall creates quite acceptable design from avoiding any of architecture phase before. I'll ask him soon if it was real improvisation or he had some thoughts upfront. I also clearly understand that everyone has experience that prevents to write explicit design bad patterns. But after participating in code retreat I hardly believe that writing test first could save us from mistakes. But I also believe that tests after code will lead to mistakes much faster. So this night question is asking for people who is using TDD for a long time share their experience about results of design without upfront thinking. If they really practice it and get mostly suitable design. Or it's my small understanding about TDD and probably agile.

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  • Doing "it all from scratch" is different than OS-specifics

    - by Bigyellow Bastion
    Many people tell me that in order to write my own operating system I need to understand the inner-workings of the one I'll be writing it on. That's nonsense. I mean I understand it for education purposes, such as studying the workings of a current OS to gain better knowledge of writing one myself. But the OS I'm writing it on is nothing but my scratchpad offering me software to write the code in, and software to assemble/compile my code into executable instructions. I've been told that I need to decide which OS I'm writing it on before I write it, but all I need is an assembler to produce flat binary, or a compiler to produce object code and a linker to link it into a flat binary .bin file. Why do people say it matters which OS you make an OS on, when it doesn't?

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  • Readability of || statements

    - by Devin G Rhode
    On HTML5 Boilerplate they use this code for jQuery: <!-- Load jQuery with a protocol relative URL; fall back to local if offline --> <script src="//ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></scrip> <script>window.jQuery || document.write('<script src="js/libs/jquery-1.7.2.min.js"><\/script>')</script> The question is simple, what's more readable: if (!jQuery) document.write( -local jQuery- ); or window.jQuery || document.write( -local jQuery- );

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  • Git Project Dependencies on GitHub

    - by VirtuosiMedia
    I've written a PHP framework and a CMS on top of the framework. The CMS is dependent on the framework, but the framework exists as a self-contained folder within the CMS files. I'd like to maintain them as separate projects on GitHub, but I don't want to have the mess of updating the CMS project every time I update the framework. Ideally, I'd like to have the CMS somehow pull the framework files for inclusion into a predefined sub-directory rather than physically committing those files. Is this possible with Git/GitHub? If so, what do I need to know to make it work? Keep in mind that I'm at a very, very basic level of experience with Git - I can make repositories and commit using the Git plugin for Eclipse, connect to GitHub, and that's about it. I'm currently working solo on the projects, so I haven't had to learn much more about Git so far, but I'd like to open it up to others in the future and I want to make sure I have it right. Also, what should my ideal workflow be for projects with dependencies? Any tips on that subject would also greatly appreciated. If you need more info on my setup, just ask in the comments.

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  • How can I thoroughly evaluate a prospective employer?

    - by glenviewjeff
    We hear much about code smells, test smells, and even project smells, but I have heard no discussion about employer "smells" outside of the Joel Test. After much frustration working for employers with a bouquet of unpleasant corporate-culture odors, I believe it's time for me to actively seek a more mature development environment. I've started assembling a list of questions to help vet employers by identifying issues during a job interview, and am looking for additional ideas. I suppose this list could easily be modified by an employer to vet an employee as well, but please answer from the interviewee's perspective. I think it would be important to ask many of these questions of multiple people to find out if consistent answers are given. For the most part, I tried to put the questions in each section in the order they could be asked. An undesired answer to an early question will often make follow-ups moot. Values What constitutes "well-written" software? What attributes does a good developer have? Same question for manager. Process Do you have a development process? How rigorously do you follow it? How do you decide how much process to apply to each project? Describe a typical project lifecycle. Ask the following if they don't come up otherwise: Waterfall/iterative: How much time is spent in upfront requirements gathering? upfront design? Testing Who develops tests (developers or separate test engineers?) When are they developed? When are the tests executed? How long do they take to execute? What makes a good test? How do you know you've tested enough? What percentage of code is tested? Review What is the review process like? What percentage of code is reviewed? Design? How frequently can I expect to participate as code/design reviewer/reviewee? What are the criteria applied to review and where do the criteria come from? Improvement What new tools and techniques have you evaluated or deployed in the past year? What training courses have your employees been given in the past year? What will I be doing for the first six months in your company (hinting at what kind of organized mentorship/training has been thought through, if any) What changes to your development process have been made in the past year? How do you improve and learn from your mistakes as an organization? What was your organizations biggest mistake in the past year, and how was it addressed? What feedback have you given to management lately? Was it implemented? If not, why? How does your company use "best practices?" How do you seek them out from the outside or within, and how do you share them with each other? Ethics Tell me about an ethical problem you or your employees experienced recently and how was it resolved? Do you use open-source software? What open-source contributions have you made? Follow-Ups I liked what @jim-leonardo said on this Stack Overflow question: Really a thing to ask yourself: "Does this person seem like they are trying to recruit me and make me interested?" I think this is one of the most important bits. If they seem to be taking the attitude that the only one being interviewed is you, then they probably will treat you poorly. Good interviewers understand they have to sell the position as much as the candidate needs to sell themselves. @SethP added: Glassdoor.com is a good web site for researching potential employers. It contains information about how specific companies conduct interviews...

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  • What is a best practice tier structure of a Java EE 6/7 application?

    - by James Drinkard
    I was attempting to find a best practice for modeling the tiers in a Java EE application yesterday and couldn't come up with anything current. In the past, say java 1.4, it was four tiers: Presentation Tier Web Tier Business Logic Tier DAL (Data Access Layer ) which I always considered a tier and not a layer. After working with Web Services and SOA I thought to add in a services tier, but that may fall under 3. the business logic tier. I did searches for quite a while and reading articles. It seems like Domain Driven Design is becoming more popular, but I couldn't find a diagram on it's tier structure. Anyone have ideas or diagrams on what the proper tier structure is for newer Java EE applications or is it really the same, but more items are ranked under the four I've mentioned?

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  • Is there a rule of thumb for what a bing map's zoom setting should be based on how many miles you want to display?

    - by Clay Shannon
    If a map contains pushpins/waypoints that span only a couple of miles, the map should be zoomed way in and show a lot of detail. If the pushpins/waypoints instead cover vast areas, such as hundreds or even thousands of miles, it should be zoomed way out. That's clear. My question is: is there a general guideline for mapping (no pun intended) Bing Maps zoom levels to a particular number of miles that separate the furthest apart points? e.g., is there some chart that has something like: Zoom level N shows 2 square miles Zoom level N shows 5 square miles etc.?

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  • When should we use weak entities when modelling a database?

    - by Songo
    This is basically a question about what are weak entities? When should we use them? How should they be modeled? What is the main difference between normal entities and weak entities? Does weak entities correspond to value objects when doing Domain Driven Design? To help keep the question on topic here is an example taken from Wikipedia that people can use to answer these question: In this example OrderItem was modeled as a weak entity, but I can't understand why it can't be modeled as a normal entity. Another question is what if I want to track the order history (i.e. the changes in it status) would that be a normal or weak entity?

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  • Do I need to know servlets and JSP to learn spring or hibernate or any other java web frameworks?

    - by KyelJmD
    I've been asking a lot of people where to start learning java web development, I already know core java (Threading,Generics,Collections, a little experience with (JDBC)) but I do not know JSPs and servlets. I did my fair share of development with several web based applications using PHP for server-side and HTML,CSS,Javascript,HTML5 for client side. Most people that I asked told me to jump right ahead to Hibernate while some told me that I do not need to learn servlets and jsps and I should immediately study the Spring framework. Is this true? do I not need to learn servlets and JSPs to learn hibernate or Spring? All of their answers confused me and now I am completely lost what to learn or study. I feel that if I skipped learning JSP and servlets I would missed a lot of important concepts that will surely help me in the future. So the question, do I need to have foundation/know servlets and JSP to learn spring or hibernate or any other java web frameworks.?

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  • Interviewing a DBA

    - by kev
    Our Company is in the Process of recuiting a DBA. I have built a group test of questions from basic questions such as Pk and Fk constraints, simple querries(fizzbuzz style) to more advanced things such as indexes, Collation, isolation levels and how to trace deadlocks. However, that is the limit of my knowledge. So my question to all the DBA's is what is the base level knowledge that all DBA's should have? We are really looking for someone that will be able to manage our replication, analyzing some of our slower running queries(that the devs can go to for help) and someone that can trace some of the deadlock issues that we are having. Any help would be most appreciated!

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  • Dark themes in IDE with multiple monitors

    - by nivlam
    There has been numerous posts about developers that prefer a dark color scheme in their IDE. Most of the themes at studiostyl.es are dark themes. Back when I had a single monitor, I did enjoy using a dark theme since it was easier on the eyes. But now that I utilize multiple monitors, I find dark themes actually hurt my eyes. Most of the time I have my IDE open on one monitor and a browser/email/documentation open on my other monitors. Only my IDE has a dark theme and most of websites/documentation have a white background. This forces my eyes to constantly adjust between my dark IDE and the white website, which puts strain on my eyes. I'm sure I'm not the only person who tries to use a dark theme for the IDE and have multiple monitors. How do other people deal with this issue?

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  • How to deal with colleagues refuse to follow practices?

    - by Adrian Shum
    I was discussing with another colleague about what we should be used when an DB entity is referring to another. I don't think there is any good reason to break the practice of putting the Primary Key in the referring entity. However, one of my colleague says: "You should use a surrogate key in the entity, but it is better to put the human-readable natural key in the referring entity. As long it is unique, it is fine and it is easier when you are doing support or maintenance job" I know it will works, but obviously it is not a good practice you are putting a non-PK unique column as "foreign key", just for gaining a bit of ease in writing SQL during support as we can have less table join. Though I mentioned the his approach is conceptual incorrect, and causing problem too practically etc, he seems rather trade off correctness in data model in exchange of ease of maintenance. And he said: "I know it is not good practice, but good practice is not golden rule" Honestly I feel frustrated when dealing with something like this. I know there are always case that we should break some rule or practice, but doubtless it is not such case now. What will you when you are facing situation like this? Please assume yourself being a senior developer which is expected to contribute in misc development direction and convention.

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  • Functional Methods on Collections

    - by GlenPeterson
    I'm learning Scala and am a little bewildered by all the methods (higher-order functions) available on the collections. Which ones produce more results than the original collection, which ones produce less, and which are most appropriate for a given problem? Though I'm studying Scala, I think this would pertain to most modern functional languages (Clojure, Haskell) and also to Java 8 which introduces these methods on Java collections. Specifically, right now I'm wondering about map with filter vs. fold/reduce. I was delighted that using foldRight() can yield the same result as a map(...).filter(...) with only one traversal of the underlying collection. But a friend pointed out that foldRight() may force sequential processing while map() is friendlier to being processed by multiple processors in parallel. Maybe this is why mapReduce() is so popular? More generally, I'm still sometimes surprised when I chain several of these methods together to get back a List(List()) or to pass a List(List()) and get back just a List(). For instance, when would I use: collection.map(a => a.map(b => ...)) vs. collection.map(a => ...).map(b => ...) The for/yield command does nothing to help this confusion. Am I asking about the difference between a "fold" and "unfold" operation? Am I trying to jam too many questions into one? I think there may be an underlying concept that, if I understood it, might answer all these questions, or at least tie the answers together.

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  • What is up with the Joy of Clojure 2nd edition?

    - by kurofune
    Manning just released the second edition of the beloved Joy of Clojure book, and while I share that love I get the feeling that many of the examples are already outdated. In particular, in the chapter on optimization the recommended type-hinting seems not to be allowed by the compiler. I don't know if this was allowable for older versions of Clojure. For example: (defn factorial-f [^long original-x] (loop [x original-x, acc 1] (if (>= 1 x) acc (recur (dec x) (*' x acc))))) returns: clojure.lang.Compiler$CompilerException: java.lang.UnsupportedOperationException: Can't type hint a primitive local, compiling:(null:3:1) Likewise, the chapter on core.logic seems be using an old API and I have to find workarounds for each example to accommodate the recent changes. For example, I had to turn this: (logic/defrel orbits orbital body) (logic/fact orbits :mercury :sun) (logic/fact orbits :venus :sun) (logic/fact orbits :earth :sun) (logic/fact orbits :mars :sun) (logic/fact orbits :jupiter :sun) (logic/fact orbits :saturn :sun) (logic/fact orbits :uranus :sun) (logic/fact orbits :neptune :sun) (logic/run* [q] (logic/fresh [orbital body] (orbits orbital body) (logic/== q orbital))) into this, leveraging the pldb lib: (pldb/db-rel orbits orbital body) (def facts (pldb/db [orbits :mercury :sun] [orbits :venus :sun] [orbits :earth :sun] [orbits :mars :sun] [orbits :jupiter :sun] [orbits :saturn :sun] [orbits :uranus :sun] [orbits :neptune :sun])) (pldb/with-db facts (logic/run* [q] (logic/fresh [orbital body] (orbits orbital body) (logic/== q orbital)))) I am still pulling teeth to get the later examples to work. I am relatively new programming, myself, so I wonder if I am naively looking over something here, or are if these points I'm making legitimate concerns? I really want to get good at this stuff like type-hinting and core.logic, but wanna make sure I am studying up to date materials. Any illuminating facts to help clear up my confusion would be most welcome.

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  • Refactoring a Single Rails Model with large methods & long join queries trying to do everything

    - by Kelseydh
    I have a working Ruby on Rails Model that I suspect is inefficient, hard to maintain, and full of unnecessary SQL join queries. I want to optimize and refactor this Model (Quiz.rb) to comply with Rails best practices, but I'm not sure how I should do it. The Rails app is a game that has Missions with many Stages. Users complete Stages by answering Questions that have correct or incorrect Answers. When a User tries to complete a stage by answering questions, the User gets a Quiz entry with many Attempts. Each Attempt records an Answer submitted for that Question within the Stage. A user completes a stage or mission by getting every Attempt correct, and their progress is tracked by adding a new entry to the UserMission & UserStage join tables. All of these features work, but unfortunately the Quiz.rb Model has been twisted to handle almost all of it exclusively. The callbacks began at 'Quiz.rb', and because I wasn't sure how to leave the Quiz Model during a multi-model update, I resorted to using Rails Console to have the @quiz instance variable via self.some_method do all the heavy lifting to retrieve every data value for the game's business logic; resulting in large extended join queries that "dance" all around the Database schema. The Quiz.rb Model that Smells: class Quiz < ActiveRecord::Base belongs_to :user has_many :attempts, dependent: :destroy before_save :check_answer before_save :update_user_mission_and_stage accepts_nested_attributes_for :attempts, :reject_if => lambda { |a| a[:answer_id].blank? }, :allow_destroy => true #Checks every answer within each quiz, adding +1 for each correct answer #within a stage quiz, and -1 for each incorrect answer def check_answer stage_score = 0 self.attempts.each do |attempt| if attempt.answer.correct? == true stage_score += 1 elsif attempt.answer.correct == false stage_score - 1 end end stage_score end def winner return true end def update_user_mission_and_stage ####### #Step 1: Checks if UserMission exists, finds or creates one. #if no UserMission for the current mission exists, creates a new UserMission if self.user_has_mission? == false @user_mission = UserMission.new(user_id: self.user.id, mission_id: self.current_stage.mission_id, available: true) @user_mission.save else @user_mission = self.find_user_mission end ####### #Step 2: Checks if current UserStage exists, stops if true to prevent duplicate entry if self.user_has_stage? @user_mission.save return true else ####### ##Step 3: if step 2 returns false: ##Initiates UserStage creation instructions #checks for winner (winner actions need to be defined) if they complete last stage of last mission for a given orientation if self.passed? && self.is_last_stage? && self.is_last_mission? create_user_stage_and_update_user_mission self.winner #NOTE: The rest are the same, but specify conditions that are available to add badges or other actions upon those conditions occurring: ##if user completes first stage of a mission elsif self.passed? && self.is_first_stage? && self.is_first_mission? create_user_stage_and_update_user_mission #creates user badge for finishing first stage of first mission self.user.add_badge(5) self.user.activity_logs.create(description: "granted first-stage badge", type_event: "badge", value: "first-stage") #If user completes last stage of a given mission, creates a new UserMission elsif self.passed? && self.is_last_stage? && self.is_first_mission? create_user_stage_and_update_user_mission #creates user badge for finishing first mission self.user.add_badge(6) self.user.activity_logs.create(description: "granted first-mission badge", type_event: "badge", value: "first-mission") elsif self.passed? create_user_stage_and_update_user_mission else self.passed? == false return true end end end #Creates a new UserStage record in the database for a successful Quiz question passing def create_user_stage_and_update_user_mission @nu_stage = @user_mission.user_stages.new(user_id: self.user.id, stage_id: self.current_stage.id) @nu_stage.save @user_mission.save self.user.add_points(50) end #Boolean that defines passing a stage as answering every question in that stage correct def passed? self.check_answer >= self.number_of_questions end #Returns the number of questions asked for that stage's quiz def number_of_questions self.attempts.first.answer.question.stage.questions.count end #Returns the current_stage for the Quiz, routing through 1st attempt in that Quiz def current_stage self.attempts.first.answer.question.stage end #Gives back the position of the stage relative to its mission. def stage_position self.attempts.first.answer.question.stage.position end #will find the user_mission for the current user and stage if it exists def find_user_mission self.user.user_missions.find_by_mission_id(self.current_stage.mission_id) end #Returns true if quiz was for the last stage within that mission #helpful for triggering actions related to a user completing a mission def is_last_stage? self.stage_position == self.current_stage.mission.stages.last.position end #Returns true if quiz was for the first stage within that mission #helpful for triggering actions related to a user completing a mission def is_first_stage? self.stage_position == self.current_stage.mission.stages_ordered.first.position end #Returns true if current user has a UserMission for the current stage def user_has_mission? self.user.missions.ids.include?(self.current_stage.mission.id) end #Returns true if current user has a UserStage for the current stage def user_has_stage? self.user.stages.include?(self.current_stage) end #Returns true if current user is on the last mission based on position within a given orientation def is_first_mission? self.user.missions.first.orientation.missions.by_position.first.position == self.current_stage.mission.position end #Returns true if current user is on the first stage & mission of a given orientation def is_last_mission? self.user.missions.first.orientation.missions.by_position.last.position == self.current_stage.mission.position end end My Question Currently my Rails server takes roughly 500ms to 1 sec to process single @quiz.save action. I am confident that the slowness here is due to sloppy code, not bad Database ERD design. What does a better solution look like? And specifically: Should I use join queries to retrieve values like I did here, or is it better to instantiate new objects within the model instead? Or am I missing a better solution? How should update_user_mission_and_stage be refactored to follow best practices? Relevant Code for Reference: quizzes_controller.rb w/ Controller Route Initiating Callback: class QuizzesController < ApplicationController before_action :find_stage_and_mission before_action :find_orientation before_action :find_question def show end def create @user = current_user @quiz = current_user.quizzes.new(quiz_params) if @quiz.save if @quiz.passed? if @mission.next_mission.nil? && @stage.next_stage.nil? redirect_to root_path, notice: "Congratulations, you have finished the last mission!" elsif @stage.next_stage.nil? redirect_to [@mission.next_mission, @mission.first_stage], notice: "Correct! Time for Mission #{@mission.next_mission.position}", info: "Starting next mission" else redirect_to [@mission, @stage.next_stage], notice: "Answer Correct! You passed the stage!" end else redirect_to [@mission, @stage], alert: "You didn't get every question right, please try again." end else redirect_to [@mission, @stage], alert: "Sorry. We were unable to save your answer. Please contact the admministrator." end @questions = @stage.questions.all end private def find_stage_and_mission @stage = Stage.find(params[:stage_id]) @mission = @stage.mission end def find_question @question = @stage.questions.find_by_id params[:id] end def quiz_params params.require(:quiz).permit(:user_id, :attempt_id, {attempts_attributes: [:id, :quiz_id, :answer_id]}) end def find_orientation @orientation = @mission.orientation @missions = @orientation.missions.by_position end end Overview of Relevant ERD Database Relationships: Mission - Stage - Question - Answer - Attempt <- Quiz <- User Mission - UserMission <- User Stage - UserStage <- User Other Models: Mission.rb class Mission < ActiveRecord::Base belongs_to :orientation has_many :stages has_many :user_missions, dependent: :destroy has_many :users, through: :user_missions #SCOPES scope :by_position, -> {order(position: :asc)} def stages_ordered stages.order(:position) end def next_mission self.orientation.missions.find_by_position(self.position.next) end def first_stage next_mission.stages_ordered.first end end Stage.rb: class Stage < ActiveRecord::Base belongs_to :mission has_many :questions, dependent: :destroy has_many :user_stages, dependent: :destroy has_many :users, through: :user_stages accepts_nested_attributes_for :questions, reject_if: :all_blank, allow_destroy: true def next_stage self.mission.stages.find_by_position(self.position.next) end end Question.rb class Question < ActiveRecord::Base belongs_to :stage has_many :answers, dependent: :destroy accepts_nested_attributes_for :answers, :reject_if => lambda { |a| a[:body].blank? }, :allow_destroy => true end Answer.rb: class Answer < ActiveRecord::Base belongs_to :question has_many :attempts, dependent: :destroy end Attempt.rb: class Attempt < ActiveRecord::Base belongs_to :answer belongs_to :quiz end User.rb: class User < ActiveRecord::Base belongs_to :school has_many :activity_logs has_many :user_missions, dependent: :destroy has_many :missions, through: :user_missions has_many :user_stages, dependent: :destroy has_many :stages, through: :user_stages has_many :orientations, through: :school has_many :quizzes, dependent: :destroy has_many :attempts, through: :quizzes def latest_stage_position self.user_missions.last.user_stages.last.stage.position end end UserMission.rb class UserMission < ActiveRecord::Base belongs_to :user belongs_to :mission has_many :user_stages, dependent: :destroy end UserStage.rb class UserStage < ActiveRecord::Base belongs_to :user belongs_to :stage belongs_to :user_mission end

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