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  • Simple aggregating query very slow in PostgreSql, any way to improve?

    - by Ash
    HI I have a table which holds files and their types such as CREATE TABLE files ( id SERIAL PRIMARY KEY, name VARCHAR(255), filetype VARCHAR(255), ... ); and another table for holding file properties such as CREATE TABLE properties ( id SERIAL PRIMARY KEY, file_id INTEGER CONSTRAINT fk_files REFERENCES files(id), size INTEGER, ... // other property fields ); The file_id field has an index. The file table has around 800k lines, and the properties table around 200k (not all files necessarily have/need a properties). I want to do aggregating queries, for example find the average size and standard deviation for all file types. But it's very slow - around 70 seconds for the latter query. I understand it needs a sequential scan, but still it seems too much. Here's the query SELECT f.filetype, avg(size), stddev(size) FROM files as f, properties as pr WHERE f.id = pr.file_id GROUP BY f.filetype; and the explain HashAggregate (cost=140292.20..140293.94 rows=116 width=13) (actual time=74013.621..74013.954 rows=110 loops=1) -> Hash Join (cost=6780.19..138945.47 rows=179564 width=13) (actual time=1520.104..73156.531 rows=179499 loops=1) Hash Cond: (f.id = pr.file_id) -> Seq Scan on files f (cost=0.00..108365.41 rows=1140941 width=9) (actual time=0.998..62569.628 rows=805270 loops=1) -> Hash (cost=3658.64..3658.64 rows=179564 width=12) (actual time=1131.053..1131.053 rows=179499 loops=1) -> Seq Scan on properties pr (cost=0.00..3658.64 rows=179564 width=12) (actual time=0.753..557.171 rows=179574 loops=1) Total runtime: 74014.520 ms Any ideas why it is so slow/how to make it faster?

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  • Methods for implementing and using graphs of nodes in C++?

    - by DistortedLojik
    I am working on a research project that deals with social networks. I have done most of the backbone of the program in C++ and am now wanting to implement a way to create the graph of nodes and the connections as well as a way to visualize the connections between people. I have looked a little into Lemon and the Boost graph library, but was wondering which one would be easier to learn and implement or if I should just code my own.

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  • Which of these methods provides for the fastest page loading?

    - by chromedude
    I am building a database in MySQL that will be accessed by PHP scripts. I have a table that is the activity stream. This includes everything that goes on on the website (following of many different things, liking, upvoting etc.). From this activity stream I am going to run an algorithm for each user depending on their activity and display relevant activity. Should I create another table that stores the activity for each user once the algorithm has been run on the activity or should I run the algorithm on the activity table every time the user accesses the site? UPDATE:(this is what is above except rephrased hopefully in an easier to understand way) I have a database table called activity. This table creates a new row every time an action is performed by a user on the website. Every time a user logs in I am going to run an algorithm on the new rows (since the users last login) in the table (activity) that apply to them. For example if the user is following a user who upvoted a post in the activity stream that post will be displayed when the user logs in. I want the ability for the user to be able to access previous content applying to them. Would it be easiest to create another table that saved the rows that have already been run over with the algorithm except attached to individual users names? (a row can apply to multiple different users)

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  • How to combine the multiple part linq into one query?

    - by user2943399
    Operator should be ‘AND’ and not a ‘OR’. I am trying to refactor the following code and i understood the following way of writing linq query may not be the correct way. Can somone advice me how to combine the following into one query. AllCompany.Where(itm => itm != null).Distinct().ToList(); if (AllCompany.Count > 0) { //COMPANY NAME if (isfldCompanyName) { AllCompany = AllCompany.Where(company => company["Company Name"].StartsWith(fldCompanyName)).ToList(); } //SECTOR if (isfldSector) { AllCompany = AllCompany.Where(company => fldSector.Intersect(company["Sectors"].Split('|')).Any()).ToList(); } //LOCATION if (isfldLocation) { AllCompany = AllCompany.Where(company => fldLocation.Intersect(company["Location"].Split('|')).Any()).ToList(); } //CREATED DATE if (isfldcreatedDate) { AllCompany = AllCompany.Where(company => company.Statistics.Created >= createdDate).ToList(); } //LAST UPDATED DATE if (isfldUpdatedDate) { AllCompany = AllCompany.Where(company => company.Statistics.Updated >= updatedDate).ToList(); } //Allow Placements if (isfldEmployerLevel) { fldEmployerLevel = (fldEmployerLevel == "Yes") ? "1" : ""; AllCompany = AllCompany.Where(company => company["Allow Placements"].ToString() == fldEmployerLevel).ToList(); }

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  • Can we execute methods / code in XCcode just like in Visual Studio?

    - by balexandre
    Visual Studio is one of the best developer IDE of all times, and now was improved with multithreading debugging and much more. My question is regarding Xcode and the ability to execute code just like we do in Visual Studio. Let's assume an object in a view and I want to run, let's say: [pickerView setHidden:YES]; in a breakpoint just to see if in that break point I could actually hide the object. I can't find any place for this in the XCode Debugger Am I missing something or I can't execute code that is not in the files already? like in Visual Studio Watch List or Immediate Window

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  • C#. Where struct methods code kept in memory?

    - by maxima120
    It is somewhat known where .NET keeps value types in memory (mostly in stack but could be in heap in certain circumstances etc)... My question is - where is the code of the struct? If I have say 16 byte of data fields in the struct and a massive computation method in it - I am presuming that 16 byte will be copied in stack and the method code is stored somewhere else and is shared for all instances of the struct. Are these presumptions correct?

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  • Is it OK to set state within Event Raising methods?

    - by Greg
    I ran across this pattern in the code of a library I'm using. It sets state within the event raising method, but only if the event is not null. protected virtual void OnMyEvent(EventArgs e) { if(MyEvent != null) { State = "Executing"; // Only sets state if MyEvent != null. MyEvent(this,e); } } Which means that the state is not set when overriding the method: protected override void OnMyEvent(EventArgs e) { base.OnMyEvent(e); Debug.Assert( State == "Executing" ); // This fails } but is only set when handling the event: foo.MyEvent += (o, args) => Debug.Assert(State == "Executing"); // This passes Setting state within the if(MyEvent != null) seems like bad form, but I've checked the Event Design Guidelines and it doesn't mention this. Do you think this code is incorrect? If so, why? (Reference to design guidelines would be helpful). Edit for Context: It's a Control, I'm trying to create subclass of it, and the state that it's setting is calling EnsureChildControls() conditionally based upon there being an event handler. I can call EnsureChildControls() myself, but I consider that something of a hack.

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  • How to use LINQ To Entities for filtering when many methods are not supported?

    - by Kinderchocolate
    Hi, I have a table in SQL database: ID Data Value 1 1 0.1 1 2 0.4 2 10 0.3 2 11 0.2 3 10 0.5 3 11 0.6 For each unique value in Data, I want to filter out the row with the largest ID. For example: In the table above, I want to filter out the third and fourth row because the fifth and sixth rows have the same Data values but their IDs (3) are larger (2 in the third and fourth row). I tried this in Linq to Entities: IQueryable<DerivedRate> test = ObjectContext.DerivedRates.OrderBy(d => d.Data).ThenBy(d => d.ID).SkipWhile((d, index) => (index == size - 1) || (d.ID != ObjectContext.DerivedRates.ElementAt(index + 1).ID)); Basically, I am sorting the list and removing the duplicates by checking if the next element has an identical ID. However, this doesn't work because SkipWhile(index) and ElementAt(index) aren't supported in Linq to Entities. I don't want to pull the entire gigantic table into an array before sorting it. Is there a way?

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  • node.js: looping, email each matching row from query but it it emails the same user by # number of matches?

    - by udonsoup16
    I have a node.js email server that works fine however I noticed a problem. If the query string found 4 rows, it would send four emails but only to the first result instead of to each found email address. var querystring1 = 'SELECT `date_created`,`first_name`,`last_name`,`email` FROM `users` WHERE TIMESTAMPDIFF(SECOND,date_created, NOW()) <=298 AND `email`!="" LIMIT 0,5'; connection.query(querystring1, function (err, row) { if (err) throw err; for (var i in row) { // Email content; change text to html to have html emails. row[i].column name will pull relevant database info var sendit = { to: row[i].email, from: '******@******', subject: 'Hi ' + row[i].first_name + ', Thanks for joining ******!', html: {path:__dirname + '/templates/welcome.html'} }; // Send emails transporter.sendMail(sendit,function(error,response){ if (error) { console.log(error); }else{ console.log("Message sent1: " + row[i].first_name);} transporter.close();} ) }}); .... How do I have it loop through each found row and send a custom email using row data individual row data?

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  • Override the methods of classes from a .war file.

    - by Sweety
    I have a base application war file say homeApp.war. This contains default operations which user can carry out on the web browser. Now I need to extend the operations available on the same application using that .war file. Like I need to add the extra menus, some shortcuts like icon for log out etc. Please let me know how can I use this .war file to extend the operations and also fix the already existing issues on the application. This web application uses java server faces.

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  • How to find hidden properties/methods in Javascript objects?

    - by ramanujan
    I would like to automatically determine all of the properties (including the hidden ones) in a given Javascript object, via a generalization of this function: function keys(obj) { var ll = []; for(var pp in obj) { ll.push(pp); } return ll; } This works for user defined objects but fails for many builtins: repl> keys({"a":10,"b":2}); // ["a","b"] repl> keys(Math) // returns nothing! Basically, I'd like to write equivalents of Python's dir() and help(), which are really useful in exploring new objects. My understanding is that only the builtin objects have hidden properties (user code evidently can't set the "enumerable" property till HTML5), so one possibility is to simply hardcode the properties of Math, String, etc. into a dir() equivalent (using the lists such as those here). But is there a better way?

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  • C++: Is there a way to limit access to certain methods to certain classes without exposing other pri

    - by dadads
    I have a class with a protected method Zig::punt() and I only want it to be accessible to the class "Avocado". In C++, you'll normally do this using the "friend Avocado" specifier, but this will cause all of the other variables to become accessible to "Avocado" class; I don't want this because this breaks encapsulation. Is what I want impossible, or does there already exist an obscure trick out there that I can use to achieve what I want? Or possibly alternative class design patterns that'll achieve the same thing? Thanks in advance for any ideas!

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  • how do i call methods from another class in android?

    - by Phani Gargey
    I have two classes in question. Both extend Activity. Class A public void displayinfo() { setContentView(R.layout.dynamicinfo); //Add some buttons dynamically here //do some processing // move on to Class B } In Class B: I want to go back to Class A state in UI if BACK button is pressed. Class B //Register a listener for this button Backbutton.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { Log.i("setOnClickListener", "Pressed Back Button "); Toast.makeText(mycontext, "Pressed Back Button", Toast.LENGTH_SHORT).show(); //HERE I want to go back class's function in UI as well as restoring the sttae for that screen. } how do I do that? I looked around some questions. they did not answer clearly what I am looking for.hence the posting. thanks.I think I was adding my own Back button on the Layout I created in the Class B's UI Screen --not using the regular "Back" button on the key board. May be that was the problem.

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  • Is it possible to use AutoMapper to map methods?

    - by Woj
    I have two classes: public class TestClass1 { public int TestInt { get; set; } public void TestMethod() { // Do something } } public class TestClass2 { public int TestInt { get; set; } public void TestMethod() { // Do something } } I want to create interface that I can use for both classes. The easiest solution is to implement the interface on TestClass1 and TestClass2 but I don;t have access to the implementation of these classes (external dll). I was wondering if I can create new interface and use AutoMapper to map TestClass1 and TestClass2 to ITestInterface: public interface ITestInterface { int TestInt { get; set; } void TestMethod(); }

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  • why can't I call methods on a for-yield expression?

    - by 1984isnotamanual
    Say I have some scala code like this: // outputs 1, 4, 9, 16, 25, 36, 49, 64, 81, 100 println( squares ) def squares = { val s = for ( count <- 1 to 10 ) yield { count * count } s.mkString(", "); } Why do I have to use the temporary val s? I tried this: def squares = for ( count <- 1 to 10 ) yield { count * count }.mkString(", ") That fails to compile with this error message: error: value mkString is not a member of Int def squares = for ( count <- 1 to 10 ) yield { count * count }.mkString(", ") Shouldn't mkString be called on the collection returned by the for loop?

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  • Which methods are good to overwrite when creating custom NSManagedObject subclasses?

    - by mystify
    The Core Data Programming Guide talks a lot about what not to overwrite. So the question is: What is good to overwrite? Like I see it, I can't overwrite -init or -initWithEntity:insertIntoManagedObjectContext: So where else would be a good overwrite point to set up some basic stuff? Or is it generally not needed to do custom initialization? Does the whole thing rely only on accessing properties which then start to do fancy things? So no custom initializations?

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