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• PostgreSQL: Why does this simple query not use the index?

  - by David

  I have a table t with a column c, which is an int and has a btree index on it. Why does the following query not utilize this index? explain select c from t group by c; The result I get is: HashAggregate (cost=1005817.55..1005817.71 rows=16 width=4) -> Seq Scan on t (cost=0.00..946059.84 rows=23903084 width=4) My understanding of indexes is limited, but I thought such queries were the purpose of indexes.

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• ASP .NET page runs slow in production

  - by Brandi

  I have created an ASP .NET page that works flawlessly and quickly from Visual Studio. It does a very large database read from a database on our network to load a gridview inside of an update panel. It displays progress in an Ajax modalpopupextender. Of course I don't expect it to be instant what with the large db reads, but it takes on the order of seconds, not on the order of minutes. This is all working great until I put it up on the server - it is very, VERY slow when I access it via the internet - takes several minutes to load the database information into the gridview. I'm baffled why it would not perform the exact same as it had from Visual Studio. (It is in release mode and I have taken off the debug flag) I have since been trying things like eliminating unneeded update panels and throwing out the ajax tool. Nothing has made it any faster on production. It is not the database as far as I know, since it has been consistently fast from my computer (from visual studio) and consistently slow from the server. I am wondering, where do I look next? Has anyone else had this problem before? Could this be caused by update panels or Ajax modalpopupextenders in different parts of the application? Why would the live behaviour differ so much from the localhost behaviour? Both the server with the ASP .NET page and the server with the database are servers on our network. I'm using Visual Studio 2008. Thank you in advance for any insight or advice.

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• How faster is java than php in web application?

  - by user198729

  Has anyone compared these two languages?

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• Grasp Controller, Does it really need a UI to exist?

  - by dbones

  I have a Domain model which can be in multiple states, and if these states go out of a given range it the domain should automatically react. For example I have a Car which is made of multiple things which have measurements the Engine - Rev counter and Temperature the Fuel Tank - capacity Is is plaseable to have a CarStateController, which observses the engine and the tank, and if these states go out of range IE the engine temperature goes above range, turn the engine fan on?? There is no UI, (you could argue it would show a light on the dash board, but for this case it does not) is this a valid use of a GRASP controller pattern? if not what is this CarStateController Called? Or have I completely missed the point and this should be the State Pattern?

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• Is there a way to rewrite the SQL query efficiently

  - by user320587

  hi, I have two tables with following definition TableA TableB ID1 ID2 ID3 Value1 Value ID1 Value1 C1 P1 S1 S1 C1 P1 S2 S2 C1 P1 S3 S3 C1 P1 S5 S4 S5 The values are just examples in the table. TableA has a clustered primary key ID1, ID2 & ID3 and TableB has p.k. ID1 I need to create a table that has the missing records in TableA based on TableB The select query I am trying to create should give the following output C1 P1 S4 To do this, I have the following SQL query SELECT DISTINCT TableA.ID1, TableA.ID2, TableB.ID1 FROM TableA a, TableB b WHERE TableB.ID1 NOT IN ( SELECT DISTINCT [ID3] FROM TableA aa WHERE a.ID1 == aa.ID1 AND a.ID2 == aa.ID2 ) Though this query works, it performs poorly and my final TableA may have upto 1M records. is there a way to rewrite this more efficiently. Thanks for any help, Javid

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• Why the difference in speed?

  - by AngryHacker

  Consider this code: function Foo(ds as OtherDLL.BaseObj) dim lngRowIndex as long dim lngColIndex as long for lngRowIndex = 1 to ubound(ds.Data, 2) for lngColIndex = 1 to ds.Columns.Count Debug.Print ds.Data(lngRowIndex, lngColIndex) next next end function OK, a little context. Parameter ds is of type OtherDLL.BaseObj which is defined in a referenced ActiveX DLL. ds.Data is a variant 2-dimensional array (one dimension carries the data, the other one carries the column index. ds.Columns is a Collection of columns in 'ds.Data`. Assuming there are at least 400 rows of data and 25 columns, this code takes about 15 seconds to run on my machine. Kind of unbelievable. However if I copy the variant array to a local variable, so: function Foo(ds as OtherDLL.BaseObj) dim lngRowIndex as long dim lngColIndex as long dim v as variant v = ds.Data for lngRowIndex = 1 to ubound(v, 2) for lngColIndex = 1 to ds.Columns.Count Debug.Print v(lngRowIndex, lngColIndex) next next end function the entire thing processes in barely any noticeable time (basically close to 0). Why?

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• Know of any Java garbage collection log analysis tools?

  - by braveterry

  I'm looking for a tool or a script that will take the console log from my web app, parse out the garbage collection information and display it in a meaningful way. I'm starting up on a Sun Java 1.4.2 JVM with the following flags: -verbose:gc -XX:+PrintGCTimeStamps -XX:+PrintGCDetails The log output looks like this: 54.736: [Full GC 54.737: [Tenured: 172798K->18092K(174784K), 2.3792658 secs] 257598K->18092K(259584K), [Perm : 20476K->20476K(20480K)], 2.4715398 secs] Making sense of a few hundred of these kinds of log entries would be much easier if I had a tool that would visually graph garbage collection trends.

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• Some specific questions about object oriented and MVC design.

  - by Samn

  I have two objects, Users and Mail. Users create Mail objects and send them to other users. If I wanted to get all mail for a User, I could create a method like GetMail() that would return an array of Mail objects owned by that User. But if I wanted to get all mail across the system, what "type" of object would be responsible for that? To solve this problem, I usually create a Manager, which is an object responsible for dealing with a collection of a particular type of object. MailManager deals with collections of Mail objects. GetMailForUser() is one method, GetAllMail() is another method. The User objects invokes the MailManager and executes GetMailForUser(me). Is this stupid? When a user executes the controller CreateMail, a new instance of the Mail object is created. The Mail object, seeing it is creating a new Mail of type 'sent', decides to go ahead and create a second Mail object for the recipient, of type 'received'. Creating one Mail object triggers the creation of a second Mail object. Is this stupid? Should the controller have created both Mail objects, or just the first 'sent' one? When two Users are friends, the association is stored in a table of Relationships. I use a simple object for Relationships. A RelationshipManager has a method called GetFriendsForUser(). The User object has a method GetFriends(), which invokes the RelationshipManager. Is this stupid?

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• Application Design: Single vs. Multiple Hits to the DB

  - by shyneman

  I'm building a service that performs a set of configured activities based on the type of request that it receives. Each activity involves going to the database and retrieving/updating some kind of information. The logic for each activity can be generalized and re-used across different request types. The activities may need to participate in a transaction for the duration of the servicing the request. One option, I'm considering is having each activity maintain its own access to DAL/database. This fully encapsulates the activity into a stand-alone re-usable piece, but hitting the database multiple times for one request doesn't seem like a viable option. I don't really know how to easily implement the concept of a transaction across the multiple activities here either. The second option is to encapsulate ALL the activities into one big activity and hit the database once. But this does not allow re-use and configuration of these activities for different requests. Does anyone have any suggestions and input about what should be the best way to approach my problem? Thanks for any help.

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• How to return a value when destroying/cleaning-up an object instance

  - by Mridang Agarwalla

  When I initiate a class in Python, I give it some values. I then call method in the class which does something. Here's a snippet: class TestClass(): def __init__(self): self.counter = 0 def doSomething(self): self.counter = self.counter + 1 print 'Hiya' if __name__ == "__main__": obj = TestClass() obj.doSomething() obj.doSomething() obj.doSomething() print obj.counter As you can see, everytime I call the doSomething method, it prints some text and increments an internal variable i.e. counter. When I initiate the class, i set the counter variable to 0. When I destroy the object, I'd like to return the internal counter variable. What would be a good way of doing this? I wanted to know if there were other ways apart from doing stuff like: accessing the variable directly. Like obj.counter. creating a method like getCounter. Thanks.

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• XSLT 1.0: restrict entries in a nodeset

  - by Mike

  Hi, Being relatively new to XSLT I have what I hope is a simple question. I have some flat XML files, which can be pretty big (eg. 7MB) that I need to make 'more hierarchical'. For example, the flat XML might look like this: <D0011> .... .... and it should end up looking like this: <D0011> .... .... I have a working XSLT for this, and it essentially gets a nodeset of all the b elements and then uses the 'following-sibling' axis to get a nodeset of the nodes following the current b node (ie. following-sibling::*[position() =$nodePos]). Then recursion is used to add the siblings into the result tree until another b element is found (I have parameterised it of course, to make it more generic). I also have a solution that just sends the position in the XML of the next b node and selects the nodes after that one after the other (using recursion) via a *[position() = $nodePos] selection. The problem is that the time to execute the transformation increases unacceptably with the size of the XML file. Looking into it with XML Spy it seems that it is the 'following-sibling' and 'position()=' that take the time in the two respective methods. What I really need is a way of restricting the number of nodes in the above selections, so fewer comparisons are performed: every time the position is tested, every node in the nodeset is tested to see if its position is the right one. Is there a way to do that ? Any other suggestions ? Thanks, Mike

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• Is this call to a function object inlined?

  - by dehmann

  In the following code, Foo::add calls a function via a function object: struct Plus { inline int operator()(int x, int y) const { return x + y; } }; template<class Fct> struct Foo { Fct fct; Foo(Fct f) : fct(f) {} inline int add(int x, int y) { return fct(x,y); // same efficiency adding directly? } }; Is this the same efficiency as calling x+y directly in Foo::add? In other words, does the compiler typically directly replace fct(x,y) with the actual call, inlining the code, when compiling with optimizations enabled?

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• How to extend this design for a generic converter in java?

  - by Jay

  Here is a small currency converter piece of code: public enum CurrencyType { DOLLAR(1), POUND(1.2), RUPEE(.25); private CurrencyType(double factor) { this.factor = factor; } private double factor; public double getFactor() { return factor; } } public class Currency { public Currency(double value, CurrencyType type) { this.value = value; this.type = type; } private CurrencyType type; private double value; public CurrencyType getCurrencyType() { return type; } public double getCurrencyValue() { return value; } public void setCurrenctyValue(double value){ this.value = value; } } public class CurrencyConversion { public static Currency convert(Currency c1, Currency c2) throws Exception { if (c1 != null && c2 != null) { c2.setCurrenctyValue(c1.getCurrencyValue() * c1.getCurrencyType().getFactor() * c2.getCurrencyType().getFactor()); return c2; } else throw new Exception(); } } I would like to improve this code to make it work for different units of conversion, for example: kgs to pounds, miles to kms, etc etc. Something that looks like this: public class ConversionManager<T extends Convertible> { public T convert(T c1, T c2) { //return null; } } Appreciate your ideas and suggestions.

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• get next/previous month from a Time object

  - by tcurdt

  I have a Time object and would like to find the next/previous month. Adding subtracting days does not work as the days per month vary. time = Time.parse('21-12-2008 10:51 UTC') next_month = time + 31 * 24 * 60 * 60 Incrementing the month also falls down as one would have to take care of the rolling time = Time.parse('21-12-2008 10:51 UTC') next_month = Time.utc(time.year, time.month+1) time = Time.parse('01-12-2008 10:51 UTC') previous_month = Time.utc(time.year, time.month-1) The only thing I found working was time = Time.parse('21-12-2008 10:51 UTC') d = Date.new(time.year, time.month, time.day) d >>= 1 next_month = Time.utc(d.year, d.month, d.day, time.hour, time.min, time.sec, time.usec) Is there a more elegant way of doing this that I am not seeing? How would you do it?

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• C# how to calculate hashcode from an object reference.

  - by Wayne

  Folks, here's a thorny problem for you! A part of the TickZoom system must collect instances of every type of object into a Dictionary< type. It is imperative that their equality and hash code be based on the instance of the object which means reference equality instead of value equality. The challenge is that some of the objects in the system have overridden Equals() and GetHashCode() for use as value equality and their internal values will change over time. That means that their Equals and GetHashCode are useless. How to solve this generically rather than intrusively? So far, We created a struct to wrap each object called ObjectHandle for hashing into the Dictionary. As you see below we implemented Equals() but the problem of how to calculate a hash code remains. public struct ObjectHandle : IEquatable<ObjectHandle>{ public object Object; public bool Equals(ObjectHandle other) { return object.ReferenceEquals(this.Object,other.Object); } } See? There is the method object.ReferenceEquals() which will compare reference equality without regard for any overridden Equals() implementation in the object. Now, how to calculate a matching GetHashCode() by only considering the reference without concern for any overridden GetHashCode() method? Ahh, I hope this give you an interesting puzzle. We're stuck over here. Sincerely, Wayne

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• What is the most efficient way to store a mapping "key -> event stream"?

  - by jkff

  Suppose there are ~10,000's of keys, where each key corresponds to a stream of events. I'd like to support the following operations: push(key, timestamp, event) - pushes event to the event queue for key, marked with the given timestamp. It is guaranteed that event timestamps for a particular key are pushed in sorted or almost sorted order. tail(key, timestamp) - get all events for key since the given timestamp. Usually the timestamp requests for a given key are almost monotonically increasing, almost synchronously with pushes for the same key. This stuff has to be persistent (although it is not absolutely necessary to persist pushes immediately and to keep tails with pushes strictly in sync), so I'm going to use some kind of database. What is the optimal kind of database structure for this task? Would it be better to use a relational database, a key-value storage, or something else?

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• Which is the best sorting algorithm: insertion,selection,bubble,shell,merge,heap,quick, or radix?

  - by flopex

  I wanted to know which of these algorithms is the best for sorting random,semi-sorted,reversed or unique data. I know that some of these are of O(n^2) and O(nlogn).

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• Why doesn't Java support generic Throwables?

  - by polygenelubricants

  class Bouncy<T> extends Throwable { } // Error: the generic class Bouncy<T> may not subclass java.lang.Throwable Why doesn't Java support generic Throwables?

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• Is opening too many datacontexts bad?

  - by ryudice

  I've been checking my application with linq 2 sql profiler, and I noticed that it opens a lot of datacontexts, most of them are opened by the linq datasource I used, since my repositories use only the instance stored in Request.Items, is it bad to open too many datacontext? and how can I make my linqdatasource to use the datacontext that I store in Request.Items for the duration of the request? thanks for any help!

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• How do I make this nested for loop, testing sums of cubes, more efficient?

  - by Brian J. Fink

  I'm trying to iterate through all the combinations of pairs of positive long integers in Java and testing the sum of their cubes to discover if it's a Fibonacci number. I'm currently doing this by using the value of the outer loop variable as the inner loop's upper limit, with the effect being that the outer loop runs a little slower each time. Initially it appeared to run very quickly--I was up to 10 digits within minutes. But now after 2 full days of continuous execution, I'm only somewhere in the middle range of 15 digits. At this rate it may end up taking a whole year just to finish running this program. The code for the program is below: import java.lang.*; import java.math.*; public class FindFib { public static void main(String args[]) { long uLimit=9223372036854775807L; //long maximum value BigDecimal PHI=new BigDecimal(1D+Math.sqrt(5D)/2D); //Golden Ratio for(long a=1;a<=uLimit;a++) //Outer Loop, 1 to maximum for(long b=1;b<=a;b++) //Inner Loop, 1 to current outer { //Cube the numbers and add BigDecimal c=BigDecimal.valueOf(a).pow(3).add(BigDecimal.valueOf(b).pow(3)); System.out.print(c+" "); //Output result //Upper and lower limits of interval for Mobius test: [c*PHI-1/c,c*PHI+1/c] BigDecimal d=c.multiply(PHI).subtract(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP)), e=c.multiply(PHI).add(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP)); //Mobius test: if integer in interval (floor values unequal) Fibonacci number! if (d.toBigInteger().compareTo(e.toBigInteger())!=0) System.out.println(); //Line feed else System.out.print("\r"); //Carriage return instead } //Display final message System.out.println("\rDone. "); } } Now the use of BigDecimal and BigInteger was delibrate; I need them to get the necessary precision. Is there anything other than my variable types that I could change to gain better efficiency?

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• Efficiency of iteration: NSArray vs C array of pointers?

  - by morgancodes

  I'm working at the audio buffer level, mixing audio signals created by a colleciton of objects. Since I'm looping through these objects at 44.1khz, efficiency is crucial. Is there any difference in the efficiency of iterating over an NSArray vs a C array of pointers? How about NSMutableArray?

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• MySQL Locking Up

  - by Ian

  I've got a innodb table that gets a lot of reads and almost no writes (like, 1 write for every 400,000 reads approx). I'm running into a pretty big problem though when I do INSERT into the table. MySQL completely locks up. It uses 100% cpu, and every single other table (in other databases even) have their statuses set to "Locked" until the INSERT is done. This is a big problem because MySQL stays locked up for up to 4 minutes. I'm using version 5.1.47 (rpm from mysql.com). Any ideas?

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• WCF high instance count: anyone knows negative sideffects?

  - by Alex

  Hi there! Did anyone experience or know of negative side effects from having a high service instance count like 60k? Aside from the memory consumption of course. I am planning to increase the threshold for the maximum allowed instance count in our production environments. I am basically sick of severe production incidents just because "something" forgot to close a proxy properly. I plan to go to something like 60k instances which will allow the service to survive using default session timeouts at a call rate average for our clients. Thanks, Alex

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• CakePHP call to member function on non-object

  - by joec

  I have the following Model and Controller files, and when i visit this url, http://....../pois/index i get this error: Notice (8): Undefined property: PoisController::$Poi [APP/controllers/pois_controller.php, line 5] Fatal error: Call to a member function find() on a non-object in /home/joecoyle/public_html/app/controllers/pois_controller.php on line 5 The Model is this, called poi.php: <?php class Poi extends AppModel { } ?> And the controller is this, named pois_controller.php <?php class PoisController extends AppController { function index(){ $this->set('pois',$this->Poi->find('all')); } } ?> As i am new to CakePHP i am not sure what is causing this error, as everything seems to be named, right, and i am following the tutorial on the CakePHP site... Thanks

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• Jmeter- HTTP Cache Manager, Unable to cache everything what it is being cached by Browser

  - by chinmay brahma

  I used HTTP Chache Manager to Cache files which are being cached in browser. I am successful of doing it for some of the pages. Number of files being cached in Jmeter is equal to Number of files being cached by browser. But in some cases : I found number files being cached is lesser than the files being cached by browser. Using Jmeter I found only 5 files are being cached but in real browser 12 files are getting cached. Thanks in advance

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