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• Is there any danger in committing to a component library such as SmartGwt or Swing?

  - by Banang

  Since February this year I have been working on an app that's built using SmartGWT components. Generally, I find the components very nice to work with, and the fact that they're open source and free to use is just fantastic. However, I can't seem to shake the feeling that it's not a durable way of developing, but I can't quite explain why. Maybe it's because I know that any minute now the team developing it could decide to stop, which would leave me and my team in a bit of a pickle, but I'm sure there must be something more. I have been trying to find ways of explaining this feeling to myself, but to no avail. Therefore I turn to you, dear community, to ask if you can come up with a good reason why committing to building your app (that's supposed to be around for many more years to come) using a component library such as SmartGWT is a bad idea? Is there any reason I should just have developed the components myself? Or did I make the right choice when deciding not to reinvent the wheel and just go for what was readily available?

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• Android OS 2.2 Permissions: I have absolutely no idea why this simple piece of code doesn't work. Wh

  - by Kevin

  I'm just playing around with some code. I create an Activity and simply do something like this: long lo = currentTimeMillis(); System.out.println(lo); lo *= 3; System.out.println(lo); SystemClock.setCurrentTimeMillis(lo); System.out.println( currentTimeMillis() ); Yes, in my AndroidManifest.xml, I've added: <uses-permission android:name="android.permission.SET_TIME"></uses-permission> <uses-permission android:name="android.permission.SET_TIME_ZONE"></uses-permission> Nothing changes. The SystemClock is never reset...it just keeps on ticking. The error that I'm getting just says that the permission "SET_TIME" was not granted to the program. Protection level 3. The permissions are there...and in the API for 2.2 it says that this feature is supported now. I have no idea what I'm doing wrong. If android.content.Intent; comes into play, please explain. I don't really understand what the idea behind intents! Thanks for any help!

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• Why doesn't java.util.Set have get(int index)?

  - by Marty Pitt

  I'm sure there's a good reason, but could someone please explain why the java.util.Set interface lacks get(int Index), or any similar get() method? It seems that sets are great for putting things into, but I can't find an elegant way of retrieving a single item from it. If I know I want the first item, I can use set.iterator().next(), but otherwise it seems I have to cast to an Array to retrieve an item at a specific index? What are the appropriate ways of retrieving data from a set? (other than using an iterator) I'm sure the fact that it's excluded from the API means there's a good reason for not doing this -- could someone please enlighten me? EDIT: Some extremely great answers here, and a few saying "more context". The specific scneario was a dbUnit test, where I could reasonalby assert that the returned set from a query had only 1 item, and I was trying to access that item. However, the question is more valid without the scenario, as it remains more focussed : What's the difference between set & list. Thanks to all for the fantastic answers below.

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• Code Golf: Find the possible ways on a numpad

  - by ikar

  I was bored today at school and so I tried to amuse myself using my calculator and a "game" I've invented which isn't really a game but keeps the boringness away. Also some time has passed since the last real code-golf here, so I decided to create this one. Imagine a simplified numpad like you know it from your phone (I'll leave the 0 out for this code-golf as it kinda destroys all the fun) 1 2 3 4 5 6 7 8 9 Now the rules of the game were always: At the end every digit must have been visited exactly once You can start at any digit you want You can always move one digit up, down, left or right. You can't move diagonally! There a quite a lot of possible ways (or not; I haven't found out yet), here some trivial examples: > > v v < < > > | The output of the golf-program should look something like the above, I'll try to explain: Symbols: Go right < Go left ^ Go up v Go down | End of the way Example solutions: (Program output can either be the numbers pressed in the right order from beginning point to end, or an (ASCII) picture like above) 147852369 569874123 523698741 So if we speak out the example above it would be: Start at 1, move right to 2, move right to 3, go down to 6, go left to 5, go left to 4, go down to 7, go right to 8 then go right to 9 and we are finished! Now there are many different ways possible: You could as well start at 5 and go around it in a circle. So the task would be: Write a program that can compute (using brute-force or whatever) the possible solutions for the numpad problem described above. (Friendly rethorical question with smiley removed because it made some people think that this is homework)

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• Help me write my LISP :) LISP environments, Ruby Hashes...

  - by MikeC8

  I'm implementing a rudimentary version of LISP in Ruby just in order to familiarize myself with some concepts. I'm basing my implementation off of Peter Norvig's Lispy (http://norvig.com/lispy.html). There's something I'm missing here though, and I'd appreciate some help... He subclasses Python's dict as follows: class Env(dict): "An environment: a dict of {'var':val} pairs, with an outer Env." def __init__(self, parms=(), args=(), outer=None): self.update(zip(parms,args)) self.outer = outer def find(self, var): "Find the innermost Env where var appears." return self if var in self else self.outer.find(var) He then goes on to explain why he does this rather than just using a dict. However, for some reason, his explanation keeps passing in through my eyes and out through the back of my head. Why not use a dict, and then inside the eval function, when a new "sub-environment" needs to be created, just take the existing dict and update the key/value pairs that need to be updated, and pass that new dict into the next eval? Won't the Python interpreter keep track of the previous "outer" envs? And won't the nature of the recursion ensure that the values are pulled out from "inner" to "outer"? I'm using Ruby, and I tried to implement things this way. Something's not working though, and it might be because of this, or perhaps not. Here's my eval function, env being a regular Hash: def eval(x, env = $global_env) ........ elsif x[0] == "lambda" then ->(*args) { eval(x[2], env.merge(Hash[*x[1].zip(args).flatten(1)])) } ........ end The line that matters of course is the "lambda" one. If there is a difference, what's importantly different between what I'm doing here and what Norvig did with his Env class? If there's no difference, then perhaps someone can enlighten me as to why Norvig uses the Env class. Thanks :)

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• C to Assembly code - what does it mean

  - by Smith

  I'm trying to figure out exactly what is going on with the following assembly code. Can someone go down line by line and explain what is happening? I input what I think is happening (see comments) but need clarification. .file "testcalc.c" .section .rodata.str1.1,"aMS",@progbits,1 .LC0: .string "x=%d, y=%d, z=%d, result=%d\n" .text .globl main .type main, @function main: leal 4(%esp), %ecx // establish stack frame andl $-16, %esp // decrement %esp by 16, align stack pushl -4(%ecx) // push original stack pointer pushl %ebp // save base pointer movl %esp, %ebp // establish stack frame pushl %ecx // save to ecx subl $36, %esp // alloc 36 bytes for local vars movl $11, 8(%esp) // store 11 in z movl $6, 4(%esp) // store 6 in y movl $2, (%esp) // store 2 in x call calc // function call to calc movl %eax, 20(%esp) // %esp + 20 into %eax movl $11, 16(%esp) // WHAT movl $6, 12(%esp) // WHAT movl $2, 8(%esp) // WHAT movl $.LC0, 4(%esp) // WHAT?!?! movl $1, (%esp) // move result into address of %esp call __printf_chk // call printf function addl $36, %esp // WHAT? popl %ecx popl %ebp leal -4(%ecx), %esp ret .size main, .-main .ident "GCC: (Ubuntu 4.3.3-5ubuntu4) 4.3.3" .section .note.GNU-stack,"",@progbits Original code: #include <stdio.h> int calc(int x, int y, int z); int main() { int x = 2; int y = 6; int z = 11; int result; result = calc(x,y,z); printf("x=%d, y=%d, z=%d, result=%d\n",x,y,z,result); }

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• What are the differences between mapping,binding and parsing?

  - by sfrj

  I am starting to learn web-services in java EE6. I did web development before, but never nothing related to web services. All is new to me and the books and the tutorials i find in the web are to technical. I started learning about .xsd schemas and also .xml. In that topic i feel confident, i understand what are the schemas used for and what validation means. Now my next step is learning about JAX-B(Java Api for XML Binding). I rode some about it and i did also some practice in my IDE. But i have lots of basic doubts, that make me stuck and cannot feel confident to continue to the next topic. Ill appreciate a lot if someone could explain me well my doubts: What does it mean mapping and what is a mapping tool? What does it mean binding and what is a binding tool? What does it mean parsing and what is a parsing tool? How is JAX-B related to mapping,binding and parsing? I am seeking for a good answer built by you, not just a copy paste from google(Ive already been online a few hours and only got confused).

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• wordpress generating slow mysql queries - is it index problem?

  - by tash

  Hello Stack Overflow I've got very slow Mysql queries coming up from my wordpress site. It's making everything slow and I think this is eating up CPU usage. I've pasted the Explain results for the two most frequently problematic queries below. This is a typical result - although very occasionally teh queries do seem to be performed at a more normal speed. I have the usual wordpress indexes on the database tables. You will see that one of the queries is generated from wordpress core code, and not from anything specific - like the theme - for my site. I have a vague feeling that the database is not always using the indexes/is not using them properly... Is this right? Does anyone know how to fix it? Or is it a different problem entirely? Many thanks in advance for any help anyone can offer - it is hugely appreciated Query: [wp-blog-header.php(14): wp()] SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_posts WHERE 1=1 AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private') ORDER BY wp_posts.post_date DESC LIMIT 0, 6 id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE wp_posts ref type_status_date type_status_date 63 const 427 Using where; Using filesort Query time: 34.2829 (ms) 9) Query: [wp-content/themes/LMHR/index.php(40): query_posts()] SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_posts WHERE 1=1 AND wp_posts.ID NOT IN ( SELECT tr.object_id FROM wp_term_relationships AS tr INNER JOIN wp_term_taxonomy AS tt ON tr.term_taxonomy_id = tt.term_taxonomy_id WHERE tt.taxonomy = 'category' AND tt.term_id IN ('217', '218', '223', '224') ) AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private') ORDER BY wp_posts.post_date DESC LIMIT 0, 6 id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY wp_posts ref type_status_date type_status_date 63 const 427 Using where; Using filesort 2 DEPENDENT SUBQUERY tr ref PRIMARY,term_taxonomy_id PRIMARY 8 func 1 Using index 2 DEPENDENT SUBQUERY tt eq_ref PRIMARY,term_id_taxonomy,taxonomy PRIMARY 8 antin1_lovemusic2010.tr.term_taxonomy_id 1 Using where Query time: 70.3900 (ms)

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• Generic version control strategy for select table data within a heavily normalized database

  - by leppie

  Hi Sorry for the long winded title, but the requirement/problem is rather specific. With reference to the following sample (but very simplified) structure (in psuedo SQL), I hope to explain it a bit better. TABLE StructureName { Id GUID PK, Name varchar(50) NOT NULL } TABLE Structure { Id GUID PK, ParentId GUID (FK to Structure), NameId GUID (FK to StructureName) NOT NULL } TABLE Something { Id GUID PK, RootStructureId GUID (FK to Structure) NOT NULL } As one can see, Structure is a simple tree structure (not worried about ordering of children for the problem). StructureName is a simplification of a translation system. Finally 'Something' is simply something referencing the tree's root structure. This is just one of many tables that need to be versioned, but this one serves as a good example for most cases. There is a requirement to version to any changes to the name and/or the tree 'layout' of the Structure table. Previous versions should always be available. There seems to be a few possibilities to tackle this issue, like copying the entire structure, but most approaches causes one to 'loose' referential integrity. Example if one followed this approach, one would have to make a duplicate of the 'Something' record, given that the root structure will be a new record, and have a new ID. Other avenues of possible solutions are looking into how Wiki's handle this or go a lot further and look how proper version control systems work. Currently, I feel a bit clueless how to proceed on this in a generic way. Any ideas will be greatly appreciated. Thanks leppie

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• structDelete doesn't affect the shallow copy?

  - by Travis

  I was playing around onError so I tried to create an error using a large xml document object. <cfset XMLByRef = variables.parsedXML.XMLRootElement.XMLChildElement> <cfset structDelete(variables.parsedXML, "XMLRootElement")> <cfset startXMLShortLoop = getTickCount()> <cfloop from = "1" to = "#arrayLen(variables.XMLByRef)#" index = "variables.i"> <cfoutput>#variables.XMLByRef[variables.i].id.xmltext#</cfoutput><br /> </cfloop> <cfset stopXMLShortLoop = getTickCount()> I expected to get an error because I deleted the structure I was referencing. From LiveDocs: Variable Assignment - Creates an additional reference, or alias, to the structure. Any change to the data using one variable name changes the structure that you access using the other variable name. This technique is useful when you want to add a local variable to another scope or otherwise change a variable's scope without deleting the variable from the original scope. instead I got 580df1de-3362-ca9b-b287-47795b6cdc17 25a00498-0f68-6f04-a981-56853c0844ed ... ... ... db49ed8a-0ba6-8644-124a-6d6ebda3aa52 57e57e28-e044-6119-afe2-aebffb549342 Looped 12805 times in 297 milliseconds <cfdump var = "#variables#"> Shows there's nothing in the structure, just parsedXML.xmlRoot.xmlName with the value of XMLRootElement. I also tried <cfset structDelete(variables.parsedXML.XMLRootElement, "XMLChildElement")> as well as structClear for both. More information on deleting from the xml document object. http://help.adobe.com/en_US/ColdFusion/9.0/Developing/WSc3ff6d0ea77859461172e0811cbec22c24-78e3.html Can someone please explain my faulty logic? Thanks.

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• UTF-8 MySQL and Charset, pls help me understand this once and for all!

  - by FFish

  Can someone explain me when I set everything to UTF-8 I keep getting those damn ??? MySQL Server version: 5.1.44 MySQL charset: UTF-8 Unicode (utf8) I create a new database name: utf8test collation: utf8_general_ci MySQL connection collation: utf8_general_ci My SQL looks like this: SET SQL_MODE="NO_AUTO_VALUE_ON_ZERO"; CREATE TABLE IF NOT EXISTS `test_table` ( `test_id` int(11) NOT NULL, `test_text` text NOT NULL, PRIMARY KEY (`test_id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; INSERT INTO `test_table` (`test_id`, `test_text`) VALUES (1, 'hééélo'), (2, 'wööörld'); My PHP / HTML: <?php $db_conn = mysql_connect("localhost", "root", "") or die("Can't connect to db"); mysql_select_db("utf8test", $db_conn) or die("Can't select db"); // $result = mysql_query("set names 'utf8'"); // this works... why?? $query = "SELECT * FROM test_table"; $result = mysql_query($query); $output = ""; while($row = mysql_fetch_assoc($result)) { $output .= "id: " . $row['test_id'] . " - text: " . $row['test_text'] . "<br />"; } ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html lang="it" xmlns="http://www.w3.org/1999/xhtml" xml:lang="it"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>UTF-8 test</title> </head> <body> <?php echo $output; ?> </body> </html>

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• Two entities with @ManyToOne should join the same table

  - by Ivan Yatskevich

  I have the following entities Student @Entity public class Student implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; //getter and setter for id } Teacher @Entity public class Teacher implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; //getter and setter for id } Task @Entity public class Task implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @ManyToOne(optional = false) @JoinTable(name = "student_task", inverseJoinColumns = { @JoinColumn(name = "student_id") }) private Student author; @ManyToOne(optional = false) @JoinTable(name = "student_task", inverseJoinColumns = { @JoinColumn(name = "teacher_id") }) private Teacher curator; //getters and setters } Consider that author and curator are already stored in DB and both are in the attached state. I'm trying to persist my Task: Task task = new Task(); task.setAuthor(author); task.setCurator(curator); entityManager.persist(task); Hibernate executes the following SQL: insert into student_task (teacher_id, id) values (?, ?) which, of course, leads to null value in column "student_id" violates not-null constraint Can anyone explain this issue and possible ways to resolve it?

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• Removing "Using temporary; Using filesort" from this MySQL select+join+group by query

  - by claytontstanley

  I have the following query: select t.Chunk as LeftChunk, t.ChunkHash as LeftChunkHash, q.Chunk as RightChunk, q.ChunkHash as RightChunkHash, count(t.ChunkHash) as ChunkCount from chunksubset as t join chunksubset as q on t.ID = q.ID group by LeftChunkHash, RightChunkHash And the following explain table: id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE subsets ref PRIMARY,IDIndex,SubsetIndex SubsetIndex 767 const 522014 "Using where; Using temporary; Using filesort" 1 SIMPLE subsets eq_ref PRIMARY,IDIndex,SubsetIndex PRIMARY 771 sotero.subsets.Id,const 1 "Using where; Using index" 1 SIMPLE c ref IDIndex IDIndex 4 sotero.subsets.Id 12 "Using where" 1 SIMPLE c ref IDIndex IDIndex 4 sotero.subsets.Id 12 note the "using temporary; using filesort". When this query is run, I quickly run out of RAM (presumably b/c of the temp table), and then the HDD kicks in, and the query slows to a halt. I thought it might be an index issue, so I started adding a few that sort of made sense: Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment chunks 0 PRIMARY 1 ChunkId A 17796190 NULL NULL BTREE chunks 1 ChunkHashIndex 1 ChunkHash A 243783 NULL NULL BTREE chunks 1 IDIndex 1 Id A 1483015 NULL NULL BTREE chunks 1 ChunkIndex 1 Chunk A 243783 NULL NULL BTREE chunks 1 ChunkTypeIndex 1 ChunkType A 2 NULL NULL BTREE chunks 1 chunkHashByChunkIDIndex 1 ChunkHash A 243783 NULL NULL BTREE chunks 1 chunkHashByChunkIDIndex 2 ChunkId A 17796190 NULL NULL BTREE chunks 1 chunkHashByChunkTypeIndex 1 ChunkHash A 243783 NULL NULL BTREE chunks 1 chunkHashByChunkTypeIndex 2 ChunkType A 261708 NULL NULL BTREE chunks 1 chunkHashByIDIndex 1 ChunkHash A 243783 NULL NULL BTREE chunks 1 chunkHashByIDIndex 2 Id A 17796190 NULL NULL BTREE But still using the temporary table. The db engine is MyISAM. How can I get rid of the using temporary; using filesort in this query? Just changing to InnoDB w/o explaining the underlying cause is not a particularly satisfying answer. Besides, if the solution is to just add the proper index, then that's much easier than migrating to another db engine.

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• What caused the rails application crash?

  - by so1o

  I'm sure someone can explain this. we have an application that has been in production for an year. recently we saw an increase in number of support requests for people having difficulty signing into the system. after scratching our head because we couldn't recreate the problem in development, we decided we'll switch on debug logger in production for a month. that was june 5th. application worked fine with the above change and we were waiting. then yesterday we noticed that the log files were getting huge so we made another change in production config.logger = Logger.new("#{RAILS_ROOT}/log/production.log", 50, 1048576) after this change, the application started crashing while processing a particular file. this particular line of code was RAILS_DEFAULT_LOGGER.info "Payment Information Request: ", request.inspect as you can see there was a comma instead of a plus sign. this piece of code was introduced in Mar. the question is this: why did the application fail now? if changing the debug level caused the application to process this line of code it should have started failing on june 5th! why today. please someone help us. Are we missing the obvious here? if you dont have an answer, at least let us know we aren't the only one that are bonkers.

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• C# Event Handlers Using an Enum

  - by Jimbo

  I have a StatusChanged event that is raised by my object when its status changes - however, the application needs to carry out additional actions based on what the new status is. e.g If the new status is Disconnected, then it must update the status bar text and send an email notification. So, I wanted to create an Enum with the possible statuses (Connected, Disconnected, ReceivingData, SendingData etc.) and have that sent with the EventArgs parameter of the event when it is raised (see below) Define the object: class ModemComm { public event CommanderEventHandler ModemCommEvent; public delegate void CommanderEventHandler(object source, ModemCommEventArgs e); public void Connect() { ModemCommEvent(this, new ModemCommEventArgs ModemCommEventArgs.eModemCommEvent.Connected)); } } Define the new EventArgs parameter: public class ModemCommEventArgs : EventArgs{ public enum eModemCommEvent { Idle, Connected, Disconnected, SendingData, ReceivingData } public eModemCommEvent eventType { get; set; } public string eventMessage { get; set; } public ModemCommEventArgs(eModemCommEvent eventType, string eventMessage) { this.eventMessage = eventMessage; this.eventType = eventType; } } I then create a handler for the event in the application: ModemComm comm = new ModemComm(); comm.ModemCommEvent += OnModemCommEvent; and private void OnModemCommEvent(object source, ModemCommEventArgs e) { } The problem is, I get a 'Object reference not set to an instance of an object' error when the object attempts to raise the event. Hoping someone can explain in n00b terms why and how to fix it :)

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• Creating a RESTful API - HELP!

  - by Martin Cox

  Hi Chaps Over the last few weeks I've been learning about iOS development, which has naturally led me into the world of APIs. Now, searching around on the Internet, I've come to the conclusion that using the REST architecture is very much recommended - due to it's supposed simplicity and ease of implementation. However, I'm really struggling with the implementation side of REST. I understand the concept; using HTTP methods as verbs to describe the action of a request and responding with suitable response codes, and so on. It's just, I don't understand how to code it. I don't get how I map a URI to an object. I understand that a GET request for domain.com/api/user/address?user_id=999 would return the address of user 999 - but I don't understand where or how that mapping from /user/address to some method that queries a database has taken place. Is this all coded in one php script? Would I just have a method that grabs the URI like so: $array = explode("/", ltrim(rtrim($_SERVER['REQUEST_URI'], "/"), "/")) And then cycle through that array, first I would have a request for a "user", so the PHP script would direct my request to the user object and then invoke the address method. Is that what actually happens? I've probably not explained my thought process very well there. The main thing I'm not getting is how that URI /user/address?id=999 somehow is broken down and executed - does it actually resolve to code? class user(id) { address() { //get user address } } I doubt I'm making sense now, so I'll call it a day trying to explain further. I hope someone out there can understand what I'm trying to say! Thanks Chaps, look forward to your responses. Martin p.s - I'm not a developer yet, I'm learning :)

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• escape sequence in c

  - by prp

  int main() { char *arr="\\0\1\8234\0"; int i=0; while(arr[i]) { switch(arr[i]) { case '0': printf("is no"); break; case '00': printf("is debugging\n"); break; case 0: printf("It is Avishkar\n"); break; case '\\': printf("This "); break; case '\1': printf("t s"); break; case '8': printf("o s"); break; case '2': printf("imp"); break; case '3': printf("le as"); break; case 2: case 3: case 4: case 8: printf("This "); break; default: printf(" it seems\n"); break;} i++; } } please explain the o/p ? i am not able to get it..

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• Boost Asio UDP retrieve last packet in socket buffer

  - by Alberto Toglia

  I have been messing around Boost Asio for some days now but I got stuck with this weird behavior. Please let me explain. Computer A is sending continuos udp packets every 500 ms to computer B, computer B desires to read A's packets with it own velocity but only wants A's last packet, obviously the most updated one. It has come to my attention that when I do a: mSocket.receive_from(boost::asio::buffer(mBuffer), mEndPoint); I can get OLD packets that were not processed (almost everytime). Does this make any sense? A friend of mine told me that sockets maintain a buffer of packets and therefore If I read with a lower frequency than the sender this could happen. ¡? So, the first question is how is it possible to receive the last packet and discard the ones I missed? Later I tried using the async example of the Boost documentation but found it did not do what I wanted. http://www.boost.org/doc/libs/1_36_0/doc/html/boost_asio/tutorial/tutdaytime6.html From what I could tell the async_receive_from should call the method "handle_receive" when a packet arrives, and that works for the first packet after the service was "run". If I wanted to keep listening the port I should call the async_receive_from again in the handle code. right? BUT what I found is that I start an infinite loop, it doesn't wait till the next packet, it just enters "handle_receive" again and again. I'm not doing a server application, a lot of things are going on (its a game), so my second question is, do I have to use threads to use the async receive method properly, is there some example with threads and async receive? Thanks for you attention.

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• MySQL Paritioning performance

  - by Imran Pathan

  Measured performance on key partitioned tables and normal tables separately. But we couldn't find any performance improvement with partitioning. Queries are pruned. Using MySQL 5.1.47 on RHEL 4. Table details: UserUsage - Will have entries for user mobile number and data usage for each date. Mobile number and Date as PRI KEY. UserProfile - Queries prev table and stores summary for each mobile number. Mobile number PRI KEY. CREATE TABLE `UserUsage` ( `Msisdn` decimal(20,0) NOT NULL, `Date` date NOT NULL, . . PRIMARY KEY USING BTREE (`Msisdn`,`Date`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 PARTITION BY KEY(Msisdn) PARTITIONS 50; CREATE TABLE `UserProfile` ( `Msisdn` decimal(20,0) NOT NULL, . . PRIMARY KEY (`Msisdn`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 PARTITION BY KEY(Msisdn) PARTITIONS 50; Second table is updated by query select and order by date in first table in a perl program, query is select * from UserUsage where Msisdn=number order by Date desc limit 7 [Process data in perl] update UserProfile values(....) where Msisdn=number explain partition for select, shows row being scanned in a particular partition only. Is something wrong with partition design or queries as partitioning is taking almost same or more time compared to normal tables?

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• How do I implement configurations and settings?

  - by Malvolio

  I'm writing a system that is deployed in several places and each site needs its own configurations and settings. A "configuration" is a named value that is necessary to a particular site (e.g., the database URL, S3 bucket name); every configuration is necessary, there is not usually a default, and it's typically string-valued. A setting is a named value but it just tweaks the behavior of the system; it's often numeric or Boolean, and there's usually some default. So far, I've been using property files or thing like them, but it's a terrible solution. Several times, a developer has added a requirement for a configuration but not added the value to file for the live configuration, so the new release passed all the tests, then failed when released to live. Better, of course, for every file to be compiled — so if there's a missing configuration, or one of the wrong type, it won't get past the compiler — and inject the site-specific class into the build for each site. As a bones, a Scala file can easy model more complex values, especially lists, but also maps and tuples. The downside is, the files are sometimes maintained by people who aren't developers, so it has to be pretty self-explanatory, which was the advantage of property files. (Someone explain XML configurations to me: all the complexity of a compilable file but the run-time risk of a property file.) What I'm looking for is an easy pattern for defining a group required names and allowable values. Any suggestions?

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• Problems breaking out of nested loops

  - by user1040281

  I have problems breaking out off these nested loops correctly. What the code is trying to do is to indicate that a customer has rented a certain movie. Both the movie and customer are compared to properties of arraylist objects and then if all checks out the name property and ID property of a movie object are added as a string to another arraylist. All this works correctly as long as I use the first movie (from movies) and the first customer (from customers) but if I try renting other movies further down my arraylist with other customers then it adds the rented movie to the customerRentedMovies arraylist but prints out the "else message". I figure I need to break out of the foreach(blabla) loops aswell? or could goto be used? Comments was removed (looked kinda messy, can explain further if needed) public void RentMovie(string titel, int movieID, string name, int customerID) { foreach (Customer customer in customers) { if (name == customer.Name && customerID == customer.CustomerID) { foreach (MovieInfo movie in movies) { if (titel == movie.Titel && movieID == movie.MovieID) { movie.rented = true; string rentedMovie = string.Format("{0} ID: {1}", movie.Titel, movie.MovieID); customer.customerRentedMovies.Add(rentedMovie); break; } else { Console.WriteLine("No movie with that titel and ID!"); } } break; } else { Console.WriteLine("No customer with that ID and name"); } } }

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• String literal recognition problem

  - by helicera

  Hello! I'm trying to recognize string literal by reading string per symbol. Here is a sample code: #region [String Literal (")] case '"': // {string literal ""} { // skipping '"' ChCurrent = Line.ElementAtOrDefault<Char>(++ChPosition); while(ChCurrent != '"') { Value.Append(ChCurrent); ChCurrent = Line.ElementAtOrDefault<Char>(++ChPosition); if(ChCurrent == '"') { // "" sequence only acceptable if(Line.ElementAtOrDefault<Char>(ChPosition + 1) == '"') { Value.Append(ChCurrent); // skip 2nd double quote ChPosition++; // move position next ChCurrent = Line.ElementAtOrDefault<Char>(++ChPosition); } } else if(default(Char) == ChCurrent) { // message: unterminated string throw new ScanningException(); } } ChPosition++; break; } #endregion When I run test: [Test] [ExpectedException(typeof(ScanningException))] public void ScanDoubleQuotedStrings() { this.Scanner.Run(@"""Hello Language Design""", default(System.Int32)); this.Scanner.Run(@"""Is there any problems with the """"strings""""?""", default(System.Int32)); this.Scanner.Run(@"""v#:';?325;.<>,|+_)""(*&^%$#@![]{}\|-_=""", default(System.Int32)); while(0 != this.Scanner.TokensCount - 1) { Assert.AreEqual(Token.TokenClass.StringLiteral, this.Scanner.NextToken.Class); } } It passes with success.. while I'm expecting to have an exception according to unmatched " mark in this.Scanner.Run(@"""v#:';?325;.<>,|+_)""(*&^%$#@![]{}\|-_=""", default(System.Int32)); Can anyone explain where is my mistake or give an advice on algorithm.

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• adding virtual function to the end of the class declaration avoids binary incompatibility?

  - by bob

  Could someone explain to me why adding a virtual function to the end of a class declaration avoids binary incompatibility? If I have: class A { public: virtual ~A(); virtual void someFuncA() = 0; virtual void someFuncB() = 0; virtual void other1() = 0; private: int someVal; }; And later modify this function to: class A { public: virtual ~A(); virtual void someFuncA(); virtual void someFuncB(); virtual void someFuncC(); virtual void other1() = 0; private: int someVal; }; I get a coredump from another .so compiled against the previous declaration. But if I put someFuncC() at the end of the class declaration (after "int someVal"), I don't see coredump anymore. Could someone tell me why this is? And does this trick always work? PS. compiler is gcc, does this work with other compilers?

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• No idea how to solve SICP exercise 1.11

  - by Javier Badia

  This is not homework. Exercise 1.11: A function f is defined by the rule that f(n) = n if n<3 and f(n) = f(n - 1) + 2f(n - 2) + 3f(n - 3) if n 3. Write a procedure that computes f by means of a recursive process. Write a procedure that computes f by means of an iterative process. Implementing it recursively is simple enough. But I couldn't figure out how to do it iteratively. I tried comparing with the Fibonacci example given, but I didn't know how to use it as an analogy. So I gave up (shame on me) and Googled for an explanation, and I found this: (define (f n) (if (< n 3) n (f-iter 2 1 0 n))) (define (f-iter a b c count) (if (< count 3) a (f-iter (+ a (* 2 b) (* 3 c)) a b (- count 1)))) After reading it, I understand the code and how it works. But what I don't understand is the process needed to get from the recursive defintion of the function to this. I don't get how the code formed in someone's head. Could you explain the thought process needed to arrive at the solution?

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• Python: Errors saving and loading objects with pickle module

  - by Peterstone

  Hi, I am trying to load and save objects with this piece of code I get it from a question I asked a week ago: Python: saving and loading objects and using pickle. The piece of code is this: class Fruits: pass banana = Fruits() banana.color = 'yellow' banana.value = 30 import pickle filehandler = open("Fruits.obj","wb") pickle.dump(banana,filehandler) filehandler.close() file = open("Fruits.obj",'rb') object_file = pickle.load(file) file.close() print(object_file.color, object_file.value, sep=', ') At a first glance the piece of code works well, getting load and see the 'color' and 'value' of the saved object. But, what I pursuit is to close a session, open a new one and load what I save in a past session. I close the session after putting the line filehandler.close() and I open a new one and I put the rest of your code, then after putting object_file = pickle.load(file) I get this error: Traceback (most recent call last): File "<pyshell#5>", line 1, in <module> object_file = pickle.load(file) File "C:\Python31\lib\pickle.py", line 1365, in load encoding=encoding, errors=errors).load() AttributeError: 'module' object has no attribute 'Fruits' Can anyone explain me what this error message means and telling me how to solve this problem? Thank so much and happy new year!!

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