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• Why do my CouchDB databases grow so fast?

  - by konrad

  I was wondering why my CouchDB database was growing to fast so I wrote a little test script. This script changes an attributed of a CouchDB document 1200 times and takes the size of the database after each change. After performing these 1200 writing steps the database is doing a compaction step and the db size is measured again. In the end the script plots the databases size against the revision numbers. The benchmarking is run twice: The first time the default number of document revision (=1000) is used (_revs_limit). The second time the number of document revisions is set to 1. The first run produces the following plot The second run produces this plot For me this is quite an unexpected behavior. In the first run I would have expected a linear growth as every change produces a new revision. When the 1000 revisions are reached the size value should be constant as the older revisions are discarded. After the compaction the size should fall significantly. In the second run the first revision should result in certain database size that is then keeps during the following writing steps as every new revision leads to the deletion of the previous one. I could understand if there is a little bit of overhead needed to manage the changes but this growth behavior seems weird to me. Can anybody explain this phenomenon or correct my assumptions that lead to the wrong expectations?

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• Is a GWT app running on Google App Engine protected from CSRF

  - by gerdemb

  I'm developing a GWT app running on the Google App Engine and wondering if I need to worry about Cross-site request forgery or is that automatically taken care of for me? For every RPC request that requires authentication, I have the following code: public class BookServiceImpl extends RemoteServiceServlet implements BookService { public void deleteInventory(Key<Inventory> inventoryKey) throws NotLoggedInException, InvalidStateException, NotFoundException { DAO dao = new DAO(); // This will throw NotLoggedInException if user is not logged in User user = dao.getCurrentUser(); // Do deletion here } } public final class DAO extends DAOBase { public User getCurrentUser() throws NotLoggedInException { currentUser = UserServiceFactory.getUserService().getCurrentUser(); if(currentUser == null) { throw new NotLoggedInException(); } return currentUser; } I couldn't find any documentation on how the UserService checks authentication. Is it enough to rely on the code above or do I need to to more? I'm a beginner at this, but from what I understand to avoid CSRF attacks some of the strategies are: adding an authentication token in the request payload instead of just checking a cookie checking the HTTP Referer header I can see that I have cookies set from Google with what look like SID values, but I can't tell from the serialized Java objects in the payloads if tokens are being passed or not. I also don't know if the Referer header is being used or not. So, am I worrying about a non-issue? If not, what is the best strategy here? This is a common enough problem, that there must be standard solutions out there...

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• CompositeDataBoundControl - databound values overwritten before event is fired due to DummyDataSourc

  - by Vidar Langberget

  I have a custom servercontrol that inherits from CompositeDataBoundControl. I have three templates: one header template, one footer template and one item template. The item template can contain a checkbox that I use to decide if I should delete the item. In the footer and/or header templates I have a button with a CommandName of "DeleteItem". When that button is clicked, I handle the event in OnBubbleEvent: if (cea.CommandName == "DeleteItem") { //loop through the item list and get the selected rows List<int> itemsToDelete = new List<int>(); foreach(Control c in this.Controls){ if (c is ItemData) { ItemData oid = (ItemData)c; CheckBox chkSel = (CheckBox)oid.FindControl("chkSelected"); if (chkSel.Checked) { itemsToDelete.Add(oid.Item.Id); } } } foreach (int id in itemsToDelete) { DeleteItem(id); } } } The problem is that Item is null since the CreateChildControls method already has been run as asp.net needs to recreate the control hierarchy before the event fire. It uses the DummyDataSource and a list of null objects to recreate the control hierarchy: IEnumerator e = dataSource.GetEnumerator(); if (e != null) { while (e.MoveNext()) { ItemData container = new ItemData (e.Current as OrderItem); ITemplate itemTemplate = this.ItemTemplate; if (itemTemplate == null) { itemTemplate = new DefaultItemTemplate(); } itemTemplate.InstantiateIn(container); Controls.Add(container); if (dataBinding) { container.DataBind(); } counter++; } } The problem is this line: ItemData container = new ItemData (e.Current as OrderItem); When the control hierarchy is rebuilt before the event is fired, the e.Current is null, so when I try to find out which item was marked for deletion, I get 0 since the original value has been overwritten. Any suggestions on how to fix this?

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• coredata using old file version on device

  - by Martin KS

  This is a follow on from my previous problems here. Resetting the simulator solved all my troubles before, and I've gone on to complete my App. I now have the exact same problem when installing the app onto my iPhone device. It picks up an old version of my database, which doesn't have the second entity in it, and crashes when I try to access the second entity: 2010-04-22 23:52:18.860 albumCloud[135:207] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '+entityForName: could not locate an NSManagedObjectModel for entity name 'Image'' 2010-04-22 23:52:18.874 albumCloud[135:207] Stack: ( 843263261, 825818644, 820669213, 20277, 844154820, 16985, 14633, 844473760, 844851728, 862896011, 843011267, 843009055, 860901832, 843738160, 843731504, 11547, 11500 ) terminate called after throwing an instance of 'NSException' I have two questions: 1) How on earth do I delete my app thoroughly enough from my phone that it removes the old data? (I've so far tried regular app deletion, deleting and then holding home and power for a reboot, cursing at and threatening the app while running it... everything) 2) How do I prevent this happening when my application is in the App store, and I for some reason decide that I want to add another entity to the store, or another attribute to the existing entities? is there an "if x doesn't exist then create it" method?

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• Which Table Should be Master and Child in Database Design

  - by Jason

  I am quickly learning the ins and outs of database design (something that, as of a week ago, was new to me), but I am running across some questions that don't seem immediately obvious, so I was hoping to get some clarification. The question I have right is about foreign keys. As part of my design, I have a Company table. Originally, I had included address information directly within the table, but, as I was hoping to achieve 3NF, I broke out the address information into its own table, Address. In order to maintain data integrity, I created a row in Company called "addressId" as an INT and the Address table has a corresponding addressId as its primary key. What I'm a little bit confused about (or what I want to make sure I'm doing correctly) is determining which table should be the master (referenced) table and which should be the child (referencing) table. When I originally set this up, I made the Address table the master and the Company the child. However, I now believe this is wrong due to the fact that there should be only one address per Company and, if a Company row is deleted, I would want the corresponding Address to be removed as well (CASCADE deletion). I may be approaching this completely wrong, so I would appreciate any good rules of thumb on how to best think about the relationship between tables when using foreign keys. Thanks!

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• How to remove a specific category on a selected mail in Outlook 2003 with Macro?

  - by szekelya

  Hi, I am trying to transform my Outlook2003 into the closest thing to gmail. I started to use categories, which are pretty similar to labels in gmail. I can assign categories automatically with rules, and I can add categories manually. I have also created "search folders", that show all mails with a given category, if they are not in the Deleted Items or Sent Items folders. This part is almost like the Label views in gmail. Two things are missing basically, which should be done with macros (VBA to be precise) which I'm totally inexperienced with. So hence my questions: -Can someone show me a macro to remove the category "Inbox"? That would act exactly like the Archive button in gmail. In fact I want to assign this macro to a toolbar button and call it Archive. I have a rule that adds the Inbox category to all incoming mail. As I said, I have a search folder displaying all mails categorized as Inbox, and I also have an All Mail search folder, that displays all messages regardless whether they have the Inbox category. Exactly like gmail, just the easy archiving is missing. -Can someone show me a macro that would delete the selected mail/mails and also would remove the Inbox category before deletion? I would replace the default delete button with this macro. (Somewhat less important, as in my search folders I can filter messages that are physically placed in the Deleted Items folder, but it would be more elegant not to have mails categorized as Inbox in the trash. Many thanks in advance, szekelya

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• How to figure out which record has been deleted in an effiecient way?

  - by janetsmith

  Hi, I am working on an in-house ETL solution, from db1 (Oracle) to db2 (Sybase). We needs to transfer data incrementally (Change Data Capture?) into db2. I have only read access to tables, so I can't create any table or trigger in Oracle db1. The challenge I am facing is, how to detect record deletion in Oracle? The solution which I can think of, is by using additional standalone/embedded db (e.g. derby, h2 etc). This db contains 2 tables, namely old_data, new_data. old_data contains primary key field from tahle of interest in Oracle. Every time ETL process runs, new_data table will be populated with primary key field from Oracle table. After that, I will run the following sql command to get the deleted rows: SELECT old_data.id FROM old_data WHERE old_data.id NOT IN (SELECT new_data.id FROM new_data) I think this will be a very expensive operation when the volume of data become very large. Do you have any better idea of doing this? Thanks.

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• Implementing list position locator in C++?

  - by jfrazier

  I am writing a basic Graph API in C++ (I know libraries already exist, but I am doing it for the practice/experience). The structure is basically that of an adjacency list representation. So there are Vertex objects and Edge objects, and the Graph class contains: list<Vertex *> vertexList list<Edge *> edgeList Each Edge object has two Vertex* members representing its endpoints, and each Vertex object has a list of Edge* members representing the edges incident to the Vertex. All this is quite standard, but here is my problem. I want to be able to implement deletion of Edges and Vertices in constant time, so for example each Vertex object should have a Locator member that points to the position of its Vertex* in the vertexList. The way I first implemented this was by saving a list::iterator, as follows: vertexList.push_back(v); v->locator = --vertexList.end(); Then if I need to delete this vertex later, then rather than searching the whole vertexList for its pointer, I can call: vertexList.erase(v->locator); This works fine at first, but it seems that if enough changes (deletions) are made to the list, the iterators will become out-of-date and I get all sorts of iterator errors at runtime. This seems strange for a linked list, because it doesn't seem like you should ever need to re-allocate the remaining members of the list after deletions, but maybe the STL does this to optimize by keeping memory somewhat contiguous? In any case, I would appreciate it if anyone has any insight as to why this happens. Is there a standard way in C++ to implement a locator that will keep track of an element's position in a list without becoming obsolete? Much thanks, Jeff

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• Git merge 2 new file with removed content and added content

  - by Loïc Faure-Lacroix

  So we are working in with 2 different repositories and both designers modified the same file. the problem is quite simple but I have no ideas how to solve it yet. Both files are marked as new since they have almost nothing in common except that file. When I try to merge from branch A to B it mark the parts added in A deleted in B and on the other side, what was added in B appears deleted in A. git seems to try to outsmart me when I know that I need almost every changes and nothing should be mark as deletion. I have 2 other branch that should merge without problem after these 2 branch. I can't merge them yet since there are some recent changes that may not merge really well too. I have to merge A and B = E then C and D = F and then hopefully E and F So the big question here is how can I do a completely manual merge that will mark every changes as conflict anything deleted anything added should be marked as conflict that I can solve by myself using an editor. Git is trying to outsmart me and fail terribly at it.

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• strange memory error when deleting object from Core Data

  - by llloydxmas

  I have an application that downloads an xml file, parses the file, and creates core data objects while doing so. In the parse code I have a function called 'emptydatacontext' that removes all items from Core Data before creating replacements from the xml file. This method looks like this: -(void) emptyDataContext { NSMutableArray* mutableFetchResults = [CoreDataHelper getObjectsFromContext:@"Condition" :@"road" :NO :managedObjectContext]; NSFetchRequest * allCon = [[NSFetchRequest alloc] init]; [allCon setEntity:[NSEntityDescription entityForName:@"Condition" inManagedObjectContext:managedObjectContext]]; NSError * error = nil; NSArray * conditions = [managedObjectContext executeFetchRequest:allCon error:&error]; [allCon release]; for (NSManagedObject * condition in conditions) { [managedObjectContext deleteObject:condition]; } } The first time this runs it deletes all objects and functions as it should - creating new objects from the xml file. I created a 'update' button that starts the exact same process of retrieving the file the preceeding as it did the first time. All is well until its time to delete the core data objects again. This 'deleteObject' call creates a "EXC_BAD_ACCESS" error each time. This only happens on the second time through. See this image for the debugger window as it appears when walking through the deletion FOR loop on the second iteration. Conditions is the fetched array of 7 objects with the objects below. Condition should be an individual condition. link text As you can see 'condition' does not match any of the objects in the 'conditions' array. I'm sure this is why I'm getting the memory access errors. Just not sure why this fetch (or the FOR) is returning a wrong reference. All the code that successfully performes this function on the first iteration is used in the second but with very different results. Thanks in advance for the help!

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• Database abstraction/adapters for ruby

  - by Stiivi

  What are the database abstractions/adapters you are using in Ruby? I am mainly interested in data oriented features, not in those with object mapping (like active record or data mapper). I am currently using Sequel. Are there any other options? I am mostly interested in: simple, clean and non-ambiguous API data selection (obviously), filtering and aggregation raw value selection without field mapping: SELECT col1, col2, col3 = [val1, val2, val3] not hash of { :col1 = val1 ...} API takes into account table schemas 'some_schema.some_table' in a consistent (and working) way; also reflection for this (get schema from table) database reflection: get list of table columns, their database storage types and perhaps adaptor's abstracted types table creation, deletion be able to work with other tables (insert, update) in a loop enumerating selection from another table without requiring to fetch all records from table being enumerated Purpose is to manipulate data with unknown structure at the time of writing code, which is the opposite to object mapping where structure or most of the structure is usually well known. I do not need the object mapping overhead. What are the options, including back-ends for object-mapping libraries?

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• Access denied from another thread

  - by Lobuno

  Hello! In a program I span a thread ("the working thread"). Hera I copy some files write some data to a database and eventually, delete some other files or directories. Everything works fine. The problem is now, that I decided to move the deleting operation to some other thread. So the working thread now copies the files or directories, writes to the database, and , if there is a need to delete some other files this thread spans another thread and that second thread deleted the needed files or directories. The problem is that,the deletion used to work 100% when done in the working thread, now when the same is done in the secondary thread, I sometimes get an "Access denied" error and the files cannot be deleted. And no, the working thread is definitely NOT acceding the files and directories to delete at this moment. Sometimes (but not always) the main thread is impersonating some user, so if needed , the deleting thread is also running under impersonation just to grant the needed permissions to delete the files, so that should not be the problem. Anybody has a clue why this could be happening?

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• How to use IO.popen to write-to and read-from a child process?

  - by mackenir

  I am running net share from a ruby script to delete a windows network share. If files on the share are in use, net share will ask the user if they want to go ahead with the deletion, so my script needs to inspect the output from the command, and write out Y if it detects that net share is asking it for input. In order to be able to write out to the process I open it with access flags "r+". When attempting to write to the process with IO#puts, I get an error: Errno::EPIPE: Broken pipe What am I doing wrong here? (The error occurs on the line net_share.puts "Y") (The question text written out by net share is not followed by a newline, so I am using IO#readpartial to read in the output.) def delete_network_share share_path command = "net share #{share_path} /DELETE" net_share = IO.popen(command, "r+") text = "" while true begin line = net_share.readpartial 1000 #read all the input that's available rescue EOFError break end text += line if text.scan("Do you want to continue this operation? (Y/N)").size > 0 net_share.puts "Y" net_share.flush #probably not needed? end end net_share.close end

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• How to read a parameter passed to a facelet from a backing bean

  - by Antonio

  Hi, I've written a facelet, and a corresponding backing bean, that implements user management (addition, deletion and so on). I'd want to be able to perform some custom processing when, for instance, a new user is added. There is a "create" button in the facelet, whose click event is handled by its backing bean. At the end of the event handler, I'd want to be able to call a method of another backing bean, which is not known because ideally the facelet can be used in several pages, with different custom processing. I thought to implement this feature by providing to the facelet a backing bean name and a method name, like this: <myfacelet:subaccounts backingBean="myBackingBean" createListener="createListener" /> and at the end of the event handler call #{myBackingBean.createListener} someway. I'm using this method (along with some overloads) to obtain a MethodExpression: protected MethodExpression getMethodExpression(String beanName, String methodName, Class<?> expectedReturnType, Class<?>[] expectedParamTypes) { ExpressionFactory expressionFactory; MethodExpression method; ELContext elContext; String el; el = String.format("#{%s['%s']}", beanName, methodName); expressionFactory = getApplication().getExpressionFactory(); elContext = getFacesContext().getELContext(); method = expressionFactory.createMethodExpression(elContext, el, expectedReturnType, expectedParamTypes); return method; } and the click event handler should look like: public void saveSubaccountListener(ActionEvent event) { MethodExpression method; ... method = getMethodExpression( "backingBean", "createSubaccountListener", SubuserBean.class); if (method != null) method.invoke( getFacesContext().getELContext(), new Object[] { _editedSubuser }); } That works fine as long as I provide an existing bean name (myBackingBean), but if I use backingBean the invoke() doesn't work due to the following error: javax.el.PropertyNotFoundException: Target Unreachable, identifier 'backingBean' resolved to null Is there a way I can retrieve from the facelet backing bean the value of a parameter that has been passed to the facelet? In my case, the value of backingBean, which should be myBackingBean? I've searched for and tried different solutions, but with no luck yet.

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• how to monitor the program code execution? (file creation and modification by code lines etc)

  - by infant programmer

  My program is about triggering XSL transformation, Its fact that this code for carrying out the transformation, creates some dll and tmp files and deletes them pretty soon after the transformation is completed. It is almost untraceable for me to monitor the creation and deletion of files manually, so I want to include some chunk of codelines to display "which codeline has created/modified which tmp and dll files" in console window. This is the relevant part of the code: string strXmlQueryTransformPath = @"input.xsl"; string strXmlOutput = string.Empty; StringReader srXmlInput = null; StringWriter swXmlOutput = null; XslCompiledTransform xslTransform = null; XPathDocument xpathXmlOrig = null; XsltSettings xslSettings = null; MemoryStream objMemoryStream = null; objMemoryStream = new MemoryStream(); xslTransform = new XslCompiledTransform(false); xpathXmlOrig = new XPathDocument("input.xml"); xslSettings = new XsltSettings(); xslSettings.EnableScript = true; xslTransform.Load(strXmlQueryTransformPath, xslSettings, new XmlUrlResolver()); xslTransform.Transform(xpathXmlOrig, null, objMemoryStream); objMemoryStream.Position = 0; StreamReader objStreamReader = new StreamReader(objMemoryStream); strXmlOutput = objStreamReader.ReadToEnd(); // make use of Data in string "strXmlOutput" google and msdn search couldn't help me much..

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• How to determine a text block of a file in one version come from which file in the previous version?

  - by Muhammad Asaduzzaman

  The problem is described below: Suppose I have a list of files in one version(say A,B,C,D). In the next version I have the following files(A,E,F,G). There are some similarities in their contents. The files in the later version comes from the previous version by file name renaming, content addition, deletion or partial modification or without any change( for example A is not changed). I take a block of text from a file(E, 2nd version) and check which files(in the 1st version) contain this text block. I found that B,C and D contain the text fragment. I want to determine from which file(B or c or d) this text block actually comes from.(I assume that E is a file whose name change in the second version). Since the contents may be changed, added or deleted in the later version, so in order to determine similarity I use LCS algorithm. But I cannot map the file with its previous version. I think one possible approach might be to use the location information of the match text blocks. But this heuristics not always work. Is there any research or algorithm exist to find so. Any direction will be helpful. Thanks in advance.

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• How to stop the submission of the form using JQUERY?

  - by Param-Ganak

  Hello frineds! I have a form which have many check boxes in it. User will check one or many checkboxes and click on Delete button which is actually submit button then the respective records for selected check boxes are get deleted. Required operation steps are as follows:- When user selects one or more checkboxes and clicks the submit button then a JQUERY code is get executed in which It should checks that if any check box is selected; if not; then is displays alert message and do not submit the form. If it founds that one or more checkboxes are selected it should ask user for his/her confirmation using confirm alert box about the confirmation of deletion. If user press YES button on confirm box then it should submit the form using javascript submit statement. If user pressed the NO button then it should unchecks the checked selected checkboxes and should not submit the form. This is the JQUERY code I had written. $(document).ready(function (){ $("#id_delete").click(function(){ var temp=$("#id_frm input:checkbox:checked"); var len=temp.length; if(len==0) { alert("Please select the order."); } else { if(confirm("Are you sure to delete the selected orders.")) { $("#id_frm").submit(); } else { temp.checked=false; } } }); }); Problems: This code is not working properly. Here 1. It submits form when there is no check box is selected. 2. It submits the form when user press NO button on confirmation dialog box. Please guide me friends in this problem.

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• Is it Possible to Use Constraints on Hierarchical Data in a Self-Referential Table?

  - by pbarney

  Suppose you have the following table, intended to represent hierarchical data: +--------+-------------+ | Field | Type | +--------+-------------+ | id | int(10) | | parent | int(10) | | name | varchar(45) | +--------+-------------+ The table is self-referential in that the parent_id refers to id. So you might have the following data: +----+--------+---------------+ | id | parent | name | +----+--------+---------------+ | 1 | 0 | fruit | | 2 | 0 | vegetable | | 3 | 1 | apple | | 4 | 1 | orange | | 5 | 3 | red delicious | | 6 | 3 | granny smith | | 7 | 3 | gala | +----+--------+---------------+ Using MySQL, I am trying to impose a (self-referential) foreign key constraint upon the data to cascade on update and prevent deletion of a record if it has any "children." So I used the following: CREATE TABLE `test`.`fruit` ( `id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT, `parent` INT(10) UNSIGNED, `name` VARCHAR(45) NOT NULL, PRIMARY KEY (`id`), CONSTRAINT `fk_parent` FOREIGN KEY (`parent`) REFERENCES `fruit` (`id`) ON UPDATE CASCADE ON DELETE RESTRICT ) ENGINE = InnoDB; From what I understand, this should fit my requirements. (And parent must default to null to allow insertions, correct?) The problem is, if I change the id of a record, it will not cascade: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`fruit`, CONSTRAINT `fk_parent` FOREIGN KEY (`parent`) REFERENCES `fruit` (`id`) ON UPDATE CASCADE) What am I missing? Feel free to correct me if my terminology is screwed up... I'm new to constraints.

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• confirm alert not working ....

  - by user318068

  I want the work of the Control Panel in my site for members ... I designed the page is displayed all the registered members on my site And i but it checkbox front each member name ,becuase it allowed to select multiple name then click delete button The following code works but now i want confirm alert before delete code working even , if clicked on ok the deletion is working , and if clicked on cancel the is not working .. how i can work it ?? while($row = mysql_fetch_array($sql1)) { ?> <tr> <td align="center" bgcolor="#FFFFFF"><input name="checkbox[]" type="checkbox" id="checkbox[]" value="<?php echo $row['MemberID']; ?>"></td> <td bgcolor="#FFFFFF"><?php echo $row['MemberName']; ; ?></td></tr> <?php } ?> <tr> <td colspan="5" align="center" bgcolor="#FFFFFF"><input name="delete" type="submit" id="delete" value="delete" onclick="javascript:return confirm('are you sure to delete this record???? ')"/></td> </tr> <?php $delete = $_REQUEST['delete']; $checkbox = $_REQUEST['checkbox']; $count = count($_REQUEST['checkbox']); // Check if delete button active, start this if($delete){ echo "<script language=\"Javascript\">\n"; for($i=0;$i<$count;$i++){ $del_id = $checkbox[$i]; $sql = "Delete FROM members where MemberID ='$del_id'"; $sq2 = "Delete FROM joinroom where MemberID ='$del_id'"; $result1 = mysql_query($sql); $result2 = mysql_query($sq2); echo "else {\n"; echo "alert ('Nothing deleted');\n }"; echo "</script>"; } } Thanks a lot.........

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• How can I determine when an InnoDB table was last changed?

  - by David M

  I've had success in the past storing the (heavily) processed results of a database query in memcached, using the last update time of the underlying tables(s) as part of the cache key. For MyISAM tables, that last changed time is available in SHOW TABLE STATUS. Unfortunately, that's usually NULL for InnoDB tables. In MySQL 4.1, the ctime for an InnoDB in its SHOW TABLE STATUS line was usually its actual last update time, but that doesn't seem to be true for MySQL 5.1. There is a DATETIME field in the table, but it only shows when a row has been modified - it cannot show the deletion time of a row that's not there anymore! So, I really cannot use MAX(update_time). Here's the really tricky part. I have a number of replicas that I do reads from. Can I figure out the state of the table that doesn't rely on when the changes have actually been applied? My conclusion after working on this for a while is that it's not going to be possible to get this information as cheaply as I'd like. I'm probably going to cache data until the time that I expect the table to change (it's updated once a day), and let the query cache help out where it can.

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• Stable/repeatable random sort (MySQL, Rails)

  - by Matt Rogish

  I'd like to paginate through a randomly sorted list of ActiveRecord models (rows from MySQL database). However, this randomization needs to persist on a per-session basis, so that other people that visit the website also receive a random, paginate-able list of records. Let's say there are enough entities (tens of thousands) that storing the randomly sorted ID values in either the session or a cookie is too large, so I must temporarily persist it in some other way (MySQL, file, etc.). Initially I thought I could create a function based on the session ID and the page ID (returning the object IDs for that page) however since the object ID values in MySQL are not sequential (there are gaps), that seemed to fall apart as I was poking at it. The nice thing is that it would require no/minimal storage but the downsides are that it is likely pretty complex to implement and probably CPU intensive. My feeling is I should create an intersection table, something like: random_sorts( sort_id, created_at, user_id NULL if guest) random_sort_items( sort_id, item_id, position ) And then simply store the 'sort_id' in the session. Then, I can paginate the random_sorts WHERE sort_id = n ORDER BY position LIMIT... as usual. Of course, I'd have to put some sort of a reaper in there to remove them after some period of inactivity (based on random_sorts.created_at). Unfortunately, I'd have to invalidate the sort as new objects were created (and/or old objects being removed, although deletion is very rare). And, as load increases the size/performance of this table (even properly indexed) drops. It seems like this ought to be a solved problem but I can't find any rails plugins that do this... Any ideas? Thanks!!

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• Find messages from certain key till certain key while being able to remove stale keys.

  - by Alfred

  My problem Let's say I add messages to some sort of datastructure: 1. "dude" 2. "where" 3. "is" 4. "my" 5. "car" Asking for messages from index[4,5] should return: "my","car". Next let's assume that after a while I would like to purge old messages because they aren't useful anymore and I want to save memory. Let's say at time x messages[1-3] became stale. I assume that it would be most efficient to just do the deletion once every x seconds. Next my datastructure should contain: 4. "my" 5. "car" My solution? I was thinking of using a concurrentskiplistset or concurrentskiplist map. Also I was thinking of deleting the old messages from inside a newSingleThreadScheduledExecutor. I would like to know how you would implement(efficiently/thread-safe) this or maybe use a library?

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• Sorted queue with dropping out elements

  - by ffriend

  I have a list of jobs and queue of workers waiting for these jobs. All the jobs are the same, but workers are different and sorted by their ability to perform the job. That is, first person can do this job best of all, second does it just a little bit worse and so on. Job is always assigned to the person with the highest skills from those who are free at that moment. When person is assigned a job, he drops out of the queue for some time. But when he is done, he gets back to his position. So, for example, at some moment in time worker queue looks like: [x, x, .83, x, .7, .63, .55, .54, .48, ...] where x's stand for missing workers and numbers show skill level of left workers. When there's a new job, it is assigned to 3rd worker as the one with highest skill of available workers. So next moment queue looks like: [x, x, x, x, .7, .63, .55, .54, .48, ...] Let's say, that at this moment worker #2 finishes his job and gets back to the list: [x, .91, x, x, .7, .63, .55, .54, .48, ...] I hope the process is completely clear now. My question is what algorithm and data structure to use to implement quick search and deletion of worker and insertion back to his position. For the moment the best approach I can see is to use Fibonacci heap that have amortized O(log n) for deleting minimal element (assigning job and deleting worker from queue) and O(1) for inserting him back, which is pretty good. But is there even better algorithm / data structure that possibly take into account the fact that elements are already sorted and only drop of the queue from time to time?

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• How to **delete-protect** a file or folder on Windows Server 2003 and onwards using C#/Vb.Net?

  - by Steve Johnson

  Hi all, Is it possible to delete-protect a file/folder using Registry or using a custom written Windows Service in C#? Using Folder Permissions it is possible, but i am looking for a solution that even restricts the admin from deleting specific folders. The requirement is that the administrator must not be easily track the nature of protection and/or may not be able to avert it easily. Obviously all administrators will be able to revert the procedure if the technique is clearly understood. Like folder Permissions/OwnerShip Settings can easily be reset by an administrator. SO that is not an option. Folder protection software can easily be uninstalled and show clear indication that a particular folder is protected by some special kind of software. SO that too is not an option. Most antivirus programs protect folders and files in Program Dir. Windows itself doesnt allow certain files such as registry files in c:\windows\system32\config to not even copied. Such a protection is desired for folders which allowse to read and write to files but not allow deletion. Similar functionality is desired. The protection has to seemless and invisible. I do not want to use any protection features like FolderLock and Invisible secrets/PC Security and Desktop password etc. Moreover, the solution has to be something other than folder encryption. The solution has to be OS-native so ** that it may implemented ** pro grammatically using C#/VB.Net. Please help. Thanks

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• remove row on click on specific td of that row by jquery

  - by I Like PHP

  i have an table <table class="oldService"> <thead> <th>name</th> <th>age</th> <th>action</th> </thead> <tbody> <?php foreach($array as $k=>$v){ ?> <tr> <td><?php echo $k[name] ?></td> <td><?php echo $k[age]?></td> <td id="<?php $k[id]" class="delme">X</td> </tr> <?php } ?> </tbody> <table> now i want to delete any row by clicking on X of each row except first and last row, and also need to confirm before deletion. i used below jquery <script type="text/javascript"> jQuery(document).ready(function(){ jQuery('table.oldService>tbody tr').not(':first').not(':last').click(function(){ if(confirm('want to delete!')){ jQuery(jQuery(this).addClass('del').fadeTo(400, 0, function() { jQuery(this).remove()})); jQuery.get('deleteService.php', {id:jQuery(this).attr('id')}); } else return false;}); }); </script> this is working perfect,but it execute by click on that row( means any td), i want that this event only occour when user click on X(third td) . please suggest me how to modify this jquery so that the event occur on click of X.

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