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  • Is READ UNCOMMITTED / NOLOCK safe in this situation?

    - by Ben Challenor
    I know that snapshot isolation would fix this problem, but I'm wondering if NOLOCK is safe in this specific case so that I can avoid the overhead. I have a table that looks something like this: drop table Data create table Data ( Id BIGINT NOT NULL, Date BIGINT NOT NULL, Value BIGINT, constraint Cx primary key (Date, Id) ) create nonclustered index Ix on Data (Id, Date) There are no updates to the table, ever. Deletes can occur but they should never contend with the SELECT because they affect the other, older end of the table. Inserts are regular and page splits to the (Id, Date) index are extremely common. I have a deadlock situation between a standard INSERT and a SELECT that looks like this: select top 1 Date, Value from Data where Id = @p0 order by Date desc because the INSERT acquires a lock on Cx (Date, Id; Value) and then Ix (Id, Date), but the SELECT acquires a lock on Ix (Id, Date) and then Cx (Date, Id; Value). This is because the SELECT first seeks on Ix and then joins to a seek on Cx. Swapping the clustered and non-clustered index would break this cycle, but it is not an acceptable solution because it would introduce cycles with other (more complex) SELECTs. If I add NOLOCK to the SELECT, can it go wrong in this case? Can it return: More than one row, even though I asked for TOP 1? No rows, even though one exists and has been committed? Worst of all, a row that doesn't satisfy the WHERE clause? I've done a lot of reading about this online, but the only reproductions of over- or under-count anomalies I've seen (one, two) involve a scan. This involves only seeks. Jeff Atwood has a post about using NOLOCK that generated a good discussion. I was particularly interested in a comment by Rick Townsend: Secondly, if you read dirty data, the risk you run is of reading the entirely wrong row. For example, if your select reads an index to find your row, then the update changes the location of the rows (e.g.: due to a page split or an update to the clustered index), when your select goes to read the actual data row, it's either no longer there, or a different row altogether! Is this possible with inserts only, and no updates? If so, then I guess even my seeks on an insert-only table could be dangerous. Update: I'm trying to figure out how snapshot isolation works. It seems to be row-based, where transactions read the table (with no shared lock!), find the row they are interested in, and then see if they need to get an old version of the row from the version store in tempdb. But in my case, no row will have more than one version, so the version store seems rather pointless. And if the row was found with no shared lock, how is it different to just using NOLOCK?

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  • Validating against a Schema with JAXB

    - by fwgx
    I've been looking for solutions to this problem for far too long considering how easy it sounds so I've come for some help. I have an XML Schema which I have used with xjc to create my JAXB binding. This works fine when the XML is well formed. Unfortunately it also doesn't complain when the XML is not well formed. I cannot figure out how to do proper full validation against the schema when I try to unmarshall an XML file. I have managed to use a ValidationEventCollector to handle events, which works for XML parsing errors such as mismatched tags but doesn't raise any events when there is a tag that is required but is completely absent. From what I have seen validation can be done againsta schema, but you must know the path to the schema in order to pass it into the setSchema() method. The problem I have is that the path to the schema is stored in the XML header and I can't knwo at run time where the schema is going to be. Which is why it's stored in the XML file: <?xml version="1.0" encoding="utf-8"?> <DDSSettings xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="/a/big/long/path/to/a/schema/file/DDSSettings.xsd"> <Field1>1</Field1> <Field2>-1</Field2> ...etc Every example I see uses setValidating(true), which is now deprecated, so throws an exception. This is the Java code I have so far, which seems to only do XML validation, not schema validation: try { JAXBContext jc = new JAXBContext() { private final JAXBContext jaxbContext = JAXBContext.newInstance("blah"); @Override public Unmarshaller createUnmarshaller() throws JAXBException { Unmarshaller unmarshaller = jaxbContext.createUnmarshaller(); ValidationEventCollector vec = new ValidationEventCollector() { @Override public boolean handleEvent(ValidationEvent event) throws RuntimeException { ValidationEventLocator vel = event.getLocator(); if (event.getSeverity() == event.ERROR || event.getSeverity() == event.FATAL_ERROR) { String error = "XML Validation Exception: " + event.getMessage() + " at row: " + vel.getLineNumber() + " column: " + vel.getColumnNumber(); System.out.println(error); } m_unmarshallingOk = false; return false; } }; unmarshaller.setEventHandler(vec); return unmarshaller; } @Override public Marshaller createMarshaller() throws JAXBException { throw new UnsupportedOperationException("Not supported yet."); } @Override @SuppressWarnings("deprecation") public Validator createValidator() throws JAXBException { throw new UnsupportedOperationException("Not supported yet."); } }; Unmarshaller unmarshaller = jc.createUnmarshaller(); m_ddsSettings = (com.ultra.DDSSettings)unmarshaller.unmarshal(new File(xmlfileName)); } catch (UnmarshalException ex) { Logger.getLogger(UniversalDomainParticipant.class.getName()).log( Level.SEVERE, null, ex); } catch (JAXBException ex) { Logger.getLogger(UniversalDomainParticipant.class.getName()).log( Level.SEVERE, null, ex); } So what is the proper way to do this validation? I was expecting there to be a validate() method on the JAXB generated classes, but I guess that would be too simple for Java.

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  • SQl function in android

    - by rui.pereira
    Cursor cursor = db.rawQuery("SELECT COUNT(rat) FROM "+ TABLE_NAME_EXTRA +" apkid=\""+apkid, null); cursor.moveToFirst(); int somatotal = cursor.getInt(0); I'm trying to do a SQL function like count and sum, but this code returns a exception saying "emptyvalues". anyone know why?

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  • Merging exists and not exists into one query - oracle magic

    - by stic
    Hi, In a WHERE part of query we have SELECT * FROM SomeTable st WHERE NOT EXISTS (SELECT 1 FROM Tab t1 WHERE t1.A = st.A OR t1.B = st.A) OR EXISTS (SELECT 1 FROM Tab t2 WHERE (t2.A = st.A OR t2.B = st.A) AND t2.C IS NULL) Seems like a good candidate for merging... But I'm staring on that for an hour without any idea. Would you have some thoughts? Thanks,

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  • Protobuf-net Deserialize Open Street Maps

    - by jonperl
    For the life of me I cannot deserialize the protobuf file from Open Street Maps. I am trying to deserialize the following extract: http://download.geofabrik.de/osm/north-america/us-northeast.osm.pbf to get Nodes and I am using http://code.google.com/p/protobuf-net/ as the library. I have tried to deserialize a bunch of different objects but they all come up null. The proto files can be found here: http://trac.openstreetmap.org/browser/applications/utils/export/osm2pgsql/protobuf Any suggestions?

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  • ALTER TABLE error

    - by Travis
    Can someone explain to me why I am receiving the following error? I want to rename the column "exerciseID" to "ID" in a mysql table using the following syntax. ALTER TABLE `exercises` CHANGE `exerciseID` `ID` INT( 11 ) NOT NULL AUTO_INCREMENT However I receive the following error: MySQL said: #1025 - Error on rename of './balance/#sql-de_110e' to './balance/exercises' (errno: 150) Any suggestions would be much appreciated

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  • Getting MySQL record count with C#

    - by she hates me
    Hello, I would like to know how can I get record count of a query with C#. Here is the code that I use.. MySqlDataReader recordset = null; query = new MySqlCommand("SELECT * FROM test ORDER BY type_ID ASC", this.conn); recordset = query.ExecuteReader(); while (recordset.Read()) { result.Add(recordset["type_ID"].ToString()); } return result;

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  • Pass variables to current tab via chrome extension

    - by iamthejeff
    I am writing my first chrome extension, and I want to pass a variable to the currently opened tab and manipulate the DOM with it. My extension has a button, and when clicked, is executing this code: chrome.tabs.getSelected(null, function(tab) { chrome.tabs.executeScript(tab.id, { file: 'tabscript.js' }); }); This works fine, but I see no way to pass a variable to tabscript.js so it can be used on the opened tab.

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  • Using c# System.DateTime like c++ time_t

    - by David Boland
    In C++ I am able to get the current time when my application starts I can use time_t appStartTime = time(null); then to find the difference in seconds from when it started I can just do the same thing, then find the difference. It looks like I should be using "System.DateTime" in C# net, but the MSDN is confusing in its explanation. How can I use System.DateTime to find the difference in time (in seconds) between when my application starts, and the current time?

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  • Retrieve names of running processes

    - by Dave DeLong
    Hi everyone, First off, I know that similar questions have been asked, but the answers provided haven't been very helpful so far (they all recommend one of the following options). I have a user application that needs to determine if a particular process is running. Here's what I know about the process: The name The user (root) It should already be running, since it's a LaunchDaemon, which means Its parent process should be launchd (pid 1) I've tried several ways to get this, but none have worked so far. Here's what I've tried: Running ps and parsing the output. This works, but it's slow (fork/exec is expensive), and I'd like this to be as fast as possible. Using the GetBSDProcessList function listed here. This also works, but the way in which they say to retrieve the process name (accessing kp_proc.p_comm from each kinfo_proc structure) is flawed. The resulting char* only contains the first 16 characters of the process name, which can be seen in the definition of the kp_proc structure: #define MAXCOMLEN 16 //defined in param.h struct extern_proc { //defined in proc.h ...snip... char p_comm[MAXCOMLEN+1]; ...snip... }; Using libProc.h to retrieve process information: pid_t pids[1024]; int numberOfProcesses = proc_listpids(PROC_ALL_PIDS, 0, NULL, 0); proc_listpids(PROC_ALL_PIDS, 0, pids, sizeof(pids)); for (int i = 0; i < numberOfProcesses; ++i) { if (pids[i] == 0) { continue; } char name[1024]; proc_name(pids[i], name, sizeof(name)); printf("Found process: %s\n", name); } This works, except it has the same flaw as GetBSDProcessList. Only the first portion of the process name is returned. Using the ProcessManager function in Carbon: ProcessSerialNumber psn; psn.lowLongOfPSN = kNoProcess; psn.highLongOfPSN = 0; while (GetNextProcess(&psn) == noErr) { CFStringRef procName = NULL; if (CopyProcessName(&psn, &procName) == noErr) { NSLog(@"Found process: %@", (NSString *)procName); } CFRelease(procName); } This does not work. It only returns process that are registered with the WindowServer (or something like that). In other words, it only returns apps with UIs, and only for the current user. I can't use -[NSWorkspace launchedApplications], since this must be 10.5-compatible. In addition, this only returns information about applications that appear in the Dock for the current user. I know that it's possible to retrieve the name of running processes (since ps can do it), but the question is "Can I do it without forking and exec'ing ps?". Any suggestions?

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  • KVO on the "windows" value of UIApplication?

    - by Ariel Malka
    The following is not working: [[UIApplication sharedApplication] addObserver:self forKeyPath:@"windows" options:(NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld) context:NULL]; Together with that, on the Observer side: - (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { NSLog(@"never reached!"); } Any clues? N.B. My uber-goal is to get a notification when a (system-generated) UIAlertView is shown.

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  • Rewriting URLs with mod_rewrite

    - by Webby
    Hey guys, I'm currently rewriting urls from http://domain.com/profile/?u=10000017564881 this to this http://domain.com/profile/10000017564881 with the following rewrite RewriteEngine On RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteRule ^(.*?)\/?$ index.php?u=$1 [L] However I'd like to optimize for seo a litte and go with : http://domain.com/profile/10000017564881/Anything-I-want-here Obviously the /Anything-I-want-here is just null ignored ... Any idea's guys? much appreciated

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  • Order SimpleXMLElement by element

    - by ron
    Hi everyone I need to order a SimpleXMLElement by a node called padre like this. $xml = new SimpleXMLElement('sitemap.xml',null,true); sort($xml, "padre" ); foreach($xml as $url ) { echo "loc}' title='".rescue_name($url-loc)."'".rescue_name($url-loc)." {$url-padre}"; } I don't know why is not working please let me know what is my error. Thanks in advance

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  • how to handle this type of things. using asp.net mvc

    - by kumar
    hello friends, i have public jsonresult update(studentinfo s) { for(i=0;i>0;i++) { var x = // i am getting some x so i am checking again if( x != null) { var updateuser = student.update(s.student,"",""); **return json(updateuser.ToString());** // if i keep it here i am getting exceptoin saying not all code paths return value bec this return i can not keep it out for loop bec each and evary updateuser i need to return json.. } } } how to overcome this type of things? thanks

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  • jQuery - How to dynamically add a validation rule

    - by Justin
    Hey, I'm trying to dynamically add a validation rule to some dynamic controls: $("input[id*=Hours]").rules("add", "required"); However this line gives me the following error: $.data(element.form, "validator") is null Defining rules the static way with the validate function works fine. What am I doing wrong? Thanks, Justin

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  • Return a value if no rows are found SQL

    - by Matt
    Here's my simple query. If I query a record that doesn't exist then I will get nothing returned. I'd prefer that false (0) is returned in that scenario. Looking for the simplist method to account for no records. SELECT CASE WHEN S.Id IS NOT NULL AND S.Status = 1 AND (S.WebUserId = @WebUserId OR S.AllowUploads = 1) THEN 1 ELSE 0 END AS [Value] FROM Sites S WHERE S.Id = @SiteId

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  • send sms in asp.net by gsm modem

    - by danar jabbar
    I devloped an asp.net application to send sms from gsm modem to destination base on URL from the browser I used a library that developed by codeproject http://www.codeproject.com/articles/20420/how-to-send-and-receive-sms-using-gsm-modem but I get problem when I request form two browsers at same time and I want to make the my code detect that the modem is use by another process at the time here is my code: DeviceConnection deviceConnection = new DeviceConnection(); protected void Page_Load(object sender, EventArgs e) { try { if (Request.QueryString["destination"] != null && Request.QueryString["text"] != null) { deviceConnection.setBaudRate(9600); deviceConnection.setPort(12); deviceConnection.setTimeout(200); SendSms sendSms = new SendSms(deviceConnection); if (deviceConnection.getConnectionStatus()) { sendSms.strReciverNo = Request.QueryString["destination"]; sendSms.strTextMessage = Request.QueryString["text"]; if (sendSms.sendSms()) { Response.Write("Mesage successfuly sent to " + Request.QueryString["destination"]); } else { Response.Write("Message was not sent"); } } } } catch (Exception ex) { Console.WriteLine("Index "+ex.StackTrace); } } This is SendSms class: class SendSms { DeviceConnection deviceConnection; public SendSms(DeviceConnection deviceConnection) { this.deviceConnection = deviceConnection; } private string reciverNo; private string textMessage; private delegate void SetTextCallback(string text); public string strReciverNo { set { this.reciverNo = value; } get { return this.reciverNo; } } public string strTextMessage { set { this.textMessage = value; } get { return this.textMessage; } } public bool sendSms() { try { CommSetting.Comm_Port = deviceConnection.getPort();//GsmCommMain.DefaultPortNumber; CommSetting.Comm_BaudRate = deviceConnection.getBaudRate(); CommSetting.Comm_TimeOut = deviceConnection.getTimeout();//GsmCommMain.DefaultTimeout; CommSetting.comm = new GsmCommMain(deviceConnection.getPort() , deviceConnection.getBaudRate(), deviceConnection.getTimeout()); // CommSetting.comm.PhoneConnected += new EventHandler(comm_PhoneConnected); if (!CommSetting.comm.IsOpen()) { CommSetting.comm.Open(); } SmsSubmitPdu smsSubmitPdu = new SmsSubmitPdu(strTextMessage, strReciverNo, ""); smsSubmitPdu.RequestStatusReport = true; CommSetting.comm.SendMessage(smsSubmitPdu); CommSetting.comm.Close(); return true; } catch (Exception exception) { Console.WriteLine("sendSms " + exception.StackTrace); CommSetting.comm.Close(); return false; } } public void recive(object sender, EventArgs e) { Console.WriteLine("Message received successfuly"); } } }

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  • strtok problem in calling

    - by Moony
    I have a function using strtok like this void f1(char *name) { ... char *tmp; tmp = strtok(names, " ,"); while(tmp) { ... tmp = strtok(NULL, " ,"); } ... } And i have a call f1("abc,def"); Problem is that in first call f1 gets abc,def and in 2nd call gets just abc I am confused.. Why is this so?

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  • How do I make sure no handlers are attached to an event?

    - by Edward Tanguay
    I am adding an event handler like this: theImage.MouseMove += new MouseEventHandler(theImage_MouseMove); but in my application, this code gets run every time the page is shown, so I want to attach the event handler only once, but how can I tell if a handler has been set yet or not, something like this: if(theImage.MouseMove == null) //error theImage.MouseMove += new MouseEventHandler(theImage_MouseMove);

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  • I can't Open my excel file in c#

    - by Ruben Guico
    Hi, Below is my code, i tried to open my excel file in my c# application but the program give's me an error message "Cannot Access "my excel.xls". But when I specify the file path in my string path variable it works, the problem is I need to get the file path from an openFileDialog. using System; using System.IO; using System.Collections.Generic; using System.Text; using System.Data; using System.Windows.Forms; using System.Data.OleDb; using System.Reflection; using MOIE = Microsoft.Office.Interop.Excel; using OFFICE = Microsoft.Office.Core; namespace EmpUploader { public class ExcelCon { private OleDbDataReader reader = null; private OleDbCommand excelCommand = new OleDbCommand(); private OleDbDataAdapter adapter = new OleDbDataAdapter(); private DataTable excelData = new DataTable(); private MOIE.ApplicationClass objExcel = new MOIE.ApplicationClass(); private MOIE.Workbook wb = null; private string myConn = ""; private string strSQL = ""; private string err = ""; private string path2 = ""; private int sheetCount = 0; private OleDbConnection Con = new OleDbConnection(""); #region "excel interop prarameters" private static object xl_missing = Type.Missing; private static object xl_true = true; private static object xl_false = false; private object xl_update_links = xl_missing; private object xl_read_only = xl_missing; private object xl_format = xl_missing; private object xl_password = xl_missing; private object xl_write_res_password = xl_missing; private object xl_ignore_read_only = xl_missing; private object xl_origin = xl_missing; private object xl_delimiter = xl_missing; private object xl_editable = xl_missing; private object xl_notify = xl_missing; private object xl_converter = xl_missing; private object xl_add_to_mru = xl_missing; private object xl_local = xl_missing; private object xl_corrupt_load = xl_missing; #endregion } //MY CODE FOR OPENING THE EXCEL //note that my file path came from an openfiledialog public void InitializeConnection(string path) { //connection string for excel myConn = @"Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" + path + "; Extended Properties =Excel 8.0"; Con.ConnectionString = myConn; Con.Open(); //this is the sample specified path that worked when i test my application //path = @"C:\shinetsu p5 emp list.xls"; objExcel.Visible = false; wb = objExcel.Workbooks.Open(path, xl_update_links, xl_read_only, xl_format, xl_password, xl_write_res_password, xl_ignore_read_only, xl_origin, xl_delimiter, xl_editable, xl_notify, xl_converter, xl_add_to_mru, xl_local, xl_corrupt_load); sheetCount = wb.Worksheets.Count; } }

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