if we execute a update statement and a delete statement parallel in sql server 2008 having isolation level at Read committed. What will be the output -

-

if transaction having multiple select statements feteching data table , parallel query runs deleting set of records fetched in previoius transaction. result of select statement within transaction executes after delete query.

isolation level set read committed.

begin trans  select * mytable id >100 , id <1000  //while loop //some time taking operation. here parallel delete query executes   select * mytable id >100 , id <1000 //**what output of query ?**  commit trans  --------  //some other delete query delete mytable id > 500 , id <1000

since rci holds locks duration of statement it's going depend on timing. assuming order have , delete happens in rci , in own transaction first select bring of data, delete starts , other select starts. deadlock (depending) 1 of statements going locks granted first , other wait until can acquire locks. it's timing problem @ point.

if run these in tight enough loop you'll hit interesting results. if wanted more stable return value set use snapshot isolation.


Comments

Post a Comment

Popular posts from this blog

double exclamation marks in haskell -

-
i have code: ghci>let listoffuns = map (*) [0..] ghci>(listoffuns !! 4) 5 20 what !! mean? i saw example double exclamation this: ghci> [1,2,3,4]!!1 ghci> 2 but seems don't apply question example. how understand function. need explanations. !! indexes lists. takes list , index, , returns item @ index. if index out of bounds, returns ⊥.
Read more

qml - Is it possible to implement SystemTrayIcon functionality in Qt Quick application -

-
i writing qtquick desktop application. use both c++ (for functionality) , qml (for ui) in it. use qquickview show interface written in qml. i want application reside in system tray when minimised. i mean functionality similar example. http://qt-project.org/doc/qt-4.8/desktop-systray.html . trying implement feature not find way in qt quick application. here main.cpp code: #include <qguiapplication> #include <qqmlengine> #include <qqmlcontext> #include <qqmlfileselector> #include <qquickview> #include "myapp.h" int main(int argc, char* argv[]) { qguiapplication app(argc,argv); app.setapplicationname(qfileinfo(app.applicationfilepath()).basename()); qdir::setcurrent(qapp->applicationdirpath()); myapp myappobject; qquickview view; view.connect(view.engine(), signal(quit()), &app, slot(quit())); view.rootcontext()->setcontextproperty("myappobject", &myappobject); new qqmlfilese...
Read more

Qt Creator - Searching files with Locator including folder -

-
one quick question qtcreator : know possible use locator open files using "ctrl-k" shortcut. however, possible search files including locations? for example, let's want locate file named "main.cpp" in folder named "myfolder" , have lots of other main.cpp files. what should type locator in order open ? just type myfolder/main.cpp in locator
Read more