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(sql2008) t-sql Concurrency question

Posted By:      Posted Date: September 18, 2010    Points: 0   Category :Sql Server
We have a table containing a single row, single column (bigint)  “counter” value (1,2,3,4…). We created a stored proc,  uspGetSetCounter,  that returns the  current value of the counter and increments the value of the counter in the table by 1  (ready for the next proc call.) I setup two Query editor sessions both pointing to the database containing our single row, single column table. Each query window contained a loop that called “uspGetSetCounter” 50,000 times.  I began running the loop in the first query editor then immediately started the loop in the second query window. I found that repeated values of “counter” were sometimes returned in the output window using this approach. I also found that by surrounding the “GetSetCounter” logic in uspGetSetCounter with  “begin transaction….commit” that the problem disappeared. (In other words, each call to the proc returned an incremented  single value. This was the behavior we wanted.) Why does adding the begin transaction… logic fix the issue? (Does the first call, in a transaction, block all other calls until the first call is finished?)   TIA, Barkingdog      

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