ics321-20091110-transaction2

ics321-20091110-transaction2 - ICS 321 Fall 2009 Overview...

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ICS 321 Fall 2009 Overview of Transaction Management (ii) Asst. Prof. Lipyeow Lim Information & Computer Science Department University of Hawaii at Manoa 11/10/2009 1 Lipyeow Lim -- University of Hawaii at Manoa
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Transactions in SQL After connection to a database, a transaction is automatically started Different connections -> different transactions Within a connection, a transaction is ended by COMMIT or COMMIT WORK ROLLBACK (= “abort”) SAVEPOINT <savepoint name> ROLLBACK TO SAVEPOINT <savepoint name> Locks obtained after savepoint can be released after rollback to that savepoint Using savepoints vs sequence of transactions Transaction rollback is to last transaction only 11/10/2009 Lipyeow Lim -- University of Hawaii at Manoa 2
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Lock Granularity What should the DBMS lock ? Row ? Page ? A Table ? 11/10/2009 Lipyeow Lim -- University of Hawaii at Manoa 3 UPDATE Sailors SET rating=0 WHERE rating>9 UPDATE Boats SET color=‘red’ WHERE bid=13 SELECT * FROM Sailors SELECT * FROM Sailors WHERE rating < 2 UPDATE Boats SET color=‘blue’ WHERE bid=100
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