Getting Started with DB2 Express-C

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234 Getting Started with DB2 Express-C db2 rollback Close the window Part 2: Testing currently committed (CC) and uncommitted read (UR) levels Procedure 1: Analyze the behavior of isolation CS without currently committed 1. Open a DB2 Command Window and issue the following statements: db2 connect to sample db2 select * from staff Inspect the contents of table STAFF, specifically look for ID value of '10'. The corresponding NAME column has a value of Sanders. Close the window. 2. Currently committed is the default for new databases. Verify it is in fact turned on for database sample: db2 get db cfg for sample Look for the line close to the end of the output that says: Currently Committed (CUR_COMMIT) = ON If the value is ON, turn it OFF first so we can analyze the behavior of isolation CS as it would be prior to DB2 9.7: db2 update db cfg for sample using CUR_COMMIT off db2 force applications all Adding the force option ensures that there are no connections so the update to CUR_COMMIT will take effect on the next connection) Confirm CUR_COMMIT is disabled. It should say: Currently Committed (CUR_COMMIT) = DISABLED 3. Open two DB2 Command Windows as in part 1, so one is on top of the other. Let's see how isolation CS works without currently committed, when an update (writer) and a select (reader) have an interest on the same row. Note we don't need to put "WITH CS" after the statements (as this is the default). From DB2 Command window #1 (this is the writer): db2 connect to sample db2 +c update staff set name = 'Chong' where id = 10 From DB2 Command window #2 (this is the reader): db2 connect to sample db2 +c select * from staff
Chapter 13 – Concurrency and Locking 235 This SELECT hangs waiting for the exclusive (X) lock to be released by the DB2 Command Window #1 application. As you can see, the default behavior of CS prior to DB2 9.7 allows for less concurrency From DB2 Command window #2: CTRL-C (press these keys to interrupt) Close the window From DB2 Command window #1: db2 rollback Close the window Procedure 2: Analyze the behavior of isolation CS with currently committed 1. Turn currently committed to ON: Open a DB2 Command Window and issue: db2 update db cfg for sample using CUR_COMMIT on db2 force applications all Close the window. 2. Open two DB2 Command Windows as in part 1 so one is on top of the other. Then issue the following: From DB2 Command window #1: db2 connect to sample db2 +c update staff set name = 'Chong' where id = 10 From DB2 Command window #2: db2 connect to sample db2 +c select * from staff Now this SELECT statement works! .It does not hang, and the value displayed is Sanders, which is the currently committed value. From DB2 Command window #1: db2 rollback Close the window.
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GETTING STARTED WITH DB2 Express-C
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Contents About this book ..........
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Contents 7 6.3 DB2 storage model ..
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Contents 9 13.4.2 Cursor stability
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About this book Notices and tradema
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About this Book 13 A book for the c
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About this Book 15 Foreword Innovat
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1 Chapter 1 - What is DB2 Express-C
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Chapter 1 - What is DB2 Express-C?
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1.8 Moving up to another DB2 editio
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4 Chapter 4 - DB2 Environment The D
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Chapter 4 - DB2 Environment 69 conf
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Chapter 4 - DB2 Environment 73 Tabl
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8 Chapter 8 - Working with Database
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Getting started with DB2 9.7 couldn
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