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I have been doing a few exercises for an exam, they dont come with answers so just looking clarification, it asks to find the errors in the table and to explain each error which 2PL principles it violates.

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I have came up with T4 at Step 14 cannot work as T1 has not released the lock it holds.

T4 at step 15 and 16 as T1 as it doesnt have the lock.

T4 at step 5 and 6 as T2 hasn't released the lock.

Is this correct

Thanks

user445714
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    T4 at 5 also attempts to lock D3 before T2 relinquishes the lock. – sarnold Jun 27 '11 at 22:35
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    T1 never releases the D1 lock, T4 never releases the D3 lock. – configurator Jun 27 '11 at 22:39
  • @sarnold and @configurator : Is it an error that `T3` unlocks at step 10 and then locks again at step 24? Doesn't that violate the growing (locking only) phase and shrinking (unlocking only) phase of the 2PL protocol? (I didn't see that mentioned as an error and so I was wondering, perhaps I don't correctly understand 2PL) – insumity Jan 04 '12 at 03:02
  • @foobar: you're probably in a better position to judge than I am -- take this table with a grain of salt, there's no indications of success / failure / blocking / etc. here, it's just a big pile of _requests_ without much in the way of consequences... – sarnold Jan 04 '12 at 03:07

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