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Transactions

Transactions . Concurrency Control. Improved lock-based concurrency with multiple writes. Update Locks. Shared & Exclusive Locks. An Example. 11 steps. Upgrading Locks. Use Shared Locks when reading Upgrade (if possible) to Exclusive Lock when just before writing

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Transactions

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  1. Transactions Concurrency Control

  2. Improved lock-based concurrency with multiple writes Update Locks

  3. Shared & Exclusive Locks

  4. An Example 11 steps

  5. Upgrading Locks • Use Shared Locks when reading • Upgrade (if possible) to Exclusive Lock when just before writing • Block if upgrade is denied.

  6. Upgrading Locks 9 steps!

  7. Deadlocks A new lock called the Update Lock (UL). Similar to a Shared Lock except only UL can be upgraded. Not symmetrical!

  8. Example

  9. Improved lock-based concurrency with hierarchical data Hierarchical locking

  10. Multiple Granularities • Relations • Blocks • Tuples

  11. Intention Locks • Represented as IS for intention to share a descendant, and IX for intention to write a descendant. • Acquire an intention lock on the parentbefore acquiring any lock on a child.

  12. Rules • Intention-lock the parents before using SL or XL on an element. • If at the element to lock, request a lock.

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