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| oracle_locking_latches_mutexes [2020/10/19 07:30] – 86.49.253.137 | oracle_locking_latches_mutexes [2021/01/07 18:48] (current) – [Enqueues] andonovj | ||
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| ======Overview====== | ======Overview====== | ||
| - | have all heard that Oracle has a great Locking mechanism, way superior than other databases. | + | We have all heard that Oracle has a great Locking mechanism, way superior than other databases. |
| While in different databases, readers can block writers and writers can block readers, Oracle doesn' | While in different databases, readers can block writers and writers can block readers, Oracle doesn' | ||
| In oracle you can select without a problem (although there is an exception to that rule) and you can write without being afraid that someone is selecting your data. | In oracle you can select without a problem (although there is an exception to that rule) and you can write without being afraid that someone is selecting your data. | ||
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| =====Enqueues===== | =====Enqueues===== | ||
| + | Enqueues are your standard locks and they come in several tyes: | ||
| + | |||
| + | * TX: Transaction lock: | ||
| + | * * mode 6: data modification, | ||
| + | * * mode 4: setting tablespace to read only, foreign key enforcement, | ||
| + | * TM: Table modification (or locking a referenced table when the foreign key is not indexed) | ||
| + | * UL: Lock used by user applications, | ||
| + | * CF: Control file: actions accessing the control file, like: log switch, redo archiving, and backup | ||
| + | * ST: Space Transaction: | ||
| + | * TT: Temporary tablespace: parallel tablespace operations | ||
| + | * CI: Cross-instance: | ||
| + | * HV: Parallel direct-path insert | ||