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What Is The Difference Between Truncate And Delete? Why Is One Faster? Can We Rollback Both? How Would A Full Table Scan Behave After? |
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Answer» TRUNCATE is nearly instantaenous, cannot be rolled back, and is FAST because Oracle simply RESETS the HWM. When a full table scan is performed on a table, such as for a sort operation, Oracle reads to the HWM. So if you delete every single solitary ROW in 10 million row table so it is now empty, sorting on that table of 0 rows would still be extremely SLOW. Truncate is nearly instantaenous, cannot be rolled back, and is fast because Oracle simply resets the HWM. When a full table scan is performed on a table, such as for a sort operation, Oracle reads to the HWM. So if you delete every single solitary row in 10 million row table so it is now empty, sorting on that table of 0 rows would still be extremely slow. |
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