ORA-12514: The Database Is Up. The Listener Just Doesn't Know It.
Lab Restarting the listener, the usual first reaction, caused a minute of ORA-12514 for every service. ALTER SYSTEM REGISTER closed it at once.
Oracle reliability & performance engineering
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ORA-01017 After a Password Change: Rotate It With Zero Downtime
Why changing an application account's password causes ORA-01017 and then ORA-28000 for every app server, including the ones that already have the new password, and how gradual password rollover (PASSWORD_ROLLOVER_TIME, 19.12 and later) lets the old and new password both work. With a lab: 6 of 6 old-password logins refused and the account locked, versus 0 of 7 with rollover, and the audit query that shows who is still on the old password.
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ORA-01652: Unable to Extend Temp Segment. Don't Just Add Space.
Lab 10x the TEMP bought 10x the runtime and the same error. Restoring one join predicate made the report need none.
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Checkpoint Not Complete: Every Commit Waits, and the SQL Is Fine
Lab The same 100,000-row update spent 11.9 of its 14.1 seconds waiting for a redo log. Bigger logs: 1.9 seconds, zero waits.
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Same SQL, Fast for One Value, Slow for Another
Lab The first bind value decided the plan for everyone. The common value inherited a nested-loops plan at 17 times the work, five runs in a row, and adaptive cursor sharing never stepped in.
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Cutover Went Perfectly. The First New Order Failed With ORA-00001.
Lab Row counts matched 10,000 to 10,000, and the first new order still failed: the target sequence was handing out 9,001 while the table already went up to 10,000.
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You Deleted 99% of the Rows. The Full Scan Didn't Get Any Faster.
Lab Deleting 99% of the rows didn't change the full scan's cost at all. SHRINK SPACE cut it 95-fold.
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