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.
Field notes
The blog
Practical, vendor-neutral Oracle engineering — 35 guides, 33 with the lab numbers up front. Every claim is reproducible on Oracle Database Free.
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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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Your Oracle Traffic Is Readable on the Wire. Here's the Proof, and the Fix.
Lab With default settings, a packet capture shows the SQL and the secret in plain text. With encryption REQUIRED on the server, it shows neither.
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The Migration Completed Successfully. Half the Names Are Now Question Marks.
Lab Every migration 'succeeded' with 10 rows and 0 errors. Only the Unicode target kept every name intact.
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ORA-00257: The Database Stopped Accepting Writes. The Archiver Is Stuck.
Lab A too-small recovery area locked every non-SYSDBA user out with ORA-00257. Backing up and deleting the archived logs through RMAN brought writes back.
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ORA-01555 Snapshot Too Old: Reproduce It, Then Make It Impossible
Lab Same query, same DML churn: on a tiny unguaranteed undo tablespace it died after 1 row; with RETENTION GUARANTEE it read all 20,000.
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Bind Variables: The Hard-Parse Storm That Melts Your Shared Pool
Lab The same query run 1,000 times: literals made 1,000 cursors and ~38 MB of shared pool; one bind variable made 1 cursor and ~39 KB.
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Oracle Indexes: When They Help, When They Hurt, and How to Tell
Lab The same index makes a query for a rare value more than 1,000× cheaper, and makes a query for a common value worse.
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Oracle Privilege Analysis: You Granted DBA. Here's What They Actually Used.
Lab Privilege Analysis showed the account used 3 of the 12 privileges it was granted, and none of the ANY privileges.
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Oracle Virtual Private Database: Row-Level Security You Can't Route Around
Lab One ORDERS table, three readers, three different answers, enforced inside the database, not in the app.
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Oracle Data Pump, Done Right: A Migration You Can Prove
Lab Counted, not assumed: the export and re-import brought back exactly the same 5,000 + 20,000 rows.
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Oracle Partition Pruning: Read One Partition, Not the Whole Table
Lab Both queries return the same 50,000 rows. Wrapping the partition key in TO_CHAR made Oracle read every partition instead of one.
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Oracle Data Redaction: Mask at Read Time, Prove It Isn't Access Control
Lab The clerk saw ****-****-****-0001, but the real card prefix was still in the datafile 161 times. Redaction masks the query, not the disk.
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Oracle Flashback: Undo at the Database Level
Lab Three disasters, each undone without restoring a backup.
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Oracle Transparent Data Encryption: Prove the Datafile Is Unreadable
Lab The same canary rows, read straight off disk: 133 hits in the ordinary datafile, none in the TDE-encrypted one.
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Oracle SQL Plan Management: Stop a Good Plan From Going Bad
Lab A routine stats change flipped a good index plan to a full scan. An accepted SQL plan baseline held the good plan.
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Oracle Optimizer Statistics, Demystified
Lab Without a column group the optimizer expected 200 rows, got 10,000, and chose a nested loop. With one on (make, model) it estimated 10,000 and switched to a hash join.
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Oracle Execution Plans, Decoded: The One Number That Matters
Lab The optimizer expected 500K rows and got 500. Fixing the estimate turned a full scan into an index plan.
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Oracle Unified Auditing Without the Noise
Lab 3 events triggered, 3 captured: after a flush, UNIFIED_AUDIT_TRAIL held the failed login, the new user and the read of the sensitive table.
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The Oracle Hardening Checklist That Actually Matters
Lab A deliberately weak database, scored against the checklist, then hardened until every check flipped from FAIL to PASS.
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OCI vs Oracle Database@Azure: Where Should Your Oracle Database Live?
Lab The same chatty workload went from 868 ms to 12,101 ms as injected latency rose from 0 to 10 ms. The batched version took 274 ms even at 10 ms.
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Oracle RMAN Recovery Runbook: Restore, Recover, Prove It
Lab One throwaway database, broken three ways: a deleted datafile, a corrupted block, and a committed bad DELETE. RMAN brought the data back every time.
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Your First Oracle Autonomous Database on OCI Always Free
Lab Asked for the rows most similar to 'cat', VECTOR_DISTANCE put 'kitten' closest and 'airplane' farthest, on Oracle Database Free with no OCI account.
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Oracle Patching, Demystified: CPU, RU, RUR — and What Changed in 2026
Lab Only one of the transcripts is actually done: opatch, version_full and DBA_REGISTRY_SQLPATCH all agree on 19.27 with SUCCESS.
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Migrating Oracle to the Cloud: Which Method, and When
Lab In all six scenarios, the method followed from four checks: the target, the endian or version boundary, the downtime budget, and the edition.
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ORA-00060 Deadlock: Find It, Fix It, Prevent It
Lab Two sessions locking the same two rows in opposite order raised ORA-00060 in one of them. The same work in a consistent lock order committed cleanly.
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Oracle Wait Events, Decoded: The Half-Dozen
Lab Each drill moved its own wait event: 730 single-block reads, 358 multi-block reads, 342 direct path reads, and 10,017 log file syncs for 10,000 commits sent one at a time.
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Data Guard Switchover vs Failover: Which Role Transition, and When
Switchover is a planned zero-loss role swap; failover is for when the primary is gone — plus Fast-Start Failover, protection modes, and the mistakes to avoid.
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RAC Node Eviction: A Troubleshooting Checklist That Starts With "Why"
Oracle RAC node eviction from the logs up: the three heartbeats, misscount vs disktimeout, split-brain and voting disks, and a checklist to find the real cause.
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How to Read an AWR Report Without Drowning
Lab DB CPU topped both reports. Even in the I/O drill, at 42,985.5 physical reads per second, direct path read was only 2.2% of DB time on fast local disk.
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The Oracle HA Decision Tree: RAC vs Data Guard vs Both
Lab A committed DELETE and a DROP TABLE are exactly what a standby would replicate. Flashback got all 1,000 rows back locally, with no standby involved.