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ORA-12528: TNS: listener: all appropriate instances are blocking new connections

What it means

The instance is mounted/restricted or starting.

How to fix it

Wait for the database to open or check restricted mode.

Catch it before it runs

ORA Error Helper
Explains ORA-/PLS- codes inside JetBrains IDEs and DataGrip.
PL/SQL Lint
Flags risky PL/SQL patterns while you type.
Oracle Plan Reader
Reads execution plans and points at the slow step.
PL/SQL in Practice
Kindle book with practical PL/SQL for working developers.

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Updated 2026-11-12.