Immutable Tables in Oracle Database 19c and 21c
(https://oracle-base.com/articles/21c/immutable-tables-21c)

An immutable table is a tamper-proof, insert-only table with an associated table-level and row-level retention period. They are similar to blockchain tables, but the rows are not chained using cryptographic hashes.

Blockchain tables were introduced in 21c and backported to 19.10. Immutable tables were introduced to Oracle 21.3 and 19.11 at the same time, so it could be considered a 19c and 21c new feature.

When learning about immutable tables, be careful not to set excessively long retention periods, or you will have to wait a long time to drop your test tables.

Prerequisites

• Create an Immutable Table
• Alter an Immutable Table
• Blocked DML and DDL Operations
• DBMS_IMMUTABLE_TABLE Package
• Considerations
• Related articles.

Immutable Tables in Oracle Database 19c and 21c 
Blockchain Tables in Oracle Database 21c 
Blockchain Tables in Oracle Database 21c
Prerequisites
The COMPATIBLE parameter must be set to the correct value before we can use an immutable table.

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