Blockchain Tables: What’s New in Oracle 23ai

Oracle introduced Blockchain Tables in Oracle 21c — append-only, tamper-evident tables where rows cannot be modified or deleted (until a configurable retention period expires). Oracle 23ai adds several enhancements to this feature.

Quick recap of Blockchain Tables:

CREATE BLOCKCHAIN TABLE audit_records (
    record_id     NUMBER,
    event_time    TIMESTAMP,
    user_name     VARCHAR2(100),
    action        VARCHAR2(500)
)
NO DROP UNTIL 365 DAYS IDLE   -- can't drop while rows exist within 365 days
NO DELETE UNTIL 90 DAYS AFTER INSERT  -- rows immutable for 90 days
HASHING USING "SHA2_512" VERSION "v1";

Each row includes a cryptographic hash of the previous row, forming a chain. Any attempt to modify historical data breaks the chain and is detectable.

Oracle 23ai: Immutable Tables

23ai also introduces Immutable Tables — a lighter-weight alternative to blockchain tables that provides tamper protection without the full cryptographic chaining overhead:

CREATE IMMUTABLE TABLE compliance_log (
    log_id    NUMBER,
    log_time  TIMESTAMP,
    log_msg   VARCHAR2(4000)
)
NO DROP UNTIL 180 DAYS IDLE
NO DELETE UNTIL 60 DAYS AFTER INSERT;

Key difference: Immutable Tables don’t maintain a hash chain — rows can’t be modified or deleted within the retention window, but the tamper detection mechanism is Oracle’s internal row-change tracking rather than cryptographic chaining. Simpler, lower overhead, still compliant for most audit requirements.

23ai Blockchain enhancements:

• Counter-signing support for third-party verification
• Improved DBMS_BLOCKCHAIN_TABLE.VERIFY_ROWS performance
• Integration with Oracle’s SQL Firewall for combined protection

For regulatory compliance, financial audit trails, and healthcare record retention, these features provide database-level immutability without external blockchain infrastructure.