Direct-path insert

Direct-path insert is an Oracle write mode that bypasses the buffer cache and places data directly into datafiles, above the segment’s high-water mark. It is activated via the /*+ APPEND */ hint on an INSERT statement and is typically used in bulk loading operations to reduce I/O overhead and the volume of redo generated.

How it works #

During a Direct-path insert, Oracle does not look for free blocks within the existing segment: it allocates new space beyond the high-water mark and writes directly to disk, skipping the buffer pool entirely. Redo generation is minimal (or zero in NOLOGGING mode), making the operation significantly faster than a conventional insert on large datasets.

INSERT /*+ APPEND */ INTO target_table
SELECT * FROM source_table;
COMMIT;

Until the COMMIT, the table is locked for writes by other sessions: no other process can insert rows into the same table during the transaction.

When to use it and limitations #

Direct-path insert is suited for ETL pipelines, bulk loads, and staging table population. It comes with several operational restrictions worth noting:

• Integrity constraints: CHECK and NOT NULL constraints are enforced, but foreign key constraints may need to be disabled or deferred to preserve performance.
• Triggers: BEFORE/AFTER INSERT ROW triggers are not fired in direct-path mode.
• Assertions (Oracle 23ai+): behavior with Assertions must be verified case by case, as the validation mechanism differs from that of a conventional insert.

In environments where Assertions are active, explicit testing is required before adopting Direct-path insert in production.