Introduction

In Oracle databases, NOLOGGING is often used to minimize redo log generation for certain operations. However, many users wonder why DELETE cannot be NOLOGGING and how to efficiently remove large volumes of data without impacting performance.

Why DELETE Always Generates Redo and Undo Logs

The DELETE statement in Oracle generates redo and undo logs for the following reasons:

1. Data Integrity & Rollback Support
   • Oracle must track changes to allow transactions to be rolled back if needed.
   • Undo logs store the original values of deleted rows.
2. Redo Logs for Crash Recovery
   • Redo logs ensure that deleted data is permanently removed, even if the system crashes mid-operation.
3. Row-by-Row Processing
   • Unlike TRUNCATE, which operates at the segment level,DELETE works row-by-row, making logging necessary.

How to Efficiently Delete Large Data Volumes

1. Use TRUNCATE Instead of DELETE (If Possible)

If you need to remove all rows from a table without undo logging, use TRUNCATE TABLE table_name;

✅ Pros: Fast, minimal redo/undo logging
❌ Cons: Cannot be rolled back, does not trigger ON DELETE triggers

2. Use CTAS (Create Table As Select) and Replace the Table

For selective deletion, create a new table with only the required data TRUNCATE

CREATE TABLE new_table NOLOGGING AS SELECT * FROM table_name WHERE condition;

TREUNCATE TABLE table_name;

ALTER TABLE new_table RENAME TO table_name;

✅ Pros: Faster than DELETE, minimal redo logging
❌ Cons: Requires reapplying indexes and constraints

3. Use DELETE in Batches to Minimize Undo/Redo Logs

If DELETE is mandatory, break it into smaller batches:

DECLARE
    v_limit NUMBER := 10000;  -- Adjust batch size as needed
BEGIN
    LOOP
        DELETE FROM table_name WHERE ROWNUM <= v_limit;
        COMMIT;
        EXIT WHEN SQL%ROWCOUNT = 0;
    END LOOP;
END;
/
✅ Pros: Reduces undo/redo pressure, avoids long transactions
❌ Cons: Slower than other methods

4. Enterprise database with Partition Enabled for database delete table

If the table is partitioned, drop or truncate partitions instead of using DELETE

ALTER TABLE table_name DROP PARTITION partition_name; 
-- or ALTER TABLE table_name TRUNCATE PARTITION partition_name;


Since DELETE always generates redo logs, alternative approaches like TRUNCATE, partitioning, or CTAS should be considered for large-scale deletions. If DELETE is required, batch processing is the best option to minimize performance impact.