Oracle Exadata Write-Back Flash Cache

Understanding How Exadata Accelerates Write Performance

What is Exadata Smart Flash Cache?

Oracle Exadata Storage Servers include high-performance flash storage that sits between the database server and traditional spinning disks. This flash layer acts as a cache to accelerate database read and write operations.

Smart Flash Cache improves performance by reducing disk I/O and serving frequently accessed data from flash memory.

Flash Cache Modes

1️⃣ Write-Through Mode (Default)

In Write-Through mode, writes go directly to disk first. Flash cache stores a copy only after disk write completes. This provides safety but no write latency improvement.

2️⃣ Write-Back Mode (Performance Mode)

In Write-Back mode, writes are sent to flash first. The write is acknowledged immediately, and data is written to disk later asynchronously. This significantly improves write performance.

Write-Through vs Write-Back Comparison

Feature	Write-Through	Write-Back
Write Latency	No Improvement	Significantly Faster
Disk I/O	All Writes Go to Disk	Writes Absorbed by Flash
Best For	General Workloads	Heavy OLTP Workloads
Risk Level	Very Safe	Managed via Mirroring

How Write-Back Improves Performance

When using Write-Back Flash Cache:

• Write operations complete faster
• Disk I/O is reduced
• Multiple updates to the same block are optimized
• Commit latency decreases significantly

In heavy OLTP systems, Write-Back Flash Cache can dramatically improve transaction throughput.

When Should You Use Write-Back?

Write-Back Flash Cache is ideal for:

• High write-intensive OLTP systems
• Applications with frequent updates
• Systems experiencing high disk latency
• Heavy commit activity environments

Final Thoughts

Oracle Exadata’s Write-Back Flash Cache is a powerful feature designed to optimize write-intensive workloads. While Write-Through provides safety, Write-Back delivers performance gains that can significantly boost database efficiency when configured properly.