A Comprehensive Guide to Using Huge Pages in Oracle Databases

Huge Pages in Oracle are a memory management feature that allows the operating system to handle large memory pages, typically 2 MB in size, as opposed to the default small memory pages, which are typically 4 KB in size.

By using larger memory pages, Huge Pages can significantly reduce the overhead associated with managing memory in systems with large memory demands, such as Oracle databases.

Oracle databases are known for their high memory usage due to the need to handle large datasets, extensive indexing, and caching for optimal performance.

In such environments, the default memory page size can become a bottleneck due to the large number of pages that the operating system needs to manage. This is where Huge Pages come into play.

1. Benefits of Using Huge Pages

Improved Memory Management

Huge Pages significantly enhance memory management by allocating larger memory blocks compared to the standard 4KB pages. In an Oracle database environment, this leads to reduced memory fragmentation, more efficient memory usage, and simplified memory allocation.

Reduced Page Table Overhead

With Huge Pages, the number of pages the system needs to manage is drastically reduced. For example, using 2MB Huge Pages instead of 4KB standard pages reduces the number of pages by a factor of 512, resulting in smaller page tables, less memory usage for maintaining these tables, and improved system performance.

Enhanced Performance

The use of Huge Pages can lead to significant performance improvements. Benefits include lower latency due to handling larger data blocks, increased throughput from reduced memory management overhead, optimized CPU usage, and more stable and predictable system performance.

2. Understanding Memory Pages

Standard Memory Pages vs. Huge Pages

Standard memory pages are typically 4KB in size, requiring extensive management by the operating system. Huge Pages, on the other hand, are 2MB in size, reducing the number of pages and the associated management overhead.

How Huge Pages Work in Oracle

Huge Pages allocate memory in larger blocks, which are directly used by Oracle processes. This reduces the overhead of memory allocation and improves access times, leading to better overall performance of the Oracle database.

3. Configuring Huge Pages in Oracle

Step-by-Step Guide to Configure Huge Pages on Linux

1. Checking Current Huge Pages Configuration:
   • Use commands like grep Huge /proc/meminfo to check the current Huge Pages setup.
2. Calculating Required Huge Pages:
   • Calculate the total memory required for the Oracle database and divide by 2MB to determine the number of Huge Pages needed.
3. Configuring Huge Pages on Linux:
   • Edit the system configuration file /etc/sysctl.conf to set the number of Huge Pages and related parameters.
   • Apply the changes using commands like sysctl -p.
4. Configuring Oracle Database to Use Huge Pages:
   • Modify Oracle initialization parameters (init.ora or spfile) to enable the use of Huge Pages, the parameter USE_LARGE_PAGES.
   • Restart the Oracle database to apply the changes.

Let’s do an example.

If you have a server with 160G of RAM, then the recommended hugepages would be half of that value which is 80000 in order to keep also some space for the operating system.

Then again half of that value (because each page is 2MB) which is 40000.

You’ll have to edit the file /etc/sysctl.conf as root

vm.nr_hugepages=40000

Once you set the value, it is recommended to reboot the server, but sometimes this command is enough

sysctl -p

Check the value of the hugepages

grep Huge /proc/meminfo

In addition to that, the databases on the server should have the parameter USE_LARGE_PAGES=ONLY

Here are some more examples.

For a 1 GB SGA you would require 512 huge pages.

For a 1.5 GB SGA you would require 768 huge pages.

For a 2 GB SGA you would require 1024 huge pages.

For a 5 GB SGA you would require 2560 huge pages.

For a 10 GB SGA you would require 5120 huge pages.

For a 15 GB SGA you would require 7680 huge pages.

4. FAQs About Huge Pages

Common Questions and Answers

• What are Huge Pages? Huge Pages are large memory pages (2MB each) used to improve memory management and performance.
• Why should I use Huge Pages with Oracle? Using Huge Pages reduces memory fragmentation, page table overhead, and improves database performance.
• How do I calculate the number of Huge Pages needed? Calculate the total memory required for the database and divide by 2MB to determine the number of Huge Pages.
• What if my system doesn’t support Huge Pages? Ensure your system meets the prerequisites and consult the operating system and Oracle documentation for specific requirements.

5. Conclusion

Summary of Benefits and Importance

Huge Pages offer substantial benefits for Oracle databases, including improved memory management, reduced overhead, and enhanced performance. By configuring and utilizing Huge Pages, database administrators can achieve more efficient and stable Oracle database operations.

Final Recommendations

To maximize the benefits, carefully calculate the required Huge Pages, follow best practices for configuration, and monitor system performance to make necessary adjustments.

6. Additional Resources

Further Reading and References

• Oracle Documentation on Huge Pages
• Huge Pages: In the context of Exadata