Database 26ai Installation Guide

 Database 26ai Installation Guide

In this topic, I explain two new and important steps when installing Oracle new versions as 26ai:

Setting Clock Source for VMs on Linux x86-64

Oracle recommends that you set the clock source to tsc for better performance in virtual

environments (VM) on Linux x86-64.

As the root user, check if the tsc clock source is available on your system.

# cat /sys/devices/system/clocksource/clocksource0/available_clocksource

kvm-clock tsc acpi_pm

If the tsc clock source is available, then set tsc as the current clock source.

# echo "tsc">/sys/devices/system/clocksource/clocksource0/

current_clocksource

Verify that the current clock source is set to tsc.

# cat /sys/devices/system/clocksource/clocksource0/current_clocksource

tsc

Using any text editor, append the clocksource directive to the GRUB_CMDLINE_LINUX line in

the /etc/default/grub file to retain this clock source setting even after a reboot.

GRUB_CMDLINE_LINUX="rd.lvm.lv=ol/root rd.lvm.lv=ol/swap rhgb quiet

numa=off transparent_hugepage=never clocksource=tsc"

Run the following command to update GRUB and ensure that these settings are retained

even after a reboot:

# grub2-mkconfig -o /boot/grub2/grub.cfg

Setting Transparent HugePages to madvise

Transparent HugePages memory is enabled by default with Oracle Linux. 

📕However, for optimal

performance, Oracle recommends that you set Transparent HugePages to madvise on all

Oracle Database servers UEK7 and later kernels and not disable Transparent HugePages as

was recommended in prior releases.👈

If you install Oracle Database Preinstallation RPM, then it sets Transparent HugePages to

madvise on all Oracle Database servers UEK7 and later kernels.

To set madvise on Transparent HugePages:

For Oracle Linux and Red Hat Enterprise Linux, add or modify the

transparent_hugepage=madvise parameter in the /etc/default/grub file:

GRUB_TIMEOUT=5

GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"

GRUB_DEFAULT=saved

GRUB_DISABLE_SUBMENU=true

GRUB_TERMINAL_OUTPUT="console"

GRUB_CMDLINE_LINUX="crashkernel=auto rhgb quiet

transparent_hugepage=madvise"

GRUB_DISABLE_RECOVERY="true"

Note:

The file name may vary depending on your operating system and hardware. For

example, on Oracle Cloud Infrastructure (OCI) the grub.cfg file is located at /boot/efi/EFI/redhat/. 

Check your operating system documentation for the exact file name.

Run the grub2–mkconfig command to regenerate the grub.cfg file.

On Oracle Linux 8

# grub2-mkconfig -o /boot/grub2/grub.cfg

On Oracle Linux 9

grub2-mkconfig -o /boot/grub2/grub.cfg --update-bls-cmdline

Restart the system to make the changes permanent. If you do not want to restart your

system, then enter the following command:

# echo madvise >

/sys/kernel/mm/transparent_hugepage/enabled

To check if Transparent HugePages is enabled and configured with madvise, run one of

the following commands as the root user:

Oracle Linux kernels:

# cat /sys/kernel/mm/transparent_hugepage/enabled

Red Hat Enterprise Linux kernels:

# cat /sys/kernel/mm/redhat_transparent_hugepage/enabled

The following is a sample output that shows Transparent HugePages is being used and set

to madvise.

always [madvise] never

What is THP:

Transparent HugePages (THP) is a Linux kernel feature that automates the use of large memory pages (typically 2MB instead of the standard 4KB) to improve memory management efficiency and application performance. Here’s a breakdown of what it is and why Oracle 26ai recommends setting it to `madvise`:

What Are Transparent HugePages?

Purpose: THP reduces overhead in memory management by using larger memory pages, which means fewer pages to track and manage.

Benefit: This can lead to better performance for applications with large memory footprints, like Oracle databases.

Modes:• `always`: Kernel tries to use hugepages for all memory allocations.

• `madvise`: Kernel uses hugepages only when applications explicitly request them via the `madvise()` system call.

• `never`: THP is disabled entirely.

Why Oracle 26ai Recommends `madvise` on UEK7+

Oracle previously advised disabling THP due to performance unpredictability and latency spikes. However, with improvements in UEK7 (Unbreakable Enterprise Kernel version 7) and later:

Improved THP behavior: Kernel enhancements have made THP more stable and predictable.

Selective usage: Setting THP to `madvise` allows Oracle to use hugepages only where beneficial, avoiding the downsides of `always` mode.

Oracle-aware optimization: Oracle Database components can now better manage memory and selectively request hugepages, leading to more consistent performance gains.

🧠 HugePages vs Transparent HugePages

Feature	HugePages (Static)	Transparent HugePages (THP)
Configuration	Manually configured by the system admin	Automatically managed by the kernel
Usage	Reserved explicitly for applications	Kernel tries to use them for anonymous memory
Control	Applications must be configured to use them	Kernel decides when to use them
Swapping	Not swappable (memory stays resident)	Can be swapped unless pinned
Performance	Predictable, stable for large memory apps	May cause latency spikes due to defragmentation
Best for	Oracle SGA, databases, performance-critical apps	General workloads, less admin overhead
Page Allocation	Static allocation at boot time	Dynamic allocation during runtime

What is `clocksource=tsc`?

The `clocksource=tsc` kernel parameter forces Linux to use the Time Stamp Counter (TSC) as the system clock source. Here’s what that means:

• TSC (Time Stamp Counter) is a CPU register that counts cycles since reset. It’s fast and low-overhead.

By default, Linux chooses the most stable and precise clock source available. TSC is often preferred for performance, but only if it’s invariant (i.e., unaffected by CPU frequency scaling or power-saving modes).

Using `clocksource=tsc` can improve performance in latency-sensitive environments like databases or real-time systems, especially when:

•The hardware supports invariant TSC.

• You want consistent timing across CPUs in multi-core systems.

• You’re running Oracle or other performance-critical workloads.

💡 Why use it? It minimizes overhead and improves timestamp precision, which is crucial for Oracle diagnostics and wait event analysis.

 Why install Oracle 26ai?

Oracle Database 26ai is Oracle’s AI-first long-term support release, packed with over 300 new features. Here’s why it’s worth installing:

Key Benefits:

• AI Integration at the Core: Native support for AI vector search, bringing AI directly to your data without external systems.

• Annotations & Metadata Enhancements: Easier documentation and tracking of database objects.

• Interval Aggregation: New support for `SUM` and `AVG` on `INTERVAL` datatypes.

• Autonomous Options: Can be deployed via Autonomous DB containers or free-tier cloud options.

• Future-Proofing: It’s the next long-term release after 19c, meaning extended support and stability for years.

Ideal Use Cases:

• AI-powered analytics

• High-performance transactional systems

• Cloud-native or hybrid deployments

• Modernizing legacy Oracle environments

Alireza Kamrani