How is Memory Utilization calculated for AIX server?

How is Memory Utilization calculated for AIX server?

AIX uses free memory as file cache to improve performance. Because of this, memory usage can look very high even when the server is healthy.

Applications Manager provides two calculation methods so customers can choose what they want to monitor:

  • Default method (Recommended) → Shows actual application memory usage (excludes file cache)

  • Alternate method → Shows total memory usage including file cache

👉 Recommendation: Use the default method unless you specifically want to monitor file cache usage.

How Applications Manager Collects Memory Data

Applications Manager uses the following AIX command:

svmon -G

Understanding AIX Memory Behavior (Important)

  • AIX aggressively uses free memory for filesystem caching

  • Cached memory is not wasted and is automatically released when applications need memory

  • High memory usage does not always mean a problem on AIX

This is why two calculation methods exist.

Method 1: Default Calculation (Used Memory – Recommended)

What It Shows

  • Actual memory used by applications

  • Excludes file cache

  • Best indicator of real memory pressure

Sample svmon -G Output



Calculation

Physical Memory Utilization (%)

(Used / Total) × 100
= (816124 / 1957888) × 100
= 41%

Physical Memory Utilization (MB)

(Used × 4) / 1024
= 3187 MB

📌 Why multiply by 4? svmon reports memory in 4 KB pages.

Method 2: Alternate Calculation (inuse Memory)

When to Use

  • When you want to monitor total memory usage including file cache

  • Useful for capacity planning or cache analysis

⚠️ This method can show 90%+ usage even on healthy systems.

Sample svmon -G Output



Calculation

Physical Memory Utilization (%)

(inuse / Total) × 100
= (1828402 / 1957888) × 100
= 93%

Physical Memory Utilization (MB)

(inuse × 4) / 1024
= 7142 MB

Comparison at a Glance

Method

Includes File Cache

Typical Usage

Recommendation

Default (Used)

❌ No

Daily monitoring

⭐ Recommended

Alternate (inuse)

✅ Yes

Cache / capacity analysis

Optional

How to Switch Calculation Method

Enable Alternate (inuse) Method

  1. Connect to your Applications Manager database (Go to Settings tab > Tools > Support > Database Summary > Query Tool)

      2. Execute the following Query:

Quoteinsert into am_globalconfig values ('am.servers.aix.physicalmem.memory.inuse','true)';

      3. Restart Applications Manager after making the change.

To switch back to the default method, set the value to 'false' or remove the entry from the table.

Swap Memory Calculation

Swap values are taken from the pg space section of svmon -G.


Swap Utilization (%)

(4939 / 131072) × 100 = 3%

Swap Utilization (MB)

(4939 × 4) / 1024 = 19 MB

Troubleshooting High Memory Usage

If Default Method Shows High Usage (90%+)

  • Indicates real memory pressure

  • Check top memory-consuming processes:

            svmon -P -t 10

  • Review recent application changes

  • Consider memory tuning or upgrade

If Only Alternate Method Shows High Usage

  • This is normal AIX file cache behavior

  • Compare Used vs inuse values

  • Large difference = healthy cache usage

✅ High memory usage on AIX is not always a problem

For accurate monitoring and fewer false alerts, use the default calculation method unless you explicitly need cache visibility.