When Oracle Express Client updates the system PATH variable, IIS worker processes maintain their own environment block initialized at process creation. This explains why recycling app pools doesn't help - the worker process inherits the environment from the parent process (either IIS or the SCM).

Option 1: Taskkill the specific w3wp.exe process

REM First identify the PID of your app pool's worker process
tasklist /svc | find "w3wp"
REM Then force kill it (example for PID 1234)
taskkill /f /pid 1234

Option 2: NET STOP/START the Windows Process Activation Service

net stop was /y
net start w3svc

Create a test ASPX page to verify PATH updates:

<%@ Page Language="C#" %>
<%
    Response.Write("Current PATH: " + Environment.GetEnvironmentVariable("PATH"));
%>

For systems where even WAS restart is undesirable:

• Use absolute paths in connection strings
• Set process-level PATH in Application_Start:

  protected void Application_Start(object sender, EventArgs e)
  {
      string newPath = "your_oracle_path;" + Environment.GetEnvironmentVariable("PATH");
      Environment.SetEnvironmentVariable("PATH", newPath);
  }

For Oracle installations specifically, consider these registry-based alternatives:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE]
"ORACLE_HOME"="C:\\oracle\\product\\11.2.0\\client_1"

When Oracle Express (or similar software) modifies the Windows PATH environment variable, IIS worker processes won't automatically pick up these changes. This occurs because IIS caches environment variables at startup and maintains them throughout the process lifetime.

Standard app pool recycling only creates new worker processes - it doesn't reload system environment variables. The cached PATH from when IIS started remains active. Here's what happens internally:

w3wp.exe (Worker Process)
├─ Loads ENV variables at creation
├─ Maintains original PATH cache
└─ AppPool recycling creates new w3wp.exe but inherits same ENV

Option 1: Touch web.config

Modify your application's web.config file to force a true restart:

<!-- Add or modify any trivial element -->
<configuration>
  <system.web>
    <compilation tempDirectory="C:\temp" />
  </system.web>
</configuration>

Option 2: Service Control Command

Restart just the Windows Process Activation Service (more surgical than full IIS reset):

net stop was /y
net start w3svc

Option 3: Programmatic Refresh (Advanced)

Create a small ASPX page with this code to refresh environment variables:

<%@ Page Language="C#" %>
<%
    Environment.SetEnvironmentVariable("PATH", 
        Environment.GetEnvironmentVariable("PATH", EnvironmentVariableTarget.Machine));
    Response.Write("PATH refreshed: " + Environment.GetEnvironmentVariable("PATH"));
%>

For complex multi-server environments, sometimes a full restart is unavoidable. The cleanest approach:

iisreset /noforce

• Consider using absolute paths in your applications
• Log PATH variable at application startup
• Create custom environment variable checks in your health monitoring