Technical Alerts

High CPU utilization running SGOS 5.5.1.1 with ADN compression enabled

Technical Alerts ID:    TFA23
Version:    3.0
Status:    Published
Published date:    02/02/2010
Updated:    02/03/2010
 

Problem description

PROBLEM BACKGROUND

The ADN protocol received many enhancements in SGOS 5.5.1.1.  One of the enhancements deals with the amount of compression that will occur between ADN enabled devices.  Here is a portion of the SGOS 5.5.1.1 release notes that explains the changes in compression:

 

Adaptive Compression

You can now enable the ProxySG to adjust its compression level based on CPU usage. When adaptive compression is enabled, the ProxySG will automatically increase its compression level when CPU usage is low and decrease its compression level when CPU usage is high. The ProxySG determines whether to increase or decrease the compression level based on its internal compression index. Because adaptive compression uses extra CPU when it is available, you will notice that your CPU usage levels are higher when this feature is enabled. If, however, you notice that the compression index remains low when adaptive compression is enabled (indicating that the compression level is decreased), this may indicate that your appliance is under-sized. In this case, you should consider a hardware upgrade. By default, adaptive compression is enabled on multiprocessor appliances and disabled on single processor appliances.

 

PROBLEM DESCRIPTION

When ProxySG appliances are upgraded to SGOS 5.5.1.1 and the ADN protocol is enabled, it is not uncommon for CPU utilization to increase on the device.  The target CPU utilization with ADN compression enabled is 73 - 78%.  When CPU utilization reaches 79% or greater, then SGOS will start decreasing the compression level used by the ADN protocol.

 

REMEDIATION

If you notice an increase in CPU utilization into the mid to high 70% range, then this utilization is normal and expected.  However, if CPU utilization increases above 78% and overall performance is impacted by this increase in CPU utilization, then please do the following items:

  1. Turn off ADN adaptive compression and see if the CPU utilization goes down or not.  If CPU utilization goes down, then the CPU increase is likely due to the ADN adaptive compression.
  2. If the CPU utilization does not go down when ADN adaptive compression is disabled, then something else is causing the high CPU utilization.
  3. Contact Blue Coat Technical Support and explain the issue that you are experiencing.  Please let Support know any test results.  NOTE:  If CPU utilization does decrease after turning off ADN adaptive compression, then Support may request that ADN compression be re-enabled so that diagnostic information and troubleshooting steps can be taken while the appliance is experiencing issues.

 


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