If the estimated total size of all cached objects is
bigger than the available memory, you can enable the disk offload option
in WAS. The files that get created on the file
system for the disk offload option are the .htod files in question, and
these contain the cache entries that were offloaded. Over time, the file
system will fill up with these .htod files, and they need to be cleaned
out. The following two Java Virtual Machine properties can be used to
configure the clean up procedure.
com.ibm.ws.cache.CacheConfig.diskCacheSizeInGB:
This property can be used to specify the maximum size (in GB) of the disk
cache. By setting this, you are limiting the number of .htod files that
get created. You must first install PK13460
if you want to use this property.
com.ibm.ws.cache.CacheConfig.htodCleanupFrequency:
By default, the disk cache cleanup is scheduled to run every 24 hours at
midnight to remove expired cache entries and cache entries that have not
been accessed in the past 24 hours. The JVM property
com.ibm.ws.cache.CacheConfig.htodCleanupFrequency can be used to change
the time interval between disk cache cleanups. The WebSphere Commerce Recommended fixes and settings
Technote recommend a value of 60 (1 hour) for this property. Note that
this property also helps performance, because a big clean up job that runs
at midnight could cause extremely heavy disk I/O.
To set the above two properties in a WAS 6.0.2.x
environment, follow these steps:
- Login to the WebSphere Administration Console.
- Click Servers > Application servers
- Select the Commerce Server.
- Under Server Infrastructure, select Java and Process
Management > Process Definition
- Under Additional Properties, select Java Virtual
Machine
- Under Additional Properties, select Custom
Properties
- Click the New button
- In the Name field, type the name of the Java Virtual Machine
property you wish to set, such
ascom.ibm.ws.cache.CacheConfig.diskCacheSizeInGB
- In the Value field, type the desired value for the JVM
property, such as 2.
- Click OK and save the changes - this setting will take effect
when the server is restarted.
To set the above two properties in a WAS 5.1.1.x
environment, follow these steps:
- Log in to the WebSphere Administration Console.
- Click Servers > Application Servers
- Select the Commerce Server.
- Under Additional Properties, select Process
Definition.
- Under Additional Properties, select Java Virtual
Machine.
- Under Additional Properties, select Custom
Properties.
- Click on the New button.
- In the Name field, type the name of the JVM property you wish
to set, such as com.ibm.ws.cache.CacheConfig.diskCacheSizeInGB
- In the Value field, type the desired value for the JVM
property, such as 2.
- Click OK and save the changes - this setting will take effect
when the server is restarted.
Like any tuning parameters, careful consideration must be given prior to
making any modifications. For more information about these JVM properties,
and about general DynaCache configuration, reference the following links:
Redbooks -
Mastering DynaCache in WebSphere Commerce
Information
Center - Java Virtual Machine cache settings
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