Troubleshoot tips for the dynamic cache service

Troubleshoot tips for the dynamic cache service

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The dynamic cache service works within an appserver JVM, intercepting calls to cacheable objects. This article describes some common runtime and configuration problems and remedies.

Servlets are not cached

Enable servlet caching. On the Web container settings page of the administrative console, select the Enable servlet caching check box.

Cache entries are not written to disk

Explanation Cache entries are written to disk when the cache is full and new entries are added to the memory cache. Cache entries also are written to disk when Flush to disk is enabled in the console and the server is stopped.
Recommended response
Verify that Disk offload is enabled on the Dynamic cache service settings page of the console. Also verify that cache entries written to disk are serializable and do not have the PersistToDisk configuration set to false.

Some servlets are not replicated or written to disk
Recommended response
Ensure that the attributes and response are serializable. If you do not want to store the attributes, use the following property in your cache policy:
<property name="save-attributes">false</property>
Dynamic cache service does not cache fragments on the Edge
Recommended response
Set the EdgeCacheable property to true in the cache policy for those entries that are to be cached on the Edge.
<property name="EdgeCacheable">true</property>
Dynamic cache invalidations are not sent to the IBM HTTP Server plug-in

Explanation The DynaCacheEsi.ear file is required to send invalidations to external caches.
Recommended response
Install DynaCacheEsi.ear using the console.

Cache entries are evicted often

Problem The cache is full and new entries are added to the cache.
Explanation Cache entries are evicted when the cache is full and new entries are added to the cache. A least recently used (LRU) eviction mechanism removes the least recently used entry to make space for the new entries.
Recommended response
Enable Disk offload on the Dynamic cache service settings page of the administrative console so the entries are written to disk. You can also increase the cache size to accommodate more entries in the cache.

Cache entries in disk with timeout set to 0 expire after one day

Explanation The maximum lifetime of an entry in disk cache is 24 hours. A timeout of 0 in the cache policy configures these entries to stay in disk cache for one whole day, unless they are evicted earlier.
Recommended response Set the timeout for the cache policy to a number less than 0.

I cannot monitor cache entries on the Edge

Explanation
Use the dynamic cache monitor to monitor the contents of the memory cache, disk cache and external caches, like the Edge cache. For the ESI processor's cache to be visible in the cache monitor, the DynaCacheEsi.ear application must be installed and the esiInvalidationMonitor property must be set to true in the plugin-cfg.xml file.
Recommended response
Set the esiInvalidationMonitor property in the plugin-cfg.xml file to true. See Displaying cache information for more information.

I want to tune cache for my environment

Recommended response Use the Tivoli Performance viewer to study the caching behavior for your applications. Also consider performing the following actions:

Increase the priority of cache entries that are expensive to regenerate.

Modify timeout of entries so that they stay in memory as long as they are valid.

Enable disk offload to store LRU evicted entries.

Increase the cache size.

Cleaning the disk cache files after installing the fix pack or a new release if you use the disk cache function

Symptom If the server is configured to use the disk cache, delete the disk cache files because the disk cache files are not compatible to the previous version.
Problem Failure to remove the old disk cache files results in a ClassCastException error in the systemerr.log file when you access the cache from the disk.
Recommended response To delete the disk cache, perform the following steps:

Note your disk offload location. If you do not know the disk cache offload location, perform the following steps:

Click Servers > Application servers > server > Container services > Dynamic cache service in the administrative console navigation tree.

The location is specified in the Disk offload field. If the location is not specified, the default directory profile_root/temp/your_node/server/_dynacache is used.

Verify the you stop the server and delete all the files under the offload location.

If you use the ND product, delete the disk cache files for each server.

Setting the flush attribute to true on every <jsp:include> tag in the cacheable JavaServer Pages file

Symptom When you obtain the JavaServer Pages file from the dynamic cache, a part of the page is not displayed.
Problem The flush attribute is set to false on the <jsp: include> tag in the JSP file.
Description When the cacheable JSP file includes another JSP file and if the flush attribute is set to false on the <jsp: include> tag, any data written to the parent output stream before the<jsp: include> tag are not cached.
Recommended response Set flush=true on every <jsp: include> tag in the cacheable JSP file.

Dynamic cache limitation when using the JSTL <c:import> tag to include a fragment
Problem When a cacheable fragment is included using the JavaServer Pages Standard Tag Library (JSTL) <c:import> tag, part of the page content disappears and part of the page content displays twice on a cache hit.
Description Dynamic cache relies on flushing the content before and after including a fragment so that the parent content before the include is not lost, and also to prevent pulling the child content into the parent fragment.
However, in the case of the JSTL <c:import> tag, the flush=true attribute, which flushes the parent writer before the child fragment is actually invoked, is not supported. Also, JSTL buffers the responses, so that the child writer is not flushed right after the child fragment is done. Subsequently, the child response is pulled into the parent.
Recommended response
To avoid this problem, surround the <c:import> statement with out.flush method statements as follows:
<% out.flush(); %>
<c:import url="DNCParent2.jsp" />
<% out.flush(); %> 
Related tasks

Task overview: Using the dynamic cache service to improve performance

Related information

Troubleshooting the dynamic cache service
Displaying cache information

Reference topic

Explanation	Cache entries are written to disk when the cache is full and new entries are added to the memory cache. Cache entries also are written to disk when Flush to disk is enabled in the console and the server is stopped.
Recommended response	Verify that Disk offload is enabled on the Dynamic cache service settings page of the console. Also verify that cache entries written to disk are serializable and do not have the PersistToDisk configuration set to false.

Explanation	The DynaCacheEsi.ear file is required to send invalidations to external caches.
Recommended response	Install DynaCacheEsi.ear using the console.

Problem	The cache is full and new entries are added to the cache.
Explanation	Cache entries are evicted when the cache is full and new entries are added to the cache. A least recently used (LRU) eviction mechanism removes the least recently used entry to make space for the new entries.
Recommended response	Enable Disk offload on the Dynamic cache service settings page of the administrative console so the entries are written to disk. You can also increase the cache size to accommodate more entries in the cache.

Explanation	The maximum lifetime of an entry in disk cache is 24 hours. A timeout of 0 in the cache policy configures these entries to stay in disk cache for one whole day, unless they are evicted earlier.
Recommended response	Set the timeout for the cache policy to a number less than 0.

Explanation	Use the dynamic cache monitor to monitor the contents of the memory cache, disk cache and external caches, like the Edge cache. For the ESI processor's cache to be visible in the cache monitor, the DynaCacheEsi.ear application must be installed and the esiInvalidationMonitor property must be set to true in the plugin-cfg.xml file.
Recommended response	Set the esiInvalidationMonitor property in the plugin-cfg.xml file to true. See Displaying cache information for more information.

Symptom	When you obtain the JavaServer Pages file from the dynamic cache, a part of the page is not displayed.
Problem	The flush attribute is set to false on the <jsp: include> tag in the JSP file.
Description	When the cacheable JSP file includes another JSP file and if the flush attribute is set to false on the <jsp: include> tag, any data written to the parent output stream before the<jsp: include> tag are not cached.
Recommended response	Set flush=true on every <jsp: include> tag in the cacheable JSP file.