https://bz.apache.org/bugzilla/show_bug.cgi?id=57752
Bug ID: 57752
Summary: WebResources Cache 'lookupCount' counts non-lookups
Product: Tomcat 8
Version: 8.0.20
Hardware: PC
Status: NEW
Severity: normal
Priority: P2
Component: Catalina
Assignee: dev@tomcat.apache.org
Reporter: adam.mlodzin...@software.dell.com
The method org.apache.catalina.webresources.Cache.getResource(String, boolean)
is used to retrieve a resource given a particular path. Some resources are
cached by the Cache class, while others bypass the cache. A request for those
resources which bypass the cache are forwarded somewhere else to find the
resource (the 'root' object).
The problem is that every request for a resource, whether for a resource that
is potentially in the cache, or for a resource which always bypasses the cache,
is counted as a resource lookup, while the hit count is incremented only if the
resource was found in the cache. This leads to a highly disproportionate ratio
of lookups to hits from the cache.
There are 2 ways to fix this:
1) If a resource request bypasses the cache, do not increment the lookup
count.
OR
2) If a resource request which bypasses the cache was found by the alternate
source, then increment the hit count.
I think the 2nd option would lead to values higher than they ought to be. The
first option ought to provide more accurate representation of the usage of the
cache.
For the fist option, the code fix is trivial:
{code}
*** Cache.java 2015-02-15 13:16:26.000000000 -0500
--- Cache.java.fixed 2015-03-24 19:08:52.630609500 -0400
***************
*** 59,70 ****
protected WebResource getResource(String path, boolean
useClassLoaderResources) {
- lookupCount.incrementAndGet();
-
if (noCache(path)) {
return root.getResourceInternal(path, useClassLoaderResources);
}
CachedResource cacheEntry = resourceCache.get(path);
if (cacheEntry != null &&
!cacheEntry.validateResource(useClassLoaderResources)) {
--- 59,70 ----
protected WebResource getResource(String path, boolean
useClassLoaderResources) {
if (noCache(path)) {
return root.getResourceInternal(path, useClassLoaderResources);
}
+ lookupCount.incrementAndGet();
+
CachedResource cacheEntry = resourceCache.get(path);
if (cacheEntry != null &&
!cacheEntry.validateResource(useClassLoaderResources)) {
{code}
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