https://bz.apache.org/bugzilla/show_bug.cgi?id=69348
Bug ID: 69348
Summary: Optimizable memory allocation in ELContext
Product: Tomcat 9
Version: 9.0.x
Hardware: All
OS: Windows XP
Status: NEW
Severity: normal
Priority: P2
Component: EL
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: -----
Heap dumps of the recently-added
org.apache.el.parser.TestELParserPerformance.testAstNotEmpty() and testAstAnd()
show extremely high memory usage, which I tracked down to the allocation of
ELContext.lambdaArguments. Specifically, this field is eagerly initialized via
"new ArrayDeque()". The default size calculation changes across JVM version so
details may vary - however it looks like 16 is the most probable.
In this particular test, lambdaArguments is never used. Lazy-initializing this
field such as:
private Deque<Map<String, Object>> getLambdaArguments() {
if (lambdaArguments == null) {
lambdaArguments = new ArrayDeque<>(2);
}
return lambdaArguments;
}
cuts the memory allocated during these tests by over 50%.
In addition to lazy loads, a more conservative size will reduce allocation even
when the object is used. For example, the sample above uses 2, although that
is probably not the right value for the real world.
Expected impact is a huge reduction in memory allocation while processing EL
expressions. The rare few Ast* nodes that require the lambdaArguments field
will also improve based on a more conservative allocation size.
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