RFR(S) Trace significant heap allocations
milan.mimica at infobip.com
Fri Mar 28 23:51:29 UTC 2014
One of my concerns recently was tracking down large memory allocations
which cause G1 GC to do a Full GC. So I came out with this patch, which
adds two diagnostic options:
1) TraceLargerAllocations - logs every heap allocation larger that the
2) G1TraceFullGCAllocations - logs allocations which trigger a STW Full GC
I see that these two options could be submitted as separate patches, but
before we discuss the details I'd like to be sure that I'm doing the
I understand that there are already at least two ways to trace
allocations - EventAllocObjectOutsideTLAB and bytecode instrumentation.
They both lack some crucial features:
The problem with EventAllocObjectOutsideTLAB is that you cannot set size
threshold, you don't get the java stacktrace, and you get loads of other
uninteresting things with -XX:+EnableTracing. I don't find it useful.
The event system could be extended to support those, but that's a bigger
undertake. And it's coded in XML(!!?).
Bytecode instrumentation, on the other hand, is intrusive, ads overhead,
and it's too complicated. Just think of it, it was easier for me to
implement these two VM options than to even start fiddling with
bytecodes. (Partly because you made the jvm too easy to build, good
job!) Having a profiler constantly connected to an instance is also not
I think these two options are generally useful for tracing GC problems,
especially G1TraceFullGCAllocations. With full java stacktrace the
developer has all the information needed to locate the problem which is
otherwise very hard to locate.
So could someone review the patch and provide feedback? First time
posting here, so I need a sponsor obviously.
Milan Mimica, Software Engineer / Team Leader
Office: Mletacka 12/III, 52100 Pula, Croatia | Fax: +38552210979 | Mobile: +385993061692
Email: Milan.Mimica at infobip.com | Skype: mmimicaib
www.infobip.com / GSMA Associate Member / Mobey Forum Member
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