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CAS Heap Tuning

gregg_kniss
Guide

I came across https://answers.dynatrace.com/questions/166357/what-is-the-best-practice-for-java-xmx-memory-sett.html while looking for information regarding the CAS heap recommendations. Our CAS has 64GB of RAM and currently 24GB heap. Since we are running 12.2.5 which has Java 1.7 we have UseCompressedOops enabled by default. Once the heap is set to 32GB or higher that is disabled leaving you with less available memory until heap is 48GB or more. However if using ObjectAlignmentInBytes=16 you can still have UseCompressedOops until heap is 64GB. I have read mixed opinions regarding using the increased object alignment size. Can anyone at Dynatrace comment on whether this has been tested?

4 REPLIES 4

andrzej_lecki
Advisor

The option ObjectAlignmentInBytes=16 was introduced in java 1.8 and we haven't tested it yet. Usually 32 GB memory is enough for CAS. Before we reach 32 GB, we usually have some other performance issues like delay of processing data, DMI is not able to serve reports, etc.

In DC RUM 2017 release, we want to set 32000 MB instead of 32 GB by installator to avoid large pointers. See Chris V. comment in mentioned post https://answers.dynatrace.com/questions/166357/what-is-the-best-practice-for-java-xmx-memory-sett.ht....

gregg_kniss
Guide

I read that it was there and just not documented until 1.8. According to this bug report it was there in 1.7, https://bugs.openjdk.java.net/browse/JDK-8021823.

andrzej_lecki
Advisor

Thanks for comment we will keep in mind that option. Currently we are in the final stage of next release so it is too late to make experiments. That option can be useful for client who have more than Xmx set to more than 32GB memory. But on the other hand if they have so much memory they are rich and they can buy some more memory ;).

harshal_pujari
Dynatrace Pro
Dynatrace Pro

Hi Gregg,

Just a FYI: 12.2.5 is not supported anymore. Support for 12.3 will end in June 2017.