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Posted to commits@pulsar.apache.org by GitBox <gi...@apache.org> on 2018/12/16 07:39:21 UTC
[GitHub] merlimat opened a new pull request #3199: Use direct memory instead
of Heap to determine a broker is "overloaded" in memory usage
merlimat opened a new pull request #3199: Use direct memory instead of Heap to determine a broker is "overloaded" in memory usage
URL: https://github.com/apache/pulsar/pull/3199
### Motivation
When a broker is configured with a relatively low JVM heap size, it might be reporting it's "overloaded" by exceeding the default threshold of max 85% of Heap memory used, when in fact it's not overloaded.
The reason is that the jvm heap will grow and shrink like:
This is typically not a problem with larger heap sizes (and using the `-XX:G1NewSizePercent=50` flag which forces G1GC to do young gen collection when the 50% threshold is filled up. In this case the heap will be cleaned well before the 85% value is reached.
On the other hand, on smaller heaps like the above example with `-Xmx512MB`, since the load report uses the instant value of the heap size, it might be signaling that the broker is overloaded (mem usage >85%) while in fact is just that JVM is deferring the GC until the 512MB are entirely filled up.
Since there is no way to get a good proxy measure for "real" heap usage from JVM, we should just rather use the direct memory for the overload considerations.
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