Add a metric for tracking heap size after last gc event

[lenin-jaganathan]

Please describe the feature request.
In most cases for performance optimizations related to memory, it is necessary to understand the GC behavior and the memory allocation/reclamation behaviors. It is in this aspect, that analyzing the various heap region sizes after GC seems to be a very useful metric. The information can be obtained from MemoryPoolMXBean#getCollectionUsage on supported JVM's.

Related metrics in this space, but having the exact snapshot data post-GC helps in applying transformations/aggregations in the backend along with the memory pool names.

• jvm.gc.memory.promoted
• jvm.gc.memory.allocated
• jvm.gc.max.data.size

[shakuzen]

We also already provide jvm.gc.live.data.size in JvmGcMetrics with the description "Size of long-lived heap memory pool after reclamation". Is that not what you're looking for?

We've abstracted the memory pool name away so the same metric can be used with different GCs.

[lenin-jaganathan]

It doesn't factor in the changes in survivor space. Also, I see most of the time it is not reporting values. longLivedAfter < longLivedBefore returns false and the metric seems to return zero.

Both seem to go away when we use the OperatingSystemMxBean. All the pre-computations are done away with and we can apply the aggregations at the back-end/UI with raw data.