Add MemoryAllocationExports #434
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Counters for total bytes allocated to each memory pool. Can be used to show allocation rate and promotion rate. Signed-off-by: Robin Karlsson <snago86@gmail.com>
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| // Visible for testing | ||
| void handleMemoryPool(String memoryPool, long before, long after) { | ||
| AtomicLong last = getOrCreate(lastMemoryUsage, memoryPool); |
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What exactly is this logic doing?
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The garbage collection notifications has info about memory in the pool before the GC and after the GC.
handleMemoryPool compares before to the after of the previous GC (or 0 for the first) to catch increase between GCs and then before and after to catch increase during the GC.
Typically eden pools will increase between GCs and old gen pools will increase during GCs, but this is written to be GC algorithm agnostic.
If you're asking about getOrCreate it gets the AtomicLong tracking the last memory usage for the pool (or crates a new one if it's the first time this pool is seen).
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Could two GCs happen concurrently for different pools?
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Not that I'm aware of. Each notification contain info about all pools. handleNotification then calls handleMemoryPool for each pool.
But I can't find any guarantees in the documentation that handleNotification won't be called concurrently. To be safe I could make handleNotification synchronized.
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Can you put in a comment explaining this?
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Done. Let me know if you want me to expand it further.
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We're already using a collector like this in production. Here is an example graph: This was created using the following two expressions in grafana: |
Signed-off-by: Robin Karlsson <snago86@gmail.com>
| public List<MetricFamilySamples> collect() { | ||
| List<MetricFamilySamples> sampleFamilies = new ArrayList<MetricFamilySamples>(); | ||
| CounterMetricFamily allocated = new CounterMetricFamily( | ||
| "jvm_memory_pool_allocated_bytes", |
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Counters should end in _total
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| // Visible for testing | ||
| void handleMemoryPool(String memoryPool, long before, long after) { | ||
| AtomicLong last = getOrCreate(lastMemoryUsage, memoryPool); |
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Can you put in a comment explaining this?
| @Override | ||
| public List<MetricFamilySamples> collect() { | ||
| List<MetricFamilySamples> sampleFamilies = new ArrayList<MetricFamilySamples>(); | ||
| CounterMetricFamily allocated = new CounterMetricFamily( |
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You can use a Counter here, rather than having to track this yourself.
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Good point! That really simplified collect.
I also removed the tests for collect since they were now only testing Counter.collect.
* Fix name * Explain handleMemoryPool * Use a Counter internally (and removed tests for collect) Also, since handleNotification is synchronized now, lastMemoryUsage can be a regular HashMap. Signed-off-by: Robin Karlsson <snago86@gmail.com>
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Thanks! |
Counters for total bytes allocated to each memory pool.
Can be used to show allocation rate and promotion rate.