GCStats

 

Exposes stats about V8 GC after it has been executed.

Usage

Create a new instance of the module and subscribe to stats-events from that:

var gc = (require('gc-stats'))();

gc.on('stats', function (stats) {
console.log('GC happened', stats);
});

This will print blobs like this whenever a GC happened:

GC happened {
startTime: 9426055813976,
endTime: 9426057735390,
pause: 1921414,
pauseMS: 1,
gctype: 1,
before: {
totalHeapSize: 11354112,
totalHeapExecutableSize: 3670016,
usedHeapSize: 7457184,
heapSizeLimit: 1501560832,
totalPhysicalSize: 9725880,
totalAvailableSize: 1488434544,
mallocedMemory: 8192,
peakMallocedMemory: 1186040
},
after: {
totalHeapSize: 12402688,
totalHeapExecutableSize: 3670016,
usedHeapSize: 6485792,
heapSizeLimit: 1501560832,
totalPhysicalSize: 10166144,
totalAvailableSize: 1489388528,
mallocedMemory: 8192,
peakMallocedMemory: 1186040
},
diff: {
totalHeapSize: 1048576,
totalHeapExecutableSize: 0,
usedHeapSize: -971392,
heapSizeLimit: 0,
totalPhysicalSize: 440264,
totalAvailableSize: 953984,
mallocedMemory: 0,
peakMallocedMemory: 0
}
}

Property insights

* totalHeapSize: Number of bytes V8 has allocated for the heap. This can grow if usedHeap needs more.
* usedHeapSize: Number of bytes in use by application data
* total HeapExecutableSize: Number of bytes for compiled bytecode and JITed code
* heapSizeLimit: The absolute limit the heap cannot exceed
* totalPhysicalSize: Committed size (node 0.11+)
* totalAvailableSize: Available heap size(node 4+)
* startTime: Nanoseconds for start, using hrtime()
* endTime: Nanoseconds for end, using hrtime()
* pause: Nanoseconds from start to end of GC using hrtime()
* pauseMS: pause expressed in milliseconds
* mallocedMemory
* peakMallocedMemory
* numberOfNativeContexts
* numberOfDetachedContexts
* gctype can have the following values(v8 source):
* 1: Scavenge (minor GC)
* 2: Mark/Sweep/Compact (major GC)
* 4: Incremental marking
* 8: Weak/Phantom callback processing
* 15: All

Installation

npm install gc-stats

Node version support

node-gcstats depends on C++ extensions which are compiled when the gc-stats module is installed. Compatibility information can be inspected via the Travis-CI build jobs.