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 {
pause: 433034,
pauseMS: 0,
gctype: 1,
before: {
totalHeapSize: 18635008,
totalHeapExecutableSize: 4194304,
usedHeapSize: 12222496,
heapSizeLimit: 1535115264
}, after: {
totalHeapSize: 18635008,
totalHeapExecutableSize: 4194304,
usedHeapSize: 8116600,
heapSizeLimit: 1535115264
}, diff: {
totalHeapSize: 0,
totalHeapExecutableSize: 0,
usedHeapSize: -4105896,
heapSizeLimit: 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: Commited size (node 0.11+)
* pause: Nanoseconds from start to end of GC using hrtime()
* pauseMS: pause expressed in milliseconds
* 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.