gc-stats

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()
• pause: Nanoseconds from start to end of GC using hrtime()
• pauseMS: pause expressed in milliseconds

gctype can have the following values:

• 1: Scavenge (minor GC)
• 2: Mark/Sweep/Compact (major GC)
• 3: Both 1 and 2

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.