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Latest commit 6a91081 Sep 12, 2016 @dainis committed on GitHub Merge pull request #20 from advait/patch-1
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Exposes stats about V8 GC after it has been executed.


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


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.