README.md

NB!

V1.4.0 was using s3 for prebuilt binaries that is not associated with project anymore use v1.4.0 at your own risk

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.