gcstats.js

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 gcStats = require('gcstats.js');

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

This will print blobs like this whenever a GC happens:

GC happened { start: 635817864674795,
  end: 635817865774643,
  gctype: 1,
  before:
   { totalHeapSize: 277510912,
     totalHeapExecutableSize: 5242880,
     usedHeapSize: 273621856,
     heapSizeLimit: 1535115264,
     totalPhysicalSize: 277510912 },
  after:
   { totalHeapSize: 277510912,
     totalHeapExecutableSize: 5242880,
     usedHeapSize: 273533760,
     heapSizeLimit: 1535115264,
     totalPhysicalSize: 277510912 } }

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()

gctype can have the following values:

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

Installation

npm install --save gcstats.js

Node version compatibility

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 and the compatibility file.

Credits

node-gcstats was written by @dainis and later adopted by @bripkens.