gcstats.js  

Exposes statistics about V8 garbage collections (GCs) after they have been executed.

• Installation
• Usage
• Property Insights
• Node Version Compatibility
• Credits

Installation

npm install --save gcstats.js

Usage

Require the module and subscribe to the stats event:

var gcStats = require('gcstats.js');

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

This will print blobs like this whenever a GC happens:

{
  "start": 271925068593439,
  "end": 271925070343402,
  "gctype": 1,
  "before": {
    "totalHeapSize": 10481664,
    "totalHeapExecutableSize": 5242880,
    "usedHeapSize": 5761048,
    "heapSizeLimit": 1535115264,
    "totalPhysicalSize": 10481664
  },
  "after": {
    "totalHeapSize": 11530240,
    "totalHeapExecutableSize": 5242880,
    "usedHeapSize": 5512464,
    "heapSizeLimit": 1535115264,
    "totalPhysicalSize": 11530240
  }
}

Property Insights

• start: Start time of the GC measured using uv_hrtime (nanoseconds).
• end: End time of the GC measured using uv_hrtime (nanoseconds).
• 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
• totalHeapExecutableSize: Number of bytes for compiled bytecode and JITed code
• heapSizeLimit: The absolute limit the heap cannot exceed
• totalPhysicalSize: Commited size (node 0.11+)
• gctype: What kind of GC was executed. Refer to the v8 docs of the GCType enum for a list of possible values.

Node Version Compatibility

GC stats depend on C++ extensions which are compiled when the gcstats.js module is installed. Compatibility information can be inspected via the Travis-CI build jobs.

Credits

node-gcstats was written by @dainis and later adapted by @bripkens and renamed to gcstats.js.