gc-heap-stats

Emits detailed stats about V8 heap usage after each V8 garbage collector run.

Install

npm install gc-heap-stats

Basic usage

var gcHeapStats = require('gc-heap-stats')();
gcHeapStats.on('stats', function (stats) {
    console.log(JSON.stringify(stats, null, 2));
});

Advanced usage

// init GC heap stats emitter as "deferred"
var gcHeapStats = require('gc-heap-stats')({deferred: true});
gcHeapStats.on('stats', function (stats) {
    console.log(JSON.stringify(stats, null, 2));
});

// no events will be emitted until you call
gcHeapStats.start();

// stop it
gcHeapStats.stop();

// ... start again, ... etc
gcHeapStats.start();

Sample output

Sample output in node.js >= 4.0 (there won't be spaces[] stats in older versions of node.js).

The output contains 3 sections: heap stats before garbage collector run was triggered, heap stats after garbage collector run and the diff (after - before).

Top level properties:

• type: type of GC (can have one of the following values):
• 1: Scavenge (minor GC)
• 2: Mark/Sweep/Compact (major GC)
• 4: Incremental marking
• 8: Weak/Phantom callback processing
• 15: All
• took: milliseconds that GC run took

Section properties:

• total_heap_size: Number of bytes V8 has allocated for the heap. This can grow if usedHeap needs more.
• used_heap_size: Number of bytes in used by application data
• total_heap_size_executable: Number of bytes for compiled bytecode and JITed code
• heap_size_limit: The absolute limit the heap cannot exceed (default limit or --max_old_space_size)
• total_physical_size: Committed size

Heap space properties:

• space_name: Name of a heap space
• space_size: Number of bytes allocated for a heap space
• space_used_size: Number of bytes allocated (used) in a heap space
• space_available_size: Number of bytes available in a heap space
• physical_space_size: Committed size of a heap space

{
  "type": 1,
  "took": 1.102,
  "before": {
    "total_heap_size": 10522624,
    "total_heap_size_executable": 5242880,
    "total_physical_size": 10522624,
    "total_available_size": 1487252192,
    "used_heap_size": 4941096,
    "heap_size_limit": 1501560832,
    "spaces": [
      {
        "space_name": "new_space",
        "space_size": 4194304,
        "space_used_size": 1638368,
        "space_available_size": 424992,
        "physical_space_size": 4194304
      },
      {
        "space_name": "old_space",
        "space_size": 3100672,
        "space_used_size": 2499536,
        "space_available_size": 192,
        "physical_space_size": 3100672
      },
      {
        "space_name": "code_space",
        "space_size": 2097152,
        "space_used_size": 631328,
        "space_available_size": 0,
        "physical_space_size": 2097152
      },
      {
        "space_name": "map_space",
        "space_size": 1130496,
        "space_used_size": 171864,
        "space_available_size": 0,
        "physical_space_size": 1130496
      },
      {
        "space_name": "large_object_space",
        "space_size": 0,
        "space_used_size": 0,
        "space_available_size": 1486827008,
        "physical_space_size": 0
      }
    ]
  },
  "after": {
    "total_heap_size": 11571200,
    "total_heap_size_executable": 5242880,
    "total_physical_size": 11571200,
    "total_available_size": 1487833096,
    "used_heap_size": 3879584,
    "heap_size_limit": 1501560832,
    "spaces": [
      {
        "space_name": "new_space",
        "space_size": 4194304,
        "space_used_size": 8832,
        "space_available_size": 2054528,
        "physical_space_size": 4194304
      },
      {
        "space_name": "old_space",
        "space_size": 4149248,
        "space_used_size": 3067560,
        "space_available_size": 136,
        "physical_space_size": 4149248
      },
      {
        "space_name": "code_space",
        "space_size": 2097152,
        "space_used_size": 631328,
        "space_available_size": 0,
        "physical_space_size": 2097152
      },
      {
        "space_name": "map_space",
        "space_size": 1130496,
        "space_used_size": 171864,
        "space_available_size": 0,
        "physical_space_size": 1130496
      },
      {
        "space_name": "large_object_space",
        "space_size": 0,
        "space_used_size": 0,
        "space_available_size": 1485778432,
        "physical_space_size": 0
      }
    ]
  },
  "diff": {
    "total_heap_size": 1048576,
    "total_heap_size_executable": 0,
    "total_physical_size": 1048576,
    "total_available_size": 580904,
    "used_heap_size": -1061512,
    "heap_size_limit": 0,
    "spaces": [
      {
        "space_name": "new_space",
        "space_size": 0,
        "space_used_size": -1629536,
        "space_available_size": 1629536,
        "physical_space_size": 0
      },
      {
        "space_name": "old_space",
        "space_size": 1048576,
        "space_used_size": 568024,
        "space_available_size": -56,
        "physical_space_size": 1048576
      },
      {
        "space_name": "code_space",
        "space_size": 0,
        "space_used_size": 0,
        "space_available_size": 0,
        "physical_space_size": 0
      },
      {
        "space_name": "map_space",
        "space_size": 0,
        "space_used_size": 0,
        "space_available_size": 0,
        "physical_space_size": 0
      },
      {
        "space_name": "large_object_space",
        "space_size": 0,
        "space_used_size": 0,
        "space_available_size": -1048576,
        "physical_space_size": 0
      }
    ]
  }
}

Compatibility

gc-heap-stats is compatible with node.js >= 0.12 however the best results (including V8 heap spaces stats) you will get with node.js >= 4.0. Version 0.10 is not supported, for node.js 0.10 please use similar package: https://github.com/dainis/node-gcstats