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Nodejs v8 getHeapSpaceStatistics method | Heap space statistics in node


Nodejs v8 getHeapSpaceStatistics method example

In this tutorial, You learn v8.getHeapSpaceStatistics() method in v8 module of nodejs with examples getHeapSpaceStatistics method returns statistics about heap sizes based on spaces. v8 is an opensource javascript engine from google chrome and used by nodejs and MongoDB

What is a space in v8? Space is a chunk of memory allocated by the v8 engine. V8 has the following different spaces for storing and garbage cleaning objects in heap memory.

  • new space: this is small memory used for new objects for garbage collection of objects quickly.
  • old pointer space: store long live objects which point to other objects
  • old data space`: these are objects, plain raw data has no reference to another object
  • code space: executable memory for compilation and JITed executions
  • Cell space, property-cell-space, and map-space: Storing the same size of cell property and map-related objects.
  • large object space: storing large objects

getHeapSpaceStatistics method return above object space statistics.

Each object holds information about space available used and physical heap sizes information.

V8 is an engine is used internally by the Nodejs environment. You can check v8 version and 32 bit or 64 bit for Nodejs

Sometimes, To debug node out of memory errors, We need to know the heap size of an environment and application.

To get the above information, Nodejs has an inbuilt module v8, It has an inbuilt getHeapSpaceStatistics to get statistical information about heap memory allocated based on spaces.

V8 has another method [getHeapStatistics](/nodejs-v8-getheapstatistics-method) about stats of heap memory in the entire system. Syntax:

getHeapSpaceStatistics()

It returns an object of the following properties.

  • space_name: Name of the space used, examples are read_only_space,new_space,old_space,code_space,map_space,large_object_space,code_large_object_space,new_large_object_space
  • space_size: Allocated space heap size in bytes
  • space_used_size: Used space heap size in bytes
  • space_available_size: Available space heap size in bytes
  • physical_space_size: Physical space heap size in bytes

It gives heap information.

v8 getHeapSpaceStatistics method example

first import v8 module using require keyword in ES5 syntax

const v8module = require('v8');

Here is a code for v8 getHeapSpaceStatistics example info.js

const v8module = require('v8');  
console.log(v8module.getHeapSpaceStatistics());  

running info.js in the command line with the node command

node info.js

It outputs an object

[
  {
    space_name: 'read_only_space',
    space_size: 151552,
    space_used_size: 150392,
    space_available_size: 0,
    physical_space_size: 151552
  },
  {
    space_name: 'new_space',
    space_size: 2097152,
    space_used_size: 881912,
    space_available_size: 165512,
    physical_space_size: 2097152
  },
  {
    space_name: 'old_space',
    space_size: 1458176,
    space_used_size: 1349464,
    space_available_size: 248,
    physical_space_size: 1458176
  },
  {
    space_name: 'code_space',
    space_size: 360448,
    space_used_size: 87456,
    space_available_size: 0,
    physical_space_size: 360448
  },
  {
    space_name: 'map_space',
    space_size: 528384,
    space_used_size: 262152,
    space_available_size: 0,
    physical_space_size: 528384
  },
  {
    space_name: 'large_object_space',
    space_size: 135168,
    space_used_size: 131112,
    space_available_size: 0,
    physical_space_size: 135168
  },
  {
    space_name: 'code_large_object_space',
    space_size: 0,
    space_used_size: 0,
    space_available_size: 0,
    physical_space_size: 0
  },
  {
    space_name: 'new_large_object_space',
    space_size: 0,
    space_used_size: 0,
    space_available_size: 1047424,
    physical_space_size: 0
  }
]

Conclusion

To Sum up, It is helpful for developers to profile a node application by using getHeapSpaceStatistics to improve performance.

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