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125 lines
3.1 KiB
Markdown
125 lines
3.1 KiB
Markdown
# V8
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The `v8` module exposes APIs that are specific to the version of [V8][]
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built into the Node.js binary. It can be accessed using:
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```js
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const v8 = require('v8');
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```
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*Note*: The APIs and implementation are subject to change at any time.
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## v8.getHeapStatistics()
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<!-- YAML
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added: v1.0.0
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-->
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Returns an object with the following properties:
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* `total_heap_size` {number}
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* `total_heap_size_executable` {number}
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* `total_physical_size` {number}
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* `total_available_size` {number}
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* `used_heap_size` {number}
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* `heap_size_limit` {number}
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For example:
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```js
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{
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total_heap_size: 7326976,
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total_heap_size_executable: 4194304,
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total_physical_size: 7326976,
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total_available_size: 1152656,
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used_heap_size: 3476208,
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heap_size_limit: 1535115264
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}
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```
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## v8.getHeapSpaceStatistics()
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<!-- YAML
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added: v6.0.0
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-->
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Returns statistics about the V8 heap spaces, i.e. the segments which make up
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the V8 heap. Neither the ordering of heap spaces, nor the availability of a
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heap space can be guaranteed as the statistics are provided via the V8
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[`GetHeapSpaceStatistics`][] function and may change from one V8 version to the
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next.
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The value returned is an array of objects containing the following properties:
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* `space_name` {string}
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* `space_size` {number}
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* `space_used_size` {number}
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* `space_available_size` {number}
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* `physical_space_size` {number}
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For example:
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```json
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[
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{
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"space_name": "new_space",
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"space_size": 2063872,
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"space_used_size": 951112,
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"space_available_size": 80824,
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"physical_space_size": 2063872
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},
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{
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"space_name": "old_space",
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"space_size": 3090560,
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"space_used_size": 2493792,
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"space_available_size": 0,
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"physical_space_size": 3090560
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},
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{
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"space_name": "code_space",
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"space_size": 1260160,
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"space_used_size": 644256,
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"space_available_size": 960,
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"physical_space_size": 1260160
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},
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{
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"space_name": "map_space",
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"space_size": 1094160,
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"space_used_size": 201608,
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"space_available_size": 0,
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"physical_space_size": 1094160
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},
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{
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"space_name": "large_object_space",
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"space_size": 0,
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"space_used_size": 0,
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"space_available_size": 1490980608,
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"physical_space_size": 0
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}
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]
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```
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## v8.setFlagsFromString(string)
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<!-- YAML
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added: v1.0.0
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-->
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The `v8.setFlagsFromString()` method can be used to programmatically set
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V8 command line flags. This method should be used with care. Changing settings
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after the VM has started may result in unpredictable behavior, including
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crashes and data loss; or it may simply do nothing.
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The V8 options available for a version of Node.js may be determined by running
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`node --v8-options`. An unofficial, community-maintained list of options
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and their effects is available [here][].
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Usage:
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```js
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// Print GC events to stdout for one minute.
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const v8 = require('v8');
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v8.setFlagsFromString('--trace_gc');
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setTimeout(function() { v8.setFlagsFromString('--notrace_gc'); }, 60e3);
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```
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[V8]: https://developers.google.com/v8/
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[here]: https://github.com/thlorenz/v8-flags/blob/master/flags-0.11.md
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[`GetHeapSpaceStatistics`]: https://v8docs.nodesource.com/node-5.0/d5/dda/classv8_1_1_isolate.html#ac673576f24fdc7a33378f8f57e1d13a4
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