查看内存
按照《深入浅出nodejs》一书所说，64位机器可使用内存大概是1.5G. 可以通过 process.memoryUsage() 查看.
Returns an object describing the memory usage of the Node.js process measured in bytes.
图片解读
垃圾回收
v8 将内存分为2部分:
- 一个是新生代区(生存周期短的).
- 一个是老生代区(生存周期长的).
如果一个变量在新生代区经过三次垃圾回收依然存在，则移动到老生代区
新生代区内存回收用 scavenge 算法, 老生代区用 mark-sweep & mark-compact 及 Incremental Marking 算法.
- scavenge
将内存区间分为2部分，from & to. 遍历 from 中的对象，将还存活对象移动到 to 中。然后回收 from， 然后 to 和 from 互换.
- mark-sweep
标记清除法。遍历老生代区，标记所有不存活的对象，然后逐一释放他们.(会产生内存碎片)
- mark-compact
在 mark-sweep 的基础上，消除内存碎片。(将存活的对象移动到内存的一端)
- Incremental Marking
因为回收内存的时候，会 stop-the-world, 而这是致命的，会导致服务器失去响应。Incremental Marking 就是分步进行，每次清理一小段，然后让js 逻辑执行一下.
进程状态分析日志
启动node 的时候，增加 node --prof somename.js 参数. 可以得到一个日志文件。
然后启动 node --prof-process isolate-0000018C066AAC90-3356-v8.log > v8.log 可以得到一个日志文件。
isolate-0000018C066AAC90-3356-v8.log 是生成的日志文件名字.
大致如下：
Statistical profiling result from .\isolate-00000260A9D5D440-5280-v8.log, (9 ticks, 0 unaccounted, 0 excluded).[Shared libraries]:ticks total nonlib name6 66.7% D:\nodejs\node.exe3 33.3% C:\Windows\SYSTEM32\ntdll.dll[JavaScript]:ticks total nonlib name[C++]:ticks total nonlib name[Summary]:ticks total nonlib name0 0.0% NaN% JavaScript0 0.0% NaN% C++0 0.0% NaN% GC9 100.0% Shared libraries[C++ entry points]:ticks cpp total name[Bottom up (heavy) profile]:Note: percentage shows a share of a particular caller in the totalamount of its parent calls.Callers occupying less than 1.0% are not shown.ticks parent name6 66.7% D:\nodejs\node.exe6 100.0% D:\nodejs\node.exe1 16.7% LazyCompile: ~patchProcessObject node:internal/process/pre_execution:112:281 100.0% LazyCompile: ~prepareMainThreadExecution node:internal/process/pre_execution:36:361 100.0% Function: ~<anonymous> node:internal/main/run_main_module:1:11 16.7% LazyCompile: ~nextTick node:internal/process/task_queues:103:181 100.0% LazyCompile: ~onwrite node:internal/streams/writable:428:171 100.0% LazyCompile: ~afterWriteDispatched node:internal/stream_base_commons:155:301 100.0% LazyCompile: ~writeGeneric node:internal/stream_base_commons:147:221 16.7% LazyCompile: ~WriteStream node:tty:84:211 100.0% LazyCompile: ~createWritableStdioStream node:internal/bootstrap/switches/is_main_thread:45:351 100.0% LazyCompile: ~getStdout node:internal/bootstrap/switches/is_main_thread:146:191 100.0% LazyCompile: ~get node:internal/console/constructor:209:141 16.7% LazyCompile: ~Module.load node:internal/modules/cjs/loader:1025:331 100.0% LazyCompile: ~Module._load node:internal/modules/cjs/loader:807:241 100.0% LazyCompile: ~executeUserEntryPoint node:internal/modules/run_main:74:311 100.0% Function: ~<anonymous> node:internal/main/run_main_module:1:11 16.7% Function: ~<anonymous> node:internal/process/esm_loader:1:11 100.0% Function: ~<anonymous> node:internal/modules/cjs/loader:1:11 100.0% LazyCompile: ~initializeCJSLoader node:internal/process/pre_execution:535:291 100.0% LazyCompile: ~prepareMainThreadExecution node:internal/process/pre_execution:36:361 16.7% Function: ~<anonymous> node:internal/modules/esm/loader:1:11 100.0% Function: ~<anonymous> node:internal/process/esm_loader:1:11 100.0% Function: ~<anonymous> node:internal/modules/cjs/loader:1:11 100.0% LazyCompile: ~initializeCJSLoader node:internal/process/pre_execution:535:293 33.3% C:\Windows\SYSTEM32\ntdll.dll1 33.3% D:\nodejs\node.exe1 100.0% LazyCompile: ~initializeCJSLoader node:internal/process/pre_execution:535:291 100.0% LazyCompile: ~prepareMainThreadExecution node:internal/process/pre_execution:36:361 100.0% Function: ~<anonymous> node:internal/main/run_main_module:1:1
第三方工具分析堆内存
linux-signal
kill -l查看所有支持的信号kill -s SIGUSR2 -- 27564想 pid 为 27564 的进程发送一个信号kill -h查看帮助手册.
node-heapdump
- 需要先安装python环境
npm install heapdump- 在脚本中使用
const heapdump = require("heapdump") - 在
windows中不会向进程发送信号. 转为linux 运行，发送信号kill -s SIGUSR2 -- 27564得到一个文件heapdump-110146120.170500.heapsnapshot. - 打开
google chrome浏览器，进入开发者模式，选择memory, 然后在左边的空白处单击右键load 刚才生成的文件。
大致如下:
还有一个问题，如何从这里发现确实存在内存泄漏???
node-memewatch
无法安装， 已经不更新了。。。
