如何衡量Erlang垃圾收集器的性能? [英] How to measure the performance of the Erlang Garbage Collector?

问题描述

我最近开始用Erlang编程，关于垃圾收集(GC)，我想了解几件事.据我了解，每个进程的专用堆都有一个世代GC，全局共享堆有一个引用计数GC.

I have started programming in Erlang recently and there are a few things I want to understand regarding garbage collection (GC). As far as I understand, there is a generational GC for the private heap of each process and a reference counting GC for the global shared heap.

我想知道的是是否有得到的东西:

What I would like to know is if there is anyway to get:

1. 收集周期数是多少?
2. 在全局级别或进程级别分配和释放了多少个字节?
3. 什么是私有堆，共享堆的大小是多少?我们可以将其定义为GC参数吗?
4. 收集垃圾需要多长时间?需要的时间百分比?
5. 是否可以在没有GC的情况下运行程序?

运行Erlang程序时，是否可以通过代码或使用某些命令来获取此类信息?

Is there a way to get this kind of information, either with code or using some commands when I run an Erlang program?

谢谢.

推荐答案

1. 要获取单个进程的信息，可以调用 erlang:process_info(Pid).(从Erlang 18.0开始)这将产生以下字段:

1. To get information for a single process, you can call erlang:process_info(Pid). This will yield (as of Erlang 18.0) the following fields:

> erlang:process_info(self()).
[{current_function,{erl_eval,do_apply,6}},
 {initial_call,{erlang,apply,2}},
 {status,running},
 {message_queue_len,0},
 {messages,[]},
 {links,[<0.27.0>]},
 {dictionary,[]},
 {trap_exit,false},
 {error_handler,error_handler},
 {priority,normal},
 {group_leader,<0.26.0>},
 {total_heap_size,4184},
 {heap_size,2586},
 {stack_size,24},
 {reductions,3707},
 {garbage_collection,[{min_bin_vheap_size,46422},
                      {min_heap_size,233},
                      {fullsweep_after,65535},
                      {minor_gcs,7}]},
 {suspending,[]}]

该过程的收集周期数可在 garbage_collection 部分下的 minor_gcs 字段中找到.

The number of collection cycles for the process is available in the field minor_gcs under the section garbage_collection.

每个进程

该进程的当前堆大小在以上结果的字段 heap_size 中可用(换句话说，在32位VM上为4字节，在64位VM上为8字节).可以通过调用 erlang:process_info(Pid，memory)获得该进程的总内存消耗，该代码例如返回上述进程的 {memory，34312} .这包括调用堆栈，堆和内部结构.

The current heap size for the process is available in the field heap_size from the results above (in words, 4 bytes on a 32-bit VM and 8 bytes on a 64-bit VM). The total memory consumption of the process can be obtained by calling erlang:process_info(Pid, memory) which returns for example {memory,34312} for the above process. This includes call stack, heap and internal structures.

可以使用 erlang来跟踪解除分配(和分配):trace/3 .如果跟踪标志是 garbage_collection ，您将以 {trace，Pid，gc_start，Info} 和 {trace，Pid，gc_end，Info} . gc_start 消息的 Info 字段包含诸如 heap_size 和 old_heap_size 之类的东西.

Deallocations (and allocations) can be traced using erlang:trace/3. If the trace flag is garbage_collection you will received messages on the form {trace, Pid, gc_start, Info} and {trace, Pid, gc_end, Info}. The Info field of the gc_start message contains such things as heap_size and old_heap_size.

每个系统

可以通过 erlang获取系统的顶级统计信息:memory/0 :

> erlang:memory().
[{total,15023008},
 {processes,4215272},
 {processes_used,4215048},
 {system,10807736},
 {atom,202481},
 {atom_used,187597},
 {binary,325816},
 {code,4575293},
 {ets,234816}]

垃圾收集统计信息可以通过 erlang:statistics(垃圾收集) 会产生:

Garbage collection statistics can be obtained via erlang:statistics(garbage_collection) which yields:

> statistics(garbage_collection).
{85,23961,0}

(从Erlang 18.0开始)第一个字段是VM执行的垃圾收集总数，第二个字段是回收的单词总数.

Where (as of Erlang 18.0) the first field is the total number of garbage collections performed by the VM and the second field is the total number of words reclaimed.

进程的堆大小在字段 total_heap_size (所有堆碎片和堆栈)和 heap_size (最年轻的堆大小)下可用从上面的过程信息中.

The heap sizes for a process are available under the fields total_heap_size (all heap fragments and stack) and heap_size (the size of the youngest heap generation) from the process info above.

可以通过生成选项(特别是 min_heap_size 设置进程的初始堆大小.

They can be controlled via spawn options, specifically min_heap_size which sets the initial heap size for a process.

要为所有进程设置它，可以调用 erlang:system_flag(min_heap_size，MinHeapSize).

To set it for all process, erlang:system_flag(min_heap_size, MinHeapSize) can be called.

您还可以通过 + M ... 选项控制Erlang VM的全局VM内存分配.在此处中描述这些标志.但是，这需要对Erlang VM及其分配器的内部知识有广泛的了解，使用它们时不应掉以轻心.

You can also control global VM memory allocation via the +M... options to the Erlang VM. The flags are described here. However, this requires extensive knowledge about the internals of the Erlang VM and its allocators and using them should not be taken lightly.

这可以通过答案2中描述的跟踪来获得.如果在跟踪时使用选项 timestamp ，则会收到带有每个跟踪消息的时间戳，可用于计算总GC时间.

This can be obtained via the tracing described in answer 2. If you use the option timestamp when tracing, you will receive a timestamp with each trace message that can be used to calculate the total GC time.

简短答案:否.

长答案:也许吧.您可以控制初始堆大小(通过 min_heap_size )，该大小将影响第一次进行垃圾收集的时间.您还可以使用 fullsweep_after 选项控制何时执行完全扫描.

Long answer: Maybe. You can control the initial heap size (via min_heap_size) which will affect when garbage collection will occur the first time. You can also control when a full sweep will be performed with the fullsweep_after option.

更多信息，请参见学术和历史问题和过程部分.

More information can be found in the Academic and Historical Questions and Processes section of the Efficiency Guide.

在运行时自省Erlang内存使用的最实用方法是通过 Recon库，如提到了史蒂夫·维诺斯基.

The most practical way of introspecting Erlang memory usage at runtime is via the Recon library, as Steve Vinoski mentioned.

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