用Valgrind检测PostgreSQL内存泄露
背景
Valgrind简介
Valgrind是一个开源工具集合，其中最有名的是Memcheck可用来检测C，C++程序的内存泄露，判断程序运行是否会crash或者产生不可预知的结果。
Valgrind Memcheck工具的用法
以下内容参考自Valgrind的quick start manual
http://www.valgrind.org/docs/manual/quick-start.html
1. 首先需要准备程序，注意程序编译时必须打开DEBUG，gcc -g参数。同时建议使用-O0编译，以免编译器优化代码后Valgrind无法给出实际的代码位置。
2. 如果你的程序是这样运行的
de >myprog arg1 arg2
de>
使用 valgrind 这样运行
de >Valgrind --leak-check=yes myprog arg1 arg2
The --leak-check option turns on the detailed memory leak detector
de>
3. 例子
需要跟踪的程序代码
这部分代码将有两处错误可以被检测到
de >#include <stdlib.h>
void f(void)
{
int* x = malloc(10 * sizeof(int));
x[10] = 0; // problem 1: heap block overrun
} // problem 2: memory leak -- x not freed
int main(void)
{
f();
return 0;
}
de>
跟踪到的结果及解释
第一个错误 heap block overrun
de >==19182== Invalid write of size 4 # 错误类型，一次越界写产生的invalid write
==19182== at 0x804838F: f (example.c:6) # 下面是进程的stack trace
==19182== by 0x80483AB: main (example.c:11)
==19182== Address 0x1BA45050 is 0 bytes after a block of size 40 alloc'd # 描述产生错误的内存地址
==19182== at 0x1B8FF5CD: malloc (vg_replace_malloc.c:130)
==19182== by 0x8048385: f (example.c:5)
==19182== by 0x80483AB: main (example.c:11)
19182表示PID
de>
第二个错误，内存泄露
de >==19182== 40 bytes in 1 blocks are definitely lost in loss record 1 of 1 # 错误类型，产生内存泄露
==19182== at 0x1B8FF5CD: malloc (vg_replace_malloc.c:130) # 请忽略该系统调用
==19182== by 0x8048385: f (a.c:5) # 这里是产生错误的根源
==19182== by 0x80483AB: main (a.c:11)
de>
产生内存泄露的类型非常多，最常见的两种
de >"definitely lost": your program is leaking memory -- fix it! 必须fix的
"probably lost": your program is leaking memory, unless you're doing funny things with pointers (such as moving them to point to the middle of a heap block). 需要关注的，做一些操作时才会触发。
de>
如果报了一些未初始化值(uninitialised values)的错误，则需要给valgrind加–track-origins=yes参数，输出更详细的信息来分析。
如何检测PostgreSQL内存泄露
PostgreSQL 9.4开始，内核层面支持valgrind。
编译前需要改一下头文件。
de >src/include/pg_config_manual.h
de>
把#define USE_VALGRIND的注释去掉
de >/*
* Include Valgrind "client requests", mostly in the memory allocator, so
* Valgrind understands PostgreSQL memory contexts. This permits detecting
* memory errors that Valgrind would not detect on a vanilla build. See also
* src/tools/valgrind.supp. "make installcheck" runs 20-30x longer under
* Valgrind. Note that USE_VALGRIND slowed older versions of Valgrind by an
* additional order of magnitude; Valgrind 3.8.1 does not have this problem.
* The client requests fall in hot code paths, so USE_VALGRIND also slows
* native execution by a few percentage points.
*
* You should normally use MEMORY_CONTEXT_CHECKING with USE_VALGRIND;
* instrumentation of repalloc() is inferior without it.
*/
#define USE_VALGRIND
/*
* Define this to check memory allocation errors (scribbling on more
* bytes than were allocated). Right now, this gets defined
* automatically if --enable-cassert or USE_VALGRIND.
*/
#if defined(USE_ASSERT_CHECKING) || defined(USE_VALGRIND)
#define MEMORY_CONTEXT_CHECKING
#endif
de>
编译参数
de >CFLAGS=-O0 ./configure --prefix=/home/digoal/pgsql9.5 --enable-debug
gmake world -j 32
gmake install-world -j 32
de>
确认编译正确
de >$ pg_config
de>
得到如下结果
de >CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -g -O0
de>
启用Valgrind调试PostgreSQL
初始化数据库集群，配置数据库配置文件等，略。
使用 Valgrind启动数据库(需要指定PostgreSQL源码中的src/tools/valgrind.supp，这个文件是按照Valgrind提供的格式写的，有兴趣可以研究一下它的内容)
de >$ cd postgresql-9.5.3_src/
$ valgrind --leak-check=yes --gen-suppressions=all \
--suppressions=src/tools/valgrind.supp --time-stamp=yes \
--log-file=/tmp/%p.log --trace-children=yes \
--track-origins=yes --read-var-info=yes \
--show-leak-kinds=all -v \
postgres --log_line_prefix="%m %p " \
--log_statement=all --shared_buffers=4GB 2>&1 | tee /tmp/postmaster.log
启动会非常慢，等待它启动完成。
Valgrind的参数略
Valgrind --help
regresstest模式
另外开启一个会话
de >cd postgresql-9.5.3_src
make installcheck
de>
观察 –log-file=/tmp/%p.log 日志
用户定制调试
另外开启一个会话
输入需要测试的SQL
观察 –log-file=/tmp/%p.log 日志
小结
参考
http://www.valgrind.org/docs/manual/quick-start.html
https://wiki.postgresql.org/wiki/Valgrind
http://windmissing.github.io/linux/2016-02/valgrind-memcheck.html
http://www.cnblogs.com/napoleon_liu/articles/2001802.html
http://blog.chaorenmao.com/?p=831