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MongoDB日志切换（Rotate Log Files）方法及注意事项
转载自：
MongoDB日志默认不会切换，生产系统尤其是压力大的系统，日志滚动速度非常快，我们上线系统最大的一个mongod进程的log每天增长5G多。目前采取策略是每天切换一次，保存一周的日志。
目前采取的方法：· SIGUSR1 方法
killall -SIGUSR1 mongod
每天0点定时执行来达切换日志。 大部分情况下并无问题，但近期集中出现了两台服务器日志切换时出现问题，0点到0点20分左右，日志是空的。mongod 或者config报警，进程重启（自动），该至少要到2.5.x才修复。MongoDB的稳定性目前确实不尽人意。
· 采取mongo shell logRotate 来避免该bug
use admin
db.runCommand( { logRotate : 1 } ) 此方法需要在mongos,mongod,config server运行，不能一次性切换所有日志。
logRotate命令也有‘bug’，这两天出现了两次（版本2.2.2）：
Sat May 4 00:01:02 [conn96028478] ERROR: Failed to rename /export/data/mongodb/log/mongod.log to /export/data/mongodb/log/mongod.log.2013-05-03T16-01-02 Fatal Assertion 16175
0xaffd31 0xac5323 0x70f4f1 0x6e8d71 0x6ea5e2 0x6eb59c 0x832c68 0x8363b0 0x7b072d 0x7b3a53 0x5703f2 0xaedfc1 0x32ad2077f1 0x32acee570d
/export/servers/mongodb/bin/mongod(_ZN5mongo15printStackTraceERSo+0x21) [0xaffd31]
/export/servers/mongodb/bin/mongod(_ZN5mongo13fassertFailedEi+0xa3) [0xac5323]
/export/servers/mongodb/bin/mongod() [0x70f4f1]
/export/servers/mongodb/bin/mongod(_ZN5mongo12_execCommandEPNS_7CommandERK***NS_7BSONObjEiRNS_14BSONObjBuilderEb+0x51) [0x6e8d71]
/export/servers/mongodb/bin/mongod(_ZN5mongo11execCommandEPNS_7CommandERNS_6ClientEiPKcRNS_7BSONObjERNS_14BSONObjBuilderEb+0xd52) [0x6ea5e2]
/export/servers/mongodb/bin/mongod(_ZN5mongo12_runCommandsEPKcRNS_7BSONObjERNS_11_BufBuilderINS_16TrivialAllocatorEEERNS_14BSONObjBuilderEbi+0x2ac) [0x6eb59c]
/export/servers/mongodb/bin/mongod(_ZN5mongo11runCommandsEPKcRNS_7BSONObjERNS_5CurOpERNS_11_BufBuilderINS_16TrivialAllocatorEEERNS_14BSONObjBuilderEbi+0x38) [0x832c68]
/export/servers/mongodb/bin/mongod(_ZN5mongo8runQueryERNS_7MessageERNS_12QueryMessageERNS_5CurOpES1_+0xc10) [0x8363b0]
/export/servers/mongodb/bin/mongod() [0x7b072d]
/export/servers/mongodb/bin/mongod(_ZN5mongo16assembleResponseERNS_7MessageERNS_10DbResponseERKNS_11HostAndPortE+0x3a3) [0x7b3a53]
/export/servers/mongodb/bin/mongod(_ZN5mongo16MyMessageHandler7processERNS_7MessageEPNS_21AbstractMessagingPortEPNS_9LastErrorE+0x82) [0x5703f2]
/export/servers/mongodb/bin/mongod(_ZN5mongo3pms9threadRunEPNS_13MessagingPortE+0x411) [0xaedfc1]
/lib64/libpthread.so.0() [0x32ad2077f1]
/lib64/libc.so.6(clone+0x6d) [0x32acee570d]
Sat May 4 00:01:02 [conn96028478]
***aborting after fassert() failure
Sat May 4 00:01:02 Got signal: 6 (Aborted).
Sat May 4 00:01:02 Backtrace:
0xaffd31 0x558bb9 0x32ace32900 0x32ace32885 0x32ace34065 0xac535e 0x70f4f1 0x6e8d71 0x6ea5e2 0x6eb59c 0x832c68 0x8363b0 0x7b072d 0x7b3a53 0x5703f2 0xaedfc1 0x32ad2077f1 0x32acee570d
/export/servers/mongodb/bin/mongod(_ZN5mongo15printStackTraceERSo+0x21) [0xaffd31]
/export/servers/mongodb/bin/mongod(_ZN5mongo10abruptQuitEi+0x399) [0x558bb9]
/lib64/libc.so.6() [0x32ace32900]
/lib64/libc.so.6(gsignal+0x35) [0x32ace32885]
/lib64/libc.so.6(abort+0x175) [0x32ace34065]
/export/servers/mongodb/bin/mongod(_ZN5mongo13fassertFailedEi+0xde) [0xac535e]
/export/servers/mongodb/bin/mongod() [0x70f4f1]
/export/servers/mongodb/bin/mongod(_ZN5mongo12_execCommandEPNS_7CommandERK***NS_7BSONObjEiRNS_14BSONObjBuilderEb+0x51) [0x6e8d71]
/export/servers/mongodb/bin/mongod(_ZN5mongo11execCommandEPNS_7CommandERNS_6ClientEiPKcRNS_7BSONObjERNS_14BSONObjBuilderEb+0xd52) [0x6ea5e2]
/export/servers/mongodb/bin/mongod(_ZN5mongo12_runCommandsEPKcRNS_7BSONObjERNS_11_BufBuilderINS_16TrivialAllocatorEEERNS_14BSONObjBuilderEbi+0x2ac) [0x6eb59c]
/export/servers/mongodb/bin/mongod(_ZN5mongo11runCommandsEPKcRNS_7BSONObjERNS_5CurOpERNS_11_BufBuilderINS_16TrivialAllocatorEEERNS_14BSONObjBuilderEbi+0x38) [0x832c68]
/export/servers/mongodb/bin/mongod(_ZN5mongo8runQueryERNS_7MessageERNS_12QueryMessageERNS_5CurOpES1_+0xc10) [0x8363b0]
/export/servers/mongodb/bin/mongod() [0x7b072d]
/export/servers/mongodb/bin/mongod(_ZN5mongo16assembleResponseERNS_7MessageERNS_10DbResponseERKNS_11HostAndPortE+0x3a3) [0x7b3a53]
/export/servers/mongodb/bin/mongod(_ZN5mongo16MyMessageHandler7processERNS_7MessageEPNS_21AbstractMessagingPortEPNS_9LastErrorE+0x82) [0x5703f2]
/export/servers/mongodb/bin/mongod(_ZN5mongo3pms9threadRunEPNS_13MessagingPortE+0x411) [0xaedfc1]
/lib64/libpthread.so.0() [0x32ad2077f1]
/lib64/libc.so.6(clone+0x6d) [0x32acee570d]
对应源码：
class LogRotateCmd : public Command {
public:
LogRotateCmd() : Command( "logRotate" ) {}
virtual LockType locktype() const { return NONE; }
virtual bool slaveOk() const { return true; }
virtual bool adminOnly() const { return true; }
virtual bool run(const string& ns, BSONObj& cmdObj, int, string& errmsg, BSONObjBuilder& result, bool fromRepl) {
fassert(16175, rotateLogs());
return 1;
}
} logRotateCmd;
rotateLogs()返回结果不对。
bool rotateLogs() {
return loggingManager.rotate();
}
rotateLogs()->rotate()
bool rotate() {
if ( ! _enabled ) {
cout << "LoggingManager not enabled" << endl;
return true;
}
if ( _file ) {
#ifdef POSIX_FADV_DONTNEED
posix_fadvise(fileno(_file), 0, 0, POSIX_FADV_DONTNEED);
#endif
// Rename the (open) existing log file to a timestamped name
stringstream ss;
ss << _path << "." << terseCurrentTime( false );
string s = ss.str();
if (0 != rename(_path.c_str(), s.c_str())) {
error() << "Failed to rename " << _path << " to " << s;
return false;
}
}
...
return true;
}
显然是rename函数运行出来问题。rename应该是boost::filesystem::rename函数，而filesystem/v3 有个bug ，rename文件时如果存在相同的目标文件名，会抛异常：
boost::filesystem::rename throw exception when target file exists, but documentation tell us that it must be replaced MongoDB 2.2.2恰恰就是用的该版本。 那么mongod down的原因只能是还有别的进程在切日志，要不没法解释，这就的查查有没有别的机器连上了切日志。结果发现该机器mongo用户下有个相同的crontab 任务，而正常情况下都是用root用户的。自此罪魁祸首找到了！再深的bug都有个简单的源头！
另外：logRotate相关bug在2.2.5、2.4.3版本解决，详见SERVER-4739。
日志切换相关两个断言：
16175 is for a failure of the 'logRotate' command (e.g. 'db.adminCommand("logRotate")'). 16176 is for a failure when SIGUSR1 has been received (not available on Windows).
· 使用syslog管理日志
2.2版本以后可采用，将日志由syslog管理。用syslog特性来切换日志。
修改/etc/rsyslog.conf .info;mail.none;authpriv.none;cron.none;user.none /var/log/messages user. /export/data/log/mongosyslog.log
修改/etc/logrotate.conf ，添加：
/export/data/log/mongosyslog.log { missingok daily rotate 7 postrotate /usr/bin/kill -HUP rsyslogd endscript }
设置了每天切换一次，手动切换方法logrotate -f /etc/logrotate.conf
more:
更新ERROR:
Failed to rename /export/data/mongodb/log/mongod.log to /export/data/mongodb/log/mongod.log.2013-05-03T16-01-02 Fatal Assertion 16175部分
日志切换另一个bug
目前2.2.5,2.4.4均已修复。