ORA-2730*引出的系统参数vm.min_free_kbytes理解

oerr ORA-2730*

[oracle@p19c01 ~]$ oerr ORA 27300
27300, 00000, "OS system dependent operation:%s failed with status: %s"
// *Cause:  OS system call error
// *Action: contact Oracle Support
[oracle@p19c01 ~]$ oerr ORA 27301
27301, 00000, "OS failure message: %s"
// *Cause:  OS system call error
// *Action: contact Oracle Support
//
[oracle@p19c01 ~]$ oerr ORA 27302
27302, 00000, "failure occurred at: %s"
// *Cause:  OS system call error
// *Action: contact Oracle Support
//

*Cause:  OS system call error

 The errors are usually caused by OS system call error or OS configuration issue 。

能够发现，若是数据库trace日志中出现ORA-2730*的错误，很大多是因为OS system的错误致使。

 

案例分析：

Tue Sep 01 04:05:33 2020
skgxpvfynet: mtype: 61 process 417356 failed because of a resource problem in the OS. The OS has most likely run out of buffers (rval: 4)
Errors in file /u01/app/oracle/diag/rdbms/*****/******/trace/******1_w001_417356.trc (incident=96021):
ORA-00603: ORACLE server session terminated by fatal error
ORA-27504: IPC error creating OSD context
ORA-27300: OS system dependent operation:sendmsg failed with status: 105
ORA-27301: OS failure message: No buffer space available
ORA-27302: failure occurred at: sskgxpsnd2
Incident details in: /u01/app/oracle/diag/rdbms/*****/******/incident/incdir_96021/******1_w001_417356_i96021.trc
opidrv aborting process W001 ospid (417356) as a result of ORA-603

以上为某一套数据库trace日志中报错的信息，能够发现几个关键点：

一、status: 105

二、 failure occurred at: sskgxpsnd2

三、No buffer space available。

Troubleshooting ORA-27300 ORA-27301 ORA-27302 Errors (Doc ID 579365.1)    

经过MOS文章能够查询到与上述报错相符的信息：

See: Oracle Linux: ORA-27301:OS Failure Message: No Buffer Space Available (Doc ID 2041723.1)

关于解决方案中提到的vm.min_free_kbytes参数，单位是KB，Oracle建议的取值范围是0.4%到5%之间，若是内存<=32G，能够忽略不设置。

查看系统vm.min_free_kbytes默认设置大小：

[root@p19c01 ~]# sysctl -a | grep vm.min_free_kbytes
vm.min_free_kbytes = 11433

查看系统开启NUMA的node数量：

numactl --hardware | grep available: | awk '{print $2}'

Notes：该参数表示Linux VM最低保留多少的空闲内存空间，当可用的内存低于配置参数时，系统会进行cache内存的回收，来进行内存的释放。

★ 参数简述
该Linux系统参数的功能是用来设置一个最小内存空间给系统内核使用
该值设置过大会浪费空间，保留太小会形成系统压力
★ 知识点
※ 用途：合理设置该值有助于Linux系统更有效地回收内存
※ 注意：对于内存较小（≤32GB）的环境不建议设置，保持默认便可
※ 危险：不要对正在运行的环境进行设置
※ 有修改操做，非原版
※ vm.min_free_kbytes参数的单位是：KB
※ 内存水位
    min水位：下的内存是保留给内核使用的；当到达min，会触发内存的direct reclaim
    low水位：比min高一些，当内存可用量小于low的时候，会触发 kswapd回收内存
    high水位：继续睡眠
※ 内存回收方式
    direct reclaim : 触发min水位线时执行
    kswapd reclaim : 触发low水位线时执行

这里摘自其余博主的一个计算脚本能够用来计算vm.min_free_kbytes，直接复制到shell控制台执行便可：

MIN_FREE_KBYTES_SYSCTL=$(egrep ^vm.min_free_kbytes /etc/sysctl.conf | awk '{print $3}')
MIN_FREE_KBYTES_MEMORY=$(cat /proc/sys/vm/min_free_kbytes)
NUMA_NODE_COUNT=$(numactl --hardware | grep available: | awk '{print $2}')
TOTAL_MEMORY_KBYTES=$(free -k | awk '/Mem:/ {print $2}')
NUMA_BASED=$(( $NUMA_NODE_COUNT * 1048576 ))
MEMORY_BASED=$(( $TOTAL_MEMORY_KBYTES / 200 ))
if [[ $NUMA_BASED -ge $MEMORY_BASED ]]
then
	RECOMMEND_VALUE=$NUMA_BASED
else
	RECOMMEND_VALUE=$MEMORY_BASED
fi
OFFSET=$(echo $RECOMMEND_VALUE*.05 | bc | cut -d"." -f1)
LOWER_BOUND=$(echo $RECOMMEND_VALUE-$OFFSET | bc)
UPPER_BOUND=$(echo $RECOMMEND_VALUE+$OFFSET | bc)
if [[ $MIN_FREE_KBYTES_SYSCTL -ge LOWER_BOUND && $MIN_FREE_KBYTES_SYSCTL -le UPPER_BOUND ]]
then
	SYSCTL_IN_RANGE=YES
else
	SYSCTL_IN_RANGE=NO
fi
#sysctl in range?
if [[ $MIN_FREE_KBYTES_MEMORY -ge LOWER_BOUND && $MIN_FREE_KBYTES_MEMORY -le UPPER_BOUND ]]
then
	MEMORY_IN_RANGE=YES
else
	MEMORY_IN_RANGE=NO
fi
DETAIL=$(
echo -e "Total Memory:       $TOTAL_MEMORY_KBYTES";
echo -e "NUMA node count:    $NUMA_NODE_COUNT";
echo -e "NUMA calculated:    $NUMA_BASED";
echo -e "memory calculated:  $MEMORY_BASED";
echo -e "recommended value:  $RECOMMEND_VALUE";
echo -e "permitted range:    $LOWER_BOUND to $UPPER_BOUND";
echo -e "in sysctl.conf:     $MIN_FREE_KBYTES_SYSCTL";
echo -e "sysctl in range?:   $SYSCTL_IN_RANGE";
echo -e "in active memory:   $MIN_FREE_KBYTES_MEMORY";
echo -e "memory in range?:   $MEMORY_IN_RANGE";
)
if [[ $SYSCTL_IN_RANGE = YES && $MEMORY_IN_RANGE = YES ]]
then
	echo -e "SUCCESS: vm.min_free_kbytes is configured as recommended.  Details:\n\n$DETAIL"
elif [[ $MIN_FREE_KBYTES_SYSCTL -lt $LOWER_BOUND || $MIN_FREE_KBYTES_MEMORY -lt $LOWER_BOUND ]]
then
	echo -e ":: Result : 【FAILURE】: vm.min_free_kbytes is not configured as recommended"
	ZZT_V1=$(( $NUMA_NODE_COUNT * 1 * 1024 * 1024 ))
	ZZT_V2=$(( $TOTAL_MEMORY_KBYTES * 5 /10 / 100 ))
	if [ $ZZT_V1 -gt $ZZT_V2 ]
	then
	ZZT_MAX=$ZZT_V1
	else
	ZZT_MAX=$ZZT_V2
	fi
	ZZT_MAX_GB=$(($ZZT_MAX/1024/1024))
	echo ">>> if output is <FAILURE>，please vi sysctl.conf and edit param's value for:vm.min_free_kbytes and reboot"
	echo ">>> [formula_oracle]vm.min_free_kbytes value (Kb) =MAX(1GB * number_numa_nodes, 0.5% * total_memory) "
	echo ">>> [calculated_zzt]vm.min_free_kbytes = $ZZT_MAX   (About: $ZZT_MAX_GB GB)"
	ZZT_V3=32
	ZZT_V4=$(($TOTAL_MEMORY_KBYTES/1024/1024))
	if [ $ZZT_V4 -gt $ZZT_V3 ]
	then
		echo ">>> [PASS]The current memory is suitable for setting system parameters."
	else
		echo ">>> [WARN]Your memory is too small to set this parameter."
	fi
	echo -e "Details:\n\n$DETAIL"
elif  [[ $MIN_FREE_KBYTES_SYSCTL -gt $UPPER_BOUND && $MIN_FREE_KBYTES_MEMORY -gt $UPPER_BOUND ]]
then
  echo -e "WARNING: vm.min_free_kbytes is not configured as recommended.  Details:\n\n$DETAIL"
else
  echo -e "ERROR: Inconsistent results.  Details:\n\n$DETAILS"
fi

测试结果以下：