昨天去南京某客户那里调优新上线的业务数据库，在查看alert.log日志时发现在过去的一段时间里，每过几个小时或间隔一段时间，就会报类以下的内容： Thu Aug 21 09:01:26 2014WARNING: Heavy swapping observed on system in last 5 mins.pct of memory swappe

There is new warning message in alert.log in 11.2.0.3 similar to

WARNING: Heavy swapping observed on system in last 5 mins.
pct of memory swapped in [2.08%] pct of memory swapped out [0.12%].
Please make sure there is no memory pressure and the SGA and PGA
are configured correctly. Look at DBRM trace file for more details.

On AIX platform this message can be seen even when there is no virtual memory swapping at all. --物理内存足够，而且根本没有使用swap交换空间

You may compare the vmstat from AIX level with DBRM trace file entries to see the differences.

The issue is caused by unpublished Bug:14731911.

Swap usage messages are based on statistics that do not reflect the actual usage.

The v$osstat does not reflect proper stats for the swap space paging.

Apply Patch:11801934 on top of your IBM AIX on POWER Systems (64-bit) platform.

P.S: Bug is port-specific. --这个bug是针对端口指定的平台的

The issue is fixed in patchset 11.2.0.4 and release 12.1. --说是在12.1的patch中修复了，但实际上12.1还是会有这个问题，会有ora-700错误，详见文档：[ID 1919850.1]

来看一下BUG：14731911的描述：

Hdr: 14731911 11.2.0.3 RDBMS 11.2.0.3 VOS PRODID-5 PORTID-212 11801934
Abstract: FALSE SWAP WARNING MESSAGES PRINTED TO ALERT.LOG ON AIX
 
*** 10/08/12 04:52 am ***
 
 
 BUG TYPE CHOSEN
 ===============
 Code
 
 SubComponent: Virtual Operating System
 ======================================
 DETAILED PROBLEM DESCRIPTION
 ============================
 Oracle process seems to check wrong OS local statistic (which include also
 FILESYSTEM caching etc.)
 
 Alert log shows WARNING: Heavy swapping observed on system in last 5 mins.
 pct of memory swapped in [2.08%] pct of memory swapped out [0.12%].
 Please make sure there is no memory pressure and the SGA and PGA 
 are configured correctly. Look at DBRM trace file for more details.
 
 but this is not reflected at OS level.
 
 DIAGNOSTIC ANALYSIS
 ===================
 1. nmon shows virtual memory swapping does not occur at all - see attached file --nmon根本没有监控到swap动作
 
 2. Oracle Database Server is 11.2.0.3 and contains fix for 10220118
 
 3. Server configuration
 real mem: 144GB
 lowest value of fre memory : 87,65 GB --剩余内存充足
 
 4. DBRM seems to use a wrong OS statistics - trace file is attached
 
 WORKAROUND?
 ===========
 No
 
 TECHNICAL IMPACT
 ================
 Wrong diagnostic analyze.
 Message is bothering customer's DBA when in fact the warning message is
 misleading
 
 RELATED ISSUES (bugs, forums, RFAs)
 ===================================
 http://myforums.oracle.com/jive3/thread.jspa?threadID=1104581 
 10220118
 
 HOW OFTEN DOES THE ISSUE REPRODUCE AT CUSTOMER SITE?
 ====================================================
 Always
 
 DOES THE ISSUE REPRODUCE INTERNALLY?
 ====================================
 No
 
 EXPLAIN WHY THE ISSUE WAS NOT TESTED INTERNALLY.
 ================================================
 Unavailable Data Volume
 
 IS A TESTCASE AVAILABLE?
 ========================
 No
 
 Link to IPS Package:
 ====================
 not available

AIX Platform

If your Platform is IBM-AIX then this is not the only possible reason for this alert log message.
For IBM AIX on POWER Systems (64-bit), there is also next known port-specific bug:
Bug 14731911 - FALSE SWAP WARNING MESSAGES PRINTED TO ALERT.LOG ON AIX
with unpublished base bug:
Bug 11801934 : WRONG PAGE-IN AND PAGE-OUT OS VM STATS IN AIX.

在vmware平台中的这个WARNING信息，如果不是bug引起，则很有可能和ora-04031/ora-04030相关，这个就严重多了

VMWare

Under VMWare, the messages may perhaps indicate a more serious issue, even when no memory related ORA-4031/ORA-4030 errors are reported.
Under circumstances, an instance in a virtual machine may be simply terminated by PMON due to error 471 without further errors in the alert log.
The OS logs may in such case report an out of memory condition like below:

通常解决OS内存swap问题有以下几种方案：

vm.min_free_kbytes:Raising the value in /proc/sys/vm/min_free_kbytes will cause the system to start reclaiming memory at an earlier time than it would have before.

vm.vfs_cache_pressure:At the default value of vfs_cache_pressure = 100 the kernel will attempt to reclaim dentries and inodes at a “fair” rate with respect to pagecache and swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100 causes the kernel to prefer to reclaim dentries and inodes.

vm.swappiness:default 60,Apparently /proc/sys/vm/swappiness on Red Hat Linux allows the admin to tune how aggressively the kernel swaps out processes'memory. Decreasing the swappiness setting may result in improved Directory performance as the kernel holds more of the server process in memory longer before swapping it out.

设置以下值，以减少OOM(Out Of Memory)的可能性:

# Oracle-Validated setting for vm.min_free_kbytes is 51200 to avoid OOM killer
vm.min_free_kbytes = 51200
vm.swappiness = 40
vm.vfs_cache_pressure = 200

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