Daily Archives: 2012 年 01 月 04 日

Liunx系统中Oracle使用HugePages配置

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一.系统当前状态

[root@node1 ora11g]#  cat /proc/meminfo | grep -i hugepages 
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
Hugepagesize:     2048 kB
[root@node1 ora11g]# uname -sr
Linux 2.6.18-238.19.1.el5
cat /proc/meminfo|grep PageT
PageTables:      44748 kB

二.计算nr_hugepages值

#!/bin/bash
#
# hugepages_settings.sh
#
# Linux bash script to compute values for the
# recommended HugePages/HugeTLB configuration
#
# Note: This script does calculation for all shared memory
# segments available when the script is run, no matter it
# is an Oracle RDBMS shared memory segment or not.
#
# This script is provided by Doc ID 401749.1 from My Oracle Support 
# http://support.oracle.com

# Welcome text
echo "
This script is provided by Doc ID 401749.1 from My Oracle Support 
(http://support.oracle.com) where it is intended to compute values for 
the recommended HugePages/HugeTLB configuration for the current shared 
memory segments. Before proceeding with the execution please make sure 
that:
 * Oracle Database instance(s) are up and running
 * Oracle Database 11g Automatic Memory Management (AMM) is not setup 
   (See Doc ID 749851.1)
 * The shared memory segments can be listed by command:
     # ipcs -m

Press Enter to proceed..."

read

# Check for the kernel version
KERN=`uname -r | awk -F. '{ printf("%d.%d\n",$1,$2); }'`

# Find out the HugePage size
HPG_SZ=`grep Hugepagesize /proc/meminfo | awk '{print $2}'`

# Initialize the counter
NUM_PG=0

# Cumulative number of pages required to handle the running shared memory segments
for SEG_BYTES in `ipcs -m | awk '{print $5}' | grep "[0-9][0-9]*"`
do
   MIN_PG=`echo "$SEG_BYTES/($HPG_SZ*1024)" | bc -q`
   if [ $MIN_PG -gt 0 ]; then
      NUM_PG=`echo "$NUM_PG+$MIN_PG+1" | bc -q`
   fi
done

RES_BYTES=`echo "$NUM_PG * $HPG_SZ * 1024" | bc -q`

# An SGA less than 100MB does not make sense
# Bail out if that is the case
if [ $RES_BYTES -lt 100000000 ]; then
   echo "***********"
   echo "** ERROR **"
   echo "***********"
   echo "Sorry! There are not enough total of shared memory segments allocated for 
HugePages configuration. HugePages can only be used for shared memory segments 
that you can list by command:

   # ipcs -m

of a size that can match an Oracle Database SGA. Please make sure that:
 * Oracle Database instance is up and running 
 * Oracle Database 11g Automatic Memory Management (AMM) is not configured"
   exit 1
fi

# Finish with results
case $KERN in
   '2.4') HUGETLB_POOL=`echo "$NUM_PG*$HPG_SZ/1024" | bc -q`;
          echo "Recommended setting: vm.hugetlb_pool = $HUGETLB_POOL" ;;
   '2.6') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
    *) echo "Unrecognized kernel version $KERN. Exiting." ;;
esac

# End

1.Configuring the Script

Create a text file named hugepages_settings.sh
Copy the contents below in the file
Run 
	$ chmod +x hugepages_settings.sh

2.Running the Script

Be sure that all applications that are meant to use HugePage / HugeTLB are running at the time the script is to be run. 
This includes the Oracle RDBMS instances and ASM instances in addition to other applications.
Be sure that you have /bin and /usr/bin in $PATH
Run
	$ ./hugepages_settings.sh

三.修改系统配置

1./etc/sysctl.conf
vm.nr_hugepages = 770

2./etc/security/limits.conf
oracle soft memlock 102400
oracle hard memlock 102400

计算公式为：>=HugePages_Total*Hugepagesize

四.重启系统检查配置是否生效

[root@node1 ~]# cat /proc/meminfo | grep -i hugepages 
HugePages_Total:   770
HugePages_Free:    770
HugePages_Rsvd:      0
Hugepagesize:     2048 kB

五.启动数据库并验证

[oracle@node1 ~]$ sqlplus / as sysdba

SQL*Plus: Release 10.2.0.5.0 - Production on Wed Jan 4 16:06:48 2012

Copyright (c) 1982, 2010, Oracle.  All Rights Reserved.

Connected to an idle instance.

SQL> startup
ORACLE instance started.

Total System Global Area 1610612736 bytes
Fixed Size                  2096632 bytes
Variable Size             486539784 bytes
Database Buffers         1107296256 bytes
Redo Buffers               14680064 bytes
Database mounted.
Database opened.
SQL> exit

[oracle@node1 ~]$ grep Huge /proc/meminfo 
HugePages_Total:   770
HugePages_Free:    591
HugePages_Rsvd:    590
Hugepagesize:     2048 kB
[oracle@node1 ~]$ cat /proc/meminfo|grep PageT
PageTables:      13216 kB

HugePages_Free<>HugePages_Total,PageTables变小
证明HugePages配置成功

六.补充说明
1.在数据库内存服务器内存比较大的时候，可以考虑使用该功能，提高系统性能
2.对于Oracl 11g,如果需要使用此功能，需要关闭AMM功能(需要衡量)

ORA-01555 caused by SQL statement below

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一.发现ORA-01555

Mon Dec 26 10:08:22 2011
ORA-01555 caused by SQL statement below (Query Duration=49146 sec, SCN: 0x0b4b.17f5ae42):
Mon Dec 26 10:08:22 2011
SELECT COMPANY_ID,
       COMPANY_MOBILE,
       TO_CHAR(NVL(REG_DATE, SYSDATE - 100), 'yyyymmddhh24miss'),
       BAK_FIELD2
  FROM TAB_XN_COMPANY
 WHERE (COMPANY_STATUS = 1 OR
       (COMPANY_STATUS = 3 AND
       NVL(UNREG_DATE, SYSDATE + 100) >=
       TO_DATE('20111226094500', 'yyyymmddhh24miss')))
   AND NVL(REG_DATE, SYSDATE - 100) <=
       TO_DATE('20111226095959', 'yyyymmddhh24miss')
   AND PAY_TYPE > 0

二.数据库状态

[oracle@ora02 ~]$ sqlplus "/ as sysdba"

SQL*Plus: Release 9.2.0.4.0 - Production on Wed Jan 4 10:48:17 2012

Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.


Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.4.0 - Production

SQL> show parameter undo;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                      string      AUTO
undo_retention                       integer     10800
undo_suppress_errors                 boolean     FALSE
undo_tablespace                      string      UNDOTBS1

SQL> select sum(maxbytes)/1024/1024/1024,
   2 SUM(USER_BYTES)/1024/1024/1024 FROM dba_data_files where tablespace_NAME='UNDOTBS1';

SUM(MAXBYTES)/1024/1024/1024 SUM(USER_BYTES)/1024/1024/1024
---------------------------- ------------------------------
                  61.9999847                     32.6834106

SQL> SELECT DISTINCT STATUS "状态",
  2                  COUNT(*) "EXTENT数量",
  3                  SUM(BYTES) / 1024 / 1024 / 1024 "UNDO大小"
  4    FROM DBA_UNDO_EXTENTS
  5   GROUP BY STATUS;

状态      EXTENT数量   UNDO大小
--------- ---------- ----------
ACTIVE             1 .000976563
EXPIRED         2549 31.2333298
UNEXPIRED          3 .000175476

通过undo_retention保留时间为10800秒，而该sql执行了49146秒，在这49146秒钟，TAB_XN_COMPANY表中的数据被修改，而且被修改的undo数据在10800秒后被覆盖导致，导致原查询语句不能获取到scn小于或者等于查询时候的数据块内容(在undo中)，所以出现ORA-01555。从这里也可以看出来，在undo空间还剩余的情况下，如果超过了undo_retention限制，undo内容还是有可能被覆盖，而不是使用未使用的undo

三.出现ORA-1555原因
The ORA-1555 errors can happen when a query is unable to access enough undo to build a copy of the data at the time the query started. Committed “versions” of blocks are maintained along with newer uncommitted “versions” of those blocks so that queries can access data as it existed in the database at the time of the query. These are referred to as “consistent read” blocks and are maintained using Oracle undo management.
就是一个查询要访问某个数据块，而这个数据块在这个查询执行过程中修改过，那么该查询需要查询undo中数据块，而undo中该数据块已经不存在，从而出现ORA-1555

四.ORA-1555解决方法
Case 1 – Rollback Overwritten
1.缩短sql运行时间
2.增加undo_retention，这个同时需要考虑undo空间大小
3.减少commit(rollback)次数
4.在一条sql中尽量使数据块访问一次
4.1)Using a full table scan rather than an index lookup
4.2)Introducing a dummy sort so that we retrieve all the data, sort it and then sequentially visit these data blocks.

Case 2 – Rollback Transaction Slot Overwritten
这种问题，主要是延迟块清理导致，一般建议在进行大批量的dml操作后，使用全表(全index)扫描执行一遍，或者收集全部统计信息