在Oracle 11.2.0.3.0上开启大页（hugepages）的详细解析

什么时侯使用大页呢，当你主机的物理内存为64G，设SGAgt;=32G时，建议开启大页，步骤如下：1、 关闭Oracle Database 11g中的AMM

什么时侯使用大页呢，，当你主机的物理内存为64G，设SGA>=32G时，建议开启大页，步骤如下：

1、 关闭Oracle Database 11g中的AMM(Automatic Memory Management)，即把两个参数MEMORY_TARGET / MEMORY_MAX_TARGET设为0

如果设考数 MEMORY_MAX_TARGET为0不成功，那么请考参

gyj@OCM> show parameter memory_max_target

NAME                                TYPE        VALUE
------------------------------------ ----------- ------------------------------
memory_max_target                    big integer 0
gyj@OCM> show parameter memory_target

NAME                                TYPE        VALUE
------------------------------------ ----------- ------------------------------
memory_target                        big integer 0

2、参考metalink(文档 ID 401749.1)提供的脚本,计算hugepages的大小
[oracle@mydb admin]$ vi /u01/app/oracle/product/11.2.0/rdbms/admin/hugepages_settings.sh

#!/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
#

# Welcome text
echo "
This script is provided by Doc ID 401749.1 from My Oracle Support
() 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 note following:
 * For ASM instance, it needs to configure ASMM instead of AMM.
 * The 'pga_aggregate_target' is outside the SGA and
  you should accommodate this while calculating SGA size.
 * In case you changes the DB SGA size,
  as the new SGA will not fit in the previous HugePages configuration,
  it had better disable the whole HugePages,
  start the DB with new SGA size and run the script again.
And 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 $2}'`
if [ -z "$HPG_SZ" ];then
    echo "The hugepages may not be supported in the system where the script is being executed."
    exit 1
fi

# Initialize the counter
NUM_PG=0

# Cumulative number of pages required to handle the running shared memory segments
for SEG_BYTES in `ipcs -m | cut -c44-300 | awk '{print $1}' | grep "[0-9][0-9]*"`
do
    MIN_PG=`echo "$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    '2.2') echo "Kernel version $KERN is not supported. Exiting." ;;
    '2.4') HUGETLB_POOL=`echo "$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" ;;
esac

# End