linux大内存页设置for 19c

关于大内存页的设置重要性不再赘述，总之为了性能着想，务必开启大内存页配置，以大大减少操作系统对于内存的管理开销成本。
本站搜索"HugePage"可查到笔者早期的博文<<linux大内存页设置>>
在19c日志里，数据库启动时，如果没有开启预期的HugePage设置，开始就会明确提出配置建议，大致内容如下所示。

2020-09-03T10:06:18.639578+08:00
 Per process system memlock (soft) limit = UNLIMITED
 Expected per process system memlock (soft) limit to lock
 instance MAX SHARED GLOBAL AREA (SGA) into memory: 10G
 Available system pagesizes:
  4K, 2048K
 Supported system pagesize(s):
  PAGESIZE  AVAILABLE_PAGES  EXPECTED_PAGES  ALLOCATED_PAGES  ERROR(s)
        4K       Configured               8         2621448        NONE
     2048K                0            5121               0        NONE
RECOMMENDATION:
 1. For optimal performance, configure system with expected number
 of pages for every supported system pagesize prior to the next
 instance restart operation.

好的，看明白了，本系统页大小有两种，4K和2M，根据SGA的设置，期望的HugePage页数为5121，都不用你自己手动计算了，其实手动计算也很简单，简单的根据sga_max_size/2M+1即可。
配置/etc/security/limits.conf：
oracle soft memlock unlimited
oracle hard memlock unlimited
配置/etc/sysctl.conf
cat >> /etc/sysctl.conf << EOF
vm.nr_hugepages=5121
EOF
重启OS/DB生效
之后再检查alertlog，配置成功：

**********************************************************************
2020-09-03T11:37:36.665863+08:00
Dump of system resources acquired for SHARED GLOBAL AREA (SGA)
 Per process system memlock (soft) limit = UNLIMITED
 Expected per process system memlock (soft) limit to lock
 instance MAX SHARED GLOBAL AREA (SGA) into memory: 10G
 Available system pagesizes:
  4K, 2048K
 Supported system pagesize(s):
  PAGESIZE  AVAILABLE_PAGES  EXPECTED_PAGES  ALLOCATED_PAGES  ERROR(s)
        4K       Configured               8               8        NONE
     2048K             5121            5121            5121        NONE
**********************************************************************