[20260426]验证11g下pre_page_sga=true的一些细节.txt

--//验证几个问题。
1.在11g下pre_page_sga=true的情况下，sga内存是否全部分配。
2.在11g下pre_page_sga=true的情况下，是否会启动或者存在sa后台进程。

1.环境：
SYS@book> @ ver1
PORT_STRING                    VERSION        BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx            11.2.0.4.0     Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

2.测试1：
--//在11g下pre_page_sga=true的情况下，sga内存是否全部分配。
SYS@book> alter system set pre_page_sga=true scope=spfile;
System altered.

SYS@book> shutdown immediate ;
Database closed.
Database dismounted.
ORACLE instance shut down.

SYS@book> startup
ORACLE instance started.
Total System Global Area  801701888 bytes
Fixed Size                  2257520 bytes
Variable Size             285216144 bytes
Database Buffers          507510784 bytes
Redo Buffers                6717440 bytes
Database mounted.
Database opened.

$ grep -i hugepages /proc/meminfo
AnonHugePages:     16384 kB
HugePages_Total:     385
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
--//可以发现全部分配，与21c的情况完全不同，21c总存在小量内存没有分配。

3.测试2：
--//在11g下pre_page_sga=true的情况下，是否会启动或者存在sa后台进程。

$ watch -n 0.1 "pgrep -l ora_sa00_book|ts.awk | tee -a p9.txt"                                                                                                                                                                   [1/1]
Every 0.1s: pgrep -l ora_sa00_book|ts.awk | tee -a p9.txt

--//启动数据库：
$ cat p9.txt

--//说明11g不存在后台进程sa。

SYS@book> alter system set use_large_pages=false scope=spfile ;
System altered.

--//不使用hugepages看看。

$ watch -n 0.1 "pgrep -l ora_sa00_book|ts.awk | tee -a pa.txt"

--//启动数据库：
$ cat p9.txt

--//说明11g不存在后台进程sa。

4.收尾还原：
SYS@book> alter system set use_large_pages=only scope=spfile ;
System altered.

SYS@book> alter system reset pre_page_sga;
System altered.

--//还发现11g还记录了分配Large Pages的使用时间。查看alert日志：
Tue Apr 21 09:15:19 2026
Adjusting the default value of parameter parallel_max_servers
from 160 to 150 due to the value of parameter processes (180)
Starting ORACLE instance (normal)
DISM started, OS id=3422
************************ Large Pages Information *******************
Parameter use_large_pages = AUTO
Per process system memlock (soft) limit = 128 GB

Total Shared Global Region in Large Pages = 770 MB (100%)

Large Pages used by this instance: 385 (770 MB)
Large Pages unused system wide = 0 (0 KB)
Large Pages configured system wide = 385 (770 MB)
Large Page size = 2048 KB
Time taken to allocate Large Pages = 0.002841 sec
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
********************************************************************

--//大部分情况记录的是0.
$ grep -i "Time taken" alert_book.log
Time taken to allocate Large Pages = 0.002841 sec
Time taken to allocate Large Pages = 0.000000 sec
Time taken to allocate Large Pages = 0.000000 sec
Time taken to allocate Large Pages = 0.000000 sec
Time taken to allocate Large Pages = 0.000000 sec
Time taken to allocate Large Pages = 0.000000 sec
Time taken to allocate Large Pages = 0.000000 sec

$ egrep -i "^Time taken|^Parameter use_large_pages =" alert_book.log | grep -A1 "Parameter use_large_pages = AUTO"
Parameter use_large_pages = AUTO
Time taken to allocate Large Pages = 0.002841 sec
Parameter use_large_pages = AUTO
Time taken to allocate Large Pages = 0.000000 sec
--
Parameter use_large_pages = AUTO
Time taken to allocate Large Pages = 0.000000 sec
Parameter use_large_pages = AUTO
Time taken to allocate Large Pages = 0.000000 sec
Parameter use_large_pages = AUTO
Time taken to allocate Large Pages = 0.000000 sec
Parameter use_large_pages = AUTO
Time taken to allocate Large Pages = 0.000000 sec
Parameter use_large_pages = AUTO
Time taken to allocate Large Pages = 0.000000 sec
--//而且仅仅设置use_large_pages = AUTO的情况下，有记录。

--//21c下没有这个记录：
$ grep -i "Time taken" alert_book.log