[20190409]pre_page_sga=true与连接缓慢的问题.txt
--//曾经遇到11g下设置pre_page_sga=true启动缓慢的问题(没有使用hugepages).
--//链接:http://blog.itpub.net/267265/viewspace-2295412/
--//实际上这样系统也会遇到连接缓慢的情况,通过测试说明问题.
1.建立pfile:
$ cat initxxxx.ora
db_name=xxxx
instance_name=xxxx
sga_target=20G
#sga_target=0
sga_max_size=20G
pre_page_sga=true
$ export ORACLE_SID=xxxx
SYS@xxxx> startup nomount
ORACLE instance started.
Total System Global Area 2.1379E+10 bytes
Fixed Size 2262656 bytes
Variable Size 2818574720 bytes
Database Buffers 1.8522E+10 bytes
Redo Buffers 36073472 bytes
$ grep -i page /proc/meminfo
AnonPages: 239336 kB
PageTables: 701008 kB
AnonHugePages: 0 kB
HugePages_Total: 104
HugePages_Free: 48
HugePages_Rsvd: 41
HugePages_Surp: 0
Hugepagesize: 2048 kB
--//才启动没有任何用户连接,PageTables=701008 kB.
2.测试登陆问题:
$ time sqlplus -s -l / as sysdba <<<quit
real 0m4.944s
user 0m0.024s
sys 0m0.016s
--//单个连接需要5秒.如果多个用户并发呢?
$ cat aa.sql
quit
$ time seq 50 | xargs -I{} -P 50 sqlplus -s -l / as sysdba @ aa.sql
real 0m13.978s
user 0m1.833s
sys 0m1.017s
--//多个用户同时登录,全部完成需要13秒.
3.分析:
$ strace -f -c sqlplus -s -l / as sysdba <<<quit
Process 3120 attached
Process 3120 detached
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
99.85 0.419648 69941 6 shmdt
0.10 0.000434 1 413 2 read
0.01 0.000046 0 287 127 open
0.01 0.000045 0 180 mmap
0.01 0.000037 0 178 close
0.01 0.000032 0&n