Oracle 体系结构概述
1.定义数据库和实例
实例（instance）和数据库（database）
- 数据库（database）：物理操作系统文件或磁盘（disk）的集合。
- 实例（instance）:一组Oracle后台进程/线程以及一个共享内存区，这些内容由同一个计算机上运行的线程/进程所共享。
- 实例和数据库之间的关系： 数据库可以由多个实例装载和打开，而实例可以在任何时间点装载和打开一个数据库。准确的讲，实例在其整个生存期中最多能装载和打开一个数据库。
实例就是一组操作系统进程（或者是一个多线程的进程）以及一些内存。
数据库只是一个文件集合（包括数据文件、临时文件、重做日志文件和控制文件）。
ps(进程状态)命令，可以看到用户运行的所有进程。
ipcs 命令，可用于显示进程间的通信设备，如共享内存，信号量等。目前系统中没有使用任何通信设备。
[oracle@MaxwellDBA dbs]$ ll
total 20
-rw-rw---- 1 oracle oinstall 1544 Sep 27 11:12 hc_ORCLCDB.dat
-rw-r--r-- 1 oracle oinstall 3079 May 14 2015 init.ora
-rw-r----- 1 oracle oinstall 24 Jun 29 05:28 lkORCLCDB
-rw-r----- 1 oracle oinstall 2048 Jun 29 09:49 orapwORCLCDB
-rw-r----- 1 oracle oinstall 3584 Sep 29 16:00 spfileORCLCDB.ora
[oracle@MaxwellDBA dbs]$
[oracle@MaxwellDBA dbs]$
[oracle@MaxwellDBA dbs]$ ps -aef | grep ora19c
oracle 91690 91536 0 19:05 pts/0 00:00:00 grep --color=auto ora19c
[oracle@MaxwellDBA dbs]$ ipcs -a
------ Message Queues --------
key msqid owner perms used-bytes messages
0x00000000 0 root 666 0 0
0x00000000 2 db2inst1 601 0 0
0x00000000 4 db2inst1 601 0 0
0x00000000 5 db2fenc1 700 0 0
0x9d852d71 6 db2inst1 663 0 0
0x00000000 7 db2inst1 601 0 0
0x9d852d72 8 db2inst1 663 0 0
0x9d852d77 9 db2inst1 665 0 0
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x0052e2c1 0 postgres 600 56 6
0x9d852d74 1 db2inst1 601 34156360 7
0x9d852d61 2 db2inst1 601 175570944 6
0x00000000 3 db2fenc1 601 268435456 6
0x43b375cc 9 oracle 600 12288 57
------ Semaphore Arrays --------
key semid owner perms nsems
0x9d852d74 0 db2inst1 645 1
0x00000000 2 db2inst1 661 1
0x00000000 3 db2inst1 661 1
0x00000000 4 db2inst1 661 1
0x00000000 5 db2inst1 661 1
0x00000000 6 db2inst1 661 1
0x00000000 7 db2inst1 661 1
0x00000000 8 db2inst1 661 1
0x00000000 9 db2inst1 661 1
0x9d852d73 10 db2inst1 667 1
0x00000000 11 db2inst1 661 1
0x00000000 12 db2inst1 661 1
0x00000000 13 db2inst1 661 1
0x00000000 14 db2inst1 661 1
0x00000000 15 db2inst1 661 1
0x00000000 17 db2fenc1 667 3
0x9d852e69 18 db2inst1 661 1
0x00000000 20 db2inst1 661 1
0x8d2a3534 28 oracle 600 250
0x8d2a3535 29 oracle 600 250
[oracle@MaxwellDBA dbs]$ sys@cdb$root:orclcdb> !ipcs -a
------ Message Queues --------
key msqid owner perms used-bytes messages
0x00000000 0 root 666 0 0
0x00000000 2 db2inst1 601 0 0
0x00000000 4 db2inst1 601 0 0
0x00000000 5 db2fenc1 700 0 0
0x9d852d71 6 db2inst1 663 0 0
0x00000000 7 db2inst1 601 0 0
0x9d852d72 8 db2inst1 663 0 0
0x9d852d77 9 db2inst1 665 0 0
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x0052e2c1 0 postgres 600 56 6
0x9d852d74 1 db2inst1 601 34156360 7
0x9d852d61 2 db2inst1 601 175570944 6
0x00000000 3 db2fenc1 601 268435456 6
0x43b375cc 9 oracle 600 12288 58
------ Semaphore Arrays --------
key semid owner perms nsems
0x9d852d74 0 db2inst1 645 1
0x00000000 2 db2inst1 661 1
0x00000000 3 db2inst1 661 1
0x00000000 4 db2inst1 661 1
0x00000000 5 db2inst1 661 1
0x00000000 6 db2inst1 661 1
0x00000000 7 db2inst1 661 1
0x00000000 8 db2inst1 661 1
0x00000000 9 db2inst1 661 1
0x9d852d73 10 db2inst1 667 1
0x00000000 11 db2inst1 661 1
0x00000000 12 db2inst1 661 1
0x00000000 13 db2inst1 661 1
0x00000000 14 db2inst1 661 1
0x00000000 15 db2inst1 661 1
0x00000000 17 db2fenc1 667 3
0x9d852e69 18 db2inst1 661 1
0x00000000 20 db2inst1 661 1
0x8d2a3534 28 oracle 600 250
0x8d2a3535 29 oracle 600 250
sys@cdb$root:orclcdb> select name from v$datafile;
NAME
----------------------------------------------------------------------------------------------------
/opt/oracle/oradata/ORCLCDB/ORCLPDB1/system01.dbf
/opt/oracle/oradata/ORCLCDB/ORCLPDB1/sysaux01.dbf
/opt/oracle/oradata/ORCLCDB/ORCLPDB1/undotbs01.dbf
/opt/oracle/oradata/ORCLCDB/ORCLPDB1/users01.dbf
4 rows selected.
sys@cdb$root:orclcdb> select member from v$logfile;
MEMBER
----------------------------------------------------------------------------------------------------
/opt/oracle/oradata/ORCLCDB/redo03.log
/opt/oracle/oradata/ORCLCDB/redo02.log
/opt/oracle/oradata/ORCLCDB/redo01.log
3 rows selected.
sys@cdb$root:orclcdb> select name from v$controlfile;
NAME
----------------------------------------------------------------------------------------------------
/opt/oracle/oradata/ORCLCDB/control01.ctl
/opt/oracle/oradata/ORCLCDB/control02.ctl
2 rows selected.
sys@cdb$root:orclcdb>
重申一遍：
- 实例是一组后台进程和共享内存组成。
- 数据库是磁盘上存储的数据集合。
- 实例“一生”只能装载并打开一个数据库。
- 数据库可以由一个或多个实例（使用RAC）装载和打开。装载一个数据库的实例数量会随时间变化。
2. SGA和后台进程
- 维护所有进程需要访问的多种内部数据结构。
- 缓存磁盘上的数据，另外重做数据写至磁盘之前先在这里缓存。
- 保存已解析的SQL计划。
Unix环境，可以用pstat查看各线程的更多详细信息。
[oracle@MaxwellDBA dbs]$
[oracle@MaxwellDBA dbs]$
[oracle@MaxwellDBA dbs]$ ps -aef | grep oracle$ORACLE_SID
oracle 88586 1 0 17:11 ? 00:00:00 oracleORCLCDB (LOCAL=NO)
oracle 88616 1 0 17:12 ? 00:00:00 oracleORCLCDB (LOCAL=NO)
oracle 88841 1 0 17:20 ? 00:00:00 oracleORCLCDB (LOCAL=NO)
oracle 89028 89027 0 17:25 ? 00:00:00 oracleORCLCDB (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
oracle 92059 92058 0 19:17 ? 00:00:00 oracleORCLCDB (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
oracle 92409 91536 0 19:30 pts/0 00:00:00 grep --color=auto oracleORCLCDB
[oracle@MaxwellDBA dbs]$
sys@cdb$root:orclcdb>
sys@cdb$root:orclcdb> !ps -aef | grep oracle$ORACLE_SID
oracle 88586 1 0 17:11 ? 00:00:00 oracleORCLCDB (LOCAL=NO)
oracle 88616 1 0 17:12 ? 00:00:00 oracleORCLCDB (LOCAL=NO)
oracle 88841 1 0 17:20 ? 00:00:00 oracleORCLCDB (LOCAL=NO)
oracle 89028 89027 0 17:25 ? 00:00:00 oracleORCLCDB (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
oracle 92059 92058 0 19:17 ? 00:00:00 oracleORCLCDB (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
oracle 92428 92426 0 19:31 pts/6 00:00:00 grep oracleORCLCDB
sys@cdb$root:orclcdb>3.连接Oracle
Oracle服务器处理请求的两种最常见的方式：
- 专用服务器（dedicated server）连接
- 共享服务器（shared server）连接
服务器上的监听器（listener）进程会以不同的方式工作，这些监听器进程负责建立与服务器的物理连接。
专用服务器
[oracle@MaxwellDBA dbs]$ sqlplus sys/sys as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Thu Sep 29 19:37:08 2022
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
sys@cdb$root:orclcdb> !ps -aef | grep oracle$ORACLE_SID
oracle 88616 1 0 17:12 ? 00:00:00 oracleORCLCDB (LOCAL=NO)
oracle 89028 89027 0 17:25 ? 00:00:00 oracleORCLCDB (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
oracle 92059 92058 0 19:17 ? 00:00:00 oracleORCLCDB (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
oracle 92587 92586 0 19:37 ? 00:00:00 oracleORCLCDB (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
oracle 92599 92597 0 19:37 pts/7 00:00:00 grep oracleORCLCDB
sys@cdb$root:orclcdb> 
共享服务器（shared server）
TCP/IP连接的基本原理
[oracle@MaxwellDBA dbs]$ sqlplus sys/sys as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Thu Sep 29 19:40:57 2022
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
sys@cdb$root:orclcdb> ALTER SESSION SET CONTAINER=ORCLPDB1;
Session altered.
sys@cdb$root:orclcdb> conn SCOTT/TIGER@ORCLPDB1
Connected.
scott@orclpdb1:orclcdb> [oracle@MaxwellDBA admin]$ cat tnsnames.ora
# tnsnames.ora Network Configuration File: /opt/oracle/product/19c/dbhome_1/network/admin/tnsnames.ora
# Generated by Oracle configuration tools.
ORCLCDB =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = MaxwellDBA)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = ORCLCDB)
)
)
LISTENER_ORCLCDB =
(ADDRESS = (PROTOCOL = TCP)(HOST = MaxwellDBA)(PORT = 1521))
ORCLPDB1 =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = MaxwellDBA)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = ORCLPDB1)
)
)
LISTENER_ORCLPDB1 =
(ADDRESS = (PROTOCOL = TCP)(HOST = MaxwellDBA)(PORT = 1521))
[oracle@MaxwellDBA admin]$ 
