疑问？
Oracle关闭DB有两种类型：一致性关库、非一致性关库；
Oracle宣传的是说Oracle数据库永远不会丢失数据！ 这句话的意思是当DB主机由于断电等异常原因造成实例崩溃，已经commit提交的数据不会丢失！
Oracle是如何保证数据不丢失的，是基于日志先行策略！ 回到问题！ 非一致性关库，Oracle如何判断需要实例恢复？？？
一、Oracle通过v$datafile last_change# 可以判断是否是一致性关库,可以判断是否需要进行实例恢复
SQL> shutdown immediate; SQL> startup mount; SQL> select file#,CHECKPOINT_CHANGE#, LAST_CHANGE#,status from v$datafile; FILE# CHECKPOINT_CHANGE# LAST_CHANGE# STATUS ---------- ------------------ ------------ ------- 1 35628021 35628021 SYSTEM 2 35628021 35628021 ONLINE 3 35628021 35628021 ONLINE 4 35628021 35628021 ONLINE 5 35628021 35628021 ONLINE 6 35628021 35628021 ONLINE 7 35628021 35628021 ONLINE 8 35628021 35628021 ONLINE 9 35628021 35628021 ONLINE 9 rows selected. SQL> select NAME,CHECKPOINT_CHANGE# from v$database; NAME CHECKPOINT_CHANGE# --------- ------------------ TT11204 35628021
SQL> alter database open;
SQL> shutdown abort; SQL> startup mount;
SQL> select file#,CHECKPOINT_CHANGE#, LAST_CHANGE#,status from v$datafile;
FILE# CHECKPOINT_CHANGE# LAST_CHANGE# STATUS
---------- ------------------ ------------ -------
1 35628024 SYSTEM
2 35628024 ONLINE
3 35628024 ONLINE
4 35628024 ONLINE
5 35628024 ONLINE
6 35628024 ONLINE
7 35628024 ONLINE
8 35628024 ONLINE
9 35628024 ONLINE
9 rows selected.
SQL> select NAME,CHECKPOINT_CHANGE# from v$database;
NAME CHECKPOINT_CHANGE#
--------- ------------------
TT11204 35628024
SQL> alter database open;
观察DB alert.log
二、实例恢复日志DB Alert.log截取
Thu Dec 31 15:41:15 2020
alter database open
Beginning crash recovery of 1 threads
parallel recovery started with 2 processes
Started redo scan
Completed redo scan
read 76 KB redo, 40 data blocks need recovery
Started redo application at
Thread 1: logseq 2945, block 14845
Recovery of Online Redo Log: Thread 1 Group 3 Seq 2945 Reading mem 0
Mem# 0: /11.2.0.4/app/oracle/tt/redo03.log
Completed redo application of 0.04MB
Completed crash recovery at
Thread 1: logseq 2945, block 14998, scn 35648364
40 data blocks read, 40 data blocks written, 76 redo k-bytes read