[20190312]关于增量检查点的疑问(补充).txt

--//有人问我以前写一个帖子的问题,关于增量检查点的问题,链接如下:http://blog.itpub.net/267265/viewspace-2136817/
--//实际上我自己看以前写的帖子一下子有点蒙,主要出现low_rba16=0xffffffff.ffffffff.ffff,为什么恢复的起点是on_disk_rba16.
--//先简单说明一下:
--//oracle现在写脏块基本采用增量检查点,即使日志切换,实际上执行也是增量检查点,除非执行alter system checkpoint,或者
--//shutdown immediate(normal)正常关闭数据库,如果异常关闭数据库,启动时执行崩溃恢复(crash recovery),恢复起点从low_rba.
--//先验证这样的情况:

1.环境:
SCOTT@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

--//写一个脚本check.sql,以前写的太复杂,简单一点:
--// x$kccrt 记录全检查点
--// x$kcccp 记录增量检查点

$ cat check.sql
column "full checkpoint_rba" format a21
column low_rba format a20
column low_rba16 format a20
column on_disk_rba format a20
column on_disk_rba16 format a20
column rtckp_rba format a20
column diff_date format 9999999.99
rem column CPOSD_ono_disk_rba_scn format 99999999999999999999999999999999
column cpdrt heading "检查点队列|脏块数量|CPDRT"
column cpodt_on_disk_rba heading "检查点队列|on disk rba|时间戳|CPODT"
column cpods heading "检查点队列|on disk rba scn|CPODS"
column cphbt heading "检查点心跳|CPHBT"
column current_sysdate heading "当前时间|SYSDATE"
set num 12

SELECT b.cplrba_seq || '.' || b.cplrba_bno || '.' || b.cplrba_bof "low_rba"
      ,b.cpodr_seq || '.' || b.cpodr_bno || '.' || b.cpodr_bof "on_disk_rba"
      ,b.CPODS "on_disk_rba_scn(CPODS)"
      ,TO_DATE (b.CPODT, 'MM-DD-YYYY HH24:MI:SS') "on_disk_rba_time(CPODT)"
      ,a.rtckp_rba_seq || '.' || a.rtckp_rba_bno || '.' || a.rtckp_rba_bof
          "full checkpoint_rba"
      ,a.rtckp_scn "full_checkpoint(rtckp_scn)"
      ,TO_DATE (a.rtckp_tim, 'MM-DD-YYYY HH24:MI:SS')
          "full_checkpoint_time_rtckp_tim"
      ,b.CPODS - a.rtckp_scn "diff_scn(on_disk_rdb-ch_scn)"
      ,a.rtcln "current_group"
      ,sysdate current_sysdate
      ,CPDRT
  FROM x$kccrt a, x$kcccp b
 WHERE a.rtnum = b.cptno AND A.INST_ID = b.inst_id;

2.测试:
SYS@book> shutdown  abort ;
ORACLE instance shut down.

SYS@book> startup mount
ORACLE instance started.
Total System Global Area    643084288 bytes
Fixed Size                    2255872 bytes
Variable Size               205521920 bytes
Database Buffers            427819008 bytes
Redo Buffers     &n