oracle checkpoint作用释疑3

关于rba(redo block address)，有可以分为如下3种:

low checkpoint rba; 某个block第一次被修改时所对应的redo recode记录，同时也就意味着
low rba是redo apply的起点

high cechkpoint rba; 某个block被经过多次修改后，最后一次修改时所对应的redo recode记录

on disk rba; 是指disk中redo log中的最后一条redo recode记录，在实例crash后进行
实例恢复时on disk rba将是redo log apply的终点。

下面通过实验来进行说明：
SQL> CREATE TABLE t1 AS SELECT * FROM dba_objects WHERE rownum<10; TABLE created. SQL> SELECT dbms_rowid.rowid_relative_fno(rowid) file#,
2 dbms_rowid.rowid_block_number(rowid) blk#
3 FROM t1;

FILE# BLK#
———- ———-
1 56034
1 56034
1 56034
1 56034
1 56034
1 56034
1 56034
1 56034
1 56034

9 ROWS selected.

SQL> UPDATE t1 SET owner=’www.killdb.com’ WHERE object_id=20;

1 ROW updated.

SQL> UPDATE t1 SET owner=’www.killdb.com’ WHERE object_id=25;

1 ROW updated.

SQL> UPDATE t1 SET owner=’www.killdb.com’ WHERE object_id=29;

1 ROW updated.

SQL> SELECT cpdrt,
2 cplrba_seq || ‘.’ || cplrba_bno || ‘.’ || cplrba_bof “low_rba”,
3 cpodr_seq || ‘.’ || cpodr_bno || ‘.’ || cpodr_bof “on_disk_rba”
4 FROM x$kcccp;

CPDRT low_rba on_disk_rba
———- —————————— ——————————
40 11.1153.0 11.1283.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0

8 ROWS selected.

SQL> SELECT cpdrt,
2 cplrba_seq || ‘.’ || cplrba_bno || ‘.’ || cplrba_bof “low_rba”,
3 cpodr_seq || ‘.’ || cpodr_bno || ‘.’ || cpodr_bof “on_disk_rba”
4 FROM x$kcccp;

CPDRT low_rba on_disk_rba
———- —————————— ——————————
22 11.1432.0 11.1450.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0

8 ROWS selected.

SQL> ALTER system switch logfile;

System altered.

SQL> commit;

Commit complete.

SQL> SELECT cpdrt,
2 cplrba_seq || ‘.’ || cplrba_bno || ‘.’ || cplrba_bof “low_rba”,
3 cpodr_seq || ‘.’ || cpodr_bno || ‘.’ || cpodr_bof “on_disk_rba”
4 FROM x$kcccp;

CPDRT low_rba on_disk_rba
———- —————————— ——————————
23 11.1432.0 12.3.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0

8 ROWS selected.

SQL> ALTER system switch logfile;

System altered.

SQL> SELECT cpdrt,
2 cplrba_seq || ‘.’ || cplrba_bno || ‘.’ || cplrba_bof “low_rba”,
3 cpodr_seq || ‘.’ || cpodr_bno || ‘.’ || cpodr_bof “on_disk_rba”
4 FROM x$kcccp;

CPDRT low_rba on_disk_rba
———- —————————— ——————————
23 11.1432.0 13.2.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0
0 0.0.0 0.0.0

8 ROWS selected.

SQL> UPDATE t1 SET owner=’www.killdb.com’ WHERE object_id=44;

1 ROW updated.

SQL> UPDATE t1 SET owner=’www.killdb.com’ WHERE object_id=51;

1 ROW updated.

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