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oracle rba一些小知识

作者:互联网

 oracle rba相当重要,与oracle恢复及redo内容,检查点进程工作机制,
有密不可分的关系与联系;理解它的构成,是进一步深入学习oracle
必备路途

摘贴网上基于rba的文章:
http://blog.csdn.net/tianlesoftware/article/details/6700080
http://space.itpub.net/9240380/viewspace-751510
http://www.doc88.com/p-331776598706.html ---非常好,通俗易懂
RBA 由以下三部分组成:

       (1)the log file sequence number (4 bytes)

       (2)the log file block number (4 bytes)

       (3)the byte offset into the block at which the redo record starts (2bytes)
      
由上可知:
   1,rba与checkpoint queue关系很大,即与dbwr关系很大。dbwr每次在dirty buffer要把哪些buffer写入到datefile中
   2,rba与lgwr也有很大的。
   3,rba与恢复也有关系.on-disk rb即实例恢复到这个rba,库就可以运行了
   4,各种不同rba的获取方式
   5,rba与controlfile

在上面提到的几种RBA 值可以通过X$BH,和 X$KCCRT 视图进行查看:

       1,The low and high RBAs for dirty buffers can be seen in X$BH.(There is also a recovery RBA which is used to record the
         progress ofpartial block recovery by PMON.)

       2,The incremental checkpoint RBA, the target RBA and theon-disk RBA can all be seen in X$TARGETRBA.
       3,The incremental checkpointRBA and the on-disk RBA can also be seen in X$KCCCP.

       4,The full thread checkpoint RBA can be seen in X$KCCRT.
         
         
先看第1种方式:
     1,The low and high RBAs for dirty buffers can be seen in X$BH.(There is also a recovery RBA which is used to record the
         progress ofpartial block recovery by PMON.)
    
   我的测试方法:
     1,构建测试表并插入一条记录,但不提交
          2,查看x$bh确认其rba相关信息
          3,dump redo rba相关信息

/*************测试开始***************************/ 
-----------会话1----
SQL> insert into t_rba values(1)
  2  ;

1 row created.

SQL>
SQL>
SQL> select dbms_rowid.rowid_object(rowid),dbms_rowid.rowid_relative_fno(rowid),
dbms_rowid.rowid_block_number(rowid) from t_rba;

DBMS_ROWID.ROWID_OBJECT(ROWID) DBMS_ROWID.ROWID_RELATIVE_FNO(ROWID)
------------------------------ ------------------------------------
DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID)
------------------------------------
                         70184                                   10
                              276646
                             
                             
---会话2-----------
--------------查看dirty buffer信息
  --你发现cr相关的列全是0因为此时不需要构建cr块                                
SQL> select TS#,FILE#,DBARFIL,DBABLK,CHANGES,OBJ,BA,CR_SCN_BAS,CR_SCN_WRP, CR_XID_USN ,CR_XID_SLT, CR_XID_SQN, CR_UBA_FIL ,CR_UBA_BLK, CR_UBA_SEQ ,CR_UBA_REC
  2  from x$bh where bj=(select object_id from dba_objects where wner='SCOTT' and object_name='T_RBA');
 
       TS#      FILE#    DBARFIL     DBABLK    CHANGES        OBJ BA               CR_SCN_BAS CR_SCN_WRP CR_XID_USN CR_XID_SLT CR_XID_SQN CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ CR_UBA_REC
---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
         8         10         10     276645          1      70184 000007FF01372000          0          0          0          0          0          0          0          0          0
         8         10         10     276642          1      70184 000007FF0135C000          0          0          0          0          0          0          0          0          0
         8         10         10     276647          1      70184 000007FF01E06000          0          0          0          0          0          0          0          0          0
         8         10         10     276644          1      70184 000007FF0123A000          0          0          0          0          0          0          0          0          0
         8         10         10     276641          1      70184 000007FF00A7E000          0          0          0          0          0          0          0          0          0
         8         10         10     276646          1      70184 000007FF00D4E000          0          0          0          0          0          0          0          0          0
         8         10         10     276643          1      70184 000007FF01DFE000          0          0          0          0          0          0          0          0          0
         8         10         10     276640          1      70184 000007FF01DFA000          0          0          0          0          0          0          0          0          0
 
8 rows selected

--我们别启一个会话,运行select * from t_rba;
--cr列有数据了,而且与v$transaction联系起来了,CR_SCN_BAS即cr块构建自这个scn开始构建
SQL> select TS#,FILE#,DBARFIL,DBABLK,CHANGES,OBJ,BA,CR_SCN_BAS,CR_SCN_WRP, CR_XID_USN ,CR_XID_SLT, CR_XID_SQN, CR_UBA_FIL ,CR_UBA_BLK, CR_UBA_SEQ ,CR_UBA_REC
  2  from x$bh where bj=(select object_id from dba_objects where wner='SCOTT' and object_name='T_RBA')
  3  ;
 
       TS#      FILE#    DBARFIL     DBABLK    CHANGES        OBJ BA               CR_SCN_BAS CR_SCN_WRP CR_XID_USN CR_XID_SLT CR_XID_SQN CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ CR_UBA_REC
---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
         8         10         10     276645          1      70184 000007FF01372000          0          0          0          0          0          0          0          0          0
         8         10         10     276642          1      70184 000007FF0135C000          0          0          0          0          0          0          0          0          0
         8         10         10     276647          1      70184 000007FF01E06000          0          0          0          0          0          0          0          0          0
         8         10         10     276644          1      70184 000007FF0123A000          0          0          0          0          0          0          0          0          0
         8         10         10     276646          1      70184 000007FF02F26000   10307069          0         72         15        134          3       7610        416         14
         8         10         10     276646          1      70184 000007FF02108000   10307068          0         72         15        134          3       7610        416         14
         8         10         10     276646          1      70184 000007FF00D4E000          0          0          0          0          0          0          0          0          0
         8         10         10     276643          1      70184 000007FF01DFE000          0          0          0          0          0          0          0          0          0
 
8 rows selected

/********转储data block***********/

---与上述的ba 000007FF00D4E000相对应,而这个ba 000007FF02108000是为了上述的select构造的cr block,它的cr_scn_bas即下述的LSCN
---HSCN即最新的scn,所以说cr block是根据current block构造的一个数据块
BH (0x000007FF00FE4538) file#: 10 rdba: 0x028438a6 (10/276646) class: 1 ba: 0x000007FF00D4E000
  set: 11 pool 3 bsz: 8192 bsi: 0 sflg: 1 pwc: 0,25
  dbwrid: 0 obj: 70184 objn: 70184 tsn: 8 afn: 10 hint: f
  hash: [0x000007FF0C325E88,0x000007FF023E1C58] lru: [0x000007FF00BEF710,0x000007FF013DACF0]
  lru-flags: hot_buffer
  obj-flags: object_ckpt_list
  ckptq: [0x000007FF0C3F8AA8,0x000007FF0C3F8AA8] fileq: [0x000007FF0C3F8BE8,0x000007FF0C3F8BE8] objq: [0x000007FF0783B2F8,0x000007FF0783B2F8]
  st: XCURRENT md: NULL tch: 1
  flags: buffer_dirty block_written_once redo_since_read
  LRBA: [0x31d.69b8.0] LSCN: [0x0.9d45fc] HSCN: [0x0.9d4661] HSUB: [1]
  cr pin refcnt: 0 sh pin refcnt: 0

----------转储undo block-------------------------
*-----------------------------
* Rec #0xe  slt: 0x0f  objn: 70184(0x00011228)  objd: 70184  tblspc: 8(0x00000008)
*       Layer:  11 (Row)   opc: 1   rci 0x00   --rci可以判断是否还往前回溯构造cr block(适用对一个记录或多记录update多次未提交),此地rci为0,不用再往上cr了
Undo type:  Regular undo    Begin trans    Last buffer split:  No
Temp Object:  No
Tablespace Undo:  No
rdba: 0x00000000Ext idx: 0
flg2: 0
*-----------------------------
uba: 0x00c01dba.01a0.0d ctl max scn: 0x0000.009cbdf1 prv tx scn: 0x0000.009cbdf2
txn start scn: scn: 0x0000.009d36ed logon user: 61 
 prev brb: 12595255 prev bcl: 0
KDO undo record:
KTB Redo
op: 0x03  ver: 0x01 
compat bit: 4 (post-11) padding: 0
op: Z
KDO Op code: DRP row dependencies Disabled
  xtype: XA flags: 0x00000000  bdba: 0x028438a6  hdba: 0x028438a2
itli: 1  ispac: 0  maxfr: 4858
tabn: 0 slot: 0(0x0) 

---同上--------------
SQL> select CR_SFL ,CR_CLS_BAS, CR_CLS_WRP,   LRBA_SEQ ,  LRBA_BNO ,  HSCN_BAS ,  HSCN_WRP,   HSUB_SCN
     from x$bh where bj=(select object_id from dba_objects where wner='SCOTT' and object_name='T_RBA');
 
    CR_SFL CR_CLS_BAS CR_CLS_WRP   LRBA_SEQ   LRBA_BNO   HSCN_BAS   HSCN_WRP   HSUB_SCN
---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
         0          0          0          0          0 4294967295      65535          1
         0          0          0          0          0 4294967295      65535          1
         0          0          0          0          0 4294967295      65535          1
         0          0          0          0          0 4294967295      65535          1
         0          0          0          0          0 4294967295      65535          1
         0          0          0          0          0 4294967295      65535          2
         0          0          0          0          0 4294967295      65535          1
         0          0          0          0          0 4294967295      65535          1
 
8 rows selected                   
---查询事务----------
SQL> select * from v$transaction;
 
ADDR                 XIDUSN    XIDSLOT     XIDSQN     UBAFIL     UBABLK     UBASQN     UBAREC STATUS           START_TIME           START_SCNB START_SCNW START_UEXT START_UBAFIL START_UBABLK START_UBASQN START_UBAREC SES_ADDR               FLAG SPACE RECURSIVE NOUNDO PTX NAME         PRV_XIDUSN PRV_XIDSLT PRV_XIDSQN PTX_XIDUSN PTX_XIDSLT PTX_XIDSQN     DSCN-B     DSCN-W  USED_UBLK  USED_UREC     LOG_IO     PHY_IO     CR_GET  CR_CHANGE START_DATE   DSCN_BASE  DSCN_WRAP  START_SCN DEPENDENT_SCN XID              PRV_XID          PTX_XID
---------------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- -------------------- ---------- ---------- ---------- ------------ ------------ ------------ ------------ ---------------- ---------- ----- --------- ------ --- ----------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------- ---------- ---------- ---------- ------------- ---------------- ---------------- ----------------
000007FF0B146238         72         15        134          3       7610        416         14 ACTIVE           03/24/13 13:34:35      10303213          0          0            3         7610          416           14 000007FF0C86B270       7683 NO    NO        NO     NO                  0          0          0          0          0          0          0          0          1          1         46          0          2          0 2013/3/24 1          0          0   10303213             0 48000F0086000000 0000000000000000 0000000000000000
 
----查看当前redo
SQL> select * from v$log where status='CURRENT';
 
    GROUP#    THREAD#  SEQUENCE#      BYTES  BLOCKSIZE    MEMBERS ARCHIVED STATUS           FIRST_CHANGE# FIRST_TIME  NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- -------- ---------------- ------------- ----------- ------------ -----------
         7          1        797  209715200        512          1 NO       CURRENT               10299796 2013/3/24 1 281474976710
 
 
SQL>  select * from v$logfile where group#=( select group# from v$log where status='CURRENT');
 
    GROUP# STATUS  TYPE    MEMBER                                                                           IS_RECOVERY_DEST_FILE
---------- ------- ------- -------------------------------------------------------------------------------- ---------------------
         7         ONLINE  D:\ORACLE11G_64BIT\ORADATA\ORCL\REDO07.LOG                                       NO
        
---看看lrba的状态变化 

---如果你未在其它会话cr或者dml,看不到lrba     
SQL> select ba,obj,lrba_seq,lrba_bno from x$bh where bj=(select object_id from dba_objects where wner='SCOTT' and object_name='T_RBA');  
BA                      OBJ   LRBA_SEQ   LRBA_BNO
---------------- ---------- ---------- ----------
000007FF01372000      70184          0          0
000007FF0135C000      70184          0          0
000007FF01E06000      70184          0          0
000007FF0123A000      70184          0          0
000007FF02106000      70184          0          0
000007FF01DFE000      70184          0          0
 
6 rows selected     

---如何看到lrba呢,在另一会话dml,再回到上述会话,

SQL> /
 
BA                      OBJ   LRBA_SEQ   LRBA_BNO
---------------- ---------- ---------- ----------
000007FF01372000      70184          0          0
000007FF0135C000      70184          0          0
000007FF01E06000      70184          0          0
000007FF0123A000      70184          0          0
000007FF02CBE000      70184        798      35439 即对应 v$log.sequence#
000007FF02CC4000      70184          0          0
000007FF01DFE000      70184          0          0
 
7 rows selected
  
   小结:可看到lrba,但未在x$bh看到hrba
 
我们看看第2种方式:  
2,The incremental checkpoint RBA, the target RBA and the on-disk RBA can all be seen in X$TARGETRBA.  


最后小结一下:
1,rba由三部分组成:
     seqno  序列号 4byte
     blockno 块号 4byte
     startbyte 起始(或叫偏移量)字节 2个字节
    
2,lrba即数据块第一次变更时在redo logfile中的rba
  引:ckpt-q进程即检查点进程根据lrba的升序维护log buffer
      ckpt-q进程会按lbra升序的方式从最小的lrba写出这些dirty buffer
     
  哪么ckpt-q写出的lrba就是checkpoint 的位置.
  从这个位置lrba一直应用到redo file的on disk rba,这个过程就是
  前滚(实例恢复)     
 
3,说了lrba,自然少不了hrba,它就是对数据块最近一次变更在redo
   logfile中的rba
  (注:如果hrba大于on-disk rba,那么hrba对应的redo entries还在
       log buffer,这样一旦数据库挂掉,哈哈,hrba就不能被恢复了)
       所以只能从lrba恢复到on-disk rba,别急:on-disk rba在后面说说)

4,checkpoint rba,这个上面已经提过了,就是ckpt-q进程要写入的脏数据块的
 lrba,而这lrba之前的脏数据说明已全部写入disk;
  换句话说,ckpt就是每次写入上次checkpoint rba到这次checkpoint rba的数据到磁盘的
 
  还有个问题:ckpt进程每次要从哪个rba开始写入到磁盘呢,其实啊,它工作时会记录
  要写的第一个rba,这个rba就是checkpoint rba,这样每次就会有针对性的去写了。其实就是
  个限制写入的范围
 
5,再来说下on-disk rba,它就是lgwr由log buffer写到log file最后面的一个rba;
  也就是实例恢复前滚的终点(自lrba到on-disk rba)  
 
 
6,target rba,是不是有些晕,哈哈;这个其实是checkpoint事件结束的rba
  也就是说:从ckpt开始产生检查点事件,自checkpoint rba开始写入到终止写入的哪个
  checkpoint rba;
 
  oracle为了提升恢复的性能和时间(实例恢复),dbwr进程会尽力把checkpoint rba设置长一点;
  (原因很简单:这样每次写入到磁盘多一些;恢复起来就快得多了) 
  它与参数:fast_start_mttr_target有关
 
 
7,相关视图:
   1,增量检查点checkpoint rba及on-disk rba
      select * from x$kcccp;
      注:cpdrt列是检查点队列中脏块数量
        cpods列是on disk rba的scn
          cpodt列是on disk rba的时间戳
          cphbt列是心跳
   2,lrba及hrba
         select lrba_seq,lrba_bno from x$bh;
        
         select hxfil,fhrba_seq,fhrba_bno,fhrba_bof from x$kcvfh;--x$kcvfh即v$datafile_header的基表
        
   3,查看target rba
          select target_rba_seq,target_rba_bno,target_rba_bof from x$targetrba;
   
      4,完全检查点checkpoint rba
         select rtckp_rba_seq,rtckp_rba,rtckp_rba_bof from x$kccrt;
        

8,再总结下:
   1,redo和checkpoint关系很大
      2,配置log_checkpoint_to_alert=true;checkpoint会写入到alert
      3,数据文件头包括checkpoint_change#,
       更重要还包括了checkpoint_change#所在logfile的sequence#,这样恢复就知道要用哪个archive log或log                                             


标签:10,70184,知识,----------,select,oracle,CR,rba
来源: https://blog.51cto.com/lhrbest/2694739