x$bh视图
首先，这篇文章是基于如下ORACLE版本。
BANNER ------------------------------------------------ Oracle Database 10g Enterprise Edition Release 1 0.2.0.5.0 - 64bi PL/SQL Release 10.2.0.5.0 - Production CORE 10.2.0.5.0 Production TNS for Solaris: Version 10.2.0.5.0 - Production NLSRTL Version 10.2.0.5.0 - Production
下面是x$bh这个视图(也许是表 :) ) 的结构。
X$BH Fixed Table Buffer Cache Diagram
Column Type Description
~~~~~~ ~~~~~ ~~~~~~~~~~~
ADDR RAW(4) Hex address of the Buffer Header.
INDX NUMBER Buffer Header number
BUF# NUMBER
HLADDR RAW(4) Hash Chain Latch Address
See . ADDR
LRU_FLAG NUMBER 8.1+ LRU flag
KCBBHLDF 0x01 8.1 LRU Dump Flag used in debug print routine
KCBBHLMT 0x02 8.1 moved to tail of lru (for extended stats)
KCBBHLAL 0x04 8.1 on auxiliary list
KCBBHLHB 0x08 8.1 hot buffer - not in cold portion of lru
FLAG NUMBER
KCBBHFBD 0x00001 buffer dirty
KCBBHFAM 0x00002 7.3 about to modify; try not to start io
KCBBHFAM 0x00002 8.0 about to modify; try not to start io
KCBBHNAC 0x00002 8.1 notify dbwr after change
KCBBHFMS 0x00004 modification started, no new writes
KCBBHFBL 0x00008 block logged
KCBBHFTD 0x00010 temporary data - no redo for changes
KCBBHFBW 0x00020 being written; can't modify
KCBBHFWW 0x00040 waiting for write to finish
KCBBHFCK 0x00080 7.3 checkpoint asap
0x00080 8.0 not used
KCBBHFMW 0x00080 8.1 multiple waiters when gc lock acquired
KCBBHFRR 0x00100 recovery reading, do not reuse, being read
KCBBHFUL 0x00200 unlink from lock element - make non-current
KCBBHFDG 0x00400 write block & stop using for lock down grade
KCBBHFCW 0x00800 write block for cross instance call
KCBBHFCR 0x01000 reading from disk into KCBBHCR buffer
KCBBHFGC 0x02000 has been gotten in current mode
KCBBHFST 0x04000 stale - unused CR buf made from current
0x08000 7.3 Not used.
KCBBHFDP 0x08000 8.0 deferred ping
KCBBHFDP 0x08000 8.1 deferred ping
KCBBHFDA 0x10000 Direct Access to buffer contents
KCBBHFHD 0x20000 Hash chain Dump used in debug print routine
KCBBHFIR 0x40000 Ignore Redo for instance recovery
KCBBHFSQ 0x80000 sequential scan only flag
KCBBHFNW 0x100000 7.3 Set to indicate a buffer that is NEW
0x100000 8.0 Not used
KCBBHFBP 0x100000 8.1 Indicates that buffer was prefetched
KCBBHFRW 0x200000 7.3 re-write if being written (sort)
0x200000 8.0 Not used
KCBBHFFW 0x200000 8.1 Buffer has been written once
KCBBHFFB 0x400000 buffer is "logically" flushed
KCBBHFRS 0x800000 ReSilvered already - do not redirty
KCBBHFKW 0x1000000 7.3 ckpt writing flag to avoid rescan */
0x1000000 8.0 Not used
KCBBHDRC 0x1000000 8.1 buffer is nocache
0x2000000 7.3 Not used
KCBBHFRG 0x2000000 8.0 Redo Generated since block read
KCBBHFRG 0x2000000 8.1 Redo Generated since block read
KCBBHFWS 0x10000000 8.0 Skipped write for checkpoint.
KCBBHFDB 0x20000000 8.1 buffer is directly from a foreign DB
KCBBHFAW 0x40000000 8.0 Flush after writing
KCBBHFAW 0x40000000 8.1 Flush after writing
TS# NUMBER 8.X Tablespace number
DBARFIL NUMBER 8.X Relative file number of block
DBAFIL NUMBER 7.3 File number of block
DBABLK NUMBER Block number of block
CLASS NUMBER See Note 33434.1
1,'data block',
2,'sort block',
3,'save undo block',
4,'segment header',
5,'save undo header',
6,'free list',
7,'extent map',
8,'1st level bmb',
9,'2nd level bmb',
10,'3rd level bmb',
11,'bitmap block',
12,'bitmap index block',
13,'file header block',
14,'unused',
15,'system undo header',
16,'system undo block',
17,'undo header',
18,'undo block' -- since 10g
STATE NUMBER
KCBBHFREE 0 buffer free
KCBBHEXLCUR 1 buffer current (and if DFS locked X)
KCBBHSHRCUR 2 buffer current (and if DFS locked S)
KCBBHCR 3 buffer consistant read
KCBBHREADING 4 Being read
KCBBHMRECOVERY 5 media recovery (current & special)
KCBBHIRECOVERY 6 Instance recovery (somewhat special)
MODE_HELD NUMBER Mode buffer held in (MODE pre 7.3)
0=KCBMNULL, KCBMSHARE, KCBMEXCL
CHANGES NUMBER
CSTATE NUMBER
X_TO_NULL NUMBER Count of PINGS out (OPS)
DIRTY_QUEUE NUMBER You wont normally see buffers on the LRUW
LE_ADDR RAW(4) Lock Element address (OPS)
SET_DS RAW(4) Buffer cache set this buffer is under
OBJ NUMBER Data object number
TCH NUMBER 8.1 Touch Count
TIM NUMBER 8.1 Touch Time
BA RAW(4)
CR_SCN_BAS NUMBER Consistent Read SCN base
CR_SCN_WRP NUMBER Consistent Read SCN wrap
CR_XID_USN NUMBER CR XID Undo segment no
CR_XID_SLT NUMBER CR XID slot
CR_XID_SQN NUMBER CR XID Sequence
CR_UBA_FIL NUMBER CR UBA file
CR_UBA_BLK NUMBER CR UBA Block
CR_UBA_SEQ NUMBER CR UBA sequence
CR_UBA_REC NUMBER CR UBA record
CR_SFL NUMBER
LRBA_SEQ NUMBER } Lowest RBA needed to recover block in cache
LRBA_BNO NUMBER }
LRBA_BOF NUMBER }
HRBA_SEQ NUMBER } Redo RBA to be flushed BEFORE this block
HRBA_BNO NUMBER } can be written out
HRBA_BOF NUMBER }
RRBA_SEQ NUMBER } Block recovery RBA
RRBA_BNO NUMBER }
RRBA_BOF NUMBER }
NXT_HASH NUMBER Next buffer on this hash chain
PRV_HASH NUMBER Previous buffer on this hash chain
NXT_LRU NUMBER Next buffer on the LRU
PRV_LRU NUMBER Previous buffer on the LRU
US_NXT RAW(4)
US_PRV RAW(4)
WA_NXT RAW(4)
WA_PRV RAW(4)
ACC RAW(4)
MOD RAW(4)
看不懂没关系，这个视图就是oracle data buffer的一个窗口。里面的每一条记录代表了data buffer中的一个记录。
下面的查询可以查到data buffer中有哪些数据对象的data block以及他们占用多少buffer。这里限定了表空间号大于2是为了除去一些系统表占用的buffer。
SQL> select 2 o.owner owner, o.object_name, blsiz , count(*) blocks 3 from x$bh b , dba_objects o 4 where b.obj = o.data_object_id 5 and b.ts# > 2 6 group by o.owner,o.object_name, blsiz 7 order by blocks desc; OWNER OBJECT_NAME BLSIZ BLOCKS ------------------ ------------------------------------------------ ---------- ---------- SATTEST AUDIT_LOG 8192 404 CITOSADMIN RMS_AUDIT_LOG 8192 68 CICOSADMIN BERTH_ALLOCATION 8192 14 CITOSADMIN EAS_DOCUMENT_DETAIL 8192 10 CITOSADMIN TEST 8192 8 CITOSADMIN TERMINAL2 8192 5 CITOSADMIN EAS_CONFIG 8192 5 CICOSADMIN BERTH_ALLOCATION_NNDX4 8192 4 CITOSADMIN SITE 8192 3 CICOSADMIN BERTH_ALLOCATION_NNDX3 8192 3 CITOSADMIN TERMINAL 8192 3 CICOSADMIN BERTH_ALLOCATION_NNDX2 8192 3 CICOSADMIN BERTH_ALLOCATION_NNDX1 8192 3 CITOSADMIN REEFER_PAYMENT_SCHEME 8192 1 CITOSADMIN CNTR 8192 1 SUMSADMIN SM_DISCHARGING_LIST 8192 1 CITOSADMIN CNTR_2 8192 1 CITOSADMIN GATE_PM_TRIP 8192 1
下面的查询可以查到data buffer中的某个数据对象(这里叫TEST)其占用的buffer的状态。这里看到TEST有两个cr块和6个xcur块。关于各个block的状态，cr是用于consistent read的。xcur表示是最新的块，scur也是最新的块，但scur存在于RAC中表示多个instance共享这个block。free很好理解，是可以被重用的块。
SQL> select o.object_name 2 3 ,decode(state,0,'free',1,'xcur',2,'scur',3,'cr', 4,'read',5,'mrec' 4 ,6,'irec',7,'write',8,'pi') state 5 , blsiz , count(*) blocks 6 from x$bh b , dba_objects o 7 where b.obj = o.data_object_id 8 and b.ts# > 0 9 and o.object_name = 'TEST' 10 group by o.object_name, state, blsiz; OBJECT_NAME STATE BLSIZ BLOCKS ------------------------------------------------ --------------- ---------- ---------- TEST cr 8192 2 TEST xcur 8192 6
下面的查询查到data buffer中特定数据对象不同状态buffer的地址信息，DBARFIL是相对文件号，是每个表空间中确定datafile的文件号，DBABLK是确定文件号后确定datablock的block number。BA是该buffer的实际addr
SQL> select 2 o.object_name 3 ,decode(state,0,'free',1,'xcur',2,'scur',3,'cr', 4,'read',5,'mrec',6,'irec',7,'write',8,'pi') state 4 , dbarfil 5 , dbablk 6 , ba 7 from x$bh b , dba_objects o 8 where b.obj = o.data_object_id 9 and b.ts# > 0 10 and o.object_name = 'TEST' 11 ; OBJECT_NAME STATE DBARFIL DBABLK BA ------------------------------------------------ --------------- ---------- ---------- ---------------- TEST xcur 4 61470 000000038A380000 TEST xcur 4 61467 00000003866EA000 TEST xcur 4 61472 0000000385E5E000 TEST cr 4 61469 000000038BF08000 TEST cr 4 61469 0000000386F20000 TEST xcur 4 61469 000000038186C000 TEST xcur 4 61471 0000000399D5E000 TEST xcur 4 61468 0000000381716000
下面做一些操作以便熟悉该视图。
首先创建一个表如下：
create table test (id1 number,id2 number,text varchar2(2000)); insert into citosadmin.test values(1,1,'a'); insert into citosadmin.test values(2,2,'b'); insert into citosadmin.test values(3,3,'c'); alter system flush buffer_cache;
然后看一下data buffer中这个表占用的情况。占用了6个buffer
SQL> select o.owner owner, o.object_name, blsiz , count(*) blocks from x$bh b , dba_objects o 2 where b.obj = o.data_object_id and o.object_name='TEST' group by o.owner,o.object_name, blsiz; OWNER OBJECT_NAME BLSIZ BLOCKS ------------------ ------------------------------------------------ ---------- ---------- CITOSADMIN TEST 8192 6
全都是xcur状态的。xcur是表示是current的最新的block。如果是rac block和其它的instance共享则是scur。
SQL> select 2 o.object_name 3 ,decode(state,0,'free',1,'xcur',2,'scur',3,'cr', 4,'read',5,'mrec' 4 ,6,'irec',7,'write',8,'pi') state 5 , blsiz , count(*) blocks 6 from x$bh b , dba_objects o 7 where b.obj = o.data_object_id 8 and b.ts# > 0 9 and o.object_name = 'TEST' 10 group by o.object_name, state, blsiz; OBJECT_NAME STATE BLSIZ BLOCKS ------------------------------------------------ --------------- ---------- ---------- TEST xcur 8192 6
每个buffer的地址如下
SQL> select o.object_name 2 ,decode(state,0,'free',1,'xcur',2,'scur',3,'cr', 4,'read',5,'mrec',6,'irec',7,'write',8,'pi') state 3 , dbarfil 4 , dbablk 5 , ba 6 from x$bh b , dba_objects o 7 where b.obj = o.data_object_id 8 and o.object_name = 'TEST'; OBJECT_NAME STATE DBARFIL DBABLK BA ------------------------------------------------ --------------- ---------- ---------- ---------------- TEST xcur 4 61478 00000003816BC000 TEST xcur 4 61475 0000000389494000 TEST xcur 4 61480 000000039CEB8000 TEST xcur 4 61477 000000039CD8A000 TEST xcur 4 61479 000000038DDD8000 TEST xcur 4 61476 000000038AB52000
为了使用GV$BH视图，对上述SQL做了些更改，下面列出了使用gv$bh视图的sql语句，两两一组，上面是用x$bh下面是用gv$bh
select INST_ID, o.owner owner, o.object_name, blsiz , count(*) blocks from x$bh b , dba_objects o where b.obj = o.data_object_id and o.object_name='T' group by INST_ID, o.owner,o.object_name, blsiz; col OBJECT_NAME for a20 col OWNER for a8 select INST_ID, o.owner owner, o.object_name, count(*) blocks from gv$bh b , dba_objects o where b.objd = o.data_object_id and o.object_name='T' group by INST_ID, o.owner,o.object_name ; ------------------------------------------------------------------ select INST_ID, o.object_name, decode(state,0,'free',1,'xcur',2,'scur',3,'cr', 4,'read',5,'mrec',6,'irec',7,'write',8,'pi') state, blsiz , count(*) blocks from x$bh b , dba_objects o where b.obj = o.data_object_id and o.object_name = 'T' group by INST_ID,o.object_name, state, blsiz; select INST_ID, o.object_name, b.STATUS, count(*) blocks from gv$bh b , dba_objects o where b.objd = o.data_object_id and o.object_name = 'T' group by INST_ID,o.object_name, b.STATUS ; ------------------------------------------------------------------ select INST_ID, o.object_name, decode(state,0,'free',1,'xcur',2,'scur',3,'cr', 4,'read',5,'mrec',6,'irec',7,'write',8,'pi') state, dbarfil, dbablk, ba from x$bh b , dba_objects o where b.obj = o.data_object_id and o.object_name = 'T'; select INST_ID, o.object_name, b.status, FILE# , BLOCK# from gv$bh b , dba_objects o where b.objd = o.data_object_id and o.object_name = 'T'; ------------------------------------------------------------------
