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3#
发表于 2012-5-10 16:27:41
接下来 我们实际体验一下 cache buffer handles latch 和 buffer pin的影响：
SESSION A :
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bi
PL/SQL Release 10.2.0.5.0 - Production
CORE 10.2.0.5.0 Production
TNS for Linux: Version 10.2.0.5.0 - Production
NLSRTL Version 10.2.0.5.0 - Production
SQL> create table test_cbc_handle(t1 int);
Table created.
SQL> insert into test_cbc_handle values(1);
1 row created.
SQL> commit;
Commit complete.
SQL> select rowid from test_cbc_handle;
ROWID
------------------
AAANO6AABAAAQZSAAA
select * from test_cbc_handle where rowid='AAANO6AABAAAQZSAAA';
SQL> select addr,name from v$latch_parent where name='cache buffer handles';
ADDR NAME
---------------- --------------------------------------------------
00000000600140A8 cache buffer handles
SQL> select to_number('00000000600140A8','xxxxxxxxxxxxxxxxxxxx') from dual;
TO_NUMBER('00000000600140A8','XXXXXXXXXXXXXXXXXXXX')
----------------------------------------------------
1610694824
注意cache buffer handles只有一个parent latch 而没有 child latch
我们让SESSION A hold 住唯一的一个 cache buffer handles parent latch
SQL> oradebug setmypid;
Statement processed.
SQL> oradebug call kslgetl 1610694824 1;
Function returned 1
另外开一个 SESSION B 来观察：
SQL> select * from v$latchholder;
PID SID LADDR NAME GETS
---------- ---------- ---------------- ---------------------------------------------------------------- ----------
15 141 00000000600140A8 cache buffer handles 119
cache buffer handles latch 确实被hold住了
SQL> select * from test_cbc_handle where rowid='AAANO6AABAAAQZSAAA';
T1
----------
1
单此时 其他 Server Process还是可以正常 read buffer， 这是因为 _db_handles_cached ， 默认process会cache 5个handle
SQL> alter system set "_db_handles_cached"=0 scope=spfile;
System altered.
并重启实例
session A:
SQL> oradebug setmypid;
Statement processed.
SQL> oradebug call kslgetl 1610694824 1;
Function returned 1
session B:
select * from test_cbc_handle where rowid='AAANO6AABAAAQZSAAA';
session B hang!!
WHY?
SQL> oradebug setmypid;
Statement processed.
SQL> oradebug dump systemstate 266;
Statement processed.
SO: 0x11b30b7b0, type: 2, owner: (nil), flag: INIT/-/-/0x00
(process) Oracle pid=22, calls cur/top: (nil)/0x11b453c38, flag: (0) -
int error: 0, call error: 0, sess error: 0, txn error 0
(post info) last post received: 0 0 0
last post received-location: No post
last process to post me: none
last post sent: 0 0 0
last post sent-location: No post
last process posted by me: none
(latch info) wait_event=0 bits=8
holding (efd=4) 600140a8 cache buffer handles level=3
SO: 0x11b305810, type: 2, owner: (nil), flag: INIT/-/-/0x00
(process) Oracle pid=10, calls cur/top: 0x11b455ac0/0x11b450a58, flag: (0) -
int error: 0, call error: 0, sess error: 0, txn error 0
(post info) last post received: 0 0 0
last post received-location: No post
last process to post me: none
last post sent: 0 0 0
last post sent-location: No post
last process posted by me: none
(latch info) wait_event=0 bits=2
Location from where call was made: kcbzgs:
waiting for 600140a8 cache buffer handles level=3
FBD93353:000019F0 10 162 10005 1 KSL WAIT BEG [latch: cache buffer handles] 1610694824/0x600140a8 125/0x7d 0/0x0
FF936584:00002761 10 144 10005 1 KSL WAIT BEG [latch: cache buffer handles] 1610694824/0x600140a8 125/0x7d 0/0x0
PID=22 holding 持有 cache buffer handles latch
PID=10 等待 cache buffer handles latch， 这是因为"_db_handles_cached"=0 导致 process自身没有缓存 cache buffer handles
这个 systemstate中找不到 kcbbfbp cache buffer handle对象， 因为 "_db_handles_cached"=0 且 cache buffer handles latch被hold 住了
我们释放 cache buffer handles latch ， 来观察 buffer 被pin住 而不是释放时的情境
session A exit
session B:
SQL> select * from v$latchholder;
no rows selected
SQL> insert into test_cbc_handle values(2);
1 row created.
SQL> commit;
Commit complete.
SQL>
SQL> select t1,rowid from test_cbc_handle;
T1 ROWID
---------- ------------------
1 AAANPAAABAAAQZSAAA
2 AAANPAAABAAAQZSAAB
SQL> select spid,pid from v$process where addr = ( select paddr from v$session where sid=(select distinct sid from v$mystat));
SPID PID
------------ ----------
19251 10
用 GDB 对 SPID=19215 做debug ， 使用 kcbrls 函数作为breakpoint 这会让 进程无法release buffer
[oracle@vrh8 ~]$ gdb $ORACLE_HOME/bin/oracle 19251
GNU gdb (GDB) Red Hat Enterprise Linux (7.0.1-37.el5)
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /s01/oracle/product/10.2.0.5/db_1/bin/oracle...(no debugging symbols found)...done.
Attaching to program: /s01/oracle/product/10.2.0.5/db_1/bin/oracle, process 19251
Reading symbols from /s01/oracle/product/10.2.0.5/db_1/lib/libskgxp10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/oracle/product/10.2.0.5/db_1/lib/libskgxp10.so
Reading symbols from /s01/oracle/product/10.2.0.5/db_1/lib/libhasgen10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/oracle/product/10.2.0.5/db_1/lib/libhasgen10.so
Reading symbols from /s01/oracle/product/10.2.0.5/db_1/lib/libskgxn2.so...(no debugging symbols found)...done.
Loaded symbols for /s01/oracle/product/10.2.0.5/db_1/lib/libskgxn2.so
Reading symbols from /s01/oracle/product/10.2.0.5/db_1/lib/libocr10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/oracle/product/10.2.0.5/db_1/lib/libocr10.so
Reading symbols from /s01/oracle/product/10.2.0.5/db_1/lib/libocrb10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/oracle/product/10.2.0.5/db_1/lib/libocrb10.so
Reading symbols from /s01/oracle/product/10.2.0.5/db_1/lib/libocrutl10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/oracle/product/10.2.0.5/db_1/lib/libocrutl10.so
Reading symbols from /s01/oracle/product/10.2.0.5/db_1/lib/libjox10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/oracle/product/10.2.0.5/db_1/lib/libjox10.so
Reading symbols from /s01/oracle/product/10.2.0.5/db_1/lib/libclsra10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/oracle/product/10.2.0.5/db_1/lib/libclsra10.so
Reading symbols from /s01/oracle/product/10.2.0.5/db_1/lib/libdbcfg10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/oracle/product/10.2.0.5/db_1/lib/libdbcfg10.so
Reading symbols from /s01/oracle/product/10.2.0.5/db_1/lib/libnnz10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/oracle/product/10.2.0.5/db_1/lib/libnnz10.so
Reading symbols from /usr/lib64/libaio.so.1...(no debugging symbols found)...done.
Loaded symbols for /usr/lib64/libaio.so.1
Reading symbols from /lib64/libdl.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libdl.so.2
Reading symbols from /lib64/libm.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib64/libm.so.6
Reading symbols from /lib64/libpthread.so.0...(no debugging symbols found)...done.
[Thread debugging using libthread_db enabled]
Loaded symbols for /lib64/libpthread.so.0
Reading symbols from /lib64/libnsl.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib64/libnsl.so.1
Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib64/libc.so.6
Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Reading symbols from /lib64/libnss_files.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libnss_files.so.2
0x00000035c000d940 in __read_nocancel () from /lib64/libpthread.so.0
(gdb) break kcbrls
Breakpoint 1 at 0x10e5d24
session B:
select * from test_cbc_handle where rowid='AAANPAAABAAAQZSAAA';
hang !!
GDB
(gdb) c
Continuing.
Breakpoint 1, 0x00000000010e5d24 in kcbrls ()
(gdb) bt
#0 0x00000000010e5d24 in kcbrls ()
#1 0x0000000002e87d25 in qertbFetchByUserRowID ()
#2 0x00000000030c62b8 in opifch2 ()
#3 0x00000000032327f0 in kpoal8 ()
#4 0x00000000013b7c10 in opiodr ()
#5 0x0000000003c3c9da in ttcpip ()
#6 0x00000000013b3144 in opitsk ()
#7 0x00000000013b60ec in opiino ()
#8 0x00000000013b7c10 in opiodr ()
#9 0x00000000013a92f8 in opidrv ()
#10 0x0000000001fa3936 in sou2o ()
#11 0x000000000072d40b in opimai_real ()
#12 0x000000000072d35c in main ()
SQL> oradebug setmypid;
Statement processed.
SQL> oradebug dump systemstate 266;
Statement processed.
此时可以看到 kcbbfbp buffer cache handle 将 SO state object 和 BH BUFFER HEADER link在一起
----------------------------------------
SO: 0x11b452348, type: 3, owner: 0x11b305810, flag: INIT/-/-/0x00
(call) sess: cur 11b41bd18, rec 0, usr 11b41bd18; depth: 0
----------------------------------------
SO: 0x1182dc750, type: 24, owner: 0x11b452348, flag: INIT/-/-/0x00
(buffer) (CR) PR: 0x11b305810 FLG: 0x108000
class bit: (nil)
kcbbfbp: [BH: 0xf2fc69f8, LINK: 0x1182dc790]
where: kdswh05: kdsgrp, why: 0
BH (0xf2fc69f8) file#: 1 rdba: 0x00410652 (1/67154) class: 1 ba: 0xf297c000
set: 3 blksize: 8192 bsi: 0 set-flg: 2 pwbcnt: 272
dbwrid: 0 obj: 54208 objn: 54202 tsn: 0 afn: 1
hash: [f2fc47f8,1181f3038] lru: [f2fc6b88,f2fc6968]
obj-flags: object_ckpt_list
ckptq: [1182ecf38,1182ecf38] fileq: [1182ecf58,1182ecf58] objq: [108712a28,108712a28]
use: [1182dc790,1182dc790] wait: [NULL]
st: XCURRENT md: SHR tch: 12
flags: buffer_dirty gotten_in_current_mode block_written_once
redo_since_read
LRBA: [0xc7.73b.0] HSCN: [0x0.1cbe52] HSUB: [1]
Using State Objects
----------------------------------------
SO: 0x1182dc750, type: 24, owner: 0x11b452348, flag: INIT/-/-/0x00
(buffer) (CR) PR: 0x11b305810 FLG: 0x108000
class bit: (nil)
kcbbfbp: [BH: 0xf2fc69f8, LINK: 0x1182dc790]
where: kdswh05: kdsgrp, why: 0
buffer tsn: 0 rdba: 0x00410652 (1/67154)
scn: 0x0000.001cbe52 seq: 0x01 flg: 0x02 tail: 0xbe520601
frmt: 0x02 chkval: 0x0000 type: 0x06=trans data
tab 0, row 0, @0x1f9a
tl: 6 fb: --H-FL-- lb: 0x0 cc: 1
col 0: [ 2] c1 02
tab 0, row 1, @0x1f94
tl: 6 fb: --H-FL-- lb: 0x2 cc: 1
col 0: [ 2] c1 15
end_of_block_dump
(buffer) (CR) PR: 0x11b305810 FLG: 0x108000
也可以通过 x$kcbbf 找到相关的 cache buffer handle
SQL> select distinct KCBBPBH from x$kcbbf ;
KCBBPBH
----------------
00
00000000F2FC69F8 ==>0xf2fc69f8
SQL> select * from x$kcbbf where kcbbpbh='00000000F2FC69F8';
ADDR INDX INST_ID KCBBFSO_TYP KCBBFSO_FLG KCBBFSO_OWN
---------------- ---------- ---------- ----------- ----------- ----------------
KCBBFFLG KCBBFCR KCBBFCM KCBBFMBR KCBBPBH
---------- ---------- ---------- ---------------- ----------------
KCBBPBF X0KCBBPBH X0KCBBPBF X1KCBBPBH
---------------- ---------------- ---------------- ----------------
X1KCBBPBF KCBBFBH KCBBFWHR KCBBFWHY
---------------- ---------------- ---------- ----------
00000001182DC750 748 1 24 1 000000011B452348
1081344 1 0 00 00000000F2FC69F8
00000001182DC750 00 00000001182DC750 00
00000001182DC7F8 00 583 0
SQL> desc x$kcbbf;
Name Null? Type
----------------------------------------- -------- ----------------------------
ADDR RAW(8)
INDX NUMBER
INST_ID NUMBER
KCBBFSO_TYP NUMBER
KCBBFSO_FLG NUMBER
KCBBFSO_OWN RAW(8)
KCBBFFLG NUMBER
KCBBFCR NUMBER
KCBBFCM NUMBER
KCBBFMBR RAW(8)
KCBBPBH RAW(8)
KCBBPBF RAW(8)
X0KCBBPBH RAW(8)
X0KCBBPBF RAW(8)
X1KCBBPBH RAW(8)
X1KCBBPBF RAW(8)
KCBBFBH RAW(8)
KCBBFWHR NUMBER
KCBBFWHY NUMBER |
|
发表于 2012-5-10 09:50:12
|
查看: 7910|
回复: 3
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