Know more about Cache Buffer Handle
- by Liu Maclean(???)
??????«latch free:cache buffer handles???SQL????»?????cache buffer handle latch?????,?????????:
“?????pin?buffer header???????buffer handle,??buffer handle?????????cache buffer handles?,??????cache buffer handles??????,???????cache???buffer handles,?????(reserved set)?????????????_db_handles_cached(???5)???,?????????????????SQL??????????????????????,????pin??????,????????handle,?????????5?cached buffer handles???handle????????????????,Oracle?????????????????pin?”????“?buffer,????????????????handle???db_block_buffers/processes,????_cursor_db_buffers_pinned???????cache buffer handles?????,??????,????????????SQL,????cache?buffer handles?????????,??????????????,???????????/?????”
????T.ASKMACLEAN.COM????,??????cache Buffer handle?????:
cache buffer handle ??:
------------------------------
| Buffer state object |
------------------------------
| Place to hang the buffer |
------------------------------
| Consistent Get? |
------------------------------
| Proc Owning SO |
------------------------------
| Flags(RIR) |
------------------------------
???? cache buffer handle
SO: 70000046fdfe530, type: 24, owner: 70000041b018630, flag: INIT/-/-/0×00(buffer) (CR) PR: 70000048e92d148 FLG: 0×500000lock rls: 0, class bit: 0kcbbfbp: [BH: 7000001c7f069b0, LINK: 70000046fdfe570]where: kdswh02: kdsgrp, why: 0BH (7000001c7f069b0) file#: 12 rdba: 0×03061612 (12/398866) class: 1 ba: 7000001c70ee000set: 75 blksize: 8192 bsi: 0 set-flg: 0 pwbcnt: 0dbwrid: 2 obj: 66209 objn: 48710 tsn: 6 afn: 12hash: [700000485f12138,700000485f12138] lru: [70000025af67790,700000132f69ee0]lru-flags: hot_bufferckptq: [NULL] fileq: [NULL] objq: [700000114f5dd10,70000028bf5d620]use: [70000046fdfe570,70000046fdfe570] wait: [NULL]st: SCURRENT md: SHR tch: 0flags: affinity_lockLRBA: [0x0.0.0] HSCN: [0xffff.ffffffff] HSUB: [65535]where: kdswh02: kdsgrp, why: 0
# Example:# (buffer) (CR) PR: 37290 FLG: 0# kcbbfbp : [BH: befd8, LINK: 7836c] (WAITING)
Buffer handle (X$KCBBF) kernel cache, buffer buffer_handles
Query x$kcbbf – lists all the buffer handles
????
_db_handles System-wide simultaneous buffer operations ,no of buffer handles_db_handles_cached Buffer handles cached each process , no of processes default 5_cursor_db_buffers_pinned additional number of buffers a cursor can pin at once_session_kept_cursor_pins Number of cursors pins to keep in a session
When a buffer is pinned it is attached to buffer state object.
??? ???????? cache buffer handles latch ? buffer pin???:
SESSION A :
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bi
PL/SQL Release 10.2.0.5.0 - Production
CORE 10.2.0.5.0 Production
TNS for Linux: Version 10.2.0.5.0 - Production
NLSRTL Version 10.2.0.5.0 - Production
SQL> create table test_cbc_handle(t1 int);
Table created.
SQL> insert into test_cbc_handle values(1);
1 row created.
SQL> commit;
Commit complete.
SQL> select rowid from test_cbc_handle;
ROWID
------------------
AAANO6AABAAAQZSAAA
SQL> select * from test_cbc_handle where rowid='AAANO6AABAAAQZSAAA';
T1
----------
1
SQL> select addr,name from v$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
??cache buffer handles????parent latch ??? child latch
???SESSION A hold ??????cache buffer handles parent latch
???? oradebug call kslgetl ??, kslgetl?oracle??get latch???
SQL> oradebug setmypid;
Statement processed.
SQL> oradebug call kslgetl 1610694824 1;
Function returned 1
?????SESSION B ???:
SQL> select * from v$latchholder;
PID SID LADDR NAME GETS
---------- ---------- ---------------- ---------------------------------------------------------------- ----------
15 141 00000000600140A8 cache buffer handles 119
cache buffer handles latch ???session A hold??,????????acquire cache buffer handle latch
SQL> select * from test_cbc_handle where rowid='AAANO6AABAAAQZSAAA';
T1
----------
1
?????Server Process?????? read buffer, ????????"_db_handles_cached",
??process?cache 5? cache buffer handle
??"_db_handles_cached"=0,?process????5????cache buffer handle ,
???? process ???pin buffer,???hold cache buffer handle latch??????cache buffer handle
SQL> alter system set "_db_handles_cached"=0 scope=spfile;
System altered.
?????
shutdown immediate;
startup;
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 ??cache buffer handles latch
PID=10 ?? cache buffer handles latch, ????"_db_handles_cached"=0 ?? process??????cache buffer handles
??systemstate???? kcbbfbp cache buffer handle??,
?? "_db_handles_cached"=0 ? cache buffer handles latch?hold ??
????cache buffer handles latch , ??? buffer?pin??????????
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$mystat));
SPID PID
------------ ----------
19251 10
? GDB ? SPID=19215 ?debug , ?? kcbrls ????breakpoint ??? ????release buffer
[oracle@vrh8 ~]$ 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'; select 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.
?????? kcbbfbp buffer cache handle ? SO state object ? BH BUFFER HEADER link???
----------------------------------------
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
st: XCURRENT md: SHR tch: 12
? buffer header?status= XCURRENT mode=KCBMSHARE KCBMSHR current share
????? x$kcbbf ????? 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$kcbbf;
Name Null? Type
----------------------------------------- -------- ----------------------------
ADDR RAW(8)
INDX NUMBER
INST_ID NUMBER
KCBBFSO_TYP NUMBER
KCBBFSO_FLG NUMBER
KCBBFSO_OWN RAW(8)
KCBBFFLG NUMBER
KCBBFCR NUMBER
KCBBFCM NUMBER
KCBBFMBR RAW(8)
KCBBPBH RAW(8)
KCBBPBF RAW(8)
X0KCBBPBH RAW(8)
X0KCBBPBF RAW(8)
X1KCBBPBH RAW(8)
X1KCBBPBF RAW(8)
KCBBFBH RAW(8)
KCBBFWHR NUMBER
KCBBFWHY NUMBER
gdb ?? ?process??????kcbrls release buffer? ???cache buffer handle???
SQL> select distinct KCBBPBH from x$kcbbf ;
KCBBPBH
----------------
00
