??????«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: 0×500000
lock rls: 0, class bit: 0
kcbbfbp: [BH: 7000001c7f069b0, LINK: 70000046fdfe570]
where: kdswh02: kdsgrp, why: 0
BH (7000001c7f069b0) file#: 12 rdba: 0×03061612 (12/398866) class: 1 ba: 7000001c70ee000
set: 75 blksize: 8192 bsi: 0 set-flg: 0 pwbcnt: 0
dbwrid: 2 obj: 66209 objn: 48710 tsn: 6 afn: 12
hash: [700000485f12138,700000485f12138] lru: [70000025af67790,700000132f69ee0]
lru-flags: hot_buffer
ckptq: [NULL] fileq: [NULL] objq: [700000114f5dd10,70000028bf5d620]
use: [70000046fdfe570,70000046fdfe570] wait: [NULL]
st: SCURRENT md: SHR tch: 0
flags: affinity_lock
LRBA: [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