sequence的cache是放在哪里的，如何调优？

lhpapa

sequence的cache是放在哪里的，如何调优？

ora-hansey

row cache . 调优就等刘大了

Maclean Liu(刘相兵

ROW CACHE 也叫做 dictionary cache ，缓存数据字典基表如 OBJ$、COL$、IND$、SEQ$的信息以便解析SQL和library cache object。
包括 KQR S PO ， KQR M PO，KQR L PO ， 等


KQR => ROW CACHE
kqr.h 1323 KSDTRADV("ROW_CACHE", FADDR(kqrdac))



V$ROWCACHE is based on X$KQRST


KQROBC : data from obj$
KQROIC : data from oid$ (object ids)


SQL> select * from v$sgastat where NAME like '%KQR%';

POOL         NAME                            BYTES
------------ -------------------------- ----------
shared pool  KQR M SO                       160368
shared pool  KQR L SO                        37888
shared pool  KQR ENQ                         53664
shared pool  KQR X PO                         5600
shared pool  KQR M PO                       399136
shared pool  KQR L PO                       125984
shared pool  KQR S SO                          768

7 rows selected.



SQL> select type,parameter from v$rowcache where parameter like '%seq%';

TYPE        PARAMETER
----------- --------------------------------
PARENT      dc_sequences



SQL>  select pid from v$process where addr = ( select paddr from v$session where sid=(select distinct sid from v$mystat));

       PID
----------
       15

SQL>  
SQL>  alter system set "_trace_events"='10000-10999:255:15';

System altered.

SQL>  
SQL>   select check_seq_cache.nextval from dual;

   NEXTVAL
----------
        43

SQL>   
SQL>   oradebug setmypid;
Statement processed.
SQL>   
SQL>   oradebug dump row_cache 10;
  
  oradebug dump errorstack 4;Statement processed.
SQL> SQL>
Statement processed.



NOCACHE情况下更新SEQUENCE的过程(， 首先 acquire SQ -> SEQUENCE ENQUEUE LOCK    da17=> 55831 object_id => SEQUENCE check_seq_cache

之后acquire SEQ$表的TM SX MODE LOCK ，并banding事务TX，update SEQ$ 表， 之后 释放 TX TM SQ。



1F9D2145:00007636    15   159 10704  83 ksqgtl: acquire SQ-0000da17-00000000 mode=X flags=SHORT why="contention"
1F9D2151:00007637    15   159 10704  19 ksqgtl: SUCCESS
1F9D2310:00007638    15   159 10704  83 ksqgtl: acquire TM-00000044-00000000 mode=SX flags=GLOBAL|XACT why="contention"
1F9D231A:00007639    15   159 10704  19 ksqgtl: SUCCESS
1F9D238C:0000763A    15   159 10811   1 0x00000000004001F3 0x0000000000000000 0x0000000000237F9F 0x0000000000000002
1F9D2398:0000763B    15   159 10811   2 0x00000000004001F3 0x0000000000000000 0x000000000023D217 0x00007F96C4D6FE40
1F9D23B5:0000763C    15   159 10813   1 ktubnd: Bind usn 8 nax 1 nbx 0 lng 0 par 0
1F9D23CC:0000763D    15   159 10813   2 ktubnd: Txn Bound xid: 8.25.542
1F9D23D5:0000763E    15   159 10704  83 ksqgtl: acquire TX-00080019-0000021e mode=X flags=GLOBAL|XACT why="contention"
1F9D23E5:0000763F    15   159 10704  19 ksqgtl: SUCCESS
1F9D249F:00007640    15   159 10005   4 KSL POST SENT postee=6 loc='ksasnd' id1=0 id2=0 name=   type=0
1F9D24CD:00007641    15   159 10021  11 0x000000000023D218 0x000000000023D217
1F9D24D9:00007642    15   159 10704 117 ksqrcl: release TX-00080019-0000021e mode=X
1F9D24E3:00007643    15   159 10813   3 ktudnx: dec cnt xid:8.25.542 nax:0 nbx:0
1F9D24F8:00007644    15   159 10704 117 ksqrcl: release TM-00000044-00000000 mode=SX
1F9D2509:00007645    15   159 10704 117 ksqrcl: release SQ-0000da17-00000000 mode=X
1F9D2544:00007649    15   159 10005   4 KSL POST SENT postee=6 loc='ksasnd' id1=0 id2=0 name=   type=0


通过关键词 da17 可以在row_cache dump中找到  dc_sequences SEQUENCE check_seq_cache的信息



BUCKET 7:
  row cache parent object: address=0x8ea0beb8 cid=13(dc_sequences)
  hash=db18fa06 typ=9 transaction=(nil) flags=00000002
  own=0x8ea0bf88[0x8ea0bf88,0x8ea0bf88] wat=0x8ea0bf98[0x8ea0bf98,0x8ea0bf98] mode=N
  status=VALID/-/-/-/-/-/-/-/-
  data=
  0000da17 00020000 000f0002 00020002 000002c1 00000000 00000000 00000000
  02c10000 00000000 00000000 00000000 00000000 64640ace 64646464 64646464
  00646464 15c10000 00000000 00000000 00000000 00000000 00003ec1 00000000
  00000000 00000000 2d2d0000 2d2d2d2d 2d2d2d2d 2d2d2d2d 2d2d2d2d 2d2d2d2d
  2d2d2d2d 2d2d2d2d 00002d2d 00000000
  BUCKET 7 total object count=10

gdpr-dba

刘大上面演示了nocache的sequence的获取过程，不过貌似没提到sequence的cache是放在哪里的？