[20211025]12g sequemce nocahe測試.txt

[20211025]12g sequemce nocahe測試.txt

--//上個星期我發現19c生產系統有幾個sequence開發給設定為nocache屬性.導致出現row cache lock.
--//當我單獨查詢該語句的等待事件時,出現一個我以前從來沒見過的row cache mutex的等待事件.
--//難道19c做了某些改進,開始使用mutex。

--//我在12c重複測試看看。

1.環境:
SCOTT@test01p> @ ver1
PORT_STRING                    VERSION        BANNER                                                                               CON_ID
------------------------------ -------------- -------------------------------------------------------------------------------- ----------
IBMPC/WIN_NT64-9.1.0           12.2.0.1.0     Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production              0

create table job_times (sid number, time_ela number,method varchar2(20));
create sequence seq1 nocache;

SCOTT@test01p> @ ddl scott.seq1
C300
------------------------------------------------------------------------------------------------------------------------------------------------------------------
CREATE SEQUENCE  "SCOTT"."SEQ1"  MINVALUE 1 MAXVALUE 9999999999999999999999999999 INCREMENT BY 1 START WITH 1 NOCACHE  NOORDER  NOCYCLE  NOKEEP  NOSCALE  GLOBAL ;

$ cat m14.txt
set verify off
--//host sleep $(echo &&3/50 | bc -l )
variable vmethod varchar2(20);
exec :vmethod := '&&2';
insert into job_times values ( sys_context ('userenv', 'sid') ,dbms_utility.get_time ,:vmethod) ;
commit ;
declare
v_id number;
v_d date;
v_val VARCHAR2(1000);
l_count PLS_INTEGER;
begin
    for i in 1 .. &&1 loop
        --//select value into v_val from v$nls_parameters where parameter = 'NLS_CHARACTERSET';
        --//select value into v_val from nls_database_parameters where parameter = 'NLS_CHARACTERSET';
        --//select sql_text into v_val from v$sql where rownum=1;
        SELECT /* &&3 */ seq1.NEXTVAL into v_id FROM DUAL;
    end loop;
end ;
/
update job_times set time_ela = dbms_utility.get_time - time_ela where sid=sys_context ('userenv', 'sid') and method=:vmethod;
commit;
quit

2.測試:
--//我沒有想到這麼慢，在沒有開啟cache的情況下,只能減少併發數量以及迴圈次數1e4:

$ zzdate;seq 20 | xargs -I{} -P 20 sqlplus -s -l scott/book@test01p @m14.txt 1e4 P=20 {} 1 >/dev/null;zzdate
trunc(sysdate)+10/24+05/1440+21/86400 == 2021/10/25 10:05:21
trunc(sysdate)+10/24+05/1440+42/86400 == 2021/10/25 10:05:42
--// 21秒。

SYS@test01p> @tpt/ashtop event,sql_id "module='SQL*Plus' and username='SCOTT'" trunc(sysdate)+10/24+05/1440+21/86400 trunc(sysdate)+10/24+05/1440+42/86400

    Total
  Seconds     AAS %This   EVENT                                    SQL_ID        FIRST_SEEN          LAST_SEEN
--------- ------- ------- ---------------------------------------- ------------- ------------------- -------------------
      338    16.1   92% | row cache lock                           9cp836a3k67w2 2021-10-25 10:05:22 2021-10-25 10:05:41
       26     1.2    7% | row cache mutex                          9cp836a3k67w2 2021-10-25 10:05:22 2021-10-25 10:05:41
        1      .0    0% |                                          9cp836a3k67w2 2021-10-25 10:05:29 2021-10-25 10:05:29
        1      .0    0% |                                                        2021-10-25 10:05:33 2021-10-25 10:05:33
--//出現row cache lock，row cache mutex 兩個等待事件。而且row cache mutex等待的出現事件在2021-10-25 10:05:22 到
--//2021-10-25 10:05:41之間,也就是從測試開始到結束。
--//你可以發現對比11g多了一個row cache mutex的等待事件。
--//11g 下類似測試：
SYS@book>  @ashtop event,sql_id "module='SQL*Plus' and username='SCOTT'" trunc(sysdate)+09/24+12/1440+14/86400 trunc(sysdate)+09/24+14/1440+24/86400
    Total
  Seconds     AAS %This   EVENT                                    SQL_ID        FIRST_SEEN          LAST_SEEN
--------- ------- ------- ---------------------------------------- ------------- ------------------- -------------------
     6288    48.4   97% | row cache lock                           9cp836a3k67w2 2021-10-25 09:12:14 2021-10-25 09:14:23
      152     1.2    2% |                                          9cp836a3k67w2 2021-10-25 09:12:14 2021-10-25 09:14:23
        4      .0    0% |                                                        2021-10-25 09:12:51 2021-10-25 09:14:21
        2      .0    0% |                                          a01fjfup7ruah 2021-10-25 09:12:52 2021-10-25 09:13:12
        2      .0    0% |                                          gxgnku5buj8cm 2021-10-25 09:13:51 2021-10-25 09:14:09
        1      .0    0% | log file switch (checkpoint incomplete)  9cp836a3k67w2 2021-10-25 09:14:07 2021-10-25 09:14:07
        1      .0    0% |                                          1mm9uymckm8z4 2021-10-25 09:12:28 2021-10-25 09:12:28
        1      .0    0% |                                          24c64p3xa1hr5 2021-10-25 09:13:28 2021-10-25 09:13:28
        1      .0    0% |                                          7b9znjngh150d 2021-10-25 09:13:17 2021-10-25 09:13:17
        1      .0    0% |                                          fsc8vbts8tu24 2021-10-25 09:12:26 2021-10-25 09:12:26
        1      .0    0% |                                          g2q7km1t9cdnj 2021-10-25 09:13:29 2021-10-25 09:13:29
        1      .0    0% |                                          gpa5h7jh3dg4d 2021-10-25 09:14:10 2021-10-25 09:14:10
        1      .0    0% |                                          gty6quqfxrgna 2021-10-25 09:13:39 2021-10-25 09:13:39
13 rows selected.
--//僅僅出現row cache lock 等待事件。

SYS@test01p> Select method,count(*),round(avg(TIME_ELA),0),sum(TIME_ELA) from scott.job_times group by method order by 3 ;
METHOD                 COUNT(*) ROUND(AVG(TIME_ELA),0) SUM(TIME_ELA)
-------------------- ---------- ---------------------- -------------
P=20                         20                   1941         38826