[20220304]測試library cache mutex遇到的疑問.txt
[20220304]測試library cache mutex遇到的疑問.txt
--//昨天測試library cache mutex如何定位時遇到的疑問,就是每次執行sql語句後gets數量不是開始不是按照1增加,而是2.
--//今天測試看看,順便加強記憶與理解。
1.環境:
SCOTT@book> @ ver1
PORT_STRING VERSION BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
SYS@book> @ hide _kghdsidx_count
NAME DESCRIPTION DEFAULT_VALUE SESSION_VALUE SYSTEM_VALUE ISSES ISSYS_MOD
---------------------------------- ------------------------------------------------------------------ ------------- ------------- ------------ ----- ---------
_kghdsidx_count max kghdsidx count TRUE 1 1 FALSE FALSE
SYS@book> @ hide _kgl_bucket_count
NAME DESCRIPTION DEFAULT_VALUE SESSION_VALUE SYSTEM_VALUE ISSES ISSYS_MOD
---------------------------------- ------------------------------------------------------------------ ------------- ------------- ------------ ----- ---------
_kgl_bucket_count Library cache hash table bucket count (2^_kgl_bucket_count * 256) TRUE 9 9 FALSE FALSE
--//還原為預設引數,並且我刪除以前測試時設定一些引數,比如db_2k_cache_size。
2.測試:
--//再使用前面的查詢,發現該地址表不再原來的位置。我重新定位看看。
SYS@book> oradebug setmypid
Statement processed.
SYS@book> oradebug dump library_cache 4
Statement processed.
--//檢查跟蹤檔案發現如下:
*** 2022-03-04 09:13:55.609
Processing Oradebug command 'dump library_cache 4'
Library Cache Dump
SGA:0x80782738 Flags=ac3
DebugContext: DebugNameSpace=0 DebugType=0 DebugLevel=0x0
Bucket: #=96 Mutex=0x807846e8(0, 4, 0, 6)
SYS@book> @ tpt/calc 0x807846e8 - 16
DEC HEX
----------------------------------- --------------------
2155366104.000000 807846D8
--//該library cache bueket的地址在 x807846D8.
--//library cache bueket 佔 16位元組,mutex結構體佔24位元組,加起來佔40.
--//96*40 = 3840 ,減去3840就是library cache bueket = 0 地址。
SYS@book> @ tpt/calc x807846D8 - 3840
DEC HEX
----------------------------------- --------------------
2155362264.000000 807837D8
--//library cache bueket = 0 地址,根據前面的測試該地址前面就是該地址表。
--//該地址表每個佔8位元組,共2^9=512條記錄。
--//512*8 = 4096
SCOTT@book> @ tpt/calc x807837D8 - 4096
DEC HEX
----------------------------------- --------------------
2155358168.000000 807827D8
SYS@book> select * from (SELECT rownum-1 rn , x$ksmmem.* FROM X$KSMMEM WHERE addr between hextoraw('00000000807827D8') and hextoraw('00000000807837D0')) where rn=246;
RN ADDR INDX INST_ID KSMMMVAL
---------- ---------------- ---------- ---------- ----------------
246 0000000080782F88 68093425 1 0000000080115020
--//我前面的查詢結果如下:
SYS@book> Select sysdate from dual ;
SYSDATE
-------------------
2022-03-03 09:12:01
SYS@book> @ hash
HASH_VALUE SQL_ID CHILD_NUMBER KGL_BUCKET PLAN_HASH_VALUE HASH_HEX SQL_EXEC_START SQL_EXEC_ID
---------- ------------- ------------ ---------- --------------- ---------- ------------------- -----------
381482536 dvk83p4bbtxj8 0 63016 1388734953 16bcf628 2022-03-03 09:12:01 16777216
--//HASH_VALUE=381482536,KGL_BUCKET=63016.
--//計算方法 381482536%(2^9*256) = 63016。 bucket值等於63016。
SYS@book> select trunc (63016 /256 ), mod(63016 ,256) from dual ;
TRUNC(63016/256) MOD(63016,256)
---------------- --------------
246 40
--//MOD(63016,256)=40, 40*40 = 1600
SYS@book> @ tpt/calc x0000000080115020 + 1600
DEC HEX
----------------------------------- --------------------
2148619872.000000 80115660
--//library cache bucket=246的地址在x80115660.
SYS@book> oradebug peek 0x80115660 40
[080115660, 080115688) = 80115660 00000000 80115660 00000000 00000000 00000000 00000002 00000000 0000F628 00000000
--//當前沒有物件,因為裡面儲存的地址指向自己0x80115660.
$ echo 'Select sysdate from dual ;'|sqlplus -s -l / as sysdba
SYSDATE
-------------------
2022-03-04 09:27:36
--//每次執行如上語句,peek1次。
SYS@book> oradebug peek 0x80115660 40
[080115660, 080115688) = 80115660 00000000 80115660 00000000 00000000 00000000 00000002 00000000 0000F628 00000000
SYS@book> oradebug peek 0x80115660 40
[080115660, 080115688) = 7BF9D5A8 00000000 7BF9D5A8 00000000 00000000 00000000 00000003 00000000 0000F628 00000000
SYS@book> oradebug peek 0x80115660 40
[080115660, 080115688) = 7BF9D5A8 00000000 7BF9D5A8 00000000 00000000 00000000 00000004 00000000 0000F628 00000000
SYS@book> oradebug peek 0x80115660 40
[080115660, 080115688) = 7BF9D5A8 00000000 7BF9D5A8 00000000 00000000 00000000 00000005 00000000 0000F628 00000000
SYS@book> oradebug peek 0x80115660 40
[080115660, 080115688) = 7BF9D5A8 00000000 7BF9D5A8 00000000 00000000 00000000 00000006 00000000 0000F628 00000000
--//預設每次執行gets計數增加1次,看來前面的測試也許是其它因素的干擾。
SYS@book> @ sharepool/shp4 dvk83p4bbtxj8 0
TEXT KGLHDADR KGLHDPAR C40 KGLHDLMD KGLHDPMD KGLHDIVC KGLOBHD0 KGLOBHD6 KGLOBHS0 KGLOBHS6 KGLOBT16 N0_6_16 N20 KGLNAHSH KGLOBT03 KGLOBT09
--------------------- ---------------- ---------------- ---------------------------------------- ---------- ---------- ---------- ---------------- ---------------- ---------- ---------- ---------- --------- ---------- ---------- ------------- ----------
child handle address 000000007D774B70 000000007BF9D5A8 Select sysdate from dual 0 0 0 000000007BF427A0 000000007BDC28D0 4528 8088 3082 15698 15698 381482536 dvk83p4bbtxj8 0
parent handle address 000000007BF9D5A8 000000007BF9D5A8 Select sysdate from dual 0 0 0 000000007C1D4A40 00 4720 0 0 4720 4720 381482536 dvk83p4bbtxj8 65535
--//你可以發現該bucket地址記錄了父遊標控制程式碼的地址x000000007BF9D5A8。
SYS@book> oradebug peek 0x000000007BF9D5A8 40
[07BF9D5A8, 07BF9D5D0) = 80115660 00000000 80115660 00000000 7BDC21F8 00000000 7BF9D700 00000000 00000000 10012841
--//而父遊標裡面有記錄了該library cahce bucket的地址,形成雙向連結。
來自 “ ITPUB部落格 ” ,連結:http://blog.itpub.net/267265/viewspace-2864491/,如需轉載,請註明出處,否則將追究法律責任。
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