云贝教育 |【技术文章】共享池内存结构之SQL内存结构父子游标解析
前言
数据库版本：Version 19.3.0.0.0
操作系统版本：CentOS Linux release 7.6.1810 (Core)
实验环境：PDB1
SQL内存结构父子游标解析
以下实验，是连接到pdb下，硬解析一条SQL的过程
一、SQL父游标解析
1.1 查看SQL的父游标句柄地址和堆0描述地址
sqlplus / as sysdba
SQL> col KGLNAOBJ for a30
select kglhdadr, kglnaobj,kglobhd0
from x$kglob
where kglnaobj like 'select * from cdh19c.t1 where object_id=199%'
and kglhdadr = kglhdpar;
KGLHDADR KGLNAOBJ KGLOBHD0
---------------- ------------------------------ ----------------
00000000724BC848 select * from cdh19c.t1 where 000000006FB55C80
object_id=199x$kglob说明
- x$kglob记录SQL的游标句柄信息
- KGLHDADR 游标句柄地址
- KGLNAOBJ 游标对应SQL信息
- KGLOBHD0 父游标堆0对应的地址，其实它是父游标堆0的描述地址，记录父游标堆0下有
- 哪些chunk
1.2 做一个共享池全量dump
sqlplus sys/oracle@pdb1 as sysdba
oradebug setmypid
alter session set events 'immediate trace name heapdump level 2050';
oradebug close_trace;
oradebug tracefile_name;1.3 查看父游标句柄对应的chunk
根据上面1.1中查的父游标句柄地址KGLHDADR=00000000724BC848
通过724BC840去1.3中生成的trc文件中搜索
Chunk 0724bc818 sz= 816 recrPT003 "KGLHD "
Dump of memory from 0x00000000724BC818 to 0x00000000724BCB48
0724BC810 00000331 80B38F00 [1.......]
0724BC820 724BC5F8 00000000 00000000 00000000 [..Kr............]
0724BC830 00000000 00000000 00000000 00000000 [................]
`0724BC840` 00000003 00080050 62BEFDF8 00000000 [....P......b....]
0724BC850 62BEFDF8 00000000 6F6A0F78 00000000 [...b....x.jo....]
0724BC860 724BC9B0 00000000 00010000 10012841 [..Kr........A(..]
0724BC870 00000001 00000001 00010001 00000002 [................]
0724BC880 00000000 00000001 00010000 00000000 [................]
#这里从根据第一列的地址来找
D7FCF1F0 00000000 00000000 0000001C 00000000 [................]
0D7FCF200 00000000 00000000 00000000 00000000 [................]
0D7FCF210 D7FCF220 00000000 1F4DC642 00000000 [ .......B.M.....]
0D7FCF220 656C6573 2A207463 6F726620 3174206D [select * from t1]
0D7FCF230 65687720 69206572 00313D64 00000000 [ where id=1.....]
0D7FCF240 00000000 00000000 00000000 00000000 [................]
末尾还可以看到SQL语句--这里用的非本例trc日志解析：
- recrPT003表示它是一个recreate类型的chunk
- sz表示它的大小为816字节
- KGLHD表示它是KGL句柄
- 同时它是一个独立的CHUNK，不属于任何子堆
通过多次实验可以确认，句柄头的地址与句柄地址相关48字节
父游标句柄头占48字节，通过计算得到句柄头地址
select replace(upper('00000000'||to_char(to_number('724BC848','xxxxxxxxxx')-48,'xxxxxxxxxx')),' ','') from dual;
--》00000000724BC818
注意要用KSMCHPTR字段查
select ksmchptr,ksmchcom,ksmchcls,ksmchsiz
from x$ksmsp where KSMCHPTR='00000000724BC818'
;1.4 查看父游标DS对应的chunk
查看DS=000000006FB55C80 CHUNK信息，用6FB55C8去搜索
Chunk 06fb55c18 sz= 504 freeable "KGLDA "
Dump of memory from 0x000000006FB55C18 to 0x000000006FB55E10
06FB55C10 000001F9 00B38F00 [........]
06FB55C20 6FB559E8 00000000 12B6CA50 00000000 [.Y.o....P.......]
06FB55C30 6FB55C80 00000000 6F6A1048 00000000 [.\.o....H.jo....]
06FB55C40 00000000 00030001 00000000 00000000 [................]
06FB55C50 00000FE8 00000A38 6F6A0F78 00000000 [....8...x.jo....]
06FB55C60 6F6A0EC8 00000000 00000000 00000000 [..jo............]
06FB55C70 03F10629 00000000 69145108 00000000 [)........Q.i....]
`06FB55C80` 6016FF60 00000000 00000000 00000000 [`..`............]
06FB55C90 6FB55C30 00000000 6F6A0EC8 00000000 [0\.o......jo....]
06FB55CA0 6F6A0F50 00000000 00000000 00000000 [P.jo............] 可以确认DS对应的chunk是freeable，大小为504字节，和父游标堆0不相邻
通过多次实验可以确认，DS头的地址与DS地址相差104字节
父游标句柄头占48字节，通过计算得到句柄头地址
select replace(upper('00000000'||to_char(to_number('6FB55C80','xxxxxxxxxx')-104,'xxxxxxxxxx')),' ','') from dual;
--》000000006FB55C18
注意要用KSMCHPTR字段查
select ksmchptr,ksmchcom,ksmchcls,ksmchsiz
from x$ksmsp where KSMCHPTR='000000006FB55C18'
;1.4 查看父游标堆0下的的chunk
1 #查看父游标堆0的CHUNK有哪些
2 SQL> select ksmchptr,ksmchcom,ksmchcls,ksmchsiz
3 from x$ksmsp where ksmchpar='000000006FB55C80';
4
5 KSMCHPTR KSMCHCOM KSMCHCLS KSMCHSIZ
6 ---------------- -------------------------------- ---------------- ----------
7 000000006F6A0E98 KGLH0^e12ae359 recr 4096 KSMCHPTR=000000006F6A0E98就是父游标堆0真正的CHUNK了，继续找
Chunk 06f6a0e98 sz= 4096 recrPC003 "KGLH0^e12ae359 "
ds 06fb55c80 sz= 4096 ct= 1 #这里是heap0的DS地址
Dump of memory from 0x000000006F6A0E98 to 0x000000006F6A1E98
`06F6A0E90` 00001001 80B38F00 [........]
06F6A0EA0 6F69FE98 00000000 00000000 00000000 [..io............]
06F6A0EB0 00000000 00000000 00000000 00000000 [................]
06F6A0EC0 00000003 000A0FFF 6FB55C80 00000000 [.........\.o....]
06F6A0ED0 00000000 00000000 00000079 40B38F00 [........y......@]
06F6A0EE0 00000000 00000000 00000000 00000000 [................]
06F6A0EF0 14B05430 00000000 00000000 00000078 [0T..........x...]
06F6A0F00 00000001 C0B38F00 00000000 00000000 [................]
06F6A0F10 6FB55CF8 00000000 6FB55CF8 00000000 [.\.o.....\.o....]
06F6A0F20 01220001 00000000 6F6A0EC8 00000000 [..".......jo....]
06F6A0F30 00000000 00000000 00000FC0 00000000 [................]
06F6A0F40 6F6A0F40 00000000 6F6A0F40 00000000 [@[email protected]....]
06F6A0F50 00000C01 40B38F00 6F6A0ED8 00000000 [[email protected]....]ds 06fb55c80就是上面查的父游标DS地址
二、SQL子游标解析
2.1 子游标句柄
SQL> select kglhdadr, kglnaobj,kglobhd0,kglobhd6
from x$kglob
where kglnaobj like 'select * from cdh19c.t1 where object_id=199%'
and kglhdadr <> kglhdpar;
KGLHDADR KGLNAOBJ KGLOBHD0 KGLOBHD6
---------------- ------------------------------ ---------------- ----------------
000000006F68D8D8 select * from cdh19c.t1 where 000000006DC82F68 000000006F6A1680
object_id=199
#子游标句柄：000000006F68D8D8，它-48就是父游标句柄chunk地址
select replace(upper('00000000'||to_char(to_number('6F68D8D8','xxxxxxxxxx')-48,'xxxxxxxxxx')),' ','') from dual;
--000000006F68D8A8通过地址6F68D8D去找子游标句柄
Chunk 06f68d8a8 sz= 560 recrPT003 "KGLHD "
Dump of memory from 0x000000006F68D8A8 to 0x000000006F68DAD8
06F68D8A0 00000231 80B38F00 [1.......]
06F68D8B0 6F68D690 00000000 00000000 00000000 [..ho............]
06F68D8C0 00000000 00000000 00000000 00000000 [................]
06F68D8D0 00000003 41080050 6F68D8D8 00000000 [....P..A..ho....]
#06F68D8E0 6F68D8D8 00000000 6F779848 00000000 [..ho....H.wo....]
06F68D8F0 00000000 00000000 00010000 10012111 [.............!..]
06F68D900 00000001 00000001 00010001 00000001 [................]
06F68D910 00000000 00000001 00010000 00000000 [................]子游标句柄也是recretable类型，KGLHD表示它是句柄，大小560字节
同时子游标句柄在父游标堆0也可以找到对应的地址
2.2 查看子游标堆0描述地址、堆6描述地址
这里因为共享池设置的太小，导致子游标的堆0和堆6被覆盖了,进一步验证freeable最容易被覆
盖
SQL> select kglhdadr, kglnaobj,kglobhd0,kglobhd6
from x$kglob
where kglnaobj like 'select * from cdh19c.t1 where object_id=199%'
and kglhdadr <> kglhdpar;
KGLHDADR KGLNAOBJ KGLOBHD0 KGLOBHD6
---------------- ------------------------------ ---------------- ----------------
000000006F68D8D8 select * from cdh19c.t1 where 000000006DC82F68 000000006F6A1680
object_id=199研究的方案和父游标一样，这样可以计算出一条SQL占用了哪些CHUNK，对共享池优化有进一步的帮助。
2.3 子游标堆0 DS信息
KGLOBHD0=000000006DC82F68
Chunk 06dc82f00 sz= 504 freeable "KGLDA "
Dump of memory from 0x000000006DC82F00 to 0x000000006DC830F8
06DC82F00 000001F9 00B38F00 6DC82D08 00000000 [.........-.m....]
06DC82F10 12B6CA50 00000000 6DC82F68 00000000 [P.......h/.m....]
06DC82F20 6F779918 00000000 00000000 00030001 [..wo............]
06DC82F30 6EE11F50 00000000 00001F98 00000E70 [P..n........p...]
06DC82F40 6F779848 00000000 6F779798 00000000 [H.wo......wo....]
06DC82F50 00000000 00000000 03F10629 00000000 [........).......]
#06DC82F60 69145108 00000000 6016FF60 00000000 [.Q.i....`..`....]
06DC82F70 00000000 00000000 6DC82F18 00000000 [........./.m....]
#子游标堆0：000000006DC82F68，它-104就是子游标heap0 chunk地址
select replace(upper('00000000'||to_char(to_number('6DC82F68','xxxxxxxxxx')-104,'xxxxxxxxxx')),' ','') from dual;
--000000006DC82F002.4 子游标堆6 DS信息
KGLOBHD0=000000006F6A1680
这里查到堆6在父游标堆6地址里
000000006F6A1680 在0x000000006F6A0E98 to 0x000000006F6A1E98
从dump信息也可以验证
06F6A0E90 00000000 00000000 [........]
Chunk 06f6a0e98 sz= 4096 recrPC003 "KGLH0^e12ae359 "
ds 06fb55c80 sz= 4096 ct= 1
Dump of memory from 0x000000006F6A0E98 to 0x000000006F6A1E98
06F6A0E90 00001001 80B38F00 [........]
06F6A0EA0 6F69FE98 00000000 00000000 00000000 [..io............]
06F6A0EB0 00000000 00000000 00000000 00000000 [................]
06F6A0EC0 00000003 000A0FFF 6FB55C80 00000000 [.........\.o....]
06F6A0ED0 00000000 00000000 00000079 40B38F00 [........y......@]
。。
06F6A1650 6F779848 00000000 6F371960 00000000 [H.wo.....7o....]
06F6A1660 00000001 00000000 00000000 00000000 [................]
06F6A1670 00000000 00000000 00000000 00000000 [................]
#06F6A1680 6016FF60 00000000 00000000 00000000 [..............] 子游标堆6描述地址在这
06F6A1690 6F6A1530 00000000 6A796D20 00000000 [0.jo.... myj....]
06F6A16A0 6F371970 00000000 00000000 00000000 [p.7o............]
。。2.5 查看子游标堆0下的chunk
SQL> select ksmchptr,ksmchcom,ksmchcls,ksmchsiz
from x$ksmsp where ksmchpar='000000006DC82F68'
;
KSMCHPTR KSMCHCOM KSMCHCLS KSMCHSIZ
---------------- -------------------------------- ---------------- ----------
000000006F779768 KGLH0^e12ae359 recr 4096
000000006F487900 KGLH0^e12ae359 freeabl 4096
#19.3下子游标堆0有两个chunk dupm相关信息
#000000006F779768
Chunk 06f779768 sz= 4096 recrPC003 "KGLH0^e12ae359 "
ds 06dc82f68 sz= 8192 ct= 2
06f487900 sz= 4096
Dump of memory from 0x000000006F779768 to 0x000000006F77A768
06F779760 00001001 80B38F00 [........]
06F779770 6F778768 00000000 00000000 00000000 [h.wo............]
06F779780 00000000 00000000 00000000 00000000 [................]
06F779790 00000003 400A0FFF 6DC82F68 00000000 [.......@h/.m....]
06F7797A0 00000000 00000000 00000079 40B38F00 [........y......@]
#000000006F487900
Chunk 06f487900 sz= 4096 freeable "KGLH0^e12ae359 " ds=0x6dc82f68
Dump of memory from 0x000000006F487900 to 0x000000006F488900
06F487900 00001001 00B38F00 6F486CE8 00000000 [.........lHo....]
06F487910 601718B8 00000000 6DC82F68 00000000 [...`....h/.m....]2.6 查看子游标堆6下的chunk
SQL> select ksmchptr,ksmchcom,ksmchcls,ksmchsiz
2 from x$ksmsp where ksmchpar='000000006F6A1680';
KSMCHPTR KSMCHCOM KSMCHCLS KSMCHSIZ
---------------- -------------------------------- ---------------- ----------
000000006A797D08 SQLA^e12ae359 freeabl 4096
000000006A796D08 SQLA^e12ae359 freeabl 4096
000000006C613668 SQLA^e12ae359 freeabl 4096
000000006F371930 SQLA^e12ae359 recr 4096
0000000070226E78 SQLA^e12ae359 freeabl 4096
0000000070207EA0 SQLA^e12ae359 freeabl 4096
0000000071238F28 SQLA^e12ae359 freeabl 4128
0000000071865A08 SQLA^e12ae359 freeabl 4096
0000000071E82F88 SQLA^e12ae359 freeabl 4096
#19.3 子游标堆6有9个chunkdupm相关信息
#000000006F371930
Chunk 06f371930 sz= 4096 recrUM003 "SQLA^e12ae359 " D08:33:23
ds 06f6a1680 sz= 36896 ct= 9
06a796d08 sz= 4096
06a797d08 sz= 4096
071238f28 sz= 4128
070207ea0 sz= 4096
071865a08 sz= 4096
071e82f88 sz= 4096
06c613668 sz= 4096
070226e78 sz= 4096
Dump of memory from 0x000000006F371930 to 0x000000006F372930
06F371930 00001001 80B38F00 6F370930 00000000 [........0.7o....]
06F371940 725DACF8 00000000 7294D050 00000000 [..]r....P..r....]
06F371950 72A70FC8 00000000 02000003 00020FFF [...r............]
06F371960 6F6A1680 00000000 00000000 00000000 [..jo............]
#000000006A797D08
Chunk 06a797d08 sz= 4096 freeableU "SQLA^e12ae359 " ds=0x6f6a1680
Dump of memory from 0x000000006A797D08 to 0x000000006A798D08
06A797D00 00001001 00B38F00 [........]
06A797D10 6A796D08 00000000 601761C0 00000000 [.myj.....a.....]
06A797D20 6F6A1680 00000000 71238F40 00000000 [..jo....@.#q....]
#000000006A796D08
Chunk 06a796d08 sz= 4096 freeableU "SQLA^e12ae359 " ds=0x6f6a1680
Dump of memory from 0x000000006A796D08 to 0x000000006A797D08
06A796D00 00001001 00B38F00 [........]
06A796D10 6A795D08 00000000 601761C0 00000000 [.]yj.....a.....]
#000000006C613668
Chunk 06c613668 sz= 4096 freeableU "SQLA^e12ae359 " ds=0x6f6a1680
Dump of memory from 0x000000006C613668 to 0x000000006C614668
06C613660 00001001 00B38F00 [........]
06C613670 6C612F00 00000000 601761C0 00000000 [./al.....a.....]
06C613680 6F6A1680 00000000 70226E90 00000000 [..jo.....n"p....]
#0000000070226E78
Chunk 070226e78 sz= 4096 freeableU "SQLA^e12ae359 " ds=0x6f6a1680
Dump of memory from 0x0000000070226E78 to 0x0000000070227E78
070226E70 00001001 00B38F00 [........]
#0000000070207EA0
Chunk 070207ea0 sz= 4096 freeableU "SQLA^e12ae359 " ds=0x6f6a1680
Dump of memory from 0x0000000070207EA0 to 0x0000000070208EA0
070207EA0 00001001 00B38F00 70207038 00000000 [........8p p....]
#0000000071238F28
71238F20 00000001 00000000 [........]
Chunk 071238f28 sz= 4128 freeableU "SQLA^e12ae359 " ds=0x6f6a1680 #这个chunk只用了4128字节
Dump of memory from 0x0000000071238F28 to 0x0000000071239F48
071238F20 00001021 00B38F00 [!.......]
#0000000071865A08
1865A00 00000000 00300030 [....0.0.]
Chunk 071865a08 sz= 4096 freeableU "SQLA^e12ae359 " ds=0x6f6a1680
Dump of memory from 0x0000000071865A08 to 0x0000000071866A08
071865A00 00001001 00B38F00 [........]
#0000000071E82F88
Chunk 071e82f88 sz= 4096 freeableU "SQLA^e12ae359 " ds=0x6f6a1680
Dump of memory from 0x0000000071E82F88 to 0x0000000071E83F88
071E82F80 00001001 00B38F00 [........]