12條語句學會oracle cbo計算(十二)
12條語句學會oracle cbo計算(十二)
工作中,你可能會遇到統計資料正確,但就是不走你想要的執行計劃的情況,最後一般透過hint或sql_profile解決.一條sql語句的效能主要依賴於好的物理結構,準確的系統統計資料,準確的物件統計資料,合理的查詢最佳化器引數,合理的系統引數.這些因素也就是cost計算基本引數.因此產生的sql最佳化技術有很多,大概包含:改變訪問結構,修改sql語句,加hint,改變執行環境,sql profile,stored outlines,sql plan baseline.其實無外乎就是透過調整sql適應環境或者透過調整環境適應sql.如果清楚Cost值的演算法,就可以透過演算法的對比,找到問題的真正原因,更有針對性的去解決問題.
全文主要參考Jonathan Lewis的<>和黃瑋(fuyuncat)的<>,特別黃瑋(fuyuncat)的這本,是非常值得去學習的.
準備用14篇來描述完,前2篇是統計資料,演算法公式說明,後12篇用12條語句分別去套用說明.
本篇例子的特徵是雙表,雜湊關聯,和上一篇差別是雙表雜湊關聯
--產生測試資料
drop table scott.t_test1 purge;
drop table scott.t_test2 purge;
create table scott.t_test1 as select * from dba_objects;
create table scott.t_test2 as select * from dba_objects;
begin
dbms_stats.gather_table_stats('scott','t_test1');
end;
begin
dbms_stats.gather_table_stats('scott','t_test2');
end;
--產生語句的執行計劃
--這裡我是在pl/sql developer,是因為不用象10053那麼麻煩就可以產生想要的幾個值用以對比.
explain plan for select /*+use_hash(a,b)*/* from scott.t_test1 a,scott.t_test2 b where a.object_id=b.object_id;
SELECT lpad(' ', 2 * (LEVEL - 1)) || operation operation,
options,
object_name,
cardinality,
bytes,
io_cost,
cpu_cost,
cost,
time
FROM plan_table
START WITH id = 0
CONNECT BY PRIOR id = parent_id;
/*
OPERATION OPTIONS OBJECT_NAME CARDINALITY BYTES IO_COST CPU_COST COST TIME
SELECT STATEMENT 86334 16921464 1585 132542679 1589 20
HASH JOIN 86334 16921464 1585 132542679 1589 20
TABLE ACCESS FULL T_TEST2 86335 8460830 343 46104186 344 5
TABLE ACCESS FULL T_TEST1 86334 8460732 343 46103756 344 5
*/
--查詢表的統計資料
select rpad(table_name, 10, ' ') table_name,
rpad(num_rows, 10, ' ') num_rows,
rpad(blocks, 10, ' ') blocks,
avg_row_len
from dba_tables
where owner = 'SCOTT'
and table_name in ('T_TEST1','T_TEST2');
/*
TABLE_NAME NUM_ROWS BLOCKS AVG_ROW_LEN
T_TEST2 86335 1261 98
T_TEST1 86334 1261 98
*/
--查詢列的統計資料
select rpad(table_name, 12, ' ') table_name,
rpad(column_name, 12, ' ') column_name,
rpad(num_distinct, 8, ' ') num_distinct,
rpad(utl_raw.cast_to_number(low_value), 15, ' ') low_value,
rpad(utl_raw.cast_to_number(high_value), 10, ' ') high_value,
rpad(nullable, 8, ' ') nullable,
rpad(num_nulls, 8, ' ') num_nulls,
rpad(avg_col_len, 6, ' ') avg_col_len,
rpad(density, 20, ' ') density,
histogram
from dba_tab_columns
where owner = 'SCOTT'
and table_name in ('T_TEST1','T_TEST2')
and column_name = 'OBJECT_ID';
/*
TABLE_NAME COLUMN_NAME NUM_DISTINCT LOW_VALUE HIGH_VALUE NULLABLE NUM_NULLS AVG_COL_LEN DENSITY HISTOGRAM
T_TEST1 OBJECT_ID 86334 2 87781 Y 0 5 .0000115829221395974 NONE
T_TEST2 OBJECT_ID 86335 2 87782 Y 0 5 .0000115827879770661 NONE
*/
--查詢各列平均長度之和
select table_name,sum(avg_col_len),count(1)
from dba_tab_col_statistics
where owner='SCOTT' and table_name in ( 'T_TEST1','T_TEST2')
group by table_name;
/*
TABLE_NAME SUM(AVG_COL_LEN) COUNT(1)
T_TEST2 100 15
T_TEST1 100 15
*/
--查詢最佳化器引數
select rpad(name,40,' ') name,rpad(value,20,' ') value,isdefault
from (select nam.ksppinm name,
val.KSPPSTVL value,
--nam.ksppdesc description,
val.ksppstdf isdefault
from sys.x$ksppi nam, sys.x$ksppcv val
where nam.inst_id = val.inst_id
and nam.indx = val.indx)
where name in
('_db_file_optimizer_read_count', 'db_file_multiblock_read_count',
'_optimizer_block_size', '_table_scan_cost_plus_one',
'_optimizer_ceil_cost', '_optimizer_cost_model',
'_optimizer_cache_stats', '_smm_auto_min_io_size',
'_smm_auto_max_io_size', '_smm_min_size', '_smm_max_size',
'_smm_px_max_size', 'sort_area_retained_size', 'sort_area_size',
'workarea_size_policy','_optimizer_percent_parallel');
/*
NAME VALUE ISDEFAULT
NAME VALUE ISDEFAULT
db_file_multiblock_read_count 116 TRUE
_db_file_optimizer_read_count 8 TRUE
sort_area_size 65536 TRUE
sort_area_retained_size 0 TRUE
_optimizer_cost_model CHOOSE TRUE
_optimizer_cache_stats FALSE TRUE
_table_scan_cost_plus_one TRUE TRUE
workarea_size_policy AUTO TRUE
_smm_auto_min_io_size 56 TRUE
_smm_auto_max_io_size 248 TRUE
_smm_min_size 286 TRUE
_smm_max_size 57344 TRUE
_smm_px_max_size 143360 TRUE
_optimizer_percent_parallel 101 TRUE
_optimizer_block_size 8192 TRUE
_optimizer_ceil_cost TRUE TRUE
*/
--查詢系統統計資料
select rpad(pname, '20', ' ') pname,
rpad(pval1, '20', ' ') pval1,
rpad(pval2, '20', ' ') pval2
from SYS.AUX_STATS$
where sname = 'SYSSTATS_MAIN';
/*
PNAME PVAL1 PVAL2
CPUSPEED
CPUSPEEDNW 3074.07407407407
IOSEEKTIM 10
IOTFRSPEED 4096
MAXTHR
MBRC
MREADTIM
SLAVETHR
SREADTIM
*/
--需要應用第二篇中的公式:
(1)NDV=dba_tab_co1umns.num_distinct
(2)DENS=dba_tab_co1umns.DENSITY
(3)ALLROWS=dba_tab1es.NUM_ROWS
(6)COLNB=dba_tab_co1umns.NULLABLE
(11)MBRC=最佳化器系統引數_db_fi1e_optimizer_read_count
(13)SAMAXIO=最佳化器系統引數_smm_auto_max_io_size*1024
(14)OPTBLKSIZE=最佳化器系統引數_optimizer_b1ock_size
(21)CPUSPEED=系統統計資料CPUSPEEDNW
(22)IOTFRSPEED=系統統計資料IOTFRSPEED
(23)IOSEEKTIM=系統統計資料IOSEEKTIM
(24)SREADTIM = IOSEEKTIM + OPTBLKSIZ/IOTFRSPEED
(25)MREADTIM = IOSEEKTIM + MBRC * OPTBLKSIZ/IOTFRSPEED
(26)SAMSIZE=最佳化器系統引數_smm_max_size*1024=58720256
(27)SASIZE=最佳化器系統引數_smm_min_size*1024=292864
(69)JOINSEL= LEASTEST(COLSEL[Outer], COLSEL[Inner])
(70)CARD[Join] = CARD[Outer]*CARD[Inner]*JOINSEL
(72)IOCOST = (#BLKS/MBRC)*(IOSEEKTIM + MBRC*OPTBLKSIZE/IOTFRSPEED)/(IOSEEKTIM+OPTBLKSIZE/IOTFRSPEED)
(73)CPUCOST = #CPUCYCLES /(CPUSPEED*SREADTIM)/1000
(92)SACL[Outer]= ACL[OuterColl]+...ACL[OuterColn]
(93)SACL[Inner]= ACL[InnerColl]+...ACL[InnerColn]
(94)HSIZE[Outer]= CARD[Outer]*(LEAST(ARL[Outer], SACL[Outer])+12)
(95)HSIZE[Inner] = CARD[Inner]*(LEAST(ARL[Inner], SACL[Inner])+12)
(96)MAXHASHAREA = CEIL(SMMAX*2/OPTBLKSIZE)
(97)HASHAREA = CEIL(LEAST(GREATEST(SAMAXIO*4/OPTBLKSIZE,SMMIN*2/OPTBLKSIZE),MAXHASHAERA*0.08))
(98)當HSIZE[Outer]>HASHAREA*OPTBLKSIZE,說明hash需要寫入磁碟,否則IOCOST[Hash]=0
(99)BULDFRAGS = TRUNC(HSIZE[Outer]/OPTBLKSIZE+ 1)
(100)PROBEFRAGS = TRUNC(HSIZE[Inner]/OPTBLKSIZE+ 1)
(101)HASHBLKS = BULDFRAGS + PROBEFRAGS
(102)IOCOST[Hash] = CEIL(2*HASHBLKS/(MBRC-1)*(MREADTIM/SREADTIM+MBRC/TRUNC(SAMAXIO/OPTBLKSIZE) - (1+MREADTIM/SREADTIM/TRUNC(SAMAXIO/OPTBLKSIZE))))
(103)IOCOST[HJ]= IOCOST[Outer] + IOCOST[Inner] + IOCOST[Hash]
--套用上面的公式及資料進行計算
表名:T_TEST1
(3)ALLROWS=dba_tab1es.NUM_ROWS=86334
列名:OBJECT_ID
(1)NDV=dba_tab_co1umns.num_distinct=86334
(2)DENS=dba_tab_co1umns.DENSITY=.0000115829221395974
(6)COLNB=dba_tab_co1umns.NULLABLE=Y
表名:T_TEST2
(3)ALLROWS=dba_tab1es.NUM_ROWS=86335
列名:OBJECT_ID
(1)NDV=dba_tab_co1umns.num_distinct=86335
(2)DENS=dba_tab_co1umns.DENSITY=.0000115827879770661
(6)COLNB=dba_tab_co1umns.NULLABLE=Y
(11)MBRC=最佳化器系統引數_db_fi1e_optimizer_read_count=8
(13)SAMAXIO=最佳化器系統引數_smm_auto_max_io_size*1024=248*1024=253952
(14)OPTBLKSIZE=最佳化器系統引數_optimizer_b1ock_size=8192
(21)CPUSPEED=系統統計資料CPUSPEEDNW=3074.07407407407
(22)IOTFRSPEED=系統統計資料IOTFRSPEED=4096
(23)IOSEEKTIM=系統統計資料IOSEEKTIM=10
(24)SREADTIM = IOSEEKTIM + OPTBLKSIZ/IOTFRSPEED=10+8192/4096=12
(25)MREADTIM = IOSEEKTIM + MBRC * OPTBLKSIZ/IOTFRSPEED=10+8*8192/4096=26
(26)SAMSIZE=最佳化器系統引數_smm_max_size*1024=58720256
(27)SASIZE=最佳化器系統引數_smm_min_size*1024=292864
--TABLE ACCESS FULL
因為兩個全表掃描都沒有過濾條件,所以
ROWS[Outer]=ALLROWS=86335
ROWS[Inner]=ALLROWS=86334
(72)IOCOST = (#BLKS/MBRC)*(IOSEEKTIM + MBRC*OPTBLKSIZE/IOTFRSPEED)/(IOSEEKTIM+OPTBLKSIZE/IOTFRSPEED)
IOCOST[Outer] = (#BLKS/MBRC)*(IOSEEKTIM + MBRC*OPTBLKSIZE/IOTFRSPEED)/(IOSEEKTIM+OPTBLKSIZE/IOTFRSPEED)
= (1261/8)*(10+8*8192/4096)/(10+8192/4096)
= 341.520833333333
由於_optimizer_ceil_cost=true,_table_scan_cost_plus_one=true,所以微調為:
IOCOST[Outer]=ceil(341.520833333333)+1=343
IOCOST[Inner] = (#BLKS/MBRC)*(IOSEEKTIM + MBRC*OPTBLKSIZE/IOTFRSPEED)/(IOSEEKTIM+OPTBLKSIZE/IOTFRSPEED)
= (1261/8)*(10+8*8192/4096)/(10+8192/4096)
= 341.520833333333
由於_optimizer_ceil_cost=true,_table_scan_cost_plus_one=true,所以微調為:
IOCOST[Inner]=ceil(341.520833333333)+1=343
--HASH JOIN
(69)JOINSEL= LEASTEST(COLSEL[Outer], COLSEL[Inner])
COLSEL[Outer]=1/NDV=1/86335
COLSEL[Inner]=1/NDV=1/86334
JOINSEL=LEAST(1/86335,1/86334)=1/86335
(70)CARD[Join] = CARD[Outer]*CARD[Inner]*JOINSEL
CARD[Outer]=ROWS[Outer]=86335
CARD[Inner]=ROWS[Inner]=86334
CARD[Join]= CARD[Outer]*CARD[Inner]*JOINSEL
=86335*86334*1/86335
=86334
(92)SACL[Outer]= ACL[OuterColl]+...ACL[OuterColn]
=100
(93)SACL[Inner]= ACL[InnerColl]+...ACL[InnerColn]
=100
(94)HSIZE[Outer]= CARD[Outer]*(LEAST(ARL[Outer], SACL[Outer])+12)
=86335*(LEAST(98, 100)+12)
=9496850
(95)HSIZE[Inner] = CARD[Inner]*(LEAST(ARL[Inner], SACL[Inner])+12)
=86334*(LEAST(98, 100)+12)
=9496740
(96)MAXHASHAREA = CEIL(SMMAX*2/OPTBLKSIZE)
=CEIL(58720256*2/8192)
=14336
(97)HASHAREA = CEIL(LEAST(GREATEST(SAMAXIO*4/OPTBLKSIZE,SMMIN*2/OPTBLKSIZE),MAXHASHAERA*0.08))
= CEIL(LEAST(GREATEST(253952*4/8192,292864*2/8192),14336*0.08))
=124
(98)當HSIZE[Outer]>HASHAREA*OPTBLKSIZE,說明hash需要寫入磁碟,否則IOCOST[Hash]=0
HSIZE[Outer](9496850)>HASHAREA*OPTBLKSIZE(124*8192=1015808)
(99)BULDFRAGS = TRUNC(HSIZE[Outer]/OPTBLKSIZE+ 1)
=TRUNC(9496850/8192+ 1)
=1160
(100)PROBEFRAGS = TRUNC(HSIZE[Inner]/OPTBLKSIZE+ 1)
=TRUNC(9496740/8192+ 1)
=1160
(101)HASHBLKS = BULDFRAGS + PROBEFRAGS
=1160+1160
=2320
(102)IOCOST[Hash] = CEIL(2*HASHBLKS/(MBRC-1)*(MREADTIM/SREADTIM+MBRC/TRUNC(SAMAXIO/OPTBLKSIZE) - (1+MREADTIM/SREADTIM/TRUNC(SAMAXIO/OPTBLKSIZE))))
=CEIL(2*2320/(8-1)*(26/12+8/TRUNC(253952/8192) - (1+26/12/TRUNC(253952/8192))))
=899
(103)IOCOST[HJ]= IOCOST[Outer] + IOCOST[Inner] + IOCOST[Hash]
=343+343+899
=1585
(73)CPUCOST = 132542679 /(3074.07407407407*12)/1000=3.5930244307229
COST=IOCOST+CPUCOST=1585+3.5930244307229=1588.5930244307229=1589
--可以看到,結果與執行計劃基本相同
ROWS=CARD[Join]=86334
IOCOST[Outer]=343
IOCOST[Inner]=343
IOCOST[HJ]=1585
CPUCOST = 3.5930244307229
COST=IOCOST[NLJ]+CPUCOST=1589
工作中,你可能會遇到統計資料正確,但就是不走你想要的執行計劃的情況,最後一般透過hint或sql_profile解決.一條sql語句的效能主要依賴於好的物理結構,準確的系統統計資料,準確的物件統計資料,合理的查詢最佳化器引數,合理的系統引數.這些因素也就是cost計算基本引數.因此產生的sql最佳化技術有很多,大概包含:改變訪問結構,修改sql語句,加hint,改變執行環境,sql profile,stored outlines,sql plan baseline.其實無外乎就是透過調整sql適應環境或者透過調整環境適應sql.如果清楚Cost值的演算法,就可以透過演算法的對比,找到問題的真正原因,更有針對性的去解決問題.
全文主要參考Jonathan Lewis的<>和黃瑋(fuyuncat)的<
準備用14篇來描述完,前2篇是統計資料,演算法公式說明,後12篇用12條語句分別去套用說明.
本篇例子的特徵是雙表,雜湊關聯,和上一篇差別是雙表雜湊關聯
--產生測試資料
drop table scott.t_test1 purge;
drop table scott.t_test2 purge;
create table scott.t_test1 as select * from dba_objects;
create table scott.t_test2 as select * from dba_objects;
begin
dbms_stats.gather_table_stats('scott','t_test1');
end;
begin
dbms_stats.gather_table_stats('scott','t_test2');
end;
--產生語句的執行計劃
--這裡我是在pl/sql developer,是因為不用象10053那麼麻煩就可以產生想要的幾個值用以對比.
explain plan for select /*+use_hash(a,b)*/* from scott.t_test1 a,scott.t_test2 b where a.object_id=b.object_id;
SELECT lpad(' ', 2 * (LEVEL - 1)) || operation operation,
options,
object_name,
cardinality,
bytes,
io_cost,
cpu_cost,
cost,
time
FROM plan_table
START WITH id = 0
CONNECT BY PRIOR id = parent_id;
/*
OPERATION OPTIONS OBJECT_NAME CARDINALITY BYTES IO_COST CPU_COST COST TIME
SELECT STATEMENT 86334 16921464 1585 132542679 1589 20
HASH JOIN 86334 16921464 1585 132542679 1589 20
TABLE ACCESS FULL T_TEST2 86335 8460830 343 46104186 344 5
TABLE ACCESS FULL T_TEST1 86334 8460732 343 46103756 344 5
*/
--查詢表的統計資料
select rpad(table_name, 10, ' ') table_name,
rpad(num_rows, 10, ' ') num_rows,
rpad(blocks, 10, ' ') blocks,
avg_row_len
from dba_tables
where owner = 'SCOTT'
and table_name in ('T_TEST1','T_TEST2');
/*
TABLE_NAME NUM_ROWS BLOCKS AVG_ROW_LEN
T_TEST2 86335 1261 98
T_TEST1 86334 1261 98
*/
--查詢列的統計資料
select rpad(table_name, 12, ' ') table_name,
rpad(column_name, 12, ' ') column_name,
rpad(num_distinct, 8, ' ') num_distinct,
rpad(utl_raw.cast_to_number(low_value), 15, ' ') low_value,
rpad(utl_raw.cast_to_number(high_value), 10, ' ') high_value,
rpad(nullable, 8, ' ') nullable,
rpad(num_nulls, 8, ' ') num_nulls,
rpad(avg_col_len, 6, ' ') avg_col_len,
rpad(density, 20, ' ') density,
histogram
from dba_tab_columns
where owner = 'SCOTT'
and table_name in ('T_TEST1','T_TEST2')
and column_name = 'OBJECT_ID';
/*
TABLE_NAME COLUMN_NAME NUM_DISTINCT LOW_VALUE HIGH_VALUE NULLABLE NUM_NULLS AVG_COL_LEN DENSITY HISTOGRAM
T_TEST1 OBJECT_ID 86334 2 87781 Y 0 5 .0000115829221395974 NONE
T_TEST2 OBJECT_ID 86335 2 87782 Y 0 5 .0000115827879770661 NONE
*/
--查詢各列平均長度之和
select table_name,sum(avg_col_len),count(1)
from dba_tab_col_statistics
where owner='SCOTT' and table_name in ( 'T_TEST1','T_TEST2')
group by table_name;
/*
TABLE_NAME SUM(AVG_COL_LEN) COUNT(1)
T_TEST2 100 15
T_TEST1 100 15
*/
--查詢最佳化器引數
select rpad(name,40,' ') name,rpad(value,20,' ') value,isdefault
from (select nam.ksppinm name,
val.KSPPSTVL value,
--nam.ksppdesc description,
val.ksppstdf isdefault
from sys.x$ksppi nam, sys.x$ksppcv val
where nam.inst_id = val.inst_id
and nam.indx = val.indx)
where name in
('_db_file_optimizer_read_count', 'db_file_multiblock_read_count',
'_optimizer_block_size', '_table_scan_cost_plus_one',
'_optimizer_ceil_cost', '_optimizer_cost_model',
'_optimizer_cache_stats', '_smm_auto_min_io_size',
'_smm_auto_max_io_size', '_smm_min_size', '_smm_max_size',
'_smm_px_max_size', 'sort_area_retained_size', 'sort_area_size',
'workarea_size_policy','_optimizer_percent_parallel');
/*
NAME VALUE ISDEFAULT
NAME VALUE ISDEFAULT
db_file_multiblock_read_count 116 TRUE
_db_file_optimizer_read_count 8 TRUE
sort_area_size 65536 TRUE
sort_area_retained_size 0 TRUE
_optimizer_cost_model CHOOSE TRUE
_optimizer_cache_stats FALSE TRUE
_table_scan_cost_plus_one TRUE TRUE
workarea_size_policy AUTO TRUE
_smm_auto_min_io_size 56 TRUE
_smm_auto_max_io_size 248 TRUE
_smm_min_size 286 TRUE
_smm_max_size 57344 TRUE
_smm_px_max_size 143360 TRUE
_optimizer_percent_parallel 101 TRUE
_optimizer_block_size 8192 TRUE
_optimizer_ceil_cost TRUE TRUE
*/
--查詢系統統計資料
select rpad(pname, '20', ' ') pname,
rpad(pval1, '20', ' ') pval1,
rpad(pval2, '20', ' ') pval2
from SYS.AUX_STATS$
where sname = 'SYSSTATS_MAIN';
/*
PNAME PVAL1 PVAL2
CPUSPEED
CPUSPEEDNW 3074.07407407407
IOSEEKTIM 10
IOTFRSPEED 4096
MAXTHR
MBRC
MREADTIM
SLAVETHR
SREADTIM
*/
--需要應用第二篇中的公式:
(1)NDV=dba_tab_co1umns.num_distinct
(2)DENS=dba_tab_co1umns.DENSITY
(3)ALLROWS=dba_tab1es.NUM_ROWS
(6)COLNB=dba_tab_co1umns.NULLABLE
(11)MBRC=最佳化器系統引數_db_fi1e_optimizer_read_count
(13)SAMAXIO=最佳化器系統引數_smm_auto_max_io_size*1024
(14)OPTBLKSIZE=最佳化器系統引數_optimizer_b1ock_size
(21)CPUSPEED=系統統計資料CPUSPEEDNW
(22)IOTFRSPEED=系統統計資料IOTFRSPEED
(23)IOSEEKTIM=系統統計資料IOSEEKTIM
(24)SREADTIM = IOSEEKTIM + OPTBLKSIZ/IOTFRSPEED
(25)MREADTIM = IOSEEKTIM + MBRC * OPTBLKSIZ/IOTFRSPEED
(26)SAMSIZE=最佳化器系統引數_smm_max_size*1024=58720256
(27)SASIZE=最佳化器系統引數_smm_min_size*1024=292864
(69)JOINSEL= LEASTEST(COLSEL[Outer], COLSEL[Inner])
(70)CARD[Join] = CARD[Outer]*CARD[Inner]*JOINSEL
(72)IOCOST = (#BLKS/MBRC)*(IOSEEKTIM + MBRC*OPTBLKSIZE/IOTFRSPEED)/(IOSEEKTIM+OPTBLKSIZE/IOTFRSPEED)
(73)CPUCOST = #CPUCYCLES /(CPUSPEED*SREADTIM)/1000
(92)SACL[Outer]= ACL[OuterColl]+...ACL[OuterColn]
(93)SACL[Inner]= ACL[InnerColl]+...ACL[InnerColn]
(94)HSIZE[Outer]= CARD[Outer]*(LEAST(ARL[Outer], SACL[Outer])+12)
(95)HSIZE[Inner] = CARD[Inner]*(LEAST(ARL[Inner], SACL[Inner])+12)
(96)MAXHASHAREA = CEIL(SMMAX*2/OPTBLKSIZE)
(97)HASHAREA = CEIL(LEAST(GREATEST(SAMAXIO*4/OPTBLKSIZE,SMMIN*2/OPTBLKSIZE),MAXHASHAERA*0.08))
(98)當HSIZE[Outer]>HASHAREA*OPTBLKSIZE,說明hash需要寫入磁碟,否則IOCOST[Hash]=0
(99)BULDFRAGS = TRUNC(HSIZE[Outer]/OPTBLKSIZE+ 1)
(100)PROBEFRAGS = TRUNC(HSIZE[Inner]/OPTBLKSIZE+ 1)
(101)HASHBLKS = BULDFRAGS + PROBEFRAGS
(102)IOCOST[Hash] = CEIL(2*HASHBLKS/(MBRC-1)*(MREADTIM/SREADTIM+MBRC/TRUNC(SAMAXIO/OPTBLKSIZE) - (1+MREADTIM/SREADTIM/TRUNC(SAMAXIO/OPTBLKSIZE))))
(103)IOCOST[HJ]= IOCOST[Outer] + IOCOST[Inner] + IOCOST[Hash]
--套用上面的公式及資料進行計算
表名:T_TEST1
(3)ALLROWS=dba_tab1es.NUM_ROWS=86334
列名:OBJECT_ID
(1)NDV=dba_tab_co1umns.num_distinct=86334
(2)DENS=dba_tab_co1umns.DENSITY=.0000115829221395974
(6)COLNB=dba_tab_co1umns.NULLABLE=Y
表名:T_TEST2
(3)ALLROWS=dba_tab1es.NUM_ROWS=86335
列名:OBJECT_ID
(1)NDV=dba_tab_co1umns.num_distinct=86335
(2)DENS=dba_tab_co1umns.DENSITY=.0000115827879770661
(6)COLNB=dba_tab_co1umns.NULLABLE=Y
(11)MBRC=最佳化器系統引數_db_fi1e_optimizer_read_count=8
(13)SAMAXIO=最佳化器系統引數_smm_auto_max_io_size*1024=248*1024=253952
(14)OPTBLKSIZE=最佳化器系統引數_optimizer_b1ock_size=8192
(21)CPUSPEED=系統統計資料CPUSPEEDNW=3074.07407407407
(22)IOTFRSPEED=系統統計資料IOTFRSPEED=4096
(23)IOSEEKTIM=系統統計資料IOSEEKTIM=10
(24)SREADTIM = IOSEEKTIM + OPTBLKSIZ/IOTFRSPEED=10+8192/4096=12
(25)MREADTIM = IOSEEKTIM + MBRC * OPTBLKSIZ/IOTFRSPEED=10+8*8192/4096=26
(26)SAMSIZE=最佳化器系統引數_smm_max_size*1024=58720256
(27)SASIZE=最佳化器系統引數_smm_min_size*1024=292864
--TABLE ACCESS FULL
因為兩個全表掃描都沒有過濾條件,所以
ROWS[Outer]=ALLROWS=86335
ROWS[Inner]=ALLROWS=86334
(72)IOCOST = (#BLKS/MBRC)*(IOSEEKTIM + MBRC*OPTBLKSIZE/IOTFRSPEED)/(IOSEEKTIM+OPTBLKSIZE/IOTFRSPEED)
IOCOST[Outer] = (#BLKS/MBRC)*(IOSEEKTIM + MBRC*OPTBLKSIZE/IOTFRSPEED)/(IOSEEKTIM+OPTBLKSIZE/IOTFRSPEED)
= (1261/8)*(10+8*8192/4096)/(10+8192/4096)
= 341.520833333333
由於_optimizer_ceil_cost=true,_table_scan_cost_plus_one=true,所以微調為:
IOCOST[Outer]=ceil(341.520833333333)+1=343
IOCOST[Inner] = (#BLKS/MBRC)*(IOSEEKTIM + MBRC*OPTBLKSIZE/IOTFRSPEED)/(IOSEEKTIM+OPTBLKSIZE/IOTFRSPEED)
= (1261/8)*(10+8*8192/4096)/(10+8192/4096)
= 341.520833333333
由於_optimizer_ceil_cost=true,_table_scan_cost_plus_one=true,所以微調為:
IOCOST[Inner]=ceil(341.520833333333)+1=343
--HASH JOIN
(69)JOINSEL= LEASTEST(COLSEL[Outer], COLSEL[Inner])
COLSEL[Outer]=1/NDV=1/86335
COLSEL[Inner]=1/NDV=1/86334
JOINSEL=LEAST(1/86335,1/86334)=1/86335
(70)CARD[Join] = CARD[Outer]*CARD[Inner]*JOINSEL
CARD[Outer]=ROWS[Outer]=86335
CARD[Inner]=ROWS[Inner]=86334
CARD[Join]= CARD[Outer]*CARD[Inner]*JOINSEL
=86335*86334*1/86335
=86334
(92)SACL[Outer]= ACL[OuterColl]+...ACL[OuterColn]
=100
(93)SACL[Inner]= ACL[InnerColl]+...ACL[InnerColn]
=100
(94)HSIZE[Outer]= CARD[Outer]*(LEAST(ARL[Outer], SACL[Outer])+12)
=86335*(LEAST(98, 100)+12)
=9496850
(95)HSIZE[Inner] = CARD[Inner]*(LEAST(ARL[Inner], SACL[Inner])+12)
=86334*(LEAST(98, 100)+12)
=9496740
(96)MAXHASHAREA = CEIL(SMMAX*2/OPTBLKSIZE)
=CEIL(58720256*2/8192)
=14336
(97)HASHAREA = CEIL(LEAST(GREATEST(SAMAXIO*4/OPTBLKSIZE,SMMIN*2/OPTBLKSIZE),MAXHASHAERA*0.08))
= CEIL(LEAST(GREATEST(253952*4/8192,292864*2/8192),14336*0.08))
=124
(98)當HSIZE[Outer]>HASHAREA*OPTBLKSIZE,說明hash需要寫入磁碟,否則IOCOST[Hash]=0
HSIZE[Outer](9496850)>HASHAREA*OPTBLKSIZE(124*8192=1015808)
(99)BULDFRAGS = TRUNC(HSIZE[Outer]/OPTBLKSIZE+ 1)
=TRUNC(9496850/8192+ 1)
=1160
(100)PROBEFRAGS = TRUNC(HSIZE[Inner]/OPTBLKSIZE+ 1)
=TRUNC(9496740/8192+ 1)
=1160
(101)HASHBLKS = BULDFRAGS + PROBEFRAGS
=1160+1160
=2320
(102)IOCOST[Hash] = CEIL(2*HASHBLKS/(MBRC-1)*(MREADTIM/SREADTIM+MBRC/TRUNC(SAMAXIO/OPTBLKSIZE) - (1+MREADTIM/SREADTIM/TRUNC(SAMAXIO/OPTBLKSIZE))))
=CEIL(2*2320/(8-1)*(26/12+8/TRUNC(253952/8192) - (1+26/12/TRUNC(253952/8192))))
=899
(103)IOCOST[HJ]= IOCOST[Outer] + IOCOST[Inner] + IOCOST[Hash]
=343+343+899
=1585
(73)CPUCOST = 132542679 /(3074.07407407407*12)/1000=3.5930244307229
COST=IOCOST+CPUCOST=1585+3.5930244307229=1588.5930244307229=1589
--可以看到,結果與執行計劃基本相同
ROWS=CARD[Join]=86334
IOCOST[Outer]=343
IOCOST[Inner]=343
IOCOST[HJ]=1585
CPUCOST = 3.5930244307229
COST=IOCOST[NLJ]+CPUCOST=1589
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/28389881/viewspace-1718686/，如需轉載，請註明出處，否則將追究法律責任。
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