Oracle 1053事件主要看是成本如何计算的?

Apress.Cost.Based.Oracle.Fundamentals. 看中文翻译版看的很吃力. 当初不知10053事件,看完该书花费了很长的时间!

10053事件

1 创建测试表 create table zengmuansha_temp01 as select * from dba_objects ;

2 在PL/SQL工具的COMMAND窗口或者SQLPLUS

3 获得会话id:SELECTSYS_CONTEXT ('USERENV', 'SID') sid FROM DUAL;

4 设置跟踪文件标识: altersession set tracefile_identifier='kk_flag';

5 alter session set events '10053 trace name context forever, level 1';

6 declare

typetype_owner istableofzengfankun_temp01.owner%typeindexbybinary_integer;

typetype_object_name istableofzengfankun_temp01.object_name%typeindexbybinary_integer;

typetype_object_id istableofzengfankun_temp01.object_id%typeindexbybinary_integer;

typetype_object_type istableofzengfankun_temp01.object_type%typeindexbybinary_integer;

typetype_last_ddl_time istableofzengfankun_temp01.last_ddl_time%typeindexbybinary_integer;

l_ary_owner type_owner;

l_ary_object_name type_object_name;

l_ary_object_id type_object_id;

l_ary_object_type type_object_type;

l_ary_last_ddl_time type_last_ddl_time;

cursorcur_object is

selectowner,object_name,object_id,object_type,last_ddl_time

from zengfankun_temp01

order by owner,object_name,object_id,object_type,last_ddl_time;

begin

open cur_object;

loop

fetchcur_object bulkcollectinto

l_ary_owner,

l_ary_object_name,

l_ary_object_id,

l_ary_object_type,

l_ary_last_ddl_time

limit100;

exitwhen cur_object%notfoundor cur_object%notfoundisnull;

endloop;

end;

7 altersession set events '10053 trace name context off';

8 获得跟踪文件名称和路径

SelectRtrim(c.Value, '/') || Decode(e.Plat_Id, 1, '\', '/') ||

d.Instance_Name || '_ora_' || Ltrim(To_Char(a.Spid))|| '.trc' Trace_File

From V$process a,

V$session b,

V$parameter c,

V$instance d,

(SelectCase

When t.Banner Like'%Windows%'Then

When t.Banner Like'%Linux%'Then

When t.Banner Like'%AIX%'Then

When t.Banner Like'%Solaris%'Then

End Plat_Id

From V$version t

Where t.BANNER Like'%TNS%') e

Where a.Addr = b.Paddr

And b.Sid = &P_SID

And c.Name = 'user_dump_dest';

9 跟踪文件内容

/home/oracle/app/oracle/admin/oss2/udump/oss2_ora_13859_kk_flag.trc

OracleDatabase 10g EnterpriseEdition Release 10.2.0.3.0 - 64bit Production

Withthe Partitioning, OLAP and Data Mining options

ORACLE_HOME= /home/oracle/app/oracle/product/10.2.0/db_1

Systemname: Linux

Nodename: db101

Release: 2.6.18-164.el5

Version: #1 SMP Tue Aug 18 15:51:48 EDT 2009

Machine: x86_64

Instancename: oss2

Redothread mounted by this instance: 1

Oracleprocess number: 58

Unixprocess pid: 13859, image: oracleoss2@db101

***2012-08-14 09:29:04.559

***ACTION NAME:(Command Window - New) 2012-08-14 09:29:04.559

*** MODULENAME:(PL/SQL Developer) 2012-08-14 09:29:04.559

***SERVICE NAME:(oss2) 2012-08-14 09:29:04.559

***SESSION ID:(1598.1946) 2012-08-14 09:29:04.559

Registeredqb: MISC$1 0x287158f8(PARSER)

signature(): NULL

**************************

PredicateMove-Around (PM)

**************************

PM:Considering predicate move-around in MISC$1 (#0).

PM: Checking validity of predicate move-aroundin MISC$1 (#0).

CBQT:Validity checks failed for 5q23guhp5t335.

CVM:Considering view merge in query block MISC$1 (#0)

CBQT:Validity checks failed for 5q23guhp5t335.

***************

SubqueryUnnest

***************

SU:Considering subquery unnesting in query block MISC$1 (#0)

*************************

Set-JoinConversion (SJC)

*************************

SJC:Considering set-join conversion in MISC$1 (#0).

**************************

PredicateMove-Around (PM)

**************************

PM:Considering predicate move-around in MISC$1 (#0).

PM: Checking validity of predicate move-aroundin MISC$1 (#0).

PM: PM bypassed: Outer query contains noviews.

Registeredqb: SEL$1 0x28712428 (PARSER)

signature (): qb_name=SEL$1 nbfros=1 flg=0

fro(0): flg=4 objn=440475hint_alias="ZENGFANKUN_TEMP01"@"SEL$1"

**************************

PredicateMove-Around (PM)

**************************

PM:Considering predicate move-around in SEL$1 (#0).

PM: Checking validity of predicate move-aroundin SEL$1 (#0).

CBQT:Validity checks failed for 7nvfsndyywp50.

CVM:Considering view merge in query block SEL$1 (#0)

CBQT:Validity checks failed for 7nvfsndyywp50.

***************

SubqueryUnnest

***************

SU:Considering subquery unnesting in query block SEL$1 (#0)

*************************

Set-JoinConversion (SJC)

*************************

SJC:Considering set-join conversion in SEL$1 (#0).

**************************

PredicateMove-Around (PM)

**************************

PM:Considering predicate move-around in SEL$1 (#0).

PM: Checking validity of predicate move-aroundin SEL$1 (#0).

PM: PM bypassed: Outer query contains no views.

FPD:Considering simple filter push in SEL$1 (#0)

FPD: Current where clause predicates in SEL$1(#0) :

apadrv-start: call(in-use=600,alloc=16344), compile(in-use=40192, alloc=41240)

kkoqbc-start

: call(in-use=600, alloc=16344), compile(in-use=41040,alloc=41240)

******************************************

CurrentSQL statement for this session:

SELECTOWNER,OBJECT_NAME,OBJECT_ID,OBJECT_TYPE,LAST_DDL_TIME FROM ZENGFANKUN_TEMP01ORDER BY OWNER,OBJECT_NAME,OBJECT_TYPE,LAST_DDL_TIME

-----PL/SQL Call Stack -----

object line object

handle number name

0x74772a68 15 anonymous block

0x74772a68 19 anonymous block

*******************************************

Legend

Thefollowing abbreviations are used by optimizer trace.

CBQT- cost-based query transformation

JPPD- join predicate push-down

FPD- filter push-down

PM -predicate move-around

CVM- complex view merging

SPJ- select-project-join

SJC- set join conversion

SU -subquery unnesting

OBYE- order by elimination

ST -star transformation

qb -query block

LB -leaf blocks

DK -distinct keys

LB/K- average number of leaf blocks per key

DB/K- average number of data blocks per key

CLUF- clustering factor

NDV- number of distinct values

Resp- response cost

Card- cardinality

Resc- resource cost

NL -nested loops (join)

SM -sort merge (join)

HA -hash (join)

CPUCSPEED- CPU Speed

IOTFRSPEED- I/O transfer speed

IOSEEKTIM- I/O seek time

SREADTIM- average single block read time

MREADTIM- average multiblock read time

MBRC- average multiblock read count

MAXTHR- maximum I/O system throughput

SLAVETHR- average slave I/O throughput

dmeth- distribution method

1: no partitioning required

2: value partitioned

4: right is random (round-robin)

512: left is random (round-robin)

8: broadcast right and partition left

16: broadcast left and partition right

32: partition left using partitioning ofright

64: partition right using partitioning ofleft

128: use hash partitioning dimension

256: use range partitioning dimension

2048: use list partitioning dimension

1024: run the join in serial

0: invalid distribution method

sel- selectivity

ptn- partition

*******************************************

Peekedvalues of the binds in SQL statement

*******************************************

***************************************

PARAMETERSUSED BY THE OPTIMIZER

********************************

*************************************

PARAMETERS WITH ALTERED VALUES

******************************

_pga_max_size = 2097140 KB

*********************************

Bug Fix Control Environment

***************************

fix 4611850 = enabled

fix 4908162 = enabled

fix 5015557 = enabled

*************************************

PARAMETERS WITH DEFAULT VALUES

******************************

optimizer_mode_hinted = false

optimizer_features_hinted = 0.0.0

parallel_execution_enabled = true

parallel_query_forced_dop = 0

parallel_dml_forced_dop = 0

parallel_ddl_forced_degree = 0

parallel_ddl_forced_instances = 0

_query_rewrite_fudge = 90

optimizer_features_enable = 10.2.0.3

_optimizer_search_limit = 5

cpu_count = 8

active_instance_count = 1

parallel_threads_per_cpu = 2

hash_area_size = 131072

bitmap_merge_area_size = 1048576

sort_area_size = 65536

sort_area_retained_size = 0

_sort_elimination_cost_ratio = 0

_optimizer_block_size = 8192

_sort_multiblock_read_count = 2

_hash_multiblock_io_count = 0

_db_file_optimizer_read_count = 16

_optimizer_max_permutations = 2000

pga_aggregate_target = 10485760 KB

_query_rewrite_maxdisjunct = 257

_smm_auto_min_io_size = 56 KB

_smm_auto_max_io_size = 248 KB

_smm_min_size = 1024 KB

_smm_max_size = 1048570 KB

_smm_px_max_size = 5242880 KB

_cpu_to_io = 0

_optimizer_undo_cost_change = 10.2.0.3

parallel_query_mode = enabled

parallel_dml_mode = disabled

parallel_ddl_mode = enabled

optimizer_mode = all_rows

sqlstat_enabled = false

_optimizer_percent_parallel = 101

_always_anti_join = choose

_always_semi_join = choose

_optimizer_mode_force = true

_partition_view_enabled = true

_always_star_transformation = false

_query_rewrite_or_error = false

_hash_join_enabled = true

cursor_sharing = exact

_b_tree_bitmap_plans = true

star_transformation_enabled = false

_optimizer_cost_model = choose

_new_sort_cost_estimate = true

_complex_view_merging = true

_unnest_subquery = true

_eliminate_common_subexpr = true

_pred_move_around = true

_convert_set_to_join = false

_push_join_predicate = true

_push_join_union_view = true

_fast_full_scan_enabled = true

_optim_enhance_nnull_detection = true

_parallel_broadcast_enabled = true

_px_broadcast_fudge_factor = 100

_ordered_nested_loop = true

_no_or_expansion = false

optimizer_index_cost_adj = 100

optimizer_index_caching = 0

_system_index_caching = 0

_disable_datalayer_sampling = false

query_rewrite_enabled = true

query_rewrite_integrity = enforced

_query_cost_rewrite = true

_query_rewrite_2 = true

_query_rewrite_1 = true

_query_rewrite_expression = true

_query_rewrite_jgmigrate = true

_query_rewrite_fpc = true

_query_rewrite_drj = true

_full_pwise_join_enabled = true

_partial_pwise_join_enabled = true

_left_nested_loops_random = true

_improved_row_length_enabled = true

_index_join_enabled = true

_enable_type_dep_selectivity = true

_improved_outerjoin_card = true

_optimizer_adjust_for_nulls = true

_optimizer_degree = 0

_use_column_stats_for_function = true

_subquery_pruning_enabled = true

_subquery_pruning_mv_enabled = false

_or_expand_nvl_predicate = true

_like_with_bind_as_equality = false

_table_scan_cost_plus_one = true

_cost_equality_semi_join = true

_default_non_equality_sel_check = true

_new_initial_join_orders = true

_oneside_colstat_for_equijoins = true

_optim_peek_user_binds = true

_minimal_stats_aggregation = true

_force_temptables_for_gsets = false

workarea_size_policy = auto

_smm_auto_cost_enabled = true

_gs_anti_semi_join_allowed = true

_optim_new_default_join_sel = true

optimizer_dynamic_sampling = 2

_pre_rewrite_push_pred = true

_optimizer_new_join_card_computation = true

_union_rewrite_for_gs = yes_gset_mvs

_generalized_pruning_enabled = true

_optim_adjust_for_part_skews = true

_force_datefold_trunc = false

statistics_level = typical

_optimizer_system_stats_usage = true

skip_unusable_indexes = true

_remove_aggr_subquery = true

_optimizer_push_down_distinct = 0

_dml_monitoring_enabled = true

_optimizer_undo_changes = false

_predicate_elimination_enabled = true

_nested_loop_fudge = 100

_project_view_columns = true

_local_communication_costing_enabled = true

_local_communication_ratio = 50

_query_rewrite_vop_cleanup = true

_slave_mapping_enabled = true

_optimizer_cost_based_transformation = linear

_optimizer_mjc_enabled = true

_right_outer_hash_enable = true

_spr_push_pred_refspr = true

_optimizer_cache_stats = false

_optimizer_cbqt_factor = 50

_optimizer_squ_bottomup = true

_fic_area_size = 131072

_optimizer_skip_scan_enabled = true

_optimizer_cost_filter_pred = false

_optimizer_sortmerge_join_enabled = true

_optimizer_join_sel_sanity_check = true

_mmv_query_rewrite_enabled = true

_bt_mmv_query_rewrite_enabled = true

_add_stale_mv_to_dependency_list = true

_distinct_view_unnesting = false

_optimizer_dim_subq_join_sel = true

_optimizer_disable_strans_sanity_checks = 0

_optimizer_compute_index_stats = true

_push_join_union_view2 = true

_optimizer_ignore_hints = false

_optimizer_random_plan = 0

_query_rewrite_setopgrw_enable =true

_optimizer_correct_sq_selectivity = true

_disable_function_based_index = false

_optimizer_join_order_control = 3

_optimizer_cartesian_enabled = true

_optimizer_starplan_enabled = true

_extended_pruning_enabled = true

_optimizer_push_pred_cost_based = true

_sql_model_unfold_forloops = run_time

_enable_dml_lock_escalation = false

_bloom_filter_enabled = true

_update_bji_ipdml_enabled = 0

_optimizer_extended_cursor_sharing = udo

_dm_max_shared_pool_pct = 1

_optimizer_cost_hjsmj_multimatch = true

_optimizer_transitivity_retain = true

_px_pwg_enabled = true

optimizer_secure_view_merging = true

_optimizer_join_elimination_enabled = true

flashback_table_rpi = non_fbt

_optimizer_cbqt_no_size_restriction = true

_optimizer_enhanced_filter_push = true

_optimizer_filter_pred_pullup = true

_rowsrc_trace_level = 0

_simple_view_merging = true

_optimizer_rownum_pred_based_fkr = true

_optimizer_better_inlist_costing = all

_optimizer_self_induced_cache_cost = false

_optimizer_min_cache_blocks = 10

_optimizer_or_expansion = depth

_optimizer_order_by_elimination_enabled =true

_optimizer_outer_to_anti_enabled = true

_selfjoin_mv_duplicates = true

_dimension_skip_null = true

_force_rewrite_enable = false

_optimizer_star_tran_in_with_clause = true

_optimizer_complex_pred_selectivity = true

_optimizer_connect_by_cost_based = true

_gby_hash_aggregation_enabled = true

_globalindex_pnum_filter_enabled = true

_fix_control_key = 0

_optimizer_skip_scan_guess = false

_enable_row_shipping = false

_row_shipping_threshold = 80

_row_shipping_explain = false

_optimizer_rownum_bind_default = 10

_first_k_rows_dynamic_proration = true

_optimizer_native_full_outer_join = off

*********************************

Bug Fix Control Environment

***************************

fix 4611850 = enabled

fix 4663804 = enabled

***************************************

PARAMETERS IN OPT_PARAM HINT

****************************

***************************************

ColumnUsage Monitoring is ON: tracking level = 1

***************************************

****************

QUERYBLOCK TEXT

****************

SELECTOWNER,OBJECT_NAME,OBJECT_ID,OBJECT_TYPE,LAST_DDL_TIME FROM ZENGFANKUN_TEMP01

*********************

QUERYBLOCK SIGNATURE

*********************

qbname was generated

signature(optimizer): qb_name=SEL$1 nbfros=1 flg=0

fro(0): flg=0 objn=440475 hint_alias="ZENGFANKUN_TEMP01"@"SEL$1"

*****************************

SYSTEMSTATISTICS INFORMATION

*****************************

Using WORKLOAD Stats

CPUSPEED: 1042 millions instructions/sec

SREADTIM: 21 milliseconds

MREADTIM: 45 millisecons

MBRC: 12.000000 blocks

MAXTHR: 54754304 bytes/sec

SLAVETHR: -1 bytes/sec

***************************************

BASESTATISTICAL INFORMATION

***********************

TableStats::

Table: ZENGFANKUN_TEMP01 Alias: ZENGFANKUN_TEMP01

#Rows: 126826 #Blks: 2099 AvgRowLen: 114.00

***************************************

SINGLETABLE ACCESS PATH

Table: ZENGFANKUN_TEMP01 Alias: ZENGFANKUN_TEMP01

Card: Original: 126826 Rounded: 126826 Computed: 126826.00 Non Adjusted: 126826.00

Access Path: TableScan

Cost: 381.36 Resp: 381.36 Degree: 0

Cost_io: 379.00 Cost_cpu: 51727443

Resp_io: 379.00 Resp_cpu: 51727443

Best:: AccessPath: TableScan

Cost: 381.36 Degree: 1 Resp: 381.36 Card: 126826.00 Bytes: 0

***************************************

OPTIMIZERSTATISTICS AND COMPUTATIONS

***************************************

GENERALPLANS

***************************************

Consideringcardinality-based initial join order.

Permutationsfor Starting Table :0

***********************

Joinorder[1]: ZENGFANKUN_TEMP01[ZENGFANKUN_TEMP01]#0

ORDERBY sort

SORT resource Sort statistics

Sort width: 6142 Area size: 1048576 Max Area size: 1073735680

Degree: 1

Blocks to Sort: 1056 Row size: 68 Total Rows: 126826

Initial runs: 2 Merge passes: 1 IO Cost / pass: 460

Total IO sort cost: 1516 Total CPU sort cost: 144803056

Total Temp space used: 17327000

***********************

Bestso far: Table#: 0 cost: 1903.9617 card: 126826.0000 bytes: 6594952

(newjo-stop-1)k:0, spcnt:0, perm:1, maxperm:80000

*********************************

Numberof join permutations tried: 1

*********************************

SORT resource Sort statistics

Sort width: 6142 Area size: 1048576 Max Area size: 1073735680

Degree: 1

Blocks to Sort: 1056 Row size: 68 Total Rows: 126826

Initial runs: 2 Merge passes: 1 IO Cost / pass: 460

Total IO sort cost: 1516 Total CPU sort cost: 144803056

Total Temp space used: 17327000

Final- All Rows Plan: Best join order: 1

Cost: 1903.9617 Degree: 1 Card: 126826.0000 Bytes: 6594952

Resc: 1903.9617 Resc_io: 1895.0000 Resc_cpu: 196530498

Resp: 1903.9617 Resp_io: 1895.0000 Resc_cpu: 196530498

kkoipt:Query block SEL$1 (#0)

*******UNPARSED QUERY IS *******

SELECT"ZENGFANKUN_TEMP01"."OWNER""OWNER","ZENGFANKUN_TEMP01"."OBJECT_NAME""OBJECT_NAME","ZENGFANKUN_TEMP01"."OBJECT_ID""OBJECT_ID","ZENGFANKUN_TEMP01"."OBJECT_TYPE""OBJECT_TYPE","ZENGFANKUN_TEMP01"."LAST_DDL_TIME""LAST_DDL_TIME"

FROM"OSS03"."ZENGFANKUN_TEMP01" "ZENGFANKUN_TEMP01"

ORDERBY"ZENGFANKUN_TEMP01"."OWNER","ZENGFANKUN_TEMP01"."OBJECT_NAME","ZENGFANKUN_TEMP01"."OBJECT_TYPE","ZENGFANKUN_TEMP01"."LAST_DDL_TIME"

kkoqbc-end

: call(in-use=26184, alloc=49080),compile(in-use=41544, alloc=45384)

apadrv-end:call(in-use=26184, alloc=49080), compile(in-use=42392, alloc=45384)

sql_id=7nvfsndyywp50.

CurrentSQL statement for this session:

SELECTOWNER,OBJECT_NAME,OBJECT_ID,OBJECT_TYPE,LAST_DDL_TIME FROM ZENGFANKUN_TEMP01ORDER BY OWNER,OBJECT_NAME,OBJECT_TYPE,LAST_DDL_TIME

-----PL/SQL Call Stack -----

object line object

handle number name

0x74772a68 15 anonymous block

0x74772a68 19 anonymous block

============

PlanTable

============

-----------------------------------------------+-----------------------------------+

-----------------------------------------------+-----------------------------------+

|0 | SELECT STATEMENT | | | | 1904 | |

|1 | SORT ORDER BY | | 124K | 6440K | 1904 | 00:00:41 |

|2 | TABLE ACCESS FULL | ZENGFANKUN_TEMP01| 124K | 6440K | 381 | 00:00:09 |

-----------------------------------------------+-----------------------------------+

PredicateInformation:

----------------------

Contentof other_xml column

===========================

db_version : 10.2.0.3

parse_schema : OSS03

plan_hash : 3659189292

Outline Data:

/*+

BEGIN_OUTLINE_DATA

IGNORE_OPTIM_EMBEDDED_HINTS

OPTIMIZER_FEATURES_ENABLE('10.2.0.3')

ALL_ROWS

OUTLINE_LEAF(@"SEL$1")

FULL(@"SEL$1""ZENGFANKUN_TEMP01"@"SEL$1")

END_OUTLINE_DATA

Optimizerenvironment:

optimizer_mode_hinted = false

optimizer_features_hinted = 0.0.0

…………………………………………………………

_optimizer_native_full_outer_join = off

*********************************

Bug Fix Control Environment

***************************

fix 4611850 = enabled

fix 5015557 = enabled

QueryBlock Registry:

*********************

SEL$10x28712428 (PARSER) [FINAL]

Optimizer State Dump: call(in-use=28536,alloc=49080), compile(in-use=65344, alloc=115056)

10 如何设置10053 事件设置本session的10053

　　开启：

　　Alter session set events’10053 trace namecontext forever[,level {1/2}]’;

　　关闭：

　　Alter session set events’10053 trace namecontext off’;

　　设置其他session 的10053

　　开启：

　　SYS.DBMS_SYSTEM.SET_EV (, , 10053, {1|2}, '''')

　　关闭：

　　SYS.DBMS_SYSTEM.SET_EV (, , 10053,0, '''')

跟其他跟踪事件不同，10053 提供了两个跟踪级别，但是级别2 的跟踪信息比级别1 少

11记载了所有影响成本计算的参数

***************************************　　PARAMETERS USEDBYTHE OPTIMIZER********************************

12基本统计信息:

***************************************　　BASE STATISTICAL INFORMATION　　***********************

　表

　　Trace label dba_tables column

　　CDN NUM_ROWS 表记录数

　　NBLKS BLOCKS 高水位以下的block 数

　　TABLE_SCAN_CST 全表扫描的I/O 成本

　　AVG_ROW_LEN AVG_ROW_LEN 平均行长

　　索引

　　Trace label dba_indexes column

　　Index#, col# 索引号及表列号

　　LVLS BLEVEL BTREE 索引高度

　　#LB LEAF_BLOCKS 索引叶块数

　　#DK DISTINCT_KEYS 不重复索引关键字

　　LB/K AVG_LEAF_BLOCKS_PER_KEY 叶块/关键字

　　DB/K AVG_DATA_BLOCKS_PER_KEY 数据块/关键字

　　CLUF CLUSTERING_FACTOR 索引聚合因子　

　基本表访问成本：这里开始CBO 将会计算单表访问的成本

　　单表访问路径　

SINGLETABLEACCESS

　　PATH..................................................................1

　　Column: ENAME Col#:2Table: EMP Alias:

　　EMP.....................................................................2

　　NDV:42NULLS:0DENS:2.3810e-002...........................................3

　　TABLE: EMP ORIG CDN:7213CMPTD CDN:

　　172.......................................................................4

　　Access path: tsc Resc:6Resp:

　　6........................................................................5

　　Access path:index

　　(equal).................................................................6

　　INDEX#:23575TABLE:

　　EMP .....................................................................7

　　CST:39IXSEL:0.0000e+000TBSEL:

　　2.3810e-002..............................................................8

　　BEST_CST:6.00PATH:2Degree:

　　1.......................................................................9

　　我们看一下上面是什么意思。首先CBO 列出了ename 列的统计信息(第2，3 行),这些

　　统计信息来自dba_tab_columns。

　　列的统计信息和dba_tab_columns 中对应的列名如下　

Trace label dba_tablescolumn

　　NDV NUM_DISTINCT 列的不重复值数

　　NULLS NUM_NULLS 列的空行数

　　DENS DENSITY 列密度，没有直方图的情况下=1/NDV

　　LO LOW_VALUE 列的最小值 (只对数字列)

　　HI HIGH_VALUE 列的最大值(只对数字列)

　　第4 行出现了表的行数ORIG CDN 和计算过的行数 CMPTD CDN (computed

　　cardinality). 计算公式如下，

　　CMPTD CDN = ORIG CDN * FF

　　在这里 FF 表示过滤因子(FilterFactor)。我们稍后再来看FF 是什么及如何计算的。

　　第5 行表示了全表扫描的成本。这里的成本是62, 是由NBLKS 和

　　db_file_multi_block_read_count 初始化参数计算出来的。.

　　第6-8 行是索引访问的成本。

　　第9 行是总结了以上信息并选出了最优的访问路径为全表扫描，成本为6。

　　表扫描成本

　　让我们来看一下全表扫描成本(tsc)是如何计算的这里有其他两个大表的基本统计信息。

　　TOTAL :: CDN: 115630 NBLKS: 4339TABLE_SCAN_CST: 265 AVG_ROW_LEN: 272

　　TOTAL :: CDN: 454503 NBLKS: 8975 TABLE_SCAN_CST:548 AVG_ROW_LEN: 151

　　你可能曾经看到过全表扫描成本=访问的块数目/db_file_multi_block_read_count.

看起来这个等式很有意义因为oracle在做全表扫描时每个I/O请求将会读取db_file_multi_block_read_count个块。

但是，我们计算以上统计信息得到

NBLKS / TABLE_SCAN_CST = 4339 / 265 = 16.373 ≠db_file_multi_block_read_count

(这里的值是32，可以看前面参数)

　　另外一个表为NBLKS / TABLE_SCAN_CST = 8975 / 548 =16.377

　　全表扫描成本和db_file_multi_block_read_count

　　CBO 将会根据NBLKS 和db_file_multiblock_read_count 来估计全表扫描成本，但是

　　db_file_multiblock_read_count 通常会被打上折扣。实际上我们可以认为等式会是

　　TABLE_SCAN_CST = NBLKS / k

　　我们来看一下k 和db_file_multiblock_read_count究竟有什么规律可寻。

我们来做一个实验，使用不同的db_file_multiblock_read_count 值4, 6,8,12,16, 24,32 来测试。

　　过滤因子(FF)

　　为了理解索引访问成本我们需要了解一下过滤因子。过滤因子是一个介于0 和1 之

　　间的数字，反映了记录的可选择性。如果一个列有10 种不同的值，我们需要查询等

　　于其中某一个值的记录时，如果这10 种值平均分布的话，你将得到1/10 的行数。

　　如果没有直方图，过滤因子为FF = 1/NDV = density

　　再来看一下过滤因子和查询条件的关系

　　不使用绑定变量的情况:　

predicate Filter factor

　　c1=value1/c1.num_distinct4

　　c1likevalue1/c1.num_distinct

　　c1>value (Hi-value)/(Hi-Lo)

　　c1>=value (Hi-value)/(Hi-Lo)+

　　c1<value (value-Lo)/(Hi-Lo)

　　c1<=value (value-Lo)/(Hi-Lo)+

　　c1betweenval1andval2 (val2 – val1)/(Hi-Lo)+

　　使用绑定变量的情况(8i):　

predicate Filter factor

　　col1=:b1 col1.density

　　col1 {like|>|>=|<|<=} :b1{5.0000e-02|col1.col1 between:b1and:b25.0000e-02*5.0000e-

　　包含and 和or 的情况:　

predicate Filter factor

　　predicate1andpredicate2FF1*FF2

　　predicate1orpredicate2FF1+FF2 – FF1*FF2

　　索引访问成本

　　现在我们知道了聚合因子的概念，我们再来看一看索引访问的成本

　SINGLETABLEACCESS

　　PATH.............................................................1

　　Column: ENAME Col#:2Table: EMP Alias:

　　EMP...............................................................2

　　NDV:42NULLS:0DENS:2.3810e-002.....................................3

　　TABLE: EMP ORIG CDN:7213CMPTD CDN:

　　172...............................................................4

　　Access path: tsc Resc:6Resp:

　　6.................................................................5

　　Access path:index

　　(equal)..........................................................6

　　INDEX#:23575TABLE:

　　EMP ..............................................................7

　　CST:39IXSEL:0.0000e+000TBSEL:

　　2.3810e-002.......................................................8

　　BEST_CST:6.00PATH:2Degree:

　　1.................................................................9

　　我们来看6-8 行，这里表示了索引访问的成本。第6 行表示这里采取索引equal 的方

　　法来访问，再来回忆一下索引的基本统计信息

　　INDEX#: 23575 COL#: 2

　　TOTAL :: LVLS: 1 #LB: 48 #DK: 42 LB/K: 1 DB/K: 36 CLUF: 1534

　　根据索引成本计算公式

　　blevel + FF*leaf_blocks +FF*clustering_factor

　　1 + 2.3810e-002-2*48 + 2.3810e-002-2*1534 =1 + 1.1429 + 36.5245 = 38.6674

　　这里的FF 就等于TBSEL=DENS=2.3810e-002,由于我们的查询条件为ename = :b1 所

　　以得出FF 为ENAME 列的DENS，其实索引访问方式的成本计算公式

　　. Unique scan blevel+1

　　. Fast full scan leaf_blocks / k ( k =1.6765x0.6581 )

　　. Index-only blevel + FF*leaf_blocks

　　让我们用别的例子证明一下索引成本计算，语句为

　 select…fromtbl a

　　wherea.col#1=:b1

　　anda.col#12=:b2

　　anda.col#8=:b3

　　索引和列的基本统计数据如下

INDEX# COL#LVLS #LB #DK LB/K DB/K CLUF

　　841727,1113100665001221469200

　　84181,12,7219000747001151176500

　　84193,1,4,22310004970012118000

　　157551,12,8112600188001301890275

　　84161,2,33,4,5,622580018903001183900

　　Col#:1NDV:10NULLS:0DENS:1.0000e-001-1

　　Col#:12NDV:8NULLS:0DENS:1.2500e-001

　　Col#:8NDV:33NULLS:0DENS:3.0303e-001

　　Access path:index

　　(scan)....................................1

　　INDEX#:8418CST:14947IXSEL:1.2500e-002TBSEL:

　　1.2500e-002...............................2

　　Access path:index

　　(equal) ...................................

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