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

    fetch cur_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

                  1

                 When t.Banner Like'%Linux%'Then

                  2

                 When t.Banner Like'%AIX%'Then

                  3

                 When t.Banner Like'%Solaris%'Then

                  4

               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

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

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

|Id  | Operation           | Name             | Rows  | Bytes | Cost  | Time     |

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

|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) ...................................