DBMS_XPLAN包以及執行計劃
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??? 一直用explain plan來查執行計劃，所以想了解一下DBMS_XPLAN包的構成。首先大致了解一下包括的方法：
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??? ■ DISPLAY - 格式化展現plan table中的內容
??? ■ DISPLAY_CURSOR - 格式化展現執行計劃中的所有載入的游標
??? ■ DISPLAY_AWR - 格式化展現執行計劃中存儲在AWR中的SQL語句.
??? ■ DISPLAY_SQLSET - 格式化展現執行計劃中存儲在SQL優化設置中的語句.
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??? 最簡單的使用方法是這樣的：
??? explain plan for (SQL statement);
??? select * from table(dbms_xplan.display);
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??? 由于輸入最后一句的時候比較麻煩，可以建立一個視圖來簡便操作：
??? CREATE VIEW PLAN AS SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);
??? SELECT * FROM PLAN;
??? 這樣每次都可以方便得渠道最新的一個執行計劃
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??? 看一下自帶說明：
-----------------------------------
?create or replace package sys.dbms_xplan AUTHID CURRENT_USER as
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? --- ------------------------------------------------------------------------
? --- DBMS_XPLAN CONSTANTS SECTION
? --- ------------------------------------------------------------------------
?
? --- The following constants designate the flags returned in the bit vector
? --- from the COMPARE_QUERY_PLANS function.
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? UNKNOWN_DIFF_CLASS???????? CONSTANT NUMBER := POWER(2,31);
?
? --- ------------------------------------------------------------------------
? --- DBMS_XPLAN PUBLIC FUNCTIONS SECTION
? --- ------------------------------------------------------------------------
? ---
? --- OVERVIEW
? ---
? ---?? This package defines several table functions which can be used to
? ---?? display execution plans.
? ---
? ---?? - DISPLAY is generally used to display the execution plan produced
? ---???????????? by an EXPLAIN PLAN command; you can either display the most
? ---???????????? recent explained statement, or the statement for a specific
? ---???????????? statement id.
? ---
? ---???????????? In addition, this table function can also be used to display any
? ---???????????? plan (with or without statistics) stored in a table as long
? ---???????????? as the columns of this table are named the same as columns
? ---???????????? of the plan_table (or v$sql_plan_statistics_all if statistics
? ---???????????? are included). A predicate on the specified table can be used
? ---???????????? to select rows of the plan to display.
? ---
? ---?? - DISPLAY_CURSOR displays the execution plans for one or several
? ---???????????? cursors in the shared SQL area, depending on a filter
? ---???????????? criteria. It can display the plan for the last executed
? ---???????????? statement, the current (if session is active) or last
? ---???????????? executed statement (if session is inactive) of a specific
? ---???????????? session, or all cursors matching an arbitrary criteria
? ---???????????? defined via SQL. In addition to the explain plan, various
? ---???????????? plan statistics (e.g. io, memory and timing) can be
? ---???????????? reported (based on the v$sql_plan_statistics_all views).
? ---
? ---???????????? Specific cursors are identified by SQL_ID and optionally a
? ---???????????? SQL_CHILD_NUMBER.
? ---
? ---???????????? The DEFAULT without any parameters shows the last executed
? ---???????????? statement of the session.
? ---
? ---???????????? NOTE: To use the DISPLAY_CURSOR functionality, the calling
? ---???????????? user must have SELECT privilege on V$SQL_PLAN_STATISTICS_ALL,
? ---???????????? V$SQL, and V$SQL_PLAN. By default, only the select_catalog
? ---???????????? role has the SELECT privilege on these views.
? ---
? ---?? - DISPLAY_AWR displays the execution plans for SQL statements stored in
? ---???????????? the Automatic Workload Repository (AWR).
? ---???????????? NOTE: To use the DISPLAY_AWR functionality, the calling user
? ---???????????? must have SELECT prvilege on DBA_HIST_SQL_PLAN and
? ---???????????? DBA_HIST_SQLTEXT. By default, select privilige for these
? ---???????????? views is granted to the select_catalog role.
? ---
? ---?? - DISPLAY_SQLSET displays the execution plans for SQL statements stored
? ---???????????? in a SQL tuning set.
? ---???????????? NOTE: To use the DISPLAY_SQLSET functionality, the calling
? ---???????????? user must have SELECT prvilege on ALL_SQLSET_PLANS and
? ---???????????? ALL_SQLSET_STATEMENTS. By default, select privilige for these
? ---???????????? views is granted to the public role.
? ---
? ---
? ---?? For example:
? ---???? To show the last explained statement
? ---??????? explain plan for select ename, deptno
? ---???????????????????????? from emp e, dept d
? ---???????????????????????? where e.deptno = d.deptno;
? ---??????? select * from table(dbms_xplan.display);
? ---
? ---???? To show the last executed statement of your session
? ---??????? select * from table(dbms_xplan.display_cursor);
? ---
? ---???? See more detailed examples below
? ---
? --- SECURITY
? ---
? ---?? The execution privilege on this package is granted to PUBLIC.
? ---?? The display procedures of this package run under the caller
? ---?? security.
? ---
? ---
? --- PROCEDURES AND FUNCTIONS
? ---
? ---?? function display(table_name?? varchar2 default 'PLAN_TABLE',
? ---??????????????????? statement_id varchar2 default null,
? ---??????????????????? format?????? varchar2 default 'TYPICAL',
? ---??????????????????? filter_preds varchar2 default null)
? ---
? ---?? - table_name:
? ---??????? specifies the table name where the plan is stored. This
? ---??????? parameter defaults to "PLAN_TABLE" which is the default
? ---??????? plan table for the explain plan. If NULL is specified,
? ---??????? the default of 'PLAN_TABLE' will be taken into account.
? ---??????? The parameter is case insensitive.
? ---
? ---?? - statement_id:
? ---??????? specifies the statement id of the plan to display. This
? ---??????? parameter defaults to NULL. If no statement_id is defined,
? ---??????? the most recent explained statement in <table_name> will
? ---??????? be displayed, assuming that the "filter_preds" parameter is
? ---??????? NULL (its default).
? ---
? ---?? - format:
? ---??????? Determines what information stored in the plan will be
? ---??????? shown. The format string can use the following predefined
? ---??????? three formats, each representing a common use case:
? ---
? ---??????? 'BASIC':?? Display only the minimum set of information, i.e. the
? ---?????????????????? operation id, the operation name and its option
? ---
? ---??????? 'TYPICAL': This is the default. Display most information
? ---?????????????????? of the explain plan (operation id, name and option,
? ---?????????????????? #rows, #bytes and optimizer cost). Pruning,
? ---?????????????????? parallel and predicate information are only
? ---?????????????????? displayed when applicable. Excludes only PROJECTION,
? ---?????????????????? ALIAS and REMOTE SQL information (see below).
? ---
? ---??????? 'ALL':???? Maximum user level, like typical with additional
? ---?????????????????? informations (PROJECTION, ALIAS and information about
? ---?????????????????? REMOTE SQL if the operation is distributed).
? ---
? ---??????? For finer control on the display output, the following keywords
? ---??????? can be added to the above three standard format to customize their
? ---??????? default behavior. Each keyword either represents a logical group
? ---??????? of plan table columns (e.g. PARTITION) or logical additions to the
? ---??????? base plan table output (e.g. PREDICATE). Format keywords must
? ---??????? be separated by either a comma or a space:
? ---
? ---??????? ROWS: if relevant, shows number of rows estimated by the optimizer
? ---
? ---??????? BYTES: if relevant, shows number of bytes estimated by the
? ---?????????????? optimizer
? ---
? ---??????? COST: if relevant, shows optimizer cost information
? ---
? ---??????? PARTITION: If relevant, shows partition pruning information
? ---
? ---??????? PARALLEL: If relevant, shows PX information (distribution method
? ---????????????????? and table queue information)
? ---
? ---??????? PREDICATE: If relevant, shows the predicate section
? ---
? ---??????? PROJECTION: If relevant, shows the projection section
? ---
? ---??????? ALIAS: If relevant, shows the "Query Block Name / Object Alias"
? ---?????????????? section
? ---
? ---??????? REMOTE: If relevant, shows the information for distributed query
? ---??????????????? (e.g. remote from serial distribution and remote SQL)
? ---
? ---??????? NOTE: If relevant, shows the note section of the explain plan.
? ---
? ---????? Format keywords can be prefixed by the sign '-' to exclude the
? ---????? specified information. For example, '-PROJECTION' exclude
? ---????? projection information.
? ---
? ---????? Finally, if the target plan table (see "table_name" parameter) also
? ---????? stores plan statistics columns (e.g. it is a table used to capture
? ---????? the content of the fixed view v$sql_plan_statistics_all), then
? ---????? additional format keywords can be used to specify which class of
? ---????? statistics to display. These additionnal format keywords are IOSTATS,
? ---????? MEMSTATS, ALLSTATS and LAST described along with the display_cursor()
? ---????? table function (see below).
? ---
? ---????? Example:
? ---??????? - use 'ALL -PROJECTION -NOTE' to display everything except the
? ---????????? projection and note sections.
? ---
? ---??????? - use 'TYPICAL PROJECTION' to display using the typical format
? ---????????? with the additional projection section (which is normally excluded
? ---????????? under the typical format). Since typical is default, using
? ---????????? simply 'PROJECTION' is equivalent.
? ---
? ---??????? - use '-BYTES -COST -PREDICATE' to display using the typical
? ---???????? format but excluding optimizer cost and byte estimates
? ---???????? as well as the predicate section.
? ---
? ---??????? - use 'BASIC ROWS' to display basic information with the
? ---????????? additional number of rows estimated by the optimizer.
? ---
? ---
? ---?? - filter_preds: SQL filter predicate(s) to restrict the set of rows
? ---?????????????????? selected from the table where the plan is stored. When
? ---?????????????????? value is NULL (the default), the plan displayed
? ---?????????????????? corresponds to the last executed explain plan.
? ---
? ---?????????????????? For example:
? ---
? ---???????????????????? filter_preds=>'plan_id = 10'
? ---
? ---?????????????????? "filter_preds" can reference any column of the table
? ---?????????????????? where the plan is stored and can contain any SQL
? ---?????????????????? construct (e.g. sub-query, function calls...).
? ---
? ---?????????????????? WARNING: Application developers should expose this
? ---?????????????????? parameter to end-users only after careful
? ---?????????????????? consideration since it could expose the application
? ---?????????????????? to SQL injection. Indeed, "filter_preds" can
? ---?????????????????? potentially reference any table or execute any server
? ---?????????????????? function for which the database user invoking the
? ---?????????????????? table function has privileges.
? ---
? ---
? ---?? function display_cursor(sql_id?????????? varchar2 default null,
? ---?????????????????????????? cursor_child_no? integer default 0,
? ---?????????????????????????? format?????????? varchar2 default 'TYPICAL')
? ---
? ---?? - sql_id:
? ---??????? specifies the sql_id value for a specific SQL statement, as
? ---??????? shown in V$SQL.SQL_ID, V$SESSION.SQL_ID, or
? ---??????? V$SESSION.PREV_SQL_ID. If no sql_id is specified, the last
? ---??????? executed statement of the current session is shown.
? ---
? ---?? - cursor_child_no:
? ---??????? specifies the child number for a specific sql cursor, as shown in
? ---??????? V$SQL.CHILD_NUMBER or in V$SESSION.SQL_CHILD_NUMBER,
? ---??????? V$SESSION.PREV_CHILD_NUMBER. This input parameter is only
? ---??????? considered when sql_id is set.
? ---
? ---??????? If not specified, all child cursors for the specified sql_id are
? ---??????? displayed.
? ---
? ---?? - format:
? ---??????? The format string has the same meaning than for the regular
? ---??????? display() table function (see format description above). In
? ---??????? addition, the following four format keywords are introduced
? ---??????? to support the various plan statistics columns available
? ---??????? in v$sql_plan_statistics_all.
? ---
? ---??????? These keywords can also be used by the display() table function
? ---??????? assuming that the specified table has the same statistics columns
? ---??????? available in v$sql_plan_statistics_all.
? ---
? ---??????? IOSTATS: Assuming that basic plan statistics are
? ---???????????????? collected when SQL statements are executed (either by
? ---???????????????? using the gather_plan_statistics hint or by setting the
? ---???????????????? parameter statistics_level to ALL), this format will show
? ---???????????????? IO statistics for all (or only for the last as shown below)
? ---???????????????? executions of the cursor.
? ---
? ---??????? MEMSTATS: Assuming that PGA memory management is enabled (i.e
? ---????????????????? pga_aggregate_target parameter is set to a non 0 value),
? ---????????????????? this format allows to display memory management
? ---????????????????? statistics (e.g. execution mode of the operator, how
? ---????????????????? much memory was used, number of bytes spilled to
? ---????????????????? disk, ...). These statistics only apply to memory
? ---????????????????? intensive operations like hash-joins, sort or some bitmap
? ---????????????????? operators.
? ---
? ---??????? ALLSTATS: A shortcut for 'IOSTATS MEMSTATS'
? ---
? ---??????? LAST: By default, plan statistics are shown for all executions of
? ---????????????? the cursor. The keyword LAST can be specified to see only
? ---????????????? the statistics for the last execution.
? ---
? ---
? ---??????? Also, the following two formats are still supported for backward
? ---??????? compatibility:
? ---
? ---??????? 'RUNSTATS_TOT':? Same as 'IOSTATS', i.e. displays IO statistics
? ---???????????????????????? for all executions of the specified cursor.
? ---??????? 'RUNSTATS_LAST': Same as 'IOSTATS LAST', i.e. displays the runtime
? ---???????????????????????? statistics for the last execution of the cursor.
? ---
? ---
? ---?? PRIVILEGES:
? ---?? -??? To use the DISPLAY_CURSOR functionality, the calling
? ---??????? user must have SELECT privilege on V$SQL_PLAN_STATISTICS_ALL,
? ---??????? V$SQL, and V$SQL_PLAN, otherwise it will show an appropriate
? ---??????? error message.
? ---
? ---?? -??? Unless used in DEFAULT mode to display the last executed
? ---??????? statement, all internal SQL statements of this package and
? ---??????? the calling SQL statement using this table function will be
? ---??????? suppressed.
? ---
? ---
? ---?? function display_awr(sql_id????????? varchar2,
? ---??????????????????????? plan_hash_value integer? default null,
? ---??????????????????????? db_id?????????? integer? default null,
? ---??????????????????????? format????????? varchar2 default 'TYPICAL')
? ---
? ---?? - sql_id:
? ---??????? specifies the sql_id value for a SQL statement having its plan(s)
? ---??????? stored in the AWR. You can find all stored SQL statements by
? ---??????? querying DBA_HIST_SQL_PLAN.
? ---
? ---?? - plan_hash_value:
? ---??????? identifies a specific stored execution plan for a SQL statement.
? ---??????? Optional parameter. If suppressed, all stored execution plans are
? ---??????? shown.
? ---
? ---?? - db_id:
? ---??????? identifies the plans for a specific dabatase. If this parameter is
? ---??????? omitted, it will be defaulted to the local database identifier.
? ---
? ---?? - format:
? ---??????? The format string has the same meaning than for the regular
? ---??????? display() table function (see format description above).
? ---
? ---
? ---?? function display_sqlset(sqlset_name???? varchar2,
? ---?????????????????????????? sql_id????????? varchar2,
? ---?????????????????????????? plan_hash_value integer? default null,
? ---?????????????????????????? format????????? varchar2 default 'TYPICAL',
? ---?????????????????????????? sqlset_owner??? varchar2 default null)
? ---
? ---?? - sqlset_name:
? ---??????? specified the name of the SQL tuning set.
? ---
? ---?? - sql_id:
? ---??????? specifies the sql_id value for a SQL statement having its plan(s)
? ---??????? stored in the SQL tuning set. You can find all stored SQL
? ---??????? statements by querying USER/DBA/ALL_SQLSET_PLANS or table function
? ---??????? SELECT_SQLSET from package dbms_sqltune.
? ---
? ---?? - plan_hash_value:
? ---??????? identifies a specific stored execution plan for a SQL statement.
? ---??????? Optional parameter. If suppressed, all stored execution plans are
? ---??????? shown.
? ---
? ---?? - format:
? ---??????? The format string has the same meaning than for the regular
? ---??????? display() table function (see format description above).
? ---
? ---?? - sqlset_owner:
? ---??????? Specifies the owner of the SQL tuning set. The default is the
? ---??????? name of the current user.
? ---
? ---
? ---?? Examples DBMS_XPLAN.DISPLAY():
? ---
? ---?? 1/ display the last explain plan stored in the plan table:
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select * from table(dbms_xplan.display);
? ---
? ---
? ---?? 2/ display from the plan table "my_plan_table":
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select * from table(dbms_xplan.display('my_plan_table'));
? ---
? ---
? ---?? 3/ display minimum plan table:
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select * from table(dbms_xplan.display(null, null,'basic'));
? ---
? ---
? ---?? 4/ display all information in plan table, excluding projection:
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select * from table(dbms_xplan.display(null, null,
? ---???????????????????????????????????????????? 'all -projection'));
? ---
? ---
? ---?? 5/ display the plan whose statement_id is 'foo':
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select * from table(dbms_xplan.display('plan_table', 'foo'));
? ---
? ---
? ---?? 6/ display statpack plan for hash_value=76725 and snap_id=245
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select * from table(dbms_xplan.display('stats$sql_plan', null,
? ---????????????????????????? 'all', 'hash_value=76725 and snap_id=245'));
? ---
? ---
? ---?? Examples DBMS_XPLAN.DISPLAY_CURSOR():
? ---
? ---?? 1/ display the currently or last executed statement
? ---????? (this will also show the usage of this package)
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select * from table(dbms_xplan.display_cursor);
? ---
? ---
? ---?? 2/ display the currently or last executed statement of session id 9
? ---????? (it will return 'no rows selected' for any SQL statement using
? ---?????? this package)
? ---
? ---??? - Identify the sql_id and the child_number in
? ---????? a separate SQL statement and use them as parameters for
? ---????? DISPLAY_CUSRSOR()
? ---
? ---????? SQL> select prev_sql_id, prev_child_number
? ---?????????? from v$session where sid=9;
? ---
? ---????? PREV_SQL_ID?? PREV_CHILD_NUMBER
? ---????? ------------- -----------------
? ---????? f98t6zufy04g5???????????????? 0
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select *
? ---????? from table(dbms_xplan.display_cursor('f98t6zufy04g5', 0));
? ---
? ---??? - Alternatively, you can combine the two statements into one
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select t.*
? ---????? from v$session s,
? ---?????????? table(dbms_xplan.display_cursor(s.prev_sql_id,
? ---?????????????????????????????????????????? s.prev_child_number)) t
? ---????? where s.sid=9;
? ---
? ---????? NOTE: the table deriving the input parameters for
? ---??????????? DBMS_XPLAN.DISPLAY_CURSOR() must be the FIRST (left-side)
? ---??????????? table(s) in the select statement relative to the table function
? ---
? ---
? ---?? 3/ display all cursors containing the case sensisitve string 'FoOoO',
? ---????? excluding SQL parsed by SYS
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select t.*
? ---????? from v$sql s,
? ---?????????? table(dbms_xplan.display_cursor(s.sql_id,
? ---?????????????????????????????????????????? s.child_number)) t
? ---????? where s.sql_text like '%FoOoO%' and s.parsing_user_id <> 0;
? ---
? ---
? ---?? 4/ display all information about all cursors containing the case
? ---????? insensitive string 'FOO', including SQL parsed by SYS
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select t.*
? ---????? from v$sql s,
? ---?????????? table(dbms_xplan.display_cursor(s.sql_id,
? ---?????????????????????????????????????????? s.child_number, 'ALL')) t
? ---????? where upper(s.sql_text) like '%FOO%';
? ---
? ---
? ---?? 5/ display the last executed runtime statistics for all cursors
? ---????? containing the case insensitive string 'sales', including SQL
? ---????? parsed by SYS
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select t.*
? ---????? from v$sql s,
? ---?????????? table(dbms_xplan.display_cursor(s.sql_id, s.child_number,
? ---?????????????????????????????????????????? 'ALLSTATS LAST')) t
? ---????? where lower(s.sql_text) like '%sales%';
? ---
? ---
? ---?? 6/ display the aggregated runtime statistics for all cursors containing
? ---????? the case sensitive string 'sAleS' and were parsed by user SH
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select t.*
? ---????? from v$sql s, dba_users u,
? ---?????????? table(dbms_xplan.display_cursor(s.sql_id, s.child_number,
? ---?????????????????????????????????????????? 'RUNSTATS_TOT')) t
? ---????? where s.sql_text like '%sAleS%'
? ---????? and u.user_id=s.parsing_user_id
? ---????? and u.username='SH';
? ---
? ---?? Examples DBMS_XPLAN.DISPLAY_AWR():
? ---
? ---?? 1/ display all stored plans in the AWR containing
? ---????? the case sensitive string 'sAleS'. Don't display predicate
? ---????? information but add the query block name / alias section.
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select t.*
? ---????? from dba_hist_sqltext ht,
? ---?????????? table(dbms_xplan.display_awr(ht.sql_id, null, null,
? ---??????????????????????????????????????? '-PREDICATE +ALIAS')) t
? ---????? where ht.sql_text like '%sAleS%';
? ---
? ---????? NOTE: the table deriving the input parameters for
? ---??????????? DBMS_XPLAN.DISPLAY_AWR() must be the FIRST (left-side)
? ---??????????? table(s) in the select statement relative to the table
? ---??????????? function.
? ---
? ---?? Examples DBMS_XPLAN.DISPLAY_SQLSET():
? ---
? ---?? 1/ display all stored plans for a given statement in the SQL tuning set
? ---?????? named 'my_sts' owner by the current user (the caller).
? ---
? ---????? set linesize 150
? ---????? set pagesize 2000
? ---????? select *
? ---????? from table(dbms_xplan.display_sqlset('my_sts',
? ---?????????????????????????????????????????? 'gcfysssf6hykh',
? ---??????????????????????????????????????????? null,
? ---?????????????????????????????????????????? 'ALL -NOTE -PROJECTION')) t
? ---
? --- -------------------------------------------------------------------------
?
? -- display from PLAN_TABLE
? function display(table_name?? varchar2????? default 'PLAN_TABLE',
?????????????????? statement_id varchar2????? default null,
?????????????????? format?????? varchar2????? default 'TYPICAL',
?????????????????? filter_preds varchar2????? default null)
? return dbms_xplan_type_table
? pipelined;
?
? -- display from V$SQL_PLAN (or V$SQL_PLAN_STATISTICS_ALL)
? function display_cursor(sql_id?????????? varchar2 default? null,
????????????????????????? cursor_child_no? integer? default? 0,
????????????????????????? format?????????? varchar2 default? 'TYPICAL')
? return dbms_xplan_type_table
? pipelined;
?
? -- display from AWR
? function display_awr(sql_id????????? varchar2,
?????????????????????? plan_hash_value integer? default null,
?????????????????????? db_id?????????? integer? default null,
?????????????????????? format????????? varchar2 default 'TYPICAL')
? return dbms_xplan_type_table
? pipelined;
?
? -- display from SQL tuning set
? function display_sqlset(sqlset_name???? varchar2,
????????????????????????? sql_id????????? varchar2,
????????????????????????? plan_hash_value integer? default null,
????????????????????????? format????????? varchar2 default 'TYPICAL',
????????????????????????? sqlset_owner??? varchar2 default null)
? return dbms_xplan_type_table
? pipelined;
?
? -- private procedure, used internally
? function? prepare_records(plan_cur??????? IN sys_refcursor,
??????????????????????????? i_format_flags? IN binary_integer)
? return dbms_xplan_type_table
? pipelined;
?
? -- private function to validate the user format (used internally)
? function validate_format(hasPlanStats? IN? boolean,
?????????????????????????? format??????? IN? VARCHAR2,
?????????????????????????? format_flags? OUT BINARY_INTEGER)
? return boolean;
?
end dbms_xplan;?
-----------------------------------------------
?
?
下面是執行計劃中各個字段的含義，再明確一下：
----------------------------------------
■ ROWS - if relevant, shows the number of rows estimated by theoptimizer
■ BYTES - if relevant, shows the number of bytes estimated bythe optimizer
■ COST - if relevant, shows optimizer cost information
■ PARTITION - if relevant, shows partition pruning information
■ PARALLEL - if relevant, shows PX information (distributionmethod and table queue information)
■ PREDICATE - if relevant, shows the predicate section
■ PROJECTION -if relevant, shows the projection section
■ ALIAS - if relevant, shows the "Query Block Name / ObjectAlias" section
■ REMOTE - if relevant, shows the information for distributedquery (for example, remote from serial distribution and remoteSQL)
■ NOTE - if relevant, shows the note section of the explain planFormat keywords can be prefixed by the sign '-' to exclude thespecified information. For example, '-PROJECTION' excludesprojection information.
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??? 關于DBMS_XPLAN包的幾個方法的用法，在注釋里已經講得很清楚了，而且還帶了比較詳細的舉例，基本上只要看一遍就會了。不過關鍵是這個包怎么用，怎么看執行計劃等問題，這就涉及到SQL tuning等一些別的問題了。
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