研究發(fā)現(xiàn)，Oracle數(shù)據(jù)庫(kù)使用的索引不會(huì)超過(guò)總數(shù)的25%，或者不易他們期望被使用的方式使用。通過(guò) 監(jiān)控?cái)?shù)據(jù)庫(kù)索引的使用，釋放那些未被使用的索引，從而節(jié)省維護(hù)索引的開(kāi)銷(xiāo)，優(yōu)化性能。 1、在oracle8i中，確定使用了那個(gè)索引的方法意味著要對(duì)存在語(yǔ)共享SQL區(qū)中的所有語(yǔ)句運(yùn)行EXPLIAN PALN，然后查詢(xún)計(jì)劃表中的OperaTION列，從而識(shí)別有OBJECT_OWNER和OBJECT_NAME列所確定的那個(gè)索引上的索引訪問(wèn)。 下面是一個(gè)監(jiān)控索引使用的腳本，這個(gè)腳本僅僅是一個(gè)樣品，在某種條件下成立： 條件： 運(yùn)行這個(gè)腳本的用戶(hù)擁有權(quán)限解釋所有的v$sqlarea中的sql，除了不是被SYS裝載的。plan_table.remarks能夠別用來(lái)決定與特權(quán)習(xí)慣的錯(cuò)誤。對(duì)所有的共享池中SQL，參數(shù)OPTIMIZER_GOAL是一個(gè)常量，無(wú)視v$sqlarea.optimizer_mode。兩次快照之間，統(tǒng)計(jì)資料被再次分析過(guò)。沒(méi)有語(yǔ)句別截?cái)唷Ｋ械膶?duì)象都是局部的。所有被引用的表或視圖或者是被運(yùn)行腳本的用戶(hù)所擁有，或者完全有資格的名字或同義詞被使用。自從上次快照以來(lái)，沒(méi)有不受"歡迎"的語(yǔ)句被沖洗出共享池(例如，在裝載)。對(duì)于所有的語(yǔ)句，v$sqlarea.version_count = 1 (children)。 腳本: Code: [Copy to clipboard] set echo off Rem Drop and recreate PLAN_TABLE for EXPLAIN PLAN drop table plan_table; create table PLAN_TABLE ( statement_id varchar2(30), timestamp date, remarks varchar2(80), operation varchar2(30), options varchar2(255), object_node varchar2(128), object_owner varchar2(30), object_name varchar2(30), object_instance numeric, object_type varchar2(30), optimizer varchar2(255), search_columns number, id numeric, parent_id numeric, position numeric, cost numeric, cardinality numeric, bytes numeric, other_tag varchar2(255), partition_start varchar2(255), partition_stop varchar2(255), partition_id numeric, other long, distribution varchar2(30), cpu_cost numeric, io_cost numeric, temp_space numeric, access_PRedicates varchar2(4000), filter_predicates varchar2(4000)); Rem Drop and recreate SQLTEMP for taking a snapshot of the SQLAREA drop table sqltemp; create table sqltemp ( ADDR VARCHAR2 (16), SQL_TEXT VARCHAR2 (2000), DISK_READS NUMBER, EXECUTIONS NUMBER, PARSE_CALLS NUMBER); set echo on Rem Create procedure to populate the plan_table by executing Rem explain plan...for 'sqltext' dynamically create or replace procedure do_explain ( addr IN varchar2, sqltext IN varchar2) as dummy varchar2 (1100); mycursor integer; ret integer; my_sqlerrm varchar2 (85); begin dummy:='EXPLAIN PLAN SET STATEMENT_ID=' ; dummy:=dummy''''addr'''' ' FOR 'sqltext; mycursor := dbms_sql.open_cursor; dbms_sql.parse(mycursor,dummy,dbms_sql.v7); ret := dbms_sql.execute(mycursor); dbms_sql.close_cursor(mycursor); commit; exception -- Insert errors into PLAN_TABLE... when others then my_sqlerrm := substr(sqlerrm,1,80); insert into plan_table(statement_id,
remarks) values (addr,my_sqlerrm); -- close cursor if exception raised on EXPLAIN PLAN dbms_sql.close_cursor(mycursor); end; / Rem Start EXPLAINing all S/I/U/D statements in the shared pool declare -- exclude statements with v$sqlarea.parsing_schema_id = 0 (SYS) cursor c1 is select address, sql_text, DISK_READS, EXECUTIONS, PARSE_CALLS from v$sqlarea where command_type in (2,3,6,7) and parsing_schema_id != 0; cursor c2 is select addr, sql_text from sqltemp; addr2 varchar(16); sqltext v$sqlarea.sql_text%type; dreads v$sqlarea.disk_reads%type; execs v$sqlarea.executions%type; pcalls v$sqlarea.parse_calls%type; begin open c1; fetch c1 into addr2,sqltext, dreads,execs,pcalls; while (c1%found) loop insert into sqltemp values (addr2,sqltext,dreads,execs,pcalls); commit; fetch c1 into addr2, sqltext,dreads,execs,pcalls; end loop; close c1; open c2; fetch c2 into addr2, sqltext; while (c2%found) loop do_explain(addr2,sqltext); fetch c2 into addr2, sqltext; end loop; close c2; end; / Rem Generate a report of index usage based on the number of times Rem a SQL statement using that index was executed select p.owner, p.name, sum(s.executions) totexec from sqltemp s, (select distinct statement_id stid, object_owner owner, object_name name from plan_table where operation = 'INDEX') p where s.addr = p.stid group by p.owner, p.name order by 2 desc; Rem Perform cleanup on exit (optional) delete from plan_table where statement_id in ( select addr from sqltemp ); drop table sqltemp;
關(guān)于這個(gè)腳本，有幾個(gè)重要的地方需要注重，即它可能一起明顯的開(kāi)銷(xiāo)，因此，應(yīng)該在仔細(xì)地進(jìn)行 權(quán)衡后才把它應(yīng)用到繁忙的生產(chǎn)應(yīng)用系統(tǒng)中區(qū)。 2、oracle9i中如何確定索引的使用情況: 在oracle9i中，情況會(huì)簡(jiǎn)單得多，因?yàn)橛幸粋€(gè)新得字典視圖V$SQL_PLAN存儲(chǔ)了實(shí)際計(jì)劃，這些計(jì)劃用于執(zhí)行共享SQL區(qū)中得語(yǔ)句。V$SQL_PLAN視圖很類(lèi)似與計(jì)劃表，但V$SQL_PLAN使用ADDRESS和HASH_VALUE列 來(lái)識(shí)別語(yǔ)句， 而計(jì)劃表使用用戶(hù)提供得STATEMENT_ID來(lái)識(shí)別語(yǔ)句。下面的SQL顯示了在一個(gè)oracle9i數(shù)據(jù)庫(kù)中，由出現(xiàn)在共享SQL區(qū)中語(yǔ)句使用的所有索引。 select object_owner, object_name, options, count(*) from v$sql_plan where operation='INDEX' and object_owner!='SYS' group by object_owner, object_name, operation, options order by count(*) desc;
所有基于共享SQL區(qū)中的信心來(lái)識(shí)別索引使用情況的方法， 都可能會(huì)收集到不完整的信息。共享SQL區(qū)是一 個(gè)動(dòng)態(tài)結(jié)構(gòu)，除非能對(duì)它進(jìn)行足夠頻繁的采樣， 否則在有關(guān)索引使用的情況的信息被收集之前，SQL語(yǔ)句可 能就已經(jīng)(因?yàn)槔匣?被移出緩存了。oracle9i提供了解決這個(gè)問(wèn)題的方案，即它為alter index提供了一個(gè)monitoring usage子句。當(dāng)啟用monitoring usage 時(shí)，oralce記錄簡(jiǎn)單的yes或no值，以指出在監(jiān)控間隔 期間某個(gè)索引是否被使用。 為了演示這個(gè)新特性，你可以使用下面的例子: (a) Create and populate a small test table (b) Create Primary Key index on that table (c) Query v$object_usage: the monitoring has not started yet (d) Start monitoring of the index usage (e) Query v$object_usage to see the monitoring in progress
(f) Issue the SELECT statement which uses the index (g) Query v$object_usage again to see that the index has been used (h) Stop monitoring of the index usage (i) Query v$object_usage to see that the monitoring sDetailed steps (a) Create and populate a small test table create table prodUCts ( prod_id number(3), prod_name_code varchar2(5)); insert into products values(1,'aaaaa'); insert into products values(2,'bbbbb'); insert into products values(3,'ccccc'); insert into products values(4,'ddddd'); commit; (b) Create Primary Key index on that table alter table products add (constraint products_pk primary key (prod_id)); (c) Query v$object_usage: the monitoring has not started yet column
