從Oracle10g開始，Oracle引入了flashback drop的新特性，這個新特性，允許你從當前數據庫中恢復一個被drop了的對象。在執行drop操作時，現在Oracle不是真正刪除它，而是將該對象自動將放入回收站。對于一個對象的刪除，其實僅僅就是簡單的重令名操作。

所謂的回收站，是一個虛擬的容器，用于存放所有被刪除的對象。在回收站中，被刪除的對象將占用創建時的同樣的空間，你甚至還可以對已經刪除的表查詢，也可以利用flashback功能來恢復它， 這個就是flashback drop功能。

這個功能雖然可以極大的簡化誤drop導致的恢復操作，但是長時間的積累可能會導致大量的空間占用(雖然Oracle具有自己的清理機制)，很多時候我們需要手工介入去清理回收站。本文主要介紹清理回收站的幾種方法.

?1.大量累計的空間占用

Connected to Oracle Database 10g Enterprise Edition Release 10.1.0.3.0 Connected as SYS SQL> col owner for a12 SQL> select owner,object_name,CREATETIME,DROPTIME from dba_recyclebin ? 2? order by droptime ? 3? / OWNER??????? OBJECT_NAME??????????????????? CREATETIME????????? DROPTIME ------------ ------------------------------ ------------------- ------------------- COMMON?????? BIN$AHsQ+pi+Kb/gRAADumkBdQ==$0 2005-08-29:16:42:19 2005-09-11:15:36:17 COMMON?????? BIN$AHsQ+pi9Kb/gRAADumkBdQ==$0 2005-08-29:16:42:19 2005-09-11:15:36:17 PDA????????? BIN$AdEb4zqqUcTgRAADumkBdQ==$0 2005-09-05:10:31:01 2005-09-28:15:40:39 ...... BJLAIS_RUN?? BIN$BtkGRT0dSwfgRAADumkBdQ==$0 2005-11-30:10:54:07 2005-12-01:16:13:17 BJLAIS_RUN?? BIN$BtkGRT0cSwfgRAADumkBdQ==$0 2005-11-30:10:54:07 2005-12-01:16:13:17 750 rows selected SQL>

2.不同用戶在回收站的對象

SQL> select owner,count(*) from dba_recyclebin group by owner;?? OWNER????????????????? COUNT(*) -------------------- ---------- BJLAIS_RUN?????????????????? 44 COMMON??????????????????????? 8 MMSBLOG???????????????????? 618 MMSHAWA_RUN?????????????????? 2 PDA?????????????????????????? 8 RING_RUN???????????????????? 70 6 rows selected.

3.我們可以指定刪除某些特定對象

SQL> purge table common.T_SERVICE_CODE_INFO; Table purged.

4.指定清除某個表空間的所有回收站對象

SQL> purge tablespace common; Tablespace purged. SQL> select owner,count(*) from dba_recyclebin group by owner;?? OWNER????????????????? COUNT(*) -------------------- ---------- BJLAIS_RUN?????????????????? 44 MMSBLOG???????????????????? 618 MMSHAWA_RUN?????????????????? 2 PDA?????????????????????????? 8 RING_RUN???????????????????? 70

5.以SYSDBA身份可以清除所有回收站對象

SQL> purge dba_recyclebin; DBA Recyclebin purged. SQL> select owner,count(*) from dba_recyclebin group by owner;?? no rows selected

6.禁用recyclebin

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如果我們不希望使用Oracle的recyclebin,可以通過參數禁用這個特性。

在Oracle10gR1中，通過修改一個隱含參數:_recyclebin 為False可以禁用這個特性:

SQL> set linesize 132 SQL> column name format a30 SQL> column value format a25 SQL> select ? 2??? x.ksppinm? name, ? y.ksppstvl? value, ? 3??? y.ksppstdf? isdefault, ? 4??? 5??? decode(bitand(y.ksppstvf,7),1,''MODIFIED'',4,''SYSTEM_MOD'',''FALSE'')? ismod, ? 6??? decode(bitand(y.ksppstvf,2),2,''TRUE'',''FALSE'')? isadj ? 7? from ? 8??? sys.x$ksppi x, ? 9??? sys.x$ksppcv y ?10? where ?11??? x.inst_id = userenv(''Instance'') and ?12??? y.inst_id = userenv(''Instance'') and ?13??? x.indx = y.indx and ?14??? x.ksppinm like ''%&par%'' ?15? order by ?16??? translate(x.ksppinm, '' _'', '' '') ?17? / Enter value for par: recyclebin old? 14:?? x.ksppinm like ''%&par%'' new? 14:?? x.ksppinm like ''%recyclebin%'' NAME?????????????????????????? VALUE???????????????????? ISDEFAULT ISMOD????? ISADJ ------------------------------ ------------------------- --------- ---------- ----- _recyclebin??????????????????? TRUE????????????????????? TRUE????? FALSE????? FALSE 1 row selected.

在Oracle10gR2中，recyclebin變成了一個常規參數，可以在session/system級動態修改:

[oracle@danaly ~]$ sqlplus "/ as sysdba" SQL*Plus: Release 10.2.0.1.0 - Production on Mon Dec 12 15:34:56 2005 Copyright (c) 1982, 2005, Oracle.? All rights reserved. Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production With the Partitioning, Oracle Label Security, OLAP and Data Mining Scoring Engine options SQL> show parameter recyclebin NAME???????????????????????????????? TYPE??????? VALUE ------------------------------------ ----------- ------------------------------ recyclebin?????????????????????????? string????? on SQL> alter session set recyclebin=off; Session altered. SQL> alter session set recyclebin=on ? 2? / Session altered. SQL> alter system set recyclebin=off; System altered. SQL> alter system set recyclebin=on; System altered.

drop table tableName后，并不能完全清除空間，可以采用以下方法：

?? ?查詢垃圾信息：

??? SELECT t.object_name,t.type ,t.original_name FROM user_recyclebin t;

??? 清除垃圾信息：purge table origenal_tableName;
??? purge index origenal_indexName;

??? 刪除回收站所有垃圾信息：
??? PURGE recyclebin;

??? 刪除Table不進入Recycle的方法：
??? drop table tableName purge;


??恢復表：
?? ?SQL> flashback table XXX to before drop;
?? ?Flashback complete.

總結

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