今天drop 了一张3.7T的表,这张表为分区本身的数据只有23G,两个lob字段和lob index加起来占到3.7T,下面处理过程:
drop index ...;
truncate table ... reuse storage;
alter table ... deallocate unused keep 2000000m;
alter table ... deallocate unused keep 1500000m;
alter table ... deallocate unused keep 1000000m;
alter table ... deallocate unused keep 500000m;
alter table ... deallocate unused keep 0;
drop table ...;
结果做完truncate table ... reuse storage;之后做alter table ... deallocate unused keep 2000000m;时一直报
alter table EAI_CT_BUILD.EA_CROSS_SYS_DATA_TBL_BAK deallocate unused keep 10000M
ERROR at line 1:
ORA-03230: segment only contains 77 blocks of unused space above high water
truncate table EAI_CT_BUILD.EA_CROSS_SYS_DATA_TBL_BAK subpartition **;......
truncate table EAI_CT_BUILD.EA_CROSS_SYS_DATA_TBL_BAK partition **;......
3.drop table EAI_CT_BUILD.EA_CROSS_SYS_DATA_TBL_BAK ;
大概在truncate subpartition时花了25分钟,之后的就快了,drop table时只发了1分29秒.
|How To Efficiently Drop A Table With Many Extents|
|Last Revision Date:||12-JUN-2008||Status:||PUBLISHED|
How to efficiently drop a table with many extents PURPOSE ~~~~~~~ This note describes why a user process can consume large amounts of CPU after dropping a table consisting of many extents, and a potential workaround to stop the problem occurring. Essentially the CPU is being used to manipulate the extents i.e. moving used extents (uet$) to free extents (fet$). In certain circumstances it may be possible to regulate this CPU activity. SCOPE & APPLICATION ~~~~~~~~~~~~~~~~~~~ This article is intended to assist DBAs who may need to drop a table consisting of many extents. RELATED DOCUMENTS ~~~~~~~~~~~~~~~~~ SMON - Temporary Segment Cleanup and Free Space Coalescing Permanent object cleanup ~~~~~~~~~~~~~~~~~~~~~~~~ If a permanent object (table) is made up of many extents, and the object is to be dropped, the user process dropping the object will consume large amounts of CPU - this is an inescapable fact. However, with some forethought it is possible to mitigate the effects of CPU usage (and hence the knock-on effect on other users of system resources) thus: 1. Identify, but do NOT drop the table 2. Truncate the table, specifying the REUSE STORAGE clause. This will be quick as extents are not deallocated; the highwater mark is simply adjusted to the segment header block. 3. Deallocate unused extents from the table, SPECIFYING THE KEEP CLAUSE. This is the crux - you can control how many extents are to be deallocated by specifying how much (in terms of Kb or Mb) of the table is NOT to be deallocated. Example: o. Table BIGTAB is 2Gb in size and consists of 262144 8Kb extents o. There is little CPU power available, and (from past experience) it is known that dropping an object of this number of extents can take days o. The system is quiet at night times (no other users or batch jobs) In the above example the table could be dropped in 'phases' over the period of a few nights as follows: 1. Truncate the table, specifying the REUSE STORAGE clause: SQL> TRUNCATE TABLE BIGTAB REUSE STORAGE; 2. If it takes 3 days (72 hours) to drop the table, spread this out over 6 nights i.e. drop 1/3 Gb per night. This can be achieved in 6 (nightly) steps as follows: Night 1: SQL> ALTER TABLE BIGTAB DEALLOCATE UNUSED KEEP 1707M; (2Gb*5/6) Night 2: SQL> ALTER TABLE BIGTAB DEALLOCATE UNUSED KEEP 1365M; (2Gb*4/6) Night 3: SQL> ALTER TABLE BIGTAB DEALLOCATE UNUSED KEEP 1024M; (2Gb*3/6) Night 4: SQL> ALTER TABLE BIGTAB DEALLOCATE UNUSED KEEP 683M; (2Gb*2/6) Night 5: SQL> ALTER TABLE BIGTAB DEALLOCATE UNUSED KEEP 341M; (2Gb*1/6) Night 6: SQL> DROP TABLE BIGTAB; The same method can be applied if LOB segments or indexes are involved. SQL> ALTER TABLE
MODIFY LOB ( ) DEALLOCATE UNUSED KEEP M; SQL> ALTER INDEX DEALLOCATE UNUSED KEEP M; Caveats ~~~~~~~ o. If you have inadvertently tried to drop the table, this method will not work. This is because the drop will first convert the segment to a temporary segment, and only then start cleaning up the now temporary segment's extents. Thus, if the drop is interrupted, the temporary segment will now be cleaned up by SMON. o. This method will only work for table, lob and index segment types. o. This method will not work for segments bigger than 4gb in size due to unpublished bug: 1190939 4G ------------------------------------------------------------------------------- Oracle Support Services
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