[20130815]12c Asynchronous Global Index Maintenance Part III.txt
参考链接：
http://richardfoote.wordpress.com/2013/08/07/12c-asynchronous-global-index-maintenance-part-iii-re-makere-model/
更多的是重复作者的测试，加深理解:
1.测试环境:
SQL> @ver
BANNER CON_ID
-------------------------------------------------------------------------------- ----------
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production 0
2.测试建立：
SQL> create table muse (id number, code number, name varchar2(30))
partition by range (id)
(partition muse1 values less than (1000001),
partition muse2 values less than (2000001),
partition muse3 values less than (maxvalue));
SQL> insert into muse
select rownum, mod(rownum,100000), 'DAVID BOWIE' from
(select 1 from dual connect by level (select 1 from dual connect by level
SQL> commit;
SQL> exec dbms_stats.gather_table_stats(ownname=>user, tabname=>'MUSE', estimate_percent=>null, method_opt=>'FOR ALL COLUMNS SIZE 1');
SQL> create unique index muse_id_i on muse(id);
Index created.
SQL> alter table muse drop partition muse1 update global indexes;
Table altered.
SQL> select index_name, num_rows, s.blocks, leaf_blocks, status, orphaned_entries
from dba_indexes i, dba_segments s where i.index_name = s.segment_name and table_name='MUSE';
INDEX_NAME NUM_ROWS BLOCKS LEAF_BLOCKS STATUS ORPHANED_ENTRIES
-------------------- ---------- ---------- ----------- -------- --------------------
MUSE_ID_I 3000000 9216 8216 VALID YES
--ORPHANED_ENTRIES=yes.
SQL> analyze index muse_id_i validate structure;
Index analyzed.
SQL> select name, blocks, lf_rows, del_lf_rows from index_stats;
NAME BLOCKS LF_ROWS DEL_LF_ROWS
-------------------- ---------- ---------- -----------
MUSE_ID_I 9216 3000000 1000000
SQL> insert into muse select rownum, 42, 'ZIGGY STARDUST' from dual connect by level 10 rows created.
SQL> commit;
Commit complete.
SQL> analyze index muse_id_i validate structure;
Index analyzed.
SQL> select name, blocks, lf_rows, del_lf_rows from index_stats;
NAME BLOCKS LF_ROWS DEL_LF_ROWS
-------------------- ---------- ---------- -----------
MUSE_ID_I 9216 3000000 999990
--可以DEL_LF_ROWS=9999990,有10条记录插入原来删除的位置。
SQL> set autot traceonly ;
SQL> select * from muse where id between 1 and 100;
10 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 2515419874
------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 23 | 4 (0)| 00:00:01 | | |
| 1 | TABLE ACCESS BY GLOBAL INDEX ROWID BATCHED| MUSE | 1 | 23 | 4 (0)| 00:00:01 | 1 | 1 |
|* 2 | INDEX RANGE SCAN | MUSE_ID_I | 100 | | 3 (0)| 00:00:01 | | |
------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("ID">=1 AND "ID"
filter(TBL$OR$IDX$PART$NUM("MUSE",0,8,0,"MUSE".ROWID)=1)
--也就是讲，对于唯一索引，oracle在插入旧键值是会重用原来的块。
--插入不再删除范围的情况呢?
SQL> insert into muse select rownum+3000000, 42, 'ZIGGY STARDUST' from dual connect by level SQL> commit;
SQL> analyze index muse_id_i validate structure;
Index analyzed.
SQL> select name, blocks, lf_rows, del_lf_rows from index_stats;
NAME BLOCKS LF_ROWS DEL_LF_ROWS
-------------------- ---------- ---------- -----------
MUSE_ID_I 11264 4000000 999990
--可以发现，插入不再删除范围的值不会重用原来的块。
We notice that the number of so-called deleted leaf entries remains the same after inserting the 1M new rows.
So in this scenario, the effectively "empty" leaf blocks containing nothing but orphaned unique index entries are
not re-cycled and reused by subsequent index block splits as they would have been had they contained nothing but deleted
index entries.
So Unique indexes in the unlikely event that such unique values are subsequently reinserted are an exception to the
general rule of orphaned global index entries having to be "cleaned out".