1. 查看表的具体情况
查看是不是分区表，有多少个分区、分区字段：
SQL col table_name for a20
SQL col column_name for a20
SQL select a.table_name,a.partitioned,b.partition_count,c.column_name
2 from user_tables a, user_part_tables b, user_part_key_columns c
3 where a.table_name="STAT_SUBMIT_CENTER"
4 and b.table_name="STAT_SUBMIT_CENTER"
5 and c.name="STAT_SUBMIT_CENTER";
TABLE_NAME PAR PARTITION_COUNT COLUMN_NAME
-------------------- --- --------------- --------------------
STAT_SUBMIT_CENTER YES 50 MSGDATE
查看已使用的每个分区的大小：
SQL select segment_name,partition_name,round(bytes/1024/1024) from user_segments
where segment_name ="STAT_SUBMIT_CENTER" and bytes/1024/10240.25 order by 3 desc;
SEGMENT_NAME PARTITION_NAME
SEGMENT_NAME PARTITION_NAME ROUND(BYTES/1024/1024)
-------------------------- ------------------------------ ----------------------
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20051101 1722
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20051021 1488
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20051111 1440
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20051121 1355
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20051221 1335
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20050911 1309
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20051211 1253
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20051201 1247
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20050921 1198
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20060101 1151
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20060111 1068
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20051001 1018
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20051011 865
STAT_SUBMIT_CENTER STAT_SUBMIT_CENTER_20060121 796
14 rows selected.
查看整个表的大小：
SQL select segment_name,sum(bytes/1024/1024) from user_segments
where segment_name ="STAT_SUBMIT_CENTER" group by segment_name;
SEGMENT_NAME
SEGMENT_NAME SUM(BYTES/1024/1024)
-------------------------------- --------------------
STAT_SUBMIT_CENTER 17234
查看表的记录数：
SQL set timing on
SQL select count(*) from STAT_SUBMIT_CENTER;
COUNT(*)
----------
170341007
Elapsed: 00:14:18.60
查看这个表上的索引情况如下：
table STAT_SUBMIT_CENTER 17234 M
index IDX_SUBCEN_ADDRUSER 5155 M ADDRUSER
PK_STAT_SUBMIT_CENTER 10653 M MSGDATE,ADDRUSER,MSGID
然后，查看一些数据库参数情况：
SQL show parameter work
NAME TYPE VALUE
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
workarea_size_policy string AUTO
SQL show parameter pga
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_target big integer 209715200
SQL select * from dba_temp_files;
FILE_NAME
------------------------------------------------------------------------------------------------------------------------
FILE_ID TABLESPACE_NAME BYTES BLOCKS STATUS RELATIVE_FNO AUT MAXBYTES MAXBLOCKS
---------- ------------------------------ ---------- ---------- --------- ------------ --- ---------- ----------
INCREMENT_BY USER_BYTES USER_BLOCKS
------------ ---------- -----------
/bgdata/oracle/temp01.dbf
1 TEMP 3563061248 434944 AVAILABLE 1 YES 4294967296 5242886400 3562012672 434816
2. 需要考虑的几个方面
1）创建的索引需要几个G的磁盘空间。
2）创建索引需要排序，使用pga_aggregate_target，要把这个值从200M加大到2G。
3）如果内存不够，需要temp表空间，则要把temp表空间加大到8G――itpub上有一个帖子说过，15亿条记录用了34G空间。
4）在线创建，时间会比较长。讨论后，停止这个表的操作，非online创建。
3. 实际操作过程
1）数据文件够，不扩展；temp数据文件扩展：
alter database tempfile "/bgdata/oracle/temp01.dbf" resize 8192m;
2）在workarea_size_policy=AUTO的情况下，改pga_aggregate_target=2048m。对于串行操作，一个session能使用的pga=MIN(5%PGA_AGGREGATE_TARGET,100MB)，这样可以使得pga用到最大的值：
alter system set pga_aggregate_target=2048m;
3）因为这是一个比较长的过程，所以写脚本让后台运行：
nohup time createind.sh &
vi createind.sh
#!/bin/sh
sqlplus user/password
create index IDX_SUBMIT_RECORDTIME on STAT_SUBMIT_CENTER(RECORDTIME) local;
exit
EOF
4）创建过程中可以观察v$sort_segment，v$sort_usage看排序情况：
nohup time createind.sh &
vi createind.sh
#!/bin/sh
sqlplus user/password
create index IDX_SUBMIT_RECORDTIME on STAT_SUBMIT_CENTER(RECORDTIME) local;
exit
EOF
5）创建完成后，把tempfile和pga_aggregate_target改回原值：
alter database tempfile "/bgdata/oracle/temp01.dbf" resize 4096m;
alter system set pga_aggregate_target=500m;
4. 实际创建过程中观察到的情况
1）开始之前：
SQL select tablespace_name,current_users,total_blocks,used_blocks,free_blocks from v$sort_segment;
TABLESPACE_NAME CURRENT_USERS TOTAL_BLOCKS USED_BLOCKS FREE_BLOCKS
------------------------------- ------------- ------------ ----------- -----------
TEMP 0 431360 0 431360
SQL select * from v$sort_usage;
no rows selected
2）创建之初，抓到这么一条sql：
insert into obj$(owner#,name,namespace,obj#,type#,ctime,mtime,st
ime,status,remoteowner,linkname,subname,dataobj#,flags,oid$,spar
e1,spare2)values(:1,:2,:3,:4,:5,:6,:7,:8,:9,:10,:11,:12,:13,:14,
:15,:16, :17)
3）然后v$sort_segment.USED_BLOCKS变大，v$sort_usage.BLOCKS变大，一直增长到：
SQL select tablespace_name,current_users,total_blocks,used_blocks,free_blocks from v$sort_segment;
TABLESPACE_NAME CURRENT_USERS TOTAL_BLOCKS USED_BLOCKS FREE_BLOCKS
------------------------------- ------------- ------------ ----------- -----------
TEMP 1 431360 46720 384640
SQL select * from v$sort_usage;
USERNAME USER SESSION_ADDR SESSION_NUM SQLADDR SQLHASH
------------------------------ ------------------------------ ---------------- ----------- ---------------- ----------
TABLESPACE CONTENTS SEGTYPE SEGFILE# SEGBLK# EXTENTS BLOCKS SEGRFNO#
------------------------------- --------- --------- ---------- ---------- ---------- ---------- ----------
DPC DPC 00000003974CFFB0 6134 0000000399CAB288 1254950678
TEMP TEMPORARY SORT 201 431113 365 46720 1
这个过程中抓到的sql为：
select file# from file$ where ts#=:1
4）v$sort_segment.USED_BLOCKS变为0，v$sort_usage.BLOCKS变为0。
5）重复3，4两步，估计这个是创建一个分区的索引。
需要解释一下的是，上面的sql只是我随机抓到的运行时间比较长的，整个create index过程会复杂很多，具体怎么样可以用sqltrace跟踪。这里主要看的是temp表空间的使用情况。
同时，在创建的过程中：
SQL select segment_name,partition_name from user_segments where segment_name="IDX_SUBMIT_RECORDTIME";
no rows selected
SQL select index_name,partition_name from user_ind_partitions where INDEX_NAME="IDX_SUBMIT_RECORDTIME";
no rows selected
当时忘了查user_segments中其实是有一个segment_name为一串数字的记录，那个才是正在创建的索引；如果这个事务失败了，将回滚。
最后耗时99分钟完成。
5. 创建完成后分析索引
但是接下来还有一件事。创建完成后要分析索引，否则就是走了索引，查询速度也会很慢。
SQL explain plan for select count(*) from stat_submit_center where recordtimetrunc(sysdate);
Explained.
SQL @?/rdbms/admin/utlxplp.sql
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost | Pstart| Pstop |
-------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 9 | 4 | | |
| 1 | SORT AGGREGATE | | 1 | 9 | | | |
| 2 | PARTITION RANGE ALL | | | | | 1 | 50 |
|* 3 | INDEX FAST FULL SCAN| IDX_SUBMIT_RECORDTIME | 8878K| 76M| 4 | 1 | 50 |
-------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("STAT_SUBMIT_CENTER"."RECORDTIME"TRUNC(SYSDATE@!))
Note: cpu costing is off
16 rows selected.
SQL set autotrace on explain
SQL set timing on
SQL select count(*) from stat_submit_center where recordtimetrunc(sysdate);
aa^Cselect count(*) from stat_submit_center where recordtimetrunc(sysdate)
*
ERROR at line 1:
ORA-01013: user requested cancel of current operation
Elapsed: 00:11:49.85
SQL
SQL set autotrace off
上面可以看到，因为没有分析索引，虽然它走的是新建的IDX_SUBMIT_RECORDTIME索引，但是查询速度很慢，10分钟后也没有结果。下面我们分析一下：
SQL Analyze index IDX_SUBMIT_RECORDTIME estimate statistics;
Index analyzed.
Elapsed: 00:00:06.84
SQL set autotrace on explain
SQL select count(*) from stat_submit_center where recordtimetrunc(sysdate);
COUNT(*)
----------
926736
Elapsed: 00:00:05.37
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=4360 Card=1 Bytes=9)
1 0 SORT (AGGREGATE)
2 1 PARTITION RANGE (ALL)
3 2 INDEX (RANGE SCAN) OF "IDX_SUBMIT_RECORDTIME" (NON-UNI
QUE) (Cost=4360 Card=8878740 Bytes=79908660)
SQL set autotrace off
索引分析之后，查询时间为5分钟左右，效率大大提高。
至此，完成全部操作。
作者简介：柔嘉维则；作者Email地址为baobaoc@hotmail.com；作者Blog为http://spaces.msn.com/roujiaweize/(e129)
