Database SOS – 第154页 – Professional Database Recovery Support@+8617813235971

asm数据文件迁移(asm–>os)

--查看当前情况
SQL> select count(*) from hr.a;
  COUNT(*)
----------
      1580
SQL>  select name from v$DATAFILE;
NAME
-----------------------------------------------------------
+DATA/tasm/system01.dbf
+DATA/tasm/undotbs01.dbf
+DATA/tasm/sysaux01.dbf
+DATA/tasm/users01.dbf
+DATA/tasm/example01.dbf
+DG2/tasm/datafile/xff.256.754902279
6 rows selected.
--创建目录
SQL>  create directory asmsrc as '+DG2/TASM/datafile';
Directory created.
SQL>  create directory osdesc as '/u01/oradata';
Directory created.
--表空间离线
SQL> alter tablespace xff offline;
Tablespace altered.
--数据文件迁移
SQL> begin
  2      dbms_file_transfer.copy_file('ASMSRC',
  3      'xff.256.754902279',
  4      'OSDESC',
  5      'xff_new_2.dbf');
  6  END;
  7  /
PL/SQL procedure successfully completed.
--修改数据库中datafile路径
SQL> alter database rename file
  2             '+DG2/tasm/datafile/xff.256.754902279'
  3             to '/u01/oradata/xff_new_2.dbf';
Database altered.
--表空间在线
SQL> alter tablespace xff online;
Tablespace altered.
--测试迁移结果
SQL> select name from v$DATAFILE;
NAME
-------------------------------------------------------------------
+DATA/tasm/system01.dbf
+DATA/tasm/undotbs01.dbf
+DATA/tasm/sysaux01.dbf
+DATA/tasm/users01.dbf
+DATA/tasm/example01.dbf
/u01/oradata/xff_new_2.dbf
6 rows selected.
SQL> select count(*) from hr.a;
  COUNT(*)
----------
      1580
--删除asm中文件
ASMCMD> rm XFF.256.754902279
ORA-15032: not all alterations performed
ORA-15028: ASM file '+dg2/tasm/datafile/XFF.256.754902279' not dropped;
currently being accessed (DBD ERROR: OCIStmtExecute)
--不能直接删除，关闭数据库后可以删除（应该是bug）

asm数据文件迁移(asm–>asm)

rman迁移操作

[oracle@localhost oradata]$ rman target /
Recovery Manager: Release 10.2.0.3.0 - Production on Mon Jun 27 05:50:03 2011
Copyright (c) 1982, 2005, Oracle.  All rights reserved.
connected to target database: TASM (DBID=3032096031)
RMAN> sql ‘alter tablespace xff offline’;
using target database control file instead of recovery catalog
sql statement: alter tablespace xff offline
RMAN> backup device type disk as copy datafile 6 format '+DG2';
Starting backup at 27-JUN-11
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=159 devtype=DISK
channel ORA_DISK_1: starting datafile copy
input datafile fno=00006 name=+DATA/tasm/xff01.dbf
output filename=+DG2/tasm/datafile/xff.256.754899605 tag=TAG20110627T062003 recid=4 stamp=754899608
channel ORA_DISK_1: datafile copy complete, elapsed time: 00:00:07
Finished backup at 27-JUN-11
RMAN> switch tablepspace xff  to copy;
datafile 6 switched to datafile copy "+DG2/tasm/datafile/xff.256.754899605"
RMAN> sql 'alter tablespace xff online';
sql statement: alter tablespace xff online

sql验证操作

SQL> select name from v$datafile;
NAME
--------------------------------------------------------------------------------
+DATA/tasm/system01.dbf
+DATA/tasm/undotbs01.dbf
+DATA/tasm/sysaux01.dbf
+DATA/tasm/users01.dbf
+DATA/tasm/example01.dbf
+DG2/tasm/datafile/xff.256.754899605
6 rows selected.
SQL> select count(*) from hr.a;
  COUNT(*)
----------
      1580

asm数据文件迁移(os–>asm)

--添加测试表空间
SQL> create tablespace xff datafile '/u01/oradata/xifenfei.dbf' size 10m autoextend on maxsize 100m;
Tablespace created.
--查看数据文件位置
SQL> select name from v$datafile;
NAME
--------------------------------------------------------------------------------
+DATA/tasm/system01.dbf
+DATA/tasm/undotbs01.dbf
+DATA/tasm/sysaux01.dbf
+DATA/tasm/users01.dbf
+DATA/tasm/example01.dbf
/u01/oradata/xifenfei.dbf
6 rows selected.
--创建测试表
SQL> create table hr.a tablespace xff
  2  as
  3  select * from dba_tables;
Table created.
SQL> select count(*) from hr.a;
  COUNT(*)
----------
      1580
--转移数据文件位置
[oracle@localhost oradata]$ rman target /
Recovery Manager: Release 10.2.0.3.0 - Production on Mon Jun 27 04:30:22 2011
Copyright (c) 1982, 2005, Oracle.  All rights reserved.
connected to target database: TASM (DBID=3032096031)
RMAN> sql 'alter tablespace xff offline';
using target database control file instead of recovery catalog
sql statement: alter tablespace xff offline
RMAN> backup as copy tablespace xff format '+DATA';
Starting backup at 27-JUN-11
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=132 devtype=DISK
channel ORA_DISK_1: starting datafile copy
input datafile fno=00006 name=/u01/oradata/xifenfei.dbf
output filename=+DATA/tasm/datafile/xff.269.754893121 tag=TAG20110627T043200 recid=2 stamp=754893123
channel ORA_DISK_1: datafile copy complete, elapsed time: 00:00:03
Finished backup at 27-JUN-11
RMAN> switch tablespace xff to copy;
datafile 6 switched to datafile copy "+DATA/tasm/datafile/xff.269.754893121"
RMAN> sql 'alter tablespace xff online';
sql statement: alter tablespace xff online
--查看转移后的数据文件位置
SQL> select name from v$datafile;
NAME
--------------------------------------------------------------------------------
+DATA/tasm/system01.dbf
+DATA/tasm/undotbs01.dbf
+DATA/tasm/sysaux01.dbf
+DATA/tasm/users01.dbf
+DATA/tasm/example01.dbf
+DATA/tasm/datafile/xff.269.754893121
6 rows selected.
--测试其中数据是否存在
SQL> select count(*) from hr.a;
  COUNT(*)
----------
      1580
--创建asm中文件别名
ASMCMD> mkalias  +DATA/tasm/datafile/xff.269.754893121 +DATA/tasm/xff01.dbf
--文件重命名
SQL> alter tablespace xff offline;
Tablespace altered.
SQL> alter database rename file '+DATA/tasm/datafile/xff.269.754893121' to '+DATA/tasm/xff01.dbf';
Database altered.
SQL> alter tablespace xff online;
Tablespace altered.
SQL> select name from v$datafile;
NAME
--------------------------------------------------------------------------------
+DATA/tasm/system01.dbf
+DATA/tasm/undotbs01.dbf
+DATA/tasm/sysaux01.dbf
+DATA/tasm/users01.dbf
+DATA/tasm/example01.dbf
+DATA/tasm/xff01.dbf
6 rows selected.
--手工删除原来数据
[oracle@localhost oradata]$ rm xifenfei.dbf

说明：可以在rman移植数据文件位置的时候，同时处理好别名，然后对表空间重命名，实现只需要表空间离线一次

如果你比较细心，会注意到两件事情：
1、添加一个32g的数据文件会报错
SQL> alter tablespace users add datafile ‘/opt/oracle/oradata/test/user32g.dbf’ size 32g;
alter tablespace users add datafile ‘/opt/oracle/oradata/test/user32g.dbf’ size 32g
*
ERROR at line 1:
ORA-01144: File size (4194304 blocks) exceeds maximum of 4194303 blocks
SQL> !oerr ora 1144
01144, 00000, “File size (%s blocks) exceeds maximum of %s blocks”
// *Cause: Specified file size is larger than maximum allowable size value.
// *Action: Specify a smaller size.
2、添加一个maxsize为unlimited的数据文件
SQL> alter tablespace users add datafile ‘/opt/oracle/oradata/test/user32g.dbf’ size 10M AUTOEXTEND ON maxsize unlimited;
Tablespace altered.
SQL> select MAXBYTES/1024/1024/1024 from dba_data_files where file_name=’/opt/oracle/oradata/test/user32g.dbf’;
MAXBYTES/1024/1024/1024
———————–
31.9999847
你是不是有疑惑，为什么我添加32g的数据文件报错，为什么我添加一个数据文件maxsize设置为unlimited了，还是没有突破32g这个坎
原因分析：
由于Oracle的Rowid中使用22位来代表Block号，这22位最多只能代表2^22-1(4194303)个数据块，而在我们一般情况下使用的数据块大小为8k，所以数据文件的理论大小最大为： 31.9999924G
至于maxsize为unlimited时候，数据文件的大小为什么只有31.9999847G(blocks：4194301.99)，比最大块数(4194303)少了一块，也许是和数据库和系统之间的衔接原因导致。
由上面的分析我们可以知道，数据文件大小和db_block_size有关，那我们可以得到这样的数据文件最大理论值

数据块	数据文件
2KB	8GB
4KB	16GB
8KB	32GB
16KB	64GB
32KB	128GB

注：以上规则适用于smallfile tablespace 下的数据文件，bigfile tablespace 下的数据文件不受此限制

ASM简单管理(2)

1、磁盘组卸载/挂载

--查看当前磁盘组状态
SQL> select group_number,name,state,total_mb,free_mb from v$asm_diskgroup;
GROUP_NUMBER NAME                 STATE                    TOTAL_MB    FREE_MB
------------ -------------------- ---------------------- ---------- ----------
           1 ARCHIVELOG           MOUNTED                     12637      12585
           2 DATA                 MOUNTED                     10228       7644
           3 FLASHBACK            MOUNTED                      7836       7786
           4 DG2                  MOUNTED                      5114       5012
--卸载dg2磁盘组
SQL> alter diskgroup dg2 dismount;
Diskgroup altered.
SQL> select group_number,name,state,total_mb,free_mb from v$asm_diskgroup;
GROUP_NUMBER NAME                 STATE                    TOTAL_MB    FREE_MB
------------ -------------------- ---------------------- ---------- ----------
           1 ARCHIVELOG           MOUNTED                     12637      12585
           2 DATA                 MOUNTED                     10228       7644
           3 FLASHBACK            MOUNTED                      7836       7786
           0 DG2                  DISMOUNTED                      0          0
--挂载dg2磁盘组
SQL> alter diskgroup dg2 mount;
Diskgroup altered.
SQL> select group_number,name,state,total_mb,free_mb from v$asm_diskgroup;
GROUP_NUMBER NAME                 STATE                    TOTAL_MB    FREE_MB
------------ -------------------- ---------------------- ---------- ----------
           1 ARCHIVELOG           MOUNTED                     12637      12585
           2 DATA                 MOUNTED                     10228       7644
           3 FLASHBACK            MOUNTED                      7836       7786
           4 DG2                  MOUNTED                      5114       5012
--卸载所有磁盘组
SQL> alter diskgroup all dismount;
Diskgroup altered.
SQL> select group_number,name,state,total_mb,free_mb from v$asm_diskgroup;
GROUP_NUMBER NAME                 STATE                    TOTAL_MB    FREE_MB
------------ -------------------- ---------------------- ---------- ----------
           0 DATA                 DISMOUNTED                      0          0
           0 DG2                  DISMOUNTED                      0          0
           0 FLASHBACK            DISMOUNTED                      0          0
           0 ARCHIVELOG           DISMOUNTED                      0          0
--挂载所有磁盘组
SQL> alter diskgroup all mount;
Diskgroup altered.
SQL> select group_number,name,state,total_mb,free_mb from v$asm_diskgroup;
GROUP_NUMBER NAME                 STATE                    TOTAL_MB    FREE_MB
------------ -------------------- ---------------------- ---------- ----------
           2 DATA                 MOUNTED                     10228       7644
           3 DG2                  MOUNTED                      5114       5012
           4 FLASHBACK            MOUNTED                      7836       7786
           1 ARCHIVELOG           MOUNTED                     12637      12585
--如果当前磁盘组有实例在访问，则不能被卸载
SQL> alter diskgroup data dismount;
alter diskgroup data dismount
*
ERROR at line 1:
ORA-15032: not all alterations performed
ORA-15027: active use of diskgroup "DATA" precludes its dismount

2、磁盘组目录

--创建目录
SQL> alter diskgroup dg2 add directory '+DG2/CHENGFEI';
Diskgroup altered.
--使用asmcmd查看（export ORACLE_SID=+ASM;asmcmd进入)
ASMCMD> pwd
+DG2
ASMCMD> ls -l
Type  Redund  Striped  Time             Sys  Name
                                        N    CHENGFEI/
--目录重命名
SQL> alter diskgroup dg2 rename directory '+DG2/CHENGFEI' TO '+DG2/XIFENFEI';
Diskgroup altered.
ASMCMD> ls
XIFENFEI/
--删除目录
SQL> alter diskgroup dg2 drop directory '+DG2/xifenfei';
Diskgroup altered.
ASMCMD> ls
ASMCMD>

3、文件别名

--添加别名
SQL> alter diskgroup dg2 add alias '+dg2/XIFENFEI' for '+dg2/tasm/datafile/XFF.256.754832383';
Diskgroup altered.
--使用asmcmd查看别名是否成功
ASMCMD> pwd
+dg2
ASMCMD> ls -l
Type      Redund  Striped  Time             Sys  Name
                                            Y    TASM/
                                            N    XIFENFEI => +DG2/TASM/DATAFILE/XFF.256.754832383
--别名重命名
SQL> alter diskgroup dg2 rename alias '+DG2/XIFENFEI' TO '+DG2/FEIFEI.DBF';
Diskgroup altered.
                                            N    XIFENFEI => +DG2/TASM/DATAFILE/XFF.256.754832383
ASMCMD> ls -l
Type      Redund  Striped  Time             Sys  Name
                                            N    FEIFEI.DBF => +DG2/TASM/DATAFILE/XFF.256.754832383
                                           Y    TASM/
--删除别名
SQL> alter diskgroup dg2 drop alias '+dg2/feifei.dbf';
Diskgroup altered.
ASMCMD> ls -l
Type  Redund  Striped  Time             Sys  Name
                                        Y    TASM/

说明：
1）asmcmd命令行操作中，目录文件名不区分大小写，命令关键字区分大小写
2）磁盘组中的一个文件，最多只能建立一个别名可以通过v$asm_alias视图查看别名的相关信息
ASM简单管理(1)

Oracle RAC10g UNKNOWN解决

1、表现出来的现象
rac2-> crs_stat -t
Name Type Target State Host
————————————————————
ora.rac1.gsd application ONLINE UNKNOWN rac1
ora.rac1.ons application ONLINE UNKNOWN rac1
ora.rac1.vip application ONLINE UNKNOWN rac1
ora.rac2.gsd application ONLINE UNKNOWN rac2
ora.rac2.ons application ONLINE UNKNOWN rac2
ora.rac2.vip application ONLINE UNKNOWN rac1
可以各种原因导致服务呈现unknown 状态，比如两个节点时间差太多，比如1分钟，可能导致这个异常
2、解决方法
因为UNKNOWN不能正常的被启动或者关闭（crs_start -all/crs_stop -all），所以解决方法有两种：
2.1）先禁用crs服务，后启用crs服务(root用户，两个节点上都要执行)
/etc/init.d/init.crs stop
/etc/init.d/init.crs start
2.2）单个服务关闭，后启动（oracle用户，一个节点上执行）
crs_stop ora.rac2.gsd（crs_stop -f ora.rac2.gsd强制关闭）
crs_start ora.rac2.gsd（crs_start -f ora.rac2.gsd强制开启）
该方法有变通，如一个个关闭服务，然后使用crs_start -all开启所有服务器

crs 10.2.0.1 bug（公网ip为私有ip时）

当crs10.2.0.1公用网卡IP段使用10、172、192段（非路由网段）的时候
1、会出现以下两种情况：
1）最后检查时出现如下错误
Checking existence of VIP node application (required)
Check failed.
Check failed on nodes:
rac1,rac2
2）在rac2上执行root.sh脚本最后
Expecting the CRS daemons to be up within 600 seconds.
CSS is active on these nodes.
rac1
rac2
CSS is active on all nodes.
Waiting for the Oracle CRSD and EVMD to start
Waiting for the Oracle CRSD and EVMD to start
……
Timed out waiting for the CRS stack to start.
2、解决方法：
在root.sh在第二个节点执行完之后，以 root 用户身份在第二个节点上手动调用 VIPCA
# /u01/app/oracle/product/10.2.0/crs_1/bin/vipca
配置虚拟ip

Oracle 10g RAC之配置时间同步（NTP）

所有节点的时间必须同步，这通常是通过配置NTP服务器实现的。如果用户的网络中已经有一台时间服务器，那么可以所有节点都指向它，否则可以从集群中挑选一个节点作为时间服务器，让其他节点与它同步。下面分别演示这两种方法：
(1)如果公司网络中已经有一台时间服务器
如：192.168.11.10是一台ntp时间服务器
此时NTP服务器的配置文件是/etc/ntp.conf，在每个节点编辑这个文件。
[root@cc-svr-a ~]# vi /etc/ntp.conf
编辑后的内容如下，首选公司的时间服务器。
server 192.168.11.10 prefer
driftfile /var/lib/ntp/drift
broadcastdelay 0.008
(2)如果没有外部时间服务器
这时公司选择集群中某个节点作为时间服务器，NTP服务只需要很少的系统资源。假设选择主节点作为时间服务器，从节点向它同步，其配置方法如下。
编辑主节点的/etc/ntp.conf文件，编辑后的内容如下：
server 127.127.1.0
fudge 127.127.1.0 stratum 11
driftfile /var/lib/ntp/drift
broadcastdelay 0.008
编辑从节点的/etc/ntp.conf文件，编辑后的内容如下：
server 192.168.11.12 prefer #注意192.168.11.12为主节点的IP地址
driftfile /var/lib/ntp/drift
broadcastdelay 0.008
配置完成后，启动NTP服务。
[root@cc-svr-a ~]# /etc/init.d/ntpd start
[root@cc-svr-a ~]# chkconfig –level 345 ntpd on
(3)查看执行情况（主从）
[root@cc-svr-a ~]# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
*CC-Node-02 LOCAL(0) 12 u 58 64 17 0.226 -22.698 29.261

Linux上NFS配置

一、rpm包准备
需要安装nfs-utils和portmap程序，使用rpm –q可以查看是否安装
rpm -q nfs-utils portmap
如果没有安装，需要使用下面命令安装（默认情况都是安装）
yum install nfs-utils
yum install portmap
二、Server端
1、编辑/etc/exports文件
设置共享/tmp/nfs目录给192.168.11.12的用户，具有读写权限
/tmp/nfs 192.168.11.12(rw,sync)
设置共享目录/mnt/sda4/share/a，仅192.168.23.129主机允许访问此共享目录，具有读写权限
/mnt/sda4/share/b 192.168.23.129(rw) *(ro)
设置共享目录/mnt/sda4/share/b，192.168.23.129可以读写该共享目录，其他主机只可以读取该共享目录
/mnt/sda4/share/d 192.168.23.0/24(rw)
设置共享目录/mnt/sda4/share/d，仅有192.168.23.0/24网段的主机才可访问和读写此目录文件
说明：
Rw：read-write可读写的权限
Ro：read-only只读权限
Sync：数据同步写入到内存与硬盘中
Async：数据先暂存于内存中，而非直接写入硬盘
2.启动portmap服务：
service portmap start[restart]
3.启动NFS服务：
service nfs start[restart]
3、exportfs的用法
如果我们修改了/etc/exports后，并不需要重启nfs服务，只要用exportfs重新扫描一次/etc/exports，并且重新加载即可
语法: exportfs [-aruv]
-a: 全部挂载(或卸载) /etc/exports档案内的设定
-r: 重新挂载/etc/exports里面的设定，也同步的更新/etc/exports和/var/lib/nfs/xtab里面的内容
-u:卸载某一目录
-v:在export的时候，将分享的目录显示到荧屏上.
#exportfs -rva //重新export一次
#exportfs -auv //全部卸载
4、补充说明：
4.1）启动NFS只需启动portmap和NFS服务即可。如果需要启动数据一致性检查，则需启动nfslock服务。
使用netstat–tnlu可以查看nfs开放了哪些端口。Portmap的端口为111，nfs的端口为2049
[root@CC-Node-01 nfs]# rpcinfo -p
program vers proto port
100000 2 tcp 111 portmapper
100000 2 udp 111 portmapper
100003 2 udp 2049 nfs
100003 3 udp 2049 nfs
100003 4 udp 2049 nfs
100021 1 udp 46231 nlockmgr
100021 3 udp 46231 nlockmgr
100021 4 udp 46231 nlockmgr
100003 2 tcp 2049 nfs
100003 3 tcp 2049 nfs
100003 4 tcp 2049 nfs
100021 1 tcp 46322 nlockmgr
100021 3 tcp 46322 nlockmgr
100021 4 tcp 46322 nlockmgr
4.2）如果portmap和nfs服务都是正常运行，修改了/etc/exports中的配置，只需要exportfs -rva 重新加载一次即可
三、Client端
1.启动portmap服务：
service portmap start[restart]
2.挂载服务器端的共享目录(假设服务器端192.168.11.11)：
[root@ECP-UC-DB1 tmp]# mount -t nfs 192.168.11.11:/tmp/nfs /tmp/nfs
[root@ECP-UC-DB1 nfs]# df -h
192.168.11.11:/tmp/nfs
19G 15G 3.6G 81% /tmp/nfs
3、修改nfs
[root@ECP-UC-DB1 tmp]# umount /tmp/nfs
4、设置成开机启动挂载
修改/etc/fstab文件
192.168.11.11:/tmp/nfs /tmp/nfs nfs defaults,rw 0 0
5、补充说明：
一开始配置完Server，Client端mount后只能读，写不了，在server上加上wx权限后问题就解决了

select max(id),min(id) from table优化

1、查看数据库版本
SQL> select * from v$version where rownum<2; BANNER -------------------------------------------------------------------------------- Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production 2、创建表和索引
create table t_a as select * from dba_objects;
create index t_a_ind on t_a(object_id);
3、查询最大值
SQL> select max(object_id) from t_a;
执行计划
———————————————————-
Plan hash value: 3226265922
————————————————————————————–
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
————————————————————————————–
| 0 | SELECT STATEMENT | | 1 | 13 | 2 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 13 | | |
| 2 | INDEX FULL SCAN (MIN/MAX)| T_A_IND | 1 | 13 | 2 (0)| 00:00:01 |
————————————————————————————–
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
0 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
431 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
4、查询最小值
SQL> select min(object_id) from t_a;
执行计划
———————————————————-
Plan hash value: 3226265922
————————————————————————————–
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
————————————————————————————–
| 0 | SELECT STATEMENT | | 1 | 13 | 2 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 13 | |
|
| 2 | INDEX FULL SCAN (MIN/MAX)| T_A_IND | 1 | 13 | 2 (0)| 00:00:01 |
————————————————————————————–
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
0 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
429 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
5、查询最大值和最小值
SQL> select max(object_id),min(object_id) from t_a;
执行计划
———————————————————-
Plan hash value: 2127980459
—————————————————————————
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
—————————————————————————
| 0 | SELECT STATEMENT | | 1 | 13 | 293 (1)| 00:00:04 |
| 1 | SORT AGGREGATE | | 1 | 13 | | |
| 2 | TABLE ACCESS FULL| T_A | 78093 | 991K| 293 (1)| 00:00:04 |
—————————————————————————
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
4 recursive calls
0 db block gets
1119 consistent gets
1044 physical reads
0 redo size
502 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
6、查询最大值和最小值（排除null）
SQL> select max(object_id),min(object_id) from t_a where object_id is not null;
执行计划
———————————————————-
Plan hash value: 1214261695
———————————————————————————
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time
|
———————————————————————————
| 0 | SELECT STATEMENT | | 1 | 13 | 50 (2)| 00:00:01
|
| 1 | SORT AGGREGATE | | 1 | 13 | |
|
|* 2 | INDEX FAST FULL SCAN| T_A_IND | 78093 | 991K| 50 (2)| 00:00:01
|
———————————————————————————
Predicate Information (identified by operation id):
—————————————————
2 – filter(“OBJECT_ID” IS NOT NULL)
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
4 recursive calls
0 db block gets
242 consistent gets
0 physical reads
0 redo size
502 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
7、分别查询最大值和最小值
SQL> select (select max(object_id) from t_a) max,(select min(object_id) from t_a) min from dual;
执行计划
———————————————————-
Plan hash value: 312201770
————————————————————————————–
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
————————————————————————————–
| 0 | SELECT STATEMENT | | 1 | | 2 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 13 | |
| 2 | INDEX FULL SCAN (MIN/MAX)| T_A_IND | 1 | 13 | 2 (0)| 00:00:01 |
| 3 | SORT AGGREGATE | | 1 | 13 | |
| 4 | INDEX FULL SCAN (MIN/MAX)| T_A_IND | 1 | 13 | 2 (0)| 00:00:01 |
| 5 | FAST DUAL | | 1 | | 2 (0)| 00:00:01 |
————————————————————————————–
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
0 recursive calls
0 db block gets
4 consistent gets
0 physical reads
0 redo size
480 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
说明：
1、单查询最大值或者最小值，sql会自动走index
2、如果同时查询最大值和最小值，sql会使用全表扫描，而不是我们想象的索引快速扫描
3、加上where 排除掉null的情况，sql使用索引快速扫描，原因是：在不能确定索引列不为null（或者没有排除掉null）的情况下，不会使用索引快速扫描，而sql为了保证正确而采用了全表扫描
4、INDEX FULL SCAN (MIN/MAX)扫描效率很搞，所以把最大值，最小值分开查询，提高执行效率
5、其他写法
SQL> select (select /*+ index_asc(t_a t_a_ind) */ object_id from t_a where rownu
m=1) min ,(select /*+ index_desc(t_a t_a_ind) */ object_id from t_a where rownum=1)
max from dual;
执行计划
———————————————————-
Plan hash value: 674626822
—————————————————————————————
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
—————————————————————————————
| 0 | SELECT STATEMENT | | 1 | | 2 (0)| 00:
00:01 |
|* 1 | COUNT STOPKEY | | | | | |
| 2 | INDEX FULL SCAN | T_A_IND | 78093 | 991K| 2 (0)| 00:
00:01 |
|* 3 | COUNT STOPKEY | | | | |
| 4 | INDEX FULL SCAN DESCENDING| T_A_IND | 78093 | 991K| 2 (0)| 00:
00:01 |
| 5 | FAST DUAL | | 1 | | 2 (0)| 00:00:01 |
—————————————————————————————
Predicate Information (identified by operation id):
—————————————————
1 – filter(ROWNUM=1)
3 – filter(ROWNUM=1)
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
0 recursive calls
0 db block gets
4 consistent gets
0 physical reads
0 redo size
480 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
注意：
1）这个要正确执行，需要一个前提条件object_id这列要为not null限制条件，不然会hint提示无效
2）从执行计划的统计信息上看，这个和INDEX FULL SCAN (MIN/MAX)方式的执行效率一样