嗨有些人可以告诉我为什么我们为索引和数据创建了不同的表空间。
答案 0 :(得分：16)
人们普遍认为，将索引和表保存在单独的表空间可以提高性能。现在许多尊敬的专家认为这是一个神话（见this Ask Tom thread - search for "myth"），但仍然是一种常见的做法，因为旧习惯会变得很难！
从asktom中提取："Index Tablespace"从2001年开始为Oracle版本8.1.6提出问题
回复的第一部分
Yes, no, maybe.
The idea, born in the 1980s when systems were tiny and user counts were in the single
digits, was that you separated indexes from data into separate tablespaces on different
disks.
In that fashion, you positioned the head of the disk in the index tablespace and the head
of the disk in the data tablespace and that would be better then seeking 2 times on the
same disk.
Drives back then were really slow at seeking and typically measured in the 10's to 100's
of megabytes (if you were lucky)
Today, with logical volumes, raid, NN gigabyte (nn is rapidly becoming NNN gigabytes)
drives, hundreds/thousands of concurrent users, thousands of tables, 10's of thousands of
indexes - this sort of "optimization" is sort of impossible.
What you strive for today is to be able to manage things, to spread IO out evenly
avoiding hot spots.
Since I believe all things should be in locally managed tablespaces with UNIFORM extent
sizes, I would say that yes, indexes would be in a different tablespace from the data but
only because they are a different SIZE then the data. My table with 50 columns and an
average row size of 4k might belong in a tablespace that has 5meg extents whereas the
index on a single number column might belong in a tablespace with 512k or 1m extents.
I tend to keep my indexes separate from the data but for the above sizing reason. The
tablespaces frequently end up on the same exact mount points. You strive for even io
across your disks and you may end up with indexes and data on the same devices.
答案 1 :(得分：2)
在80年代，当没有多少用户且数据库大小不是太大时，这是有道理的。那时，将索引和表存储在不同的物理卷中是很有用的。
现在有逻辑卷，raid等，没有必要将索引和表存储在不同的表空间中。
但是所有表空间必须使用统一的扩展大小进行本地管理。从这个角度来看，索引必须存储在不同的表空间中，因为具有50列的表可以存储在具有5Mb exteds大小的表空间中，而索引的表空间将是512Kb扩展大小。
答案 2 :(得分：1)