是否有任何逻辑上的原因为索引具有不同的表空间？

Question

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.

Answer 1

人们普遍认为,将索引和表保存在单独的表空间中可以提高性能.这被许多受人尊敬的专家认为是一个神话(请参阅这个问汤姆线程 - 寻找"神话"),但仍然是一种常见的做法,因为旧习惯会变得难受!

第三方编辑

从asktom中提取:"索引表空间"从2001年开始针对Oracle版本8.1.6提出问题

• 将索引保存在自己的表空间中仍然是一个好主意吗？
• 这会提高性能还是更多的恢复问题？
• 答案是否因平台而异？

答复的第一部分

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.