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嗨，有人可以告诉我为什么我们为索引和数据创建不同的表空间。

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3 回答 3

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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。这现在被许多受人尊敬的专家认为是一个神话（见这个问汤姆线程 - 搜索“神话”），但仍然是一种常见的做法，因为旧习惯很难改掉！

第三方编辑

从 asktom 中摘录：“Index Tablespace” from 2001 for Oracle version 8.1.6 the question

  • 将索引保留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是恢复问题？
  • 答案是否因平台而异？

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.
于 2009-11-30T12:43:22.833 回答
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这在 80 年代是有道理的，当时用户并不多，数据库规模也不是太大。那时将索引和表存储在不同的物理卷中很有用。

现在有了逻辑卷、raid 等，没有必要将索引和表存储在不同的表空间中。

但是所有表空间都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 5Mb 扩展大小的表空间中，当索引的表空间足够 512Kb 扩展大小时。

于 2009-11-30T12:44:08.730 回答
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  • 表现。应该逐案分析。我认为将所有内容放在一个表空间中也成为另一个神话！它应该有足够的主轴、足够的 lun 并负责操作系统中的排队。如果有人认为创建一个表空间就足够了，并且在不考虑所有其他因素的情况下与许多表空间一样，这又意味着另一个神话。这取决于！
  • 高可用性。在某些文件损坏、文件系统损坏、块损坏的情况下，使用单独的表空间可以提高系统的高可用性。如果问题仅出现在索引表空间，则可以在线进行恢复，并且我们的应用程序仍然可供客户使用。另见：http ://richardfoote.wordpress.com/2008/05/02/indexes-in-their-own-tablespace-recoverability-advantages-get-back/
  • 为索引、数据、blob、clob 使用单独的表空间，最终某些单独的表对于可管理性和成本可能很重要。我们可以使用我们的存储系统来存储我们的 blob、clob，最终归档到具有不同服务质量的不同存储层
于 2014-08-28T14:14:34.977 回答