从底向上第三篇--了解index的compress

Yong Huang

> 这时索引维护的开销会增加多少？

I'm sure the answer is It depends. A compressed index is generally one that should not be updated often. If you do, either don't compress or do extensive testing before you compress (if the test proves it worthwhile).

> alter index index_name rebuild compress; 有哪些需要注意的地方，比如：Tablespace/Cpu/Memory 有啥要注意的吗？

If the application has high concurrency, it's better to do it with online option, so the index is locked only for a very short time when the rebuild starts and when it completes. If you don't want the process to abort due to space problem, alter session enable resumable before your rebuild, and keep checking the process at least once every 2 hours (default resumable timeout). In any case, do it when the database is relatively quiet.

> 为什么这种压缩方式没效果？索引的大小并未变小

Need more info. Is the index unique? How many columns are in the index? What type of data are in the index? What's Oracle's version? Can you show your test case?