通过分析SQL语句的执行计划优化SQL(总结)

dbaxp · 发表于 2006-3-21 13:05

好文章!!

foreverlee · 发表于 2006-3-21 15:27

An Index full scan will not perform single block i/o's and so it may prove to be inefficient. --- 这句话是不是矛盾了.

index fast full scan则应当是采用了多块读.

鸿云 · 发表于 2006-3-21 16:49

感谢！精神可嘉

jgwang · 发表于 2006-3-26 01:39

最初由 foreverlee 发布
[B]An Index full scan will not perform single block i/o's and so it may prove to be inefficient. --- 这句话是不是矛盾了.

index fast full scan则应当是采用了多块读. [/B]

这个概念作者理解错了.

Tom said in "effective Oracle by design",

"An index full scan uses single-block I/O to read the index in order. It starts at the root block and branches down to the very first leaf block. Each of these blocks is read a single block at a time. Once you get to the first leaf block, you read each leaf block in order, a single block at a time."

So usually we see index full scan when database is using the index in order to read the data sorted.