數據庫中NESTED_TABLE_SET_REFS hint有什么用

這篇文章將為大家詳細講解有關數據庫中NESTED_TABLE_SET_REFS hint有什么用，小編覺得挺實用的，因此分享給大家做個參考，希望大家閱讀完這篇文章后可以有所收獲。

NESTED_TABLE_SET_REFS hint 是 相當于數據泵的操作 expdp 、impdp的操作
INSERT /*+NESTED_TABLE_SET_REFS+*/ 

一個Oracle未公開的hint提示出現了我的面前，再看這個session對應的后臺應用，原來是一個export操作,以前還真沒注意過，到metalink上查到了如下的解釋：

This hint specifies that nested tables should be retrieved as refs.It is used for exporting, importing and loading. It should never be issued by 
user queries, and in fact is unlikely to make a difference if tried.

This is also consistent with seeing large amounts of queries with this hint, and that those queries are not reused. If this is a problem for you, try to export at another time of day. If the exports are really long-running or the system load is constant, try to find out what you are using exports for and suggest alternatives (eg. backup and recovery purposes, etc). If this is a DSS system, you probably have a smaller shared pool and use import/export heavily. If so, it might be a good idea to use a bigger shared pool when doing this activity.

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