物理读与逻辑读

最新推荐文章于 2024-04-08 22:19:02 发布

Root__Liu

最新推荐文章于 2024-04-08 22:19:02 发布

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分类专栏： Oracle 文章标签： Oracle物理读 Oracle逻辑读逻辑读与物理读的区别

本文链接：https://blog.youkuaiyun.com/Root__Liu/article/details/80672416

1、物理读即是把数据从磁盘读入到buffer catch的过程。

通常情况下是，如果需要数据的时候发现不存在于buffer catch当中，即oracle就会执行物理读。
　例子如下：
C:/Documents and Settings/Administrator>sqlplus jenny/jenny
SQL> set autotrace traceonly;
SQL> select * from t_test1;
----------------------------------------------------------
Plan hash value: 1883417357
----------------------------------------------------------
0 recursive calls
0 db block gets
11 consistent gets
3 physical reads --发生了3次物理读写
0 redo size
10632 bytes sent via SQL*Net to client
451 bytes received via SQL*Net from client
8 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
97 rows processed

　SQL> select * from t_test1;
　----------------------------------------------------------
　Plan hash value: 1883417357
----------------------------------------------------------
0 recursive calls
0 db block gets
11 consistent gets
0 physical reads　--这里没有发生物理读取，因为这时数据已存在buffer catche中
0 redo size
10632 bytes sent via SQL*Net to client
451 bytes received via SQL*Net from client
8 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
97 row