执行统计信息中db block gets和consistent gets

physical reads：物理读 来自datafile
logical reads：逻辑读 来自buffer cache（bufer中读取的block数量，用于insert,update,delete,selectfor update）
db block gets：强制读当前版本的数据,只能看来源于data file（是一致读次数（一个block可能会被读多次），bufer中读取的用于查询（除掉select forupdate）的block数量）
consistent gets：一致性读，根据session的scn读，可以来自于undo或者data file

recursive calls :递归调用。一般原因：dictionary cache未命中；动态存储扩展；PL/SQL语句

第一次执行：

SQL> insert into tn(a) values(3);

统计信息

----------------------------------------------------------

        166  recursive calls

          4  db block gets

         20  consistent gets

         2  physical reads

       484  redo size

       670  bytes sent via SQL*Net to client

       560  bytes received via SQL*Net from client

         3  SQL*Net roundtrips to/from client

         7  sorts (memory)

         0  sorts (disk)

1     rows processed

 

SQL> insert into tn(a) values(4);

统计信息

----------------------------------------------------------

          1  recursive calls

          4  db block gets

          1  consistent gets

         0  physical reads

       532  redo size

       670  bytes sent via SQL*Net to client

       560  bytes received via SQL*Net from client

         3  SQL*Net roundtrips to/from client

         1  sorts (memory)

         0  sorts (disk)

1     rows processed

SQL> select * from tn;

统计信息

----------------------------------------------------------

          4  recursive calls

          0  db block gets

         16  consistent gets

         0  physical reads

         0  redo size

       700  bytes sent via SQL*Net to client

       400  bytes received via SQL*Net from client

         2  SQL*Net roundtrips to/from client

         0  sorts (memory)

         0  sorts (disk)

        10  rows processed