Format of Index Blocks【每日一译】--20121214

Space available for index data is the Oracle block size minus block overhead, entry

overhead, rowid, and one length byte for each value indexed.

When you create an index, Oracle fetches and sorts the columns to be indexed and
stores the rowid along with the index value for each row. Then Oracle loads the index

from the bottom up. For example, consider the statement:

对于索引数据的可用空间等于ORACLE块大小减去块的消耗，条目消耗，ROWID，和对于每个索引化值的长度字节。

当你创建一个索引，ORACLE获取并且排序索引化的列并且存储每行的索引值相关的ROWID。然后ORACLE加载索引

从底部向上。比如，确认以下的语句：

CREATE INDEX employees_last_name ON employees(last_name);
Oracle sorts the employees table on the last_name column. It then loads the index
with the last_name and corresponding rowid values in this sorted order. When it
uses the index, Oracle does a quick search through the sorted last_name values and
then uses the associated rowid values to locate the rows having the sought last_

name value.

ORACLE排序EMPLOYEES表在LAST_NAME列上。然后它加载关于LAST_NAME和对应ROWID值的索引以这样的排序

顺序。当使用索引时，ORACLE执行一个快速查找通过排序LAST_NAME值和使用ROWID值相关去定位被查找的名的值

的行。