如何改善Oracle的索引？
欢迎进入Oracle社区论坛，与200万技术人员互动交流 >>进入 当我们使用CREATE INDEX来创建索引时，Oracle提供了很多参数来改善创建索引的速度、索引所占用的空间和索引树的层次。 1、速度因素 PARALLEL选项：当创建索引时，Oracle首先会进行全表扫描来收集符
欢迎进入Oracle社区论坛，与200万技术人员互动交流 >>进入
当我们使用CREATE INDEX来创建索引时，Oracle提供了很多参数来改善创建索引的速度、索引所占用的空间和索引树的层次。
1、速度因素
>>PARALLEL选项：当创建索引时，Oracle首先会进行全表扫描来收集符号键和ROWID对，而PARALLEL选项允许多处理器并行扫描表，这样就会加速索引的创建过程。一般推荐的PARALLEL值为CPU数减1。
>>NOLOGGING选项：NOLOGGING选项因为不写日志，所以大大提高了性能，比不使用NOLOGGING选项大约会节省70%的时间。使用NOLOGGING创建索引的唯一风险就是如果数据库需要做前滚恢复，你将不得不重建索引。
2、空间和结构因素
>>COMPRESS选项：COMPRESS选项用于在创建非唯一性索引时压缩重复值。对于连接索引（即索引包含多列）来说，COMPRESS选项会使索引的大小减少一半以上。COMPRESS选项也可以设置连接索引的前置长度。
>>使用大BLOCKSIZE的表空间：将索引建立在大BLOCKSIZE的表空间上，将大大降低索引树的层次。
[06.16]：如何禁止某IP访问ORACLE？
在$ORACLE_HOME/network/admin/中创建protocol.ora文件╋其?容如下?
tcp.validnode_checking=yes
#下面两行取其一：
tcp.invited_nodes=(ip1,ip2,....) #允许访问的IP
tcp.excluded_nodes=(ip1,ip2,...) #禁止访问的IP
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