本篇文章为大家展示了Oracle调优中常用表KEEP到内存中的示例分析，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。
数据迁移后性能受到影响，需要将老数据库中keep到内存中的表在新库中keep到内存中，使用如下方法。
新库设置db_keep_cache_size为适当值，这个值的大小不能小于需要keep的表的大小。
查看老库中需要keep的表信息：
select s.owner,
s.segment_name,
s.partition_name,
s.bytes / 1024 / 1024 as "size(m)"
from dba_segments s
where owner = 'XXX'
and segment_name in
(select table_name from dba_tables where owner = 'XXX' and buffer_pool='KEEP')
order by 4 desc
查询老库中需要keep表总大小：
select sum(s.bytes / 1024 / 1024 / 1024) as "total keep size(G)"
from dba_segments s
where segment_name in
(select table_name from dba_tables where owner = 'XXX' and buffer_pool='KEEP')
生成keep脚本：
select 'alter table XXX.'||s.segment_name||' storage(buffer_pool keep);' as "脚本"
from dba_segments s
where owner = 'XXX'
and segment_name in
(select table_name from dba_tables where owner = 'XXX' and buffer_pool='KEEP')
keep表到内存中：
select 'alter table XXX.'||s.segment_name||' cache;' as "脚本2"
from dba_segments s
where owner = 'XXX'
and segment_name in
(select table_name from dba_tables where owner = 'XXX' and buffer_pool='KEEP')
上两个脚本整合：
select 'alter table XXX.'||s.segment_name||' storage(buffer_pool keep) cache;' as "脚本"
from dba_segments s
where owner = 'XXX'
and segment_name in
(select table_name from dba_tables where owner = 'XXX' and buffer_pool='KEEP')
上述三个脚本输出结果放在plsql中执行即可。
附录：与cache到内存相关的命令
--表缓存
alter table ..... storage(buffer_pool keep);
--查看哪些表被放在缓存区 但并不意味着该表已经被缓存
select table_name from dba_tables where buffer_pool='keep';
--查询到该表是否已经被缓存
select table_name,cache,buffer_pool from user_TABLES where cache like '%Y';
--已经加入到KEEP区的表想要移出缓存，使用
alter table table_name nocache;
--查询当前用户下表的情况
select table_name,cache,buffer_pool from user_TABLES;
--对于普通LOB类型的segment的cache方法
alter table t2 modify lob(c2) (storage (buffer_pool keep) cache);
--取消缓存
alter table test modify lob(address) (storage (buffer_pool keep) nocache);
--查询段
select segment_name,segment_type,buffer_pool from user_segments;
--对基于CLOB类型的对象的cache方法
alter table lob1 modify lob(c1.xmldata) (storage (buffer_pool keep) cache);
--查询该用户下所有表内的大字段情况
select column_name,segment_name from user_lobs;
--取消表缓存
alter table XXX storage(buffer_pool default);
ps：
查看keep空间的剩余大小：
select p.name,a.cnum_repl "total buffers",a.anum_repl "free buffers"
from x$kcbwds a, v$buffer_pool p
where a.set_id=p.LO_SETID and p.name='KEEP';
查看keep空间的大小：
select component,current_size from v$sga_dynamic_components
where component='KEEP buffer cache';
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