Oracle調優中常用表KEEP到內存中的示例分析

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數據遷移后性能受到影響，需要將老數據庫中keep到內存中的表在新庫中keep到內存中，使用如下方法。

新庫設置db_keep_cache_size為適當值，這個值的大小不能小于需要keep的表的大小。

查看老庫中需要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


查詢老庫中需要keep表總大小：
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腳本：   
select 'alter table XXX.'||s.segment_name||' storage(buffer_pool keep);' as "腳本"
  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表到內存中：
select 'alter table XXX.'||s.segment_name||' cache;' as "腳本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')
  
上兩個腳本整合：
select 'alter table XXX.'||s.segment_name||' storage(buffer_pool keep) cache;' as "腳本"
  from dba_segments s
 where owner = 'XXX'
   and segment_name in
       (select table_name from dba_tables where owner = 'XXX' and buffer_pool='KEEP')

上述三個腳本輸出結果放在plsql中執行即可。

附錄：與cache到內存相關的命令
--表緩存 
alter table ..... storage(buffer_pool keep);  
--查看哪些表被放在緩存區 但并不意味著該表已經被緩存 
select table_name from dba_tables where buffer_pool='keep';
--查詢到該表是否已經被緩存 
select table_name,cache,buffer_pool from user_TABLES where cache like '%Y';
--已經加入到KEEP區的表想要移出緩存，使用 
alter table table_name nocache;  
--查詢當前用戶下表的情況 
select table_name,cache,buffer_pool from user_TABLES;  
--對于普通LOB類型的segment的cache方法 
alter table t2 modify lob(c2) (storage (buffer_pool keep) cache);  
--取消緩存 
alter table test modify lob(address) (storage (buffer_pool keep) nocache);  
--查詢段 
select segment_name,segment_type,buffer_pool from user_segments;  
--對基于CLOB類型的對象的cache方法   
alter table lob1 modify lob(c1.xmldata) (storage (buffer_pool keep) cache);   
--查詢該用戶下所有表內的大字段情況 
select column_name,segment_name from user_lobs;   
--取消表緩存
alter table XXX storage(buffer_pool default);



ps：
查看keep空間的剩余大小：
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空間的大小：
select component,current_size from v$sga_dynamic_components
    where component='KEEP buffer cache';

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