oracle 9i 性能调优2

五、Tuning
the Buffer Cache

1、Oracle Architecture

 


2、Default buffer cache

db_cache_advice

v$db_cache_advice

select name,size_for_estimate,estd_physical_read_factor,estd_physical_reads

 from v$db_cache_advice order by name,size_for_estimate;

select size_for_estimate,buffers_for_estimate,estd_physical_read_factor,estd_physical_reads

from v$db_cache_advice 

where name ='DEFAULT' and block_size=(select value from v$parameter where name ='db_block_size') and advice_status='ON';

3、Managing Buffer Cache







4、Performance Indicators



--v$sysstat

select name,value from v$sysstat where name ='free buffer inspected';

--v$system_event

select event,total_waits from v$system_event where event in ('free buffer waits','buffer busy waits');

--v$event_name

select * from v$event_name where name='buffer busy waits';

--v$session_wait

select * from v$session_wait;

5、Measuring Cache Hit Ratio

--v$sysstat              --oracle9i

select 1-(phy.value - lob.value - dir.value) / ses.value "CACHE HIT RATIO"

from     v$sysstat ses, v$sysstat lob, v$sysstat dir, v$sysstat phy

where  ses.name = 'session logical reads' 

and dir.name = 'physical reads direct'

and lob.name='physical reads direct (lob)'

and phy.name='physical reads';







select name,value

 from v$sysstat

where name in ('db block gets from cache','consistent gets from cache', 'physical reads cache');

-- v$session_wait

-- v$session_event

--v$system_event

6、How Many Buffer in the Pool?

select o.object_name,count(*) "Num of Blks"

from dba_objects o, v$bh bh

where o.data_object_id = bh.objd

    and o.owner != 'SYS'

group by o.object_name

order by count(*);

1) select data_object_id,object_type

  from dba_objects

where object_name = UPPER('segment_name');

2) select count(*) buffers from v$bh where objd = data_object_id_value;

3) select name,block_size,sum(buffers) from v$buffer_pool 

group by name,block_size

having sum(buffers) > 0;  

4) cache used by segment_name = [buffers(step2) / total buffers(Step3)]

SQL>
execute dbms_stats.gather_table_stats('HR','DEPARTMENTS');              --更新表

 

PL/SQL procedure successfully completed

 

SQL> select table_name,blocks from dba_tables

  2  where owner='HR' and table_name='DEPARTMENTS';

 

TABLE_NAME                         BLOCKS

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

DEPARTMENTS                             5

 

SQL>

6、Recycle Buffer Pool

-- v$cache

-- v$sess_io

select s.username,io.block_gets ,io.consistent_gets,io.physical_reads

from v$sess_io io, v$session s

where io.sid = s.sid;

7、Calculating Hit Ratio

-- v$buffer_pool_statistics

select name, 1-(physical_reads /(db_block_gets + consistent_gets)) "HIT_RATIO"

from v$buffer_pool_statistics

where db_block_gets + consistent_gets >0;

--  v$buffer_pool

select id,name,block_size,buffers from v$buffer_pool;

8、Caching Tables

select /*+ CACHE */ item_no, from items;

六、Dynamic
Instance Resizing

1、

select name,block_size,resize_state,current_size,buffers from v$buffer_pool;

七、Sizing
Other SGA Structures

1、Using Dynamic Views

-- v$session_wait

select sid,event,seconds_in_wait,state from v$session_wait where event like 'log buffer space%';

--v$sysstat    <%1

Redo Buffer Allocation Retries

Redo Entries

2、Tuning Guidelines

select event,total_waits,time_waited,average_wait

from v$system_event where event like 'log file switch completing%' ;

select event,total_waits,time_waits,average_wait

from v$system_event where event like 'log file switch (check%'

select event,total_waits,time_waits,average_wait

from v$system_event where event like 'log file switch (arch%'

八、Tuning
the Oracle Shared Server

1、Parameters

--dispatchers

--max_dispatchers

--shared_servers

--max_shared_servers

--circuits

--processes

2、Monitoring Dispatchers

-- v$dispatchers

-- v$dispatcher_rate

--v$circuit

select sum(owned) "Clients", sum(busy)*100/(sum(busy)+sum(idle)) "Busy Rate" from v$dispatcher;

select * from v$queue