Data Buffer Cache Quality

Question

Hi All,
Can somebody please please tell some ways in which i can improve the data buffer quality? Presently it is 51.2%. The DB is 10.2.0.2.0
I want to know, wat all factors do i need to keep in mind if i want to increase DB_CACHE_SIZE?
Also, i want to know how can i find out Cache Hit ratio?
Further, i want to know which are the most frequently accessed objects in my DB?
Thanks and Regards,
Nick.

Answer 1

Nick-- wud b DBA wrote:
Hi Aman,
Thanks. Can u please give the appropriate query for that?
And moreover when i'm giving:
SQL>desc V$SEGMENT-STATISTICS; It is giving the following error:
SP2-0565: Illegal identifier.
Regards,
Nick.LOL dude I put it by mistake. Its dash(-) sign but we need underscore(_) sign.
About the query, it may vary what you really mean by "most used obect". If you mean to find the object that is undergoing lots of reads,writes than this may help,
SELECT Rownum AS Rank,
Seg_Lio.*
FROM (SELECT St.Owner,
St.Obj#,
St.Object_Type,
St.Object_Name,
St.VALUE,
'LIO' AS Unit
FROM V$segment_Statistics St
WHERE St.Statistic_Name = 'logical reads'
ORDER BY St.VALUE DESC) Seg_Lio
WHERE Rownum <= 10
UNION ALL
SELECT Rownum AS Rank,
Seq_Pio_r.*
FROM (SELECT St.Owner,
St.Obj#,
St.Object_Type,
St.Object_Name,
St.VALUE,
'PIO Reads' AS Unit
FROM V$segment_Statistics St
WHERE St.Statistic_Name = 'physical reads'
ORDER BY St.VALUE DESC) Seq_Pio_r
WHERE Rownum <= 10
UNION ALL
SELECT Rownum AS Rank,
Seq_Pio_w.*
FROM (SELECT St.Owner,
St.Obj#,
St.Object_Type,
St.Object_Name,
St.VALUE,
'PIO Writes' AS Unit
FROM V$segment_Statistics St
WHERE St.Statistic_Name = 'physical writes'
ORDER BY St.VALUE DESC) Seq_Pio_w
WHERE Rownum <= 10; But if you are looking for the objects which are most highly in the waits than this query may help
select * from
   select
      DECODE
      (GROUPING(a.object_name), 1, 'All Objects', a.object_name)
   AS "Object",
sum(case when
   a.statistic_name = 'ITL waits'
then
   a.value else null end) "ITL Waits",
sum(case when
   a.statistic_name = 'buffer busy waits'
then
   a.value else null end) "Buffer Busy Waits",
sum(case when
   a.statistic_name = 'row lock waits'
then
   a.value else null end) "Row Lock Waits",
sum(case when
   a.statistic_name = 'physical reads'
then
   a.value else null end) "Physical Reads",
sum(case when
   a.statistic_name = 'logical reads'
then
   a.value else null end) "Logical Reads"
from
   v$segment_statistics a
where
   a.owner like upper('&owner')
group by
   rollup(a.object_name)) b
where (b."ITL Waits">0 or b."Buffer Busy Waits">0)This query's reference:http://www.dba-oracle.com/t_object_wait_v_segment_statistics.htm
So it would depend upon that on what ground you want to get the objects.
About the cache increase, are you seeing any wait events related to buffer cache or DBWR in the statspack report?
HTH
Aman....