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Fix shared pool latch contention

Oracle Database Tips by Donald BurlesonFebruary 9, 2015

Question:  I have shared pool latch contention and I don't know what to do about the latch contention.  How do you identify latch contention in the shared pool and how to you relieve shared pool latch contention?

Answer: The Oracle shared pool contains Oracle's library cache, which is responsible for collecting, parsing, interpreting, and executing all of the SQL statements that go against the Oracle database.

It's also critical to remember that the shared_pool_size is the most important parameter relating to shared pool resource usage.

Hence, the shared pool is a key component which can experience frequent contention, so it's necessary for the Oracle database administrator to check for shared pool contention.

See these related notes on latch contention and related shared pool contention articles.

Oracle also published a script using x$ksmsp to give a listing of the RAM heap to see how free space is allocated within the shared pool, and the sizes of available chunks on the freelist for he shared pool, RAM.

select
'0 (<140)' BUCKET, KSMCHCLS, KSMCHIDX,
10*trunc(KSMCHSIZ/10) "From",
count(*) "Count" ,
max(KSMCHSIZ) "Biggest",
trunc(avg(KSMCHSIZ)) "AvgSize",
trunc(sum(KSMCHSIZ)) "Total"
from
x$ksmsp
where
KSMCHSIZ<140
and
KSMCHCLS='free'
group by
KSMCHCLS, KSMCHIDX, 10*trunc(KSMCHSIZ/10)
UNION ALL
select
'1 (140-267)' BUCKET,
KSMCHCLS,
KSMCHIDX,
20*trunc(KSMCHSIZ/20) ,
count(*) ,
max(KSMCHSIZ) ,
trunc(avg(KSMCHSIZ)) "AvgSize",
trunc(sum(KSMCHSIZ)) "Total"
from
x$ksmsp
where
KSMCHSIZ between 140 and 267
and
KSMCHCLS='free'
group by
KSMCHCLS, KSMCHIDX, 20*trunc(KSMCHSIZ/20)
UNION ALL
select
'2 (268-523)' BUCKET,
KSMCHCLS,
KSMCHIDX,
50*trunc(KSMCHSIZ/50) ,
count(*) ,
max(KSMCHSIZ) ,
trunc(avg(KSMCHSIZ)) "AvgSize",
trunc(sum(KSMCHSIZ)) "Total"
from
x$ksmsp
where
KSMCHSIZ between 268 and 523
and
KSMCHCLS='free'
group by
KSMCHCLS, KSMCHIDX, 50*trunc(KSMCHSIZ/50)
UNION ALL
select
'3-5 (524-4107)' BUCKET,
KSMCHCLS,
KSMCHIDX,
500*trunc(KSMCHSIZ/500) ,
count(*) ,
max(KSMCHSIZ) ,
trunc(avg(KSMCHSIZ)) "AvgSize",
trunc(sum(KSMCHSIZ)) "Total"
from
x$ksmsp
where
KSMCHSIZ between 524 and 4107
and
KSMCHCLS='free'
group by
KSMCHCLS, KSMCHIDX, 500*trunc(KSMCHSIZ/500)
UNION ALL
select
'6+ (4108+)' BUCKET,
KSMCHCLS,
KSMCHIDX,
1000*trunc(KSMCHSIZ/1000) ,
count(*) ,
max(KSMCHSIZ) ,
trunc(avg(KSMCHSIZ)) "AvgSize",
trunc(sum(KSMCHSIZ)) "Total"
from
x$ksmsp
where
KSMCHSIZ >= 4108
and
KSMCHCLS='free'
group by
KSMCHCLS, KSMCHIDX, 1000*trunc(KSMCHSIZ/1000)

 
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