DB Cache issue

Question

Hello, I am troubleshooting performance issues on a customer database. I was looking at issues with disk i/o and was wondering if this output may indicate an issue. There are a few tablespaces that use a 16k block size and several that use an 8k block size. Below indicates that db_8k_cache_size is 0. Does that mean that there is no db cache for the 8k tables and indexes. db_cache_size is also 0.
NAME                                 TYPE        VALUE
=======================================================
db_16k_cache_size                    big integer 687865856
db_2k_cache_size                     big integer 0
db_32k_cache_size                    big integer 0
db_4k_cache_size                     big integer 0
db_8k_cache_size                     big integer 0
db_cache_size                        big integer 0
db_keep_cache_size                   big integer 0
db_recycle_cache_size                big integer 0

Answer 1

Have you identified which datafile or tempfile this I/O is related to? You can check DB Cache Advice
SET PAGES 44
SET LINES 140
COLUMN size_for_estimate FORMAT 9,999,999,999,999 heading 'Cache Size (MB)'
COLUMN buffers_for_estimate FORMAT 9,999,999,999 heading 'Buffers'
COLUMN estd_physical_read_factor FORMAT 999.90 heading 'Estd Phys|Read Factor'
COLUMN estd_physical_reads FORMAT 9,999,999,999 heading 'Estd Phys| Reads'
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';
But do not focus on only DB Cache. Also check PGA usage if it is Tempfile usage that is causing it.
column name  format a60
column value format 9,999,999,999,999,999
select * from gv$pgastat order by inst_id,name
column BYTES_PROCESSED format 9,999,999,999,999,999
column EST_RW_EXTRA_BYTES format 9,999,999,999,999,999
select inst_id,round(pga_target_for_estimate/1024/1024) as target_size_MB,
              bytes_processed,estd_extra_bytes_rw as est_rw_extra_bytes,
              estd_pga_cache_hit_percentage as est_hit_pct,
              estd_overalloc_count as est_overalloc
from gv$pga_target_advice  order by inst_id,target_size_mb
/