Oracle recommends that DISM should be disabled on Solaris SPARC and x86_64. In addition, one need to restart instance after setting SGA_TARGET to SGA_MAX_SIZE to reallocate shard memory in a bid to disable DISM.
In addition, these lessons are learned from my own experience.
Our database is Oracle 18.104.22.168.8 RAC
OS: Solaris 10u11
Storage: IBM DS8800
1 Set SGA_MAX_SIZE to 125G and SGA_TARGET=100G, which enables DISM 2 alter system set SGA_TARGET=125G scope=both sid='RETDBS1'; alter system set SGA_TARGET=125G scope=both sid='RETDBS2';
select owner, segment_name, bytes/1024/1024 from dba_segments where owner='CFETS261' and segment_type='INDEX' and bytes/1024/1024 > 20;
After manually setting SGA_TARGET, the above query could execute for 4 minutes. The other symptom is that the wait event ‘db file sequential read’ could wait for up to 300 ms.
We must disable DISM on Solaris.
RAC Performance and Eviction Issues on Solaris when DISM in Use (Doc ID 1606318.1)
When Will DISM Start On Oracle Database? (Doc ID 778777.1)
ISM or DISM Misconfiguration can Slow Down Oracle Database Performance ( Doc ID 1472108.1 )
DISM Process not Disabled After Setting SGA_TARGET Equal to SGA_MAX_SIZE and Unsetting MEMORY_TARGET and MEMORY_MAX_TARGET in RAC Environment (Doc ID 2024253.1)