DBA SGA+PGA Memory Configuration

➜ Back to Library
Description
Categories: DBA, Enginatics
A frequent configuration problem is not making full use of the available hardware resources, especially the physical RAM of the database server. This report shows the servers SGA, PGA and CPU configuration in comparison to the available hardware. For maximum performance, configure the SGA+PGA to use the full available memory of your server minus a few gig for OS level caching, e.g. for writing and...  A frequent configuration problem is not making full use of the available hardware resources, especially the physical RAM of the database server.
This report shows the servers SGA, PGA and CPU configuration in comparison to the available hardware.
For maximum performance, configure the SGA+PGA to use the full available memory of your server minus a few gig for OS level caching, e.g. for writing and reading of PLSQL output files on the DB node and for process memory (an estimated 4MB per process, see below).

Oracle's performance tuning guide:
https://docs.oracle.com/en/database/oracle/oracle-database/12.2/tgdba/database-memory-allocation.html

Oracle's exadata best practices whitepaper:
SUM of databases (SGA_TARGET + PGA_AGGREGATE_TARGET) + 4 MB * (Maximum PROCESSES) < Physical Memory per Database Node

Tom Kyte's recommendation:
"... if you want it all automatic, give ALL FREE MEMORY on your machine to the SGA and be done with it. No more monitoring, no more thinking about how it could be, should be, would be used.
Set the PGA aggregate target and the SGA target to be a tad less than physical memory on the machine and you are done."
https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:30011178429375

The report also shows the status of system statistics.
select * from sys.aux_stats$

If CPUSPEEDNW still shows the default of 4096, it either means that the stats have never been gathered or it could also mean that your storage is too fast to gather them with the standard NOWORKLOAD method and you should set reasonable values manually then.
exec dbms_stats.gather_system_stats();
exec dbms_stats.set_system_stats('IOSEEKTIM',1);
exec dbms_stats.set_system_stats('IOTFRSPEED',85782);

There is also an Exadata mode, considering the faster storage correctly and updating the MBRC too
exec dbms_stats.gather_system_stats(‘EXADATA');   more 
select
*
from
(
select
x.inst_id,
x.name,
case when x.name not like '%cpu%' then x.value/1024/1024/1024 else x.value end value
from
(
select go.inst_id, 'cpu physical' name, go.value, 10 order_by from gv$osstat go where go.stat_name='NUM_CPUS' union all
select go.inst_id, 'memory physical' name, go.value, 1 order_by from gv$osstat go where go.stat_name='PHYSICAL_MEMORY_BYTES' union all
select go.inst_id, 'memory unused' name, go.value-(select sum(gp.value) from gv$parameter gp where go.inst_id=gp.inst_id and gp.name in ('sga_target','memory_target','pga_aggregate_target')) value, 2 order_by from gv$osstat go where go.stat_name='PHYSICAL_MEMORY_BYTES' union all
select gp.inst_id, gp.name, to_number(gp.value) value,
decode(gp.name,
'cpu_count',11,
'sga_max_size',3,
'sga_target',4,
'pga_aggregate_target',5,
'pga_aggregate_limit',6,
'memory_max_target',7,
'memory_target',8
) order_by
from gv$parameter gp where gp.name in ('cpu_count','pga_aggregate_limit','pga_aggregate_target','sga_max_size','sga_target','memory_max_target','memory_target')
) x
order by
x.inst_id,
x.order_by
)
union all
select
gi.inst_id,
'PGA record date: '||least(gi.startup_time,(select min(dhs.begin_interval_time) from dba_hist_snapshot dhs where vd.dbid=dhs.dbid and gi.instance_number=dhs.instance_number)) name,
null value
from
gv$instance gi,
v$database vd
union all
select
gi.inst_id,
'average PGA' name,
(select avg(dhp.value)/1024/1024/1024 from dba_hist_pgastat dhp where vd.dbid=dhp.dbid and gi.instance_number=dhp.instance_number and dhp.name='total PGA allocated') value
from
gv$instance gi,
v$database vd
union all
select
gi.inst_id,
'maximum PGA' name,
(select max(dhp.value)/1024/1024/1024 from dba_hist_pgastat dhp where vd.dbid=dhp.dbid and gi.instance_number=dhp.instance_number and dhp.name='maximum PGA allocated') value
from
gv$instance gi,
v$database vd
union all
select
to_number(null) inst_id,
case when ass.pname='DSTART' then 'System Stats record date: '||ass.pval2 else ass.pname end name,
to_number(decode(ass.pname,'DSTART',null,ass.pval1)) value
from sys.aux_stats$ ass
where
ass.pname in ('DSTART','CPUSPEEDNW','IOSEEKTIM','IOTFRSPEED','MBRC')
Download
Related Blitz Reports
DBA AWR SQL Performance Summary
DBA AWR System Metrics Summary
DBA AWR Active Session History
DBA AWR Blocking Session Summary
DBA AWR PGA History
DBA AWR Latch Summary
DBA AWR System Time Summary
DBA AWR Settings
DBA AWR Latch by Time
Blitz Report In Action