I did more testing, findings are below.
If we consider the minimal sga_target as a function of cpu_count:
- In the subdomain 1 << cpu_count < #CPU threads (i.e. large machines),
the minimal sga_target linearly depends on cpu_count.
- Since in this range, the cpu_count is the main contributor to the
minimal sga_target, other dependencies can be treated as a constant.
- With the values of two experiments, we can solve two linear equations
to get the slope and the y intercept.
- The slope is ~2.5 lower in 12c than in 19c
Why bother?
1. Hardware upgrades: we can proactively check if all sga_targets are above
the new minimum, instead of dealing with startup problems after hardware
upgrade,
2. Oracle database upgrades: anticipate new requirement and avoid failed
upgrades.
Being proactive is particularly important when your test system has less CPUs
than production!
Best regards,
Nenad
From: Noveljic Nenad
Sent: Mittwoch, 14. Juli 2021 15:58
To: ORACLE-L (oracle-l@xxxxxxxxxxxxx) <oracle-l@xxxxxxxxxxxxx>
Subject: RE: minimal sga_target
Apparently, there’s a linear dependency to cpu_count for cpu_count <= CPU
threads.
For example, after reducing cpu_count from 120 to 60, the minimal sga_target
dropped from 2576M to 1348M.
But after increasing the cpu_count to 192, the minimal sga_target remained
unchanged, i.e.2576M. Maybe it was capped by the number of CPU threads on the
host, which is 120.
There doesn’t seem to be a dependency to open_cursors. The minimal value hasn’t
changed at all after increasing open_cursors from 50 to 200.
Best regards,
Nenad
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