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
From: oracle-l-bounce@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> On Behalf
Of Jonathan Lewis
Sent: Mittwoch, 14. Juli 2021 15:30
To: ORACLE-L (oracle-l@xxxxxxxxxxxxx) <oracle-l@xxxxxxxxxxxxx>
Subject: Re: minimal sga_target
A bit of hand-waving, but it's probably mostly down to CPU_COUNT, and might be
fairly easy to kick around.
I have notes that
processes = cpu_count * 80 + 40
sessions = processes * 1.5 + 24
transactions = sessions * 1.1
Then public redo thread count = cpu_count/16
Private redo thread count = transactions / 10
Oracle likes 1MB of buffer cache per process (or maybe it's session - I always
forget), so that probably gets assumed.
The size of the private redo thread is 128KB - so that's a chunk of the SGA to
calculate
Somewhere I've seen a note about the public redo thread default size.
So the main component left would be the shared_pool demanded per process and
for some reason I think it's 4MB - but I don't know where that idea came from.
If no-one else has any better answers - just keep on bouncing.
Regards
Jonathan Lewis
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