Hello Cheng,
FYI - the behavior that is described in the Tweet is kinda different. I just
copy & paste my reply: "Buffer cache was shrinking from 130 GB to 118 GB over a
time period of one month but at the time when it was 118 GB the DB only got
2.077.979 buffer headers (2.077.979 x 8k = 16623832 k = 16234 M) within the 118
GB."
... so the buffer cache size was still 118 GB but only round about 16 GB of it
was used.
Best Regards
Stefan Koehler
Independent Oracle performance consultant and researcher
Website: http://www.soocs.de
Twitter: @OracleSK
Ls Cheng <exriscer@xxxxxxxxx> hat am 24. Januar 2020 um 11:27 geschrieben:--
Hi
I have also observed behaviour stated in
[https://twitter.com/jolliffe/status/1094195271448186881?s=20](https://twitter.com/jolliffe/status/1094195271448186881?s=20.)
I have seen it when no minimum memory parameters are set. For example I have
a customer who has a database with 40GB sga_target set, no other memory
parameters and after 3 or 4 weeks the buffer cache was left with 64MB only.
So I think the best practice would be setting minimum and sga_target.
BR
