From: Scalone, Galen (Galen.Scalone@vacationclub.com)
Date: Thu Sep 12 2002 - 10:24:59 EDT
List,
Many Replies, too many to list, but the jist of it is this:
The Symmetrix box has 2 gb of cache in it, if I bump up dbc_max_pct to 15,
it "probably" will not make a difference for the better, and could possibly
make a difference for the worse. I could be running into double buffering,
once on the HP, and once on the EMC.
So... I'll leave the kernel as is, and look into the SQL statements that
people are complaining about.
Some good Ideas for testing purposes:
>From Jim Turner (always a great answer)Thanks Jim!
Hi Galen,
Oracle does its own caching as you probably know, so no need to pay
twice by letting those mountpoints use the OS dbc. Set all Oracle
mountpoints except orahome and applhome to convosync=direct and
mincache=direct in /etc/fstab. (These options require OnlineJFS.) Have
your DBA's crank up the SGA(s) and be generous with the sort areas.
My testing as well as advice from the likes of Bill Hassell and Stephen
Cuillo (friends with Dennis Richie since Bell Labs) indicates that any
dbc beyond around 300MB generally offers diminishing returns. The
memory is better used as Oracle SGA. With 16GB of RAM, I'd set min and
max_dbc_pct at 2 to make it static and about 328MB. Setting it static
also has the favorable effect of removing arm-wrestling between vhand,
swapper, and the buffer cache algorithm if you experience memory pressure.
If I get the opportunity, I will try this method.
Thank you again.
List,
> V2500 16gb 16 procs. dbc_min_cache set at 2, and dbc_mak_pct set at 3.
> Is this any good, I suggested 5, and 15, and was shot down. Machine is
> running Oracle, on a Symmetrix 8340.
>
> I will summarize.
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