IMHO, Jonathan really says all that needs to be said right here.
Also consider the relative gains - how much gain do you really expect, and is
that gain worth the effort around testing and then maintaining "non-default"
values.
Clay Jackson
From: oracle-l-bounce@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> On Behalf
Of Jonathan Lewis
Sent: Sunday, January 17, 2021 1:59 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: db file multiblock read count
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There are only two points you have to consider -
a) does a non-default value have any effect on the actual activity at the time
of execution
b) does a non-default value have any effect on the cost of the query, and would
that make any critical plans change in an undesirable way.
Both points can be investigated with some very simple modelling, though the
"actual activity" testing may require a little though to cover variations like
parallel execution, direct path reads in general, possible effects on "small"
tables; and the "costing" testing needs to consider the effects of system
statistics (dbms_stats.xxx_system_stats) and/or the calibrate_io calls.
Once you've done the tests that are most relevent to your application and setup
you may still find that leaving everything to default is the safest strategy.
Regards
Jonathan Lewis
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On Fri, 15 Jan 2021 at 22:17, Moustafa Ahmed
<moustafa_dba@xxxxxxxxxxx<mailto:moustafa_dba@xxxxxxxxxxx>> wrote:
Hello
There are many opinions out there about the right value for
db file multiblock read count
And the more I look it seems like it started to be of less significance than 10
years ago!
Say a value of 1024 which is considerably high
On Exadata and a DW system
What would be the concerns with that?
