to various sources in the web,
_very_large_object_threshold is expressed in megabytes
and defines the upper level thresholds for using
direct path reads.
As we know, a direct path read will bypass the data buffer
and Saibabu Devabhaktuni has these notes on the effects of
set to any level will disable direct path reads for serial
scans only if the size of an object is less then 5 times the
size of buffer cache.
It is important to remember not to to change any hidden parameters unless
directed by Oracle technical support.
The combination of setting
"event 10949" and "_very_large_object_threshold" parameter
will disable direct path reads for serial scans if the size
of an object is less than 5 times the size of buffer cache
or the value of "_very_large_object_threshold" is less than
about 0.8 times the size of an object.
So, if you
want to disable direct path reads for serial scans for any
object, then set event 10949 at any level and set
"_very_large_object_threshold" to greater than the size of
largest object in MB."
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