_external_scn_rejection_threshold_hours High Rate

_external_scn_rejection_threshold_hours

11.2.0.3 releases Static Default value = 1 day (24 hours)
11.2.0.2 releases Static Default value = 1 day (24 hours)
11.1.0.7 releases Static Default value = 31 days in CPUJan2012, 1 day CPUApr2012 onwards
10.2.0.5 releases Static Default value = 31 days in CPUJan2012, 1 day CPUApr2012 onwards
10.2.0.4 releases Static Default value = 31 days in CPUJan2012, 1 day CPUApr2012 onwards
10.2.0.3 releases Static Default value = 31 days in CPUJan2012
10.1.0.5 releases Static Default value = 31 days in CPUJan2012



The parameter can have a different value on different instances in RAC.
Support Notes for "_EXTERNAL_SCN_REJECTION_THRESHOLD_HOURS"
@Identifier: kcmmsn



This parameter controls an SCN threshold below the "Maximum Reasonable SCN" above which the database will
reject SCN adjustments, such as those due to attempts to connect to or from a remote database over a database
link. The default value depends on the version.
This may be best illustrated by example. Assume the threshold is set to 10 days = 10*24 hours = 240. If this
database tries to connect to a remote database that has an SCN higher than the local database SCN then
normally the local SCN would "jump" up to match the remote SCN. However if that jump would make the current
headroom value less than 10 days the connect attempt will fail with an ORA-19706. (a headroom of 10 days
being an SCN within 10*24*60*60*SCN Rate SCNs of the current "Maximum Reasonable SCN").
11.1 , 10.2 and 10.1 customers are advised to set the parameter value to 24 (1 day) rather than keeping the
default (unless a different value has been advised by support).
This parameter usually needs to be set to the same value on all databases that talk to each other over database

links , especially if any one of those databases has a "high SCN". The parameter is only available in releases that
include content introduced in CPUJAN2012 - see Note:1393385.1 for base patch levels needed to get this
parameter. Any database without this parameter available can be considered as already having the parameter
set to 0. The lowest value for the actual parameter is 1 (hour).
In most releases the current setting of the parameter cannot be altered dynamically so it is important to ensure
that the parameter is set appropriately when each database instance is started up.
eg:
In init.ora:
# Set threshold on dd/mon/yyyy - See SR xxxxxxxx.x
_external_scn_rejection_threshold_hours = 1
In the spfile:
alter system set "_external_scn_rejection_threshold_hours" = 1
comment='Set threshold on dd/mon/yyyy - See SR xxxxxxx.x'
scope=spfile ;
If you do set the parameter to a value lower than 24 then it advisable to review whether the setting needs to
remain in place every few days.



After a few days rerun the "scnhealthcheck.sql " script from Note:1393363.1 on all databases. If all
databases now show "Result: A" then the parameter setting can be reverted back to 24 (or removed in
11.2)

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