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Oracle9i offers fast-start
fault recovery functionality to control instance recovery.
This reduces the time required for cache recovery and makes
the recovery bounded and predictable.Many Service Level Agreements
include a bound on the "mean time to recover" (MTTR)
and the DBA must be able to reliably set a limit on the time
it will take to recover the database.
Administrators specify a bounded
time to complete the cache recovery phase of recovery with
the FAST_START_MTTR_TARGET initialization parameter.The FAST_START_MTTR_TARGET initialization parameter lets you specify
in seconds the expected mean time to recover, which is the
expected amount of time Oracle takes to perform crash/instance
recovery for a single instance.
This is accomplished by limiting the number of dirty
buffers and the number of redo records generated between the
most recent redo record and the last checkpoint.
The database server
automatically adjusts the write rate to meet the specified
recovery target.
Where
do you find the MTTR?
The TARGET_MTTR column of V$INSTANCE_RECOVERY
contains the MTTR target in effect and the ESTIMATED_MTTR
column contains the estimated MTTR should a crash happen right
away. Query these two fields to see if the system can keep
up with your specified MTTR target.
You see that TARGET_MTTR is 15 seconds, which
is lower than the value of FAST_START_MTTR_TARGET specified
of 30 seconds.This means that it is possible to recover the
database within 15 seconds.
If you set the fast fault recovery
to an unrealistic value, the target and estimated MTTR values
will reflect the estimated number of seconds your database requires
to perform crash recovery.Initially, internal defaults are used to populate the
column values of TARGET_MTTR and ESTIMATED_MTTR.These defaults are periodically updated with
execution time estimates during system operation.
More Info
Oracle9i
Database Daily Features
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