Is Zero is the Automatic Value for fast_start_mttr_target in ORacle10g

Question

Dear Friends ,
I am working in Oracle 10g . In Oracle 9i the default value of fast_start_mttr_target is 600 . Now my question is :
In Oracle10g , is the '0' value is automatic recovery activities for fast_start_mttr_target (i.e., fast_start_mttr_target=0, here MTTR performs auto) ?
Is it correct ?
And also using the query , How can I measure the MTTR value :
Estimate the value for FAST_START_MTTR_TARGET as follows:
SELECT TARGET_MTTR,
ESTIMATED_MTTR,
CKPT_BLOCK_WRITES
FROM V$INSTANCE_RECOVERY;
TARGET_MTTR ESTIMATED_MTTR CKPT_BLOCK_WRITES
103 12 169
How can I measure MTTR terget using this value ? plz help .. ...

Answer 1

"Unset" means 'not set, non-existent'.
If you're using a text init.ora, you simply delete the line on which that parameter is set.
If you're using a binary spfile, you issue the command
alter system reset fast_start_mttr_target scope=spfile sid='*';
Either way, you end up with the parameter physically not being specified in your configuration file. As opposed to it being set to a zero value, in which case it is physically present in the configuration file, set to a value which will switch off auto-tuning of checkpoints.
You want it "not existing", not "existing but set to a value of zero".
I'm afraid I don't know of any other way to explain the difference between non-existence and existence at value zero to you.
One slight twist is that if the parameter does not exist in the spfile at all, a "show parameter fast_start_mttr_target" in SQL*Plus will show its value to be set to zero. For example:
show parameter fast_start
NAME                                 TYPE        VALUE
fast_start_io_target                 integer     0
fast_start_mttr_target               integer     0
fast_start_parallel_rollback         string      LOWShowing a zero value because it is explicitly set to zero.
alter system reset fast_start_mttr_target scope=spfile sid='*';
System altered.
show parameter fast_start
NAME                                 TYPE        VALUE
fast_start_io_target                 integer     0
fast_start_mttr_target               integer     0
fast_start_parallel_rollback         string      LOWShowing a zero value because it doesn't exist in the spfile at all (which is what the 'reset' command did for me.
The only way I know to tell the difference between 'showing zero because it exists and it's been set to zero' and 'showing zero because it doesn't exist at all and zero happens to be the default value' is to try and delete the thing as shown above (with the alter system reset) command: if the parameter doesn't exist at all, and is showing a value of zero because that's merely the default value, then you'll get this error message displayed:
alter system reset fast_start_mttr_target scope=spfile sid='*'
ERROR at line 1:
ORA-32010: cannot find entry to delete in SPFILE