Double Underscore Sign In Parameters....

[Aman Sharma]

Hi there,
DB: 11106
OS: Win Xp Proff
I understand that with the underscore prefixed , the parameters are
called undocumented parameters. But I am seeing at times, parameters
having 2 undrescores attached to it too. What's these parameters and
why we have two underscores attached to them?
For example,
SQL> select ksppinm,ksppstvl,ksppstdvl
2 from x$ksppcv a,x$ksppi b
3 where a.indx=b.indx and b.ksppinm like '%shared_io%';

KSPPINM KSPPSTVL
KSPPSTDVL
------------------------------ ------------------------------
----------------
__shared_io_pool_size 4194304 4M
_shared_io_pool_size 4194304 4M
_shared_iop_max_size 536870912 512M
_shared_io_pool_buf_size 1048576 1M
_shared_io_pool_debug_trc 0 0
_shared_io_set_value FALSE FALSE

6 rows selected.
You can see that the first one is having a double underscore attached.
Similarly, in PGA also , there is __pga_aggregate_target parameter.
If anyone can explain this, it would be really great.
Thanks
Aman....

[Michel Cadot]

"Aman Sharma" <amansha...@gmail.com> a écrit dans le message de news:
30135c20-c849-4d7c...@o4g2000pra.googlegroups.com...

They are dynamic values calculated by Oracle.
You can see some of them in V$SGA_DYNAMIC_COMPONENTS.

Regards
Michel

[sri...@hotmail.com]

As michael said, oracle automatically adjusts the dynamic parameters
as per instance load. (from 10g. Automatic shared memory management)
The values that oracle comes up with could be different from what you
have supplied at the starting of the instance or the defaulted values.
If you use a pfile, these deduced values are lost during the next
reboot and oracle will again have to repeat the process to deduce the
best values for the given workload.
If you use a spfile, this can be avoided as the values are preserved
with a double underscore and will be used to set values for thos
parameters duing the the next startup.
regards
srivenu