rollback segs suggestions

[Prasy]

Hello Guys,

I had high values in undo_header in v$waitstat, so according to the suggestion given in different threads i increased number of rollback segments , but now the value has increased much more than the previous value. Whats wrong here.

Initial value:

632 and 152 for count & time respectively in v$waitstat

recent

664 and 201

Any suggestions ??

[julian]

Here is how you should procede:

Run the following:

select sum(value) "Data Requests" from v$SYSSTAT
where name in ('db block gets', 'consistent gets');

If "Data Requests" is less than 66400, i.e., the number of waits for any of the rollback segment blocks or headers exceeds more than one percent of the total number of requests, only then, you need to add more rollback segments!

You may first want to verify that 664 value again, so run:

select class, count from v$WAITSTAT where class in ('undo header','undo block','system undo header', 'system undo block');

and add together all values you get for count.

[Prasy]

Hi Julian,

My count goes like this

CLASS COUNT
------------------ ----------
system undo header 0
system undo block 0
undo header 664
undo block 159


Data Reque
----------
4604093664

Wats ur suggestion ??

[julian]

The ratio (823/4604093664) is much less than 1/100. You are doing fine.