rollback questions

I am trying to understand rollbacks, at least understanding how SAP uses them and to tune them. We have been getting more ORA-01555s since our database crossed the 100G size. Right now the rollbacks are set to the default install. Here are the stats from a program called orastat (plug:GREAT TOOL!):

sapprd:oraprd 3> ./orastat -ra
2002/12/20-16:19:35 orastat | oraver=8.1.7 oraver3=8.1 sqlcmd=sp 2002/12/20-16:19:35 orastat | ORACLE_SID=PRD ORACLE_HOME=/oracle/PRD/817_64
2002/12/20-16:19:35 orastat | Version=2.33 orastat | Rollback Segments Statistics

RSSize : Current rollback segment size in bytes

-column removed, all 10641408 bytes (10M)

A Xn's : Number of current transactions using the rollback segment

-column removed, all currently 0

HWMSize : High Water Mark size in bytes
Wraps : Cumulative # of times a X'n continues writing from one

          extents to another existing extent Avg Actv: Avg # of bytes in active extents in the rbs

        measured over time

Name Extends Gets HWMSize Wraps Avg Actv Waits ------ ------- ------ ---------- ------ --------- ------

PRS_0       7  130478  25550848    176    2345674    12
PRS_1       6  124295  19161088    162    2210725     2
PRS_2       4  123095  19161088    161    2232942     0
PRS_3       1  125297  12771328    163    2136828     1
PRS_4      12  153932  36200448    154   17202515     3
PRS_5      28  150456  63889408    178    2647096     5
PRS_6      31  144235  42590208    210    8988732    15
PRS_7       4  127866  19161088    172    2810635     1
PRS_8      65  143432 138436608    232   95312420     2
PRS_9       4  129341  19161088    175    2206473     2
PRS_10     12  127924  31940608    174    2222152     3
PRS_11      0  121028  10641408    143    2130736     0
PRS_12      0  121148  10641408    146    2147608     0
PRS_13     62  142333 142696448    222    2131274     1
PRS_14     42  141261  91578368    223    6116854     3
PRS_15      5  130087  19161088    179    2132704     4
PRS_16     48  137197 108617728    210    2602272     2
PRS_17    120  166012 191684608    310    2893642     2
PRS_18     17  128125  38330368    175    4018525     1
PRS_19     20  131124  53239808    186   15698495     0

Questions:
  If the rollbacks are 10M each, how can the high-watermark be higher?   Since SAP doesn't seem to use all of them equally, should a few smaller but LARGER ones work better?

Thanks!
Vince Received on Fri Dec 20 2002 - 16:31:20 CST