Using of temporay table geneartes giant ammount of UNDO-Writes?

Question

Database 9.2.0.5
Sun Os 5.8 64Bit
Hello we are benchmarking an application which stores data for temporary processing in global temporary tables.
What i see in the stastpack now is that 99%!!!! of physical writes run against the UNDO tablespace, this seems very strange to me!
Q1 : We reduced undo_rentention from 10000 to 900
does this reduce realy Number Writes to UNDO?
Q2 : Is there a side effect hat using temporay tables generates to much undo?
Regards
Carl r.
Statspack :
Tablespace IO Stats for DB: RPMS_R01 Instance: RPMS_R01 Snaps: 3761 -3767
->ordered by IOs (Reads + Writes) desc
Tablespace
Av Av Av Av Buffer Av Buf
Reads Reads/s Rd(ms) Blks/Rd Writes Writes/s Waits Wt(ms)
UNDOTBS1
8 0 1.3 1.0 813,494 110 8,873 ######
SYSTEM
8,556 1 0.1 1.0 349 0 248 ######
STATSPACK
205 0 2.8 1.0 3,492 0 0 0.0
TEMP
2,999 0 1.1 1.0 571 0 0 0.0
RPMS_DATA
27 0 0.4 1.0 1,158 0 42 113.3
RPMS_INDX
25 0 1.2 1.0 160 0 71 13.8
KUR_INDX
148 0 1.5 1.0 14 0 0 0.0
TOOLS
152 0 0.1 1.0 8 0 0 0.0
AUDITS
11 0 2.7 1.0 99 0 0 0.0
KUR_DATA
45 0 0.0 1.0 12 0 0 0.0
KOBEW_DATA
25 0 6.4 1.0 8 0 0 0.0
KOBEW_INDX
8 0 0.0 1.0 8 0 0 0.0
ORDER_DATA
8 0 0.0 1.0 8 0 0 0.0
ORDER_INDX
8 0 0.0 1.0 8 0 0 0.0
QUEST
8 0 0.0 1.0 8 0 0 0.0
REP_DATA
8 0 0.0 1.0 8 0 0 0.0
SAL_DATA
8 0 0.0 1.0 8 0 0 0.0
SAL_INDX
8 0 1.3 1.0 8 0 0 0.0
USERS
8 0 0.0 1.0 8 0 0 0.0
XDB
8 0 0.0 1.0 8 0 0 0.0

Answer 1

UNDO_RETENTION actually determines how long to keep already committed data in the UNDO tablespace, so decreasing the retention will only keep less undo in the undo tablespace and require less space for the UNDO tablespace, it should not increase the number of UNDO writes, the number would be the same for a transaction, no matter what the undo_retention.