Oracle Database Discussions

Hi All,

I came across performance issue that I think results from mis-configuration of something between Oracle and JDBC. The logic of my system executes 12 threads in java. Each thread performs simple 'select a,b,c...f from table_xyz' on different tables. (so I have 12 different tables with cardinality from 3 to 48 millions and one working thread per table).
In each thread I'm creating result set that is explicitly marked as forward_only, transaction is set read only, fetch size is set to 100000 records. Java logic processes records in standard while(rs.next()) {...} loop.

I'm experiencing performance degradation between execution on Oracle 9i and Oracle 10g of the same java code, on the same machine, on the same data. The difference is enormous, 9i execution takes 26 hours while 10g execution takes 39 hours.

I have collected statspack for 9i and awr report for 10g. Below I've enclosed top wait events for 9i and 10g
===== 9i ===================
Avg
Total Wait wait Waits
Event Waits Timeouts Time (s) (ms) /txn
---------------------------- ------------ ---------- ---------- ------ --------
db file sequential read 22,939,988 0 6,240 0 0.7
control file parallel write 6,152 0 296 48 0.0
SQL*Net more data to client 2,877,154 0 280 0 0.1
db file scattered read 26,842 0 91 3 0.0
log file parallel write 3,528 0 83 23 0.0
latch free 94,845 0 50 1 0.0
process startup 93 0 5 50 0.0
log file sync 34 0 2 46 0.0
log file switch completion 2 0 0 215 0.0
db file single write 9 0 0 33 0.0
control file sequential read 4,912 0 0 0 0.0
wait list latch free 15 0 0 12 0.0
LGWR wait for redo copy 84 0 0 1 0.0
log file single write 2 0 0 18 0.0
async disk IO 263 0 0 0 0.0
direct path read 2,058 0 0 0 0.0
slave TJ process wait 1 1 0 12 0.0


===== 10g ==================
Avg
%Time Total Wait wait Waits
Event Waits -outs Time (s) (ms) /txn
---------------------------- -------------- ------ ----------- ------- ---------
db file scattered read 268,314 .0 2,776 10 0.0
SQL*Net message to client 278,082,276 .0 813 0 7.1
io done 20,715 .0 457 22 0.0
control file parallel write 10,971 .0 336 31 0.0
db file parallel write 15,904 .0 294 18 0.0
db file sequential read 66,266 .0 257 4 0.0
log file parallel write 3,510 .0 145 41 0.0
SQL*Net more data to client 2,221,521 .0 102 0 0.1
SGA: allocation forcing comp 2,489 99.9 27 11 0.0
log file sync 564 .0 23 41 0.0
os thread startup 176 4.0 19 106 0.0
latch: shared pool 372 .0 11 29 0.0
latch: library cache 537 .0 5 10 0.0
rdbms ipc reply 57 .0 3 49 0.0
log file switch completion 5 40.0 3 552 0.0
latch free 4,141 .0 2 0 0.0


I put full blame for the slowdown on SQL*Net message to client wait event. All I could find about this event is that it is a network related problem. I assume it would be true if database and client were on different machines.. However in my case they are on them very same machine.

I'd be very very grateful if someone could point me in the right direction, i.e. give a hint what statistics should I analyze further? what might cause this event to appear? why probable cause (that is said be outside db) affects only 10g instance?

Thanks in advance,
Rafi.