Server Utilities :: Slow Exports Using Exp Command Due To Open Sessions

I have had the following problem open with Oracle support since March 2011 (8 months), and still no resolution.

When I export all our schema's on Sunday night it takes about 1 hour 50 minutes. When I export the same schema's on any other night it takes 7 hours. The only difference is that on Sunday at 4:00am we drop all connections in the connection pools and reestablish new connections. Then 19hours later on Sunday at 23:00 we perform the exports which only take 2 hours to complete.

I have also tried recreating the connections in the connection pools during the week, and the exports have then only taken 2 hours to complete. But the following night after the connections have been used during the day, the exports again take 7 hours. So it appears the export speed gets significantly slower when there are many open connections that have been used and not closed.

From the stats pack report I found 2 SQL statements internal to the export command, that had an order of magnitude in difference when looking at the elapsed execution time between the fast export, and the slow export (see below).

How to speed up the exports without having to drop and recreate the database connections in the connection pools each night.

FAST:
elapsed_time: 430.90
executions: 161,388
Module: exp@Oracle1 (TNS V1-V3)
SELECT COLNAME, COLNO, PROPERTY, NOLOG FROM SYS.EXU10CCL
WHERE CNO = :1 ORDER BY COLNO

elapsed_time: 264.29
executions: 50,349
Module: exp@Oracle1 (TNS V1-V3)
SELECT TOWNER, TNAME, NAME, LENGTH, PRECISION, SCALE, TYPE, ISNULL, CONNAME, COLID, INTCOLID, SEGCOLID, COMMENT$, DEFAULT$, DFLTLEN, ENABLED, DEFER, FLAGS, COLPROP, ADTNAME, ADTOWNER, CHARSETID, CHARSETFORM, FSPRECISION, LFPRECISION, CHARLEN, TFLAGS, 100 FROM SYS.EXU8COL
WHERE TOBJID = :1 ORDER BY INTCOLID

SLOW:
elapse_time: 8264.16
executions: 124,662
Module: exp@Oracle1 (TNS V1-V3)
SELECT COLNAME, COLNO, PROPERTY, NOLOG FROM SYS.EXU10CCL
WHERE CNO = :1 ORDER BY COLNO

elapsed_time: 3877.78
executions: 38,813
Module: exp@Oracle1 (TNS V1-V3)
SELECT TOWNER, TNAME, NAME, LENGTH, PRECISION, SCALE, TYPE, ISNULL, CONNAME, COLID, INTCOLID, SEGCOLID, COMMENT$, DEFAULT$, DFLTLEN, ENABLED, DEFER, FLAGS, COLPROP, ADTNAME, ADTOWNER, CHARSETID, CHARSETFORM, FSPRECISION, LFPRECISION, CHARLEN, TFLAGS, 100 FROM SYS.EXU8COL
WHERE TOBJID = :1 ORDER BY INTCOLID

I use the following export command for each schema:
$ORACLE_HOME/bin/exp user/pass file=somefile.dmp owner=$SCHEMA log=somelog.log buffer=9000000

I have an Oracle Standard edition 11.1.0.7 database on 64bit Linux with a 7GB SGA. I currently export (I use exp not datapump because datapump is a lot slower and we can't use parallel processing features of datapump on a standard edition database) approx 200 schema's each night. The export normally takes 1 hour 50 minutes which is approximately 2 schema's exported every minute. When the exports run slowly each export takes almost 2 minutes to complete.

The database has about 20 GB data and 50 GB indexes. The database has also approx 500 connections via toplink connection pools from 8 application servers.