Question of performance of version 8

Hello.
I tried performance test of version 8.0.0 beta4 by osdl-dbt-1.
The result is that throughput of version 8 fell to about 70 percent
compared with V7.4.6.
Test result is below. (measurement was repeated 3 times)

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Hardware spec
　CPU　　　Pentium Ⅲ  531.986 MHz
　Memory　　125660 Kb
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Software version
　OS　Linux Kernel:2.4.21-4.EL
　Distribution: Red Hat Enterprise Linux AS release 3
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Result（transaction per second）
             first  second third
  7.4.6   　  6.8    6.8    5.9
  8.0 beta4   4.3    4.6  　4.4
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Parameter of DBT1,PostgreSQL
　Database Size (items): 1000
　Database Size (customers): 10
　number of cache: 1
　number of connections between cache and database: 10
　number of application server: 1
　number of connections between server and database: 20
　number of drivers: 1
　eus/driver: 100
　rampuprate/driver: 60
　duration/driver: 900
　thinktime/driver: 1.6
　Put WAL on different driver: 0
　Put pgsql_tmp on different driver: 0
　database parameters: -i -c listen_addresses='*'
　shmmax: 33554432
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- Both version 8 and version 7 are performed under the same condition.
- Tuning of adjustment of a parameter was not carried out at all.
- The server and client process are performed in the same machine.

Is there the weak point on the performance in version 8.0.0 ?

Any help would greatly appreciated.

  kondou