why after increase the hash table partitions, TPMC decrease

From: Xiaoyulei <xiaoyulei(at)huawei(dot)com>
To: "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: why after increase the hash table partitions, TPMC decrease
Date: 2014-09-02 08:39:06
Message-ID: E8870A2F6A4B1045B1C292B77EAB207C5BA392E6@SZXEMA501-MBX.china.huawei.com
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We use benchmarksql to start tpcc test in postgresql 9.3.3.
Before test we set benchmarksql client number about 800. And we increase the hash partitions from 16 to 1024 , in order to reduce the hash partition locks competition.
We expect that after increase the number of partitions, reduces lock competition, TPMC should be increased. But the test results on the contrary, after modified to 1024, TPMC did not increase, but decrease.
Why such result?

We modify the following macro definition:
NUM_BUFFER_PARTITIONS 1024
LOG2_NUM_PREDICATELOCK_PARTITIONS 10
LOG2_NUM_LOCK_PARTITIONS 10

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