Testlink 1.8.1:Performance

[Solemio]

Hello.
I've used testlink for a long time yet and been troubled by the performance problem of testlink for a long time.
There are 12,000 cases in my database, when i open the tree of cases or test report,i have to wait over 5 minutes, it's so slow that I can't stand.
I did some surveys on it and thought that a function waste a lot of time by executing everytime.

the function is Unset() as the following:
++++++++++++++++++++++
xampplite\htdocs\testlink\lib\results\printDocOptions.php
GenerateTestSpecTree()
{
PrepareNode()
{
Unset($tplan_tcases[$node['id']])
}
}
++++++++++++++++++++++

Who would like to help me judge the result is right or wrong.
Otherwise who can tell me the way to fix the performance problem.

My e-mail : solemio.liu@live.jp

Thank you very much.

[Solemio]

who can tell me the reason,Thanks a lot.