[Zope] weired zope behaviour

[Bak@kedai]

hi all

i have a zope site that uses ZEO, runs behind apache and on RH6.x

what puzzles me is that only *one* zserver thread is alive after some time 
and it consumes most of the processors cycle. 
the top snapshots are at the bottom of this message

anybody got any ideas why this happened?  i think this may have contributed 
to the slow response to the site.  if i restart zope, everything works 
dandy... until some time when only one thread is used, instead of 4

what are others seeing?  is it my codes?
thanks

----8<---------------------
ZC1

 4515 nobody     0   0 99.2M  99M  1592 S       0  4.1  2.5 183:37 python
 4537 nobody     0   0 99.2M  99M  1592 S       0  0.0  2.5   0:07 python
 4538 nobody     0   0 99.2M  99M  1592 S       0  0.0  2.5 724:16 python
 4539 nobody     0   0 99.2M  99M  1592 S       0  0.0  2.5 751:47 python
 4540 nobody     0   0 99.2M  99M  1592 S       0  0.0  2.5 735:11 python
 4541 nobody     0   0 99.2M  99M  1592 S       0  0.0  2.5 749:27 python
 4542 nobody     0   0 99.2M  99M  1592 S       0  0.0  2.5 741:45 python
 4543 nobody    13   0 99.2M  99M  1592 R       0 94.0  2.5  1734m python  

ZC2 
 4348 nobody     0   0  102M 102M  1828  2 S     2.1 13.5 214:33 python
 4350 nobody     0   0  102M 102M  1828  2 S     0.0 13.5   0:10 python
 4351 nobody     0   0  102M 102M  1828  2 S     0.0 13.5 398:08 python
 4352 nobody     0   0  102M 102M  1828  2 S     0.0 13.5 407:02 python
 4353 nobody     0   0  102M 102M  1828  3 S     0.0 13.5 406:32 python
 4354 nobody     0   0  102M 102M  1828  3 S     0.0 13.5 392:10 python
 4355 nobody    14   0  102M 102M  1828  2 R    95.5 13.5  4712m python
 4356 nobody     0   0  102M 102M  1828  2 S     0.0 13.5 388:41 python    

Z3
18567 nobody     0   0 73652  71M  1724 S       0  4.4 14.2 273:56 python
18571 nobody     0   0 73652  71M  1724 S       0  0.0 14.2   0:44 python
18572 nobody     0   0 73652  71M  1724 S       0  0.0 14.2  42:03 python
18573 nobody     0   0 73652  71M  1724 S       0  0.0 14.2  63:13 python
18574 nobody    19   0 73652  71M  1724 R       0 91.2 14.2  6144m python
18575 nobody     0   0 73652  71M  1724 S       0  0.0 14.2  47:54 python
18576 nobody     0   0 73652  71M  1724 S       0  0.0 14.2  57:10 python
18577 nobody     0   0 73652  71M  1724 S       0  0.0 14.2  57:13 python     
 
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