locked up backends

Hello,

We are running Postgres 7.0.2 on Linux RH 6.2 Dell servers.

When traffic gets heavy we often get one of the backend locked up in an 
UPDATE, INSERT or COMMIT request. Eventually all the other backends end 
up locking too as they try to access a row locked by the original 
backend. The output of 'ps' shows that the locked up backend is sleeping 
waiting for 'select' to return.

This has been occurring once or twice a day for the past few months. We 
just stop the postmaster (sometimes we need to kill -USR1 one of the 
backends before they all disappear) and then we restart postmaster and 
everything works fine until the next lock up.

Any idea what might be wrong? I'd be happy to provide more info, if only 
I knew what.

Thanks in advance,

--Maurice