Re: [SQL] inserts/updates problem under stressing !

Tom Lane wrote:
> 
> I wonder whether this doesn't have a problem with concurrent access:
> 
> 1. Transaction A does 'Select count into cnt', gets (say) 200.
> 2. Transaction B does 'Select count into cnt', gets 200.
> 3. Transaction A writes 201 into hits record.
> 4. Transaction B writes 201 into hits record.
> 
> and variants thereof.  (Even if A has already written 201, I don't think
> B will see it until A has committed...)

You're right, Tom.

> I am not too clear on MVCC yet, but I think you need "SELECT FOR UPDATE"
> or possibly an explicit lock on the hits table in order to avoid this
> problem.  Vadim, any comments?

SELECT FOR UPDATE will not help: if there was not record for
particular key then nothing will be locked and