Re: [PATCHES] log session end - again

Tom Lane wrote:

>Andrew Dunstan <andrew@dunslane.net> writes:
>  
>
>>Bruce Momjian wrote:
>>    
>>
>>>Also, Andrew, on your other patch for log_session_info line, Magnus had
>>>the idea of giving each session an id based on the first transaction of
>>>the session.
>>>      
>>>
>
>  
>
>>I did think about using a cluster-wide sequence, if we can make such a 
>>thing (might also be useful for system generated UIDs too).
>>    
>>
>
>Not a good idea IMHO.  If you do that, then there will be no such thing
>as a purely read-only transaction, because *every* transaction will
>include a nextval() call.  That means even read-only transactions cannot
>commit till the disk spins.
>
>If we want a unique id for transient purposes like logging, then make
>some kind of counter in shared memory.  Don't use a sequence, it's much
>too heavyweight.
>
>  
>

I'm not sure I understand. I didn't suggest that a sequence should be 
used for txn ids. For the purpose I had in mind we would call nextval() 
once per connection, and, for the other purpose where I suggested it 
would be useful, once per "create user". That doesn't seem very heavyweight.

cheers

andrew