Re: MVCC, undo log, and HOT

Josh Berkus wrote:
> Bruce Momjian wrote:
>> Those who have been with the community from long ago might remember
>> discussion about implementing a undo log.  The big advantage of this is
>> that it allows UPDATE to _replace_ rows and limits the amount of cleanup
>> required for UPDATEs.
>>
>> I am hoping that with HOT we will no longer have any need to even
>> consider undo.
>>
> 
> We were considering it?

I don't ever remember us considering it seriously.

> 
> I certainly wasn't.  I've enough experience with Oracle and InnoDB to 
> see that an undo log is its own set of performane issues.   No thanks.
> 

It certainly does.

Joshua D. Drake