Re: MVCC, undo log, and HOT

Bruce Momjian wrote:
> Josh Berkus wrote:
>   
>> Bruce,
>>
>>     
>>> We never actually considred undo, but high UPDATE activity was one of
>>> the areas we historically handled poorly compared to undo systems, and
>>> undo would have been one way to improve that area.  I think with HOT we
>>> have improved high UPDATE activity enough that the undo benefits are no
>>> longer attractive (and of course the undo disadvantages were never
>>> attractive).
>>>
>>>       
>> If you're asking if we should remove the TODO (is there one?) and 
>> replace it with a FAQ item called "Why PostgreSQL doesn't have an UNDO 
>> LOG", then my vote is "yes".
>>     
>
> No, it never got close to being a TODO item.  It was more a limitation
> we had that is now fixed.
>   

HOT is cool, but it really doesn't solve the whole problem. It works for 
a significant class of problems, but for example it won't have any 
significant effect on the app I'm currently working on which is very 
index-rich. It would be a major mistake to think there's no work left to 
do in improving update performance.

cheers

andrew