Re: Persist MVCC forever - retain history

Konstantin Knizhnik schrieb am 05.07.2020 um 19:31:
>> I am surprised that you are saying you didn't feel big interest. My
>> reading of the thread is the opposite, that there was quite some
>> interest, but that there are technical challenges to overcome. So you
>> gave up on that work?
> No, I have not gave up.
> But...
> There are well known problems of proposed approach:
> 1. Not supporting schema changes
> 2. Not compatible with DROP/TRUNCATE
> 3. Presence of large number of aborted transaction can slow down data access.
> 4. Semantic of join of tables with different timestamp is obscure.

Oracle partially solved this (at least 1,3 and 4 - don't know about 3) by storing the old versions in a separate table that is automatically managed if you enable the feature. If a query uses the AS OF to go "back in time", it's rewritten to access the history table.

Thomas