FAQ

On Sat, 2004-07-10 at 15:04, Jan Wieck wrote:
On 7/5/2004 6:16 PM, Simon Riggs wrote:
On Mon, 2004-07-05 at 22:30, Tom Lane wrote:
Simon Riggs <simon@2ndquadrant.com> writes:
...While recovering, it is very straightforward to simply ignore every
record associated with one (or more) transactions. That gives us the
ability to recover "all apart from txnid X".
Don't even *think* of going there.
Hmmm... thinking is important, as are differing viewpoints. I value
yours and those of everyone else on this list, hence the post.
What will happen when transaction Y comes along and wants to modify or
delete a row that was inserted by X? There's no chance of staying
consistent.
I did point out this downside...a few sentences down.
**This is awful because: transactions are isolated from each other, but
they also provide changes of state that rely on previous committed
transactions. If you change the past, you could well invalidate the
future. If you blow away a transaction and a later one depends upon it,
then you will have broken the recovery chain and will not be able to
recover to present time.**

Theoretically, this is a disaster area.

Practically, Oracle10g provides similar-ish features...
IF ... the recovery process would be primary key based, and IF the
database definitions would allow for balance type field handling (the
log contains value deltas for balance fields instead of overwriting
them), THEN this would be a direction I would be looking into.

But as things are, the whole recovery is ctid and binary block based. So
you would now leave out the ctid based changes to several tuples because
of belonging to said transaction. Later on, an original whole block
appears in the WAL and overwrites ... so you get what ... partial
transactions into the recoverd DB?
...Nobody is shouting YES, so its a dodo...
No way!
Sorry...I meant "this idea is dead, just like the extinct Dodo bird".-
I've been trying to be succinct, but that has led to information loss.

...you've come up with an even better reason why the idea is not good.

Many thanks,

Best Regards, Simon Riggs

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