Re: Nested transactions: low level stuff

> Given all the flak we got about WAL growth during the time we had that
> code enabled, I think there's no chance that UNDO will be the preferred
> path.  It's not workable with big transactions.

Somehow it's working in other DB systems.

> There are other problems besides WAL bloat, too.  I realized while I was
> working on the btree code a few weeks ago that it's fundamentally
> unfriendly to UNDO, because there are some operations you'd want to
> UNDO (viz, insertion of a leaf item pointing at a heap tuple) and some
> you would not (viz, splitting of index pages and subsequent insertion of
> items into upper tree levels).  But the same WAL entry might include
> both kinds of operation.  This could be got round, perhaps, but that
> code is overcomplicated already ...

Each access-method requires specific UNDO code (like REDO).
Once again, it works in other DB-es.

Vadim