Re: Nested transactions and tuple header info

Alvaro Herrera wrote:
> > Also, we will need a phantom xid for every xid1/xid2 pair. You can't
> > just create one phantom xid per subtransaction because you must be able
> > to control independently commit/rollback rows based on the status of the
> > insert transaction.
>
> Oh, sure. This could get huge pretty fast.
>
> We still need to think on the effects this could have on crash recovery
> though -- we'd have to write the phantom Xids to Xlog somehow
> (indicating which ones are committed and which are aborted). And we
> still don't know what effect it would have on CPU cost for every
> visibility check.

As I understand, this overhead would only be needed for subtransactions.
I also don't think there will be a lot of them because it is only for
creation/expire in the same main transaction, and it is only needed for
unique creation/expire combinations, which should be pretty small.

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