Re: serializable transactions ...

I think that's exactly what Oracle does do.

I assume your original comment relates to the need to increase INITRANS on table involved in serializable transactions. And I think you have assumed that Oracle uses the extra
slots to hold actual undo information.

I believe the extra ITL entry is there so that Oracle can guarantee that a transaction can use one for the current transaction, and use the other whilst rolling back interfering transactions to the correct point in time.

--
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Jonathan Lewis
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Oliver S. wrote in message ...


>> Does anyone know why Oracle provides serializable transactions through

>> the history information in the data blocks (set by the INITRANS parameter

>> when creating the table) - why isn't the undo-retention used for that ?

>

> Reading two pages further in my book got me to the idea why Oracle

>doesn't use the undo-retention: Oracle would have to check every

>previous version of the data-block in which the row lies up to the

>SCN when the transaction started. That wouldn't be really efficient.