Re: what's xidsql and ubasqn in v$transaction?

<niy38_at_hotmail.com> wrote in message
news:1149096123.160158.303290_at_y43g2000cwc.googlegroups.com...
> Thanks, great answer!
>
> xidsqn can be used to identify the unique transaction. what ubasqn is
> used for?
>
> Jonathan Lewis wrote:
>> The slots in the transaction table in the undo segment header
>> are continuously being reused. Each time a slot it re-used,
>> its sequence number (xidsqn) goes up.
>>
>> Similarly, undo blocks are re-used (though it takes more
>> time to get round to re-using them than transaction slots).
>> Each time an undo block is "newed" and reused, its
>> sequence number UBASQN goes up.
>>

Undo blocks are re-used over time - so if the undo block address recorded in a data block (ITL entry) points just to an undo block, it may be an undo block that has since been re-used. So the complete specification for an Undo Block Address (UBA) entry includes the sequence number.

-- 
Regards

Jonathan Lewis
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