Indexes and rollback segments

From: <rtgraf_at_sintec.de>
Date: Fri, 12 Jun 1998 07:46:07 GMT
Message-ID: <6lqmbv$9mb$1@nnrp1.dejanews.com>

Hi,
we have just been discussing the topic of Oracle Indexes and the rollback segments. The Oracle documentation states that index entries are not

physically deleted but marked as "free". We understand that this is
necessary to reduce reorganization cost. Updated index entries are deleted
(i.e. marked as "free") and re-inserted.

The question now is: How *exactly* does Oracle ensure its multi-version read consistency regarding the indexes? Oracle Customer Support says that when writing to indexed tables, the amount of around 180 bytes plus the before images of the indexed columns is written to the rollback segment.
Does this mean that the index is completely created in the rollback segment? Do long-running read transactions read index blocks from the rollback segment? Are SCN-stamps used, just like in the data segment blocks? How do these SCN-stamps work, anyway? (Are SCNs assigned when the transaction starts or when it commits?)

Just thinking and wondering a lot,

Robert.

-----== Posted via Deja News, The Leader in Internet Discussion ==----- http://www.dejanews.com/ Now offering spam-free web-based newsreading Received on Fri Jun 12 1998 - 02:46:07 CDT