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Home -> Community -> Usenet -> c.d.o.server -> Re: rollback question
On Thu, 09 Oct 1997 19:22:15 +0200, Norbert Ferstl <ferstl_at_netway.at> wrote:
>Chuck Hamilton wrote:
>>
>> Someone recently told me that all rollback extents for a transaction must
>> be contiguous. If a transaction attempts to allocate the next RBS extent,
>> and that extent was already assigned to another transaction, that the first
>> transaction will fail with a "snapshot too old" error. It will not skip
>> over that extent and grab the next one. Is this true?
>> --
Thats not correct. All rollback entries for a transaction must be in the same rollback segment but can span many extents (which may or may not be contigous).
>> Chuck Hamilton
>> Xchuckh_at_dvol.com
>>
>> In an effort to reduce spam, my return address has been altered.
>> To reply, remove the X from the address.
>
>
>You are wrong
>
>1. extents must not be contiguos but every extent can only hold
> one transaction at one time
>
>
Thats not quite right either.
<quote src=server concepts manual>
A transaction writes sequentially to a single rollback segment.
Each transaction writes to only one extent of the rollback segment at any given time.
Furthermore, many active transactions (transactions in progress, not committed or rolled back) can write concurrently to a single rollback segment, even the same extent of a rollback segment; however, each block in a rollback segment’s extent can contain information for a single transaction only. </quote>
Chapter 3 of the Server Concepts Manual has a good section on rollback segment allocation/deallocation. Much more information there.
>2. snapshot too old occurs if a consistent read cannot get
> consistent data previous to a commited transaction, that has
> not been commited at the start of the consistent read.
>
>
>=====================================
>Norbert Ferstl
>DI Forsthuber GmbH
>Kohlbauernstr. 17
>A-2630 Ternitz, AUSTRIA
>Tel: +43 2630 382500
>Fax: +43 2630 3825014
><ferstl_at_netway.at>
>=====================================
Thomas Kyte
tkyte_at_us.oracle.com
Oracle Government
Bethesda MD
http://govt.us.oracle.com/ -- downloadable utilities
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