Thomas Kellerer wrote:

>--- In firebird-support@yahoogroups.com, "Leyne, Sean" <Sean@B...> wrote:
>
>
>>I'll spare us all the intricacies of the nature of an index in MGA based
>>database, but suffice it to say, that the index provides 'guidance' to
>>the engine regarding the rows which should match the criteria. The
>>engine must, however, read each data row to confirm the actual field
>>value.
>>
>>
>
>Hmm. Oracle does not scan the table, if all I request is index fields.
>It returns the data directly from the index. Actually Oracle has taken
>this further to allow "index organized tables" which will completely
>reside in the index storage. Very handy for link tables which only
>contain foreign keys to other tables.
>
>Thomas
>
>

I am not Oracle guru, developed just one system for Oracle 7, and use it
just as persistence layer, no logic, no triggers, no SP.

Does Oracle use MGA ? (I think it implements something like a log for
it, don't know how it could be considered MGA)

Ann has writen sometimes about the need FB has to look on the Data pages
to know for sure if an index entry (in fact the record pointed by the
index) is "visible" to the current transaction.

Index Organized tables are Clustered Indices ?
You can have only one clustered index per table, if you store all
information on the index page (making a clone of the data for each
clustered index, it will increase a lot on every table modification), I
think I didn't get it... Could you explain a bit more ?

See you !

--

Alexandre Benson Smith
Development
THOR Software e Comercial Ltda.
Santo Andre - Sao Paulo - Brazil
www.thorsoftware.com.br



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