--- In firebird-support@yahoogroups.com, Alexandre Benson Smith
<iblist@t...> wrote:

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

I'm not sure what MGA stands for. My understanding is, that it's the
same as Multiversion Concurrency Control. If that is true, then yes
Oracle is using that.

> Index Organized tables are Clustered Indices ?

Not really. Somewhat similar, but not the same.
In a nutshell, when you create an index organized table, the table
data is *only* stored in the index, not in the table itself (there are
variations from this, but this is the basic concept). With an IOT
there is no "real" table data, thus reducing disk space and increasing
access time, because only the index needs to be scanned.

To quote Oracle's manual: "In an index-organized table, the data rows
are held in an index defined on the primary key for the table."

But Oracle will in general use the values from the index during a
retrieval if the columns in the SELECT list are all available in the
index used.

Hope this helps
Thomas