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Re: Indexes and Logical design

From: VC <>
Date: Sun, 11 Sep 2005 20:51:55 -0400
Message-ID: <>

"David Cressey" <> wrote in message news:St2Ve.10432$ [...]
>> > Not true. In DEC Rdb/VMS a unique constraint can be declared without
>> > creating an index, if you want to.

It's unclear to what part of my first response to your original message "Not true" refers.

Earlier, I wrote this: "One can easily imagine a unique constraint enforcement without any index whatsoever although such enforcement would be impractical". I did not claim that no database could implement a unique constraint without an index did I.

It's interesting to note that by mentioning Rgb's ability to create a unique constraint without an index you actually reinforce my argument that the index is just a performance tool.

>> For toy tables probably. In 'real world', no.
> In the real world, yes.

It appears that in the "real world" you model the tables you want to have unique constraints on are either small, or you do not care much about concurrency when accessing such tables, or both. As is well known, accessing a table without an index will lead to a full table scan thereby impacting performance if the table is larger than a couple dozen rows. Besides, sequential retrieval for a read/write transaction requires locks on the entire table, which results in coarser locks and degraded concurrency.

>> What kind of argument in favour of indexes being part of logical model is
>> that ? Are you familiar with the notion of relevancy ?
> Yes, the notion of relevancy IS important. But as long as you and I are
> as
> divided as we are about the nature of the real world, we are unlikely to
> come to a consensus about relevancy.

Does it mean that you actually do not have any technical arguments to substantiate your claim that indexes belong to the logical model, or in other words indexes are something else beyond being a performance tool ?

Received on Sun Sep 11 2005 - 19:51:55 CDT

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