>>> if the primary key cannot be modified, that is one less index to update.
>>
>> That is only true for databases with an overwriting storage manager.
>
> ???
> You mean database that overwrite deleted records?
Yes.
> Why?
Because if they don't overwrite on updates, the position of the
record changes. That requires a change in the index too.
> Actually, I meant auto-increment primary key, or timestamp keys.
> Since they cannot be modified, there is no need to recalculate the index position
> even if the whole rest of the record is modified.
Only for an overwriting storage manager. If for instance a MVCC
storage manager is used, a new record is written to a position
different from the previous position (that is why it is called
"non-overwriting") with every update, even when the primary key
is not changed. Naturally that requires you to modify the index.
Jochem
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