Subject Re: [firebird-support] Does added column cause all records to be touched or what happens?
Author Kjell Rilbe
Kjell Rilbe skriver:
> Ann W. Harrison skriver:
>> What's taking the time is creating an index on 150,000,000 records
>> all of which have exactly the same key value. I seriously doubt
>> that the index will be of any value to you, and now that it's created,
>> it will have a selectivity of 1.0 - as bad as it gets. When you do
>> put values in that field, you should at least reset the selectivity.
>> Though it sounds unkind, given how much work Firebird has put into
>> creating a worthless index, I suggest you drop it and recreate it
>> when you've actually got more than one value.
> Yes, I realized that once it had started executing - that the index
> should have been created a bit later in the process. Oh, well... It will
> get a lot more selective later on, I promise! ;-)

...and after having filled the new column with data and rebuilt the
index, it now has selectivity 0.000022. :-) The update took 12 hours,
probably because silly me forgot to deactivate the index before running
the update... Live and learn!

Kjell Rilbe
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