insertion times ..

hi guys

I am trying to create a search facility for our site using udm search..
While reading about udm search along with postgresql i cam across this
line in one of the mailing list archived mails.

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> I don't know what kind of queries are executed during the indexing, if
> the insertions don't need indexes you could try to drop the index and
> recreate them when the indexing is done.

THIS SHOULD SIGNIFICANTLY INCREASE INDEXING TIME.
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Is it true that creating indexes after the insertion has been done takes
more time..
If so why ..

Thanx
Anand