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Help with SQL Tuning Advisor Recommendations

Posted on 2008-10-16
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Last Modified: 2012-05-05
i'm playing around with the Tuning Advisor...
in the index recommendations, i can see where it's recommending an index:
_dta_index_tablename_blahblah

i can see that the index recommendation covers several columns by looking at the Target of Recommendation.
1.  how do i know what type of index it is recommending?

2.  should i always take the Tuning recommendation?  for example, if i'm running the advisor on a query that isn't executed all that often, and the recommendation is to create a covered index on a table, and i have another query that does get executed often and uses different columns in the same table (but not all of the columns in the covered index), could i unintentionally be causing overhead from that covered index when changes are made to the table?

3. the Tuning Advisor is also recommending something called dta_stat.  is that statistics, and if so, is it just saying the statistics should be updated?
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Question by:zephyr_hex
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chapmandew earned 250 total points
ID: 22735626
>>should i always take the Tuning recommendation?

Absolutely not.  In fact, I rarely do.  I don't use it that much, just when I want to get a general idea as to what fields should have indexes.  Never implement them directly...always research the ideas it gives you....and take them at that...ideas.
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by:David Todd
David Todd earned 250 total points
ID: 22735765
Hi,

If the second query that is executed a lot has its own indexes and is a select only, the additional covering index will have little or no effect.

On the other hand, if the second query involves inserts/updates/deletes, then any additional index will tend to slow that process down.

Look and see how much improvement Tuning Adviser things it will get - is 5% worth it? Maybe. is 50% + worth it, quite likely.

That is, if one or several recommendations gets 80% say, and the rest are small, then the two that give you the 80% improvement are the ones you need to concentrate on, and maybe completely ignore the others.

HTH
  David

PS I noted that you list yourself as intermediate. Chapmandew is GENIUS or better, and probably can transverse the index chain in his sleep. Definitely take note of the Tuning Advisers recommendations, but verify them. Use it as a learning tool, and do verify everything, until you get to Genius <grin>
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