Re: Hints
- From: Robert Hanuschke <robert.hanuschke@xxxxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Mon, 15 Aug 2011 09:37:43 +0200
Hi,
The first sentences of the Oracle documentation (performance tuning
guide) regarding hints explain the pros and cons pretty well, I think:
"Hints let you make decisions usually made by the optimizer. As an
application designer, you might know information about your data that
the optimizer does not know. Hints provide a mechanism to instruct the
optimizer to choose a certain query execution plan based on the
specific criteria.
For example, you might know that a certain index is more selective for
certain queries. Based on this information, you might be able to
choose a more efficient execution plan than the optimizer. In such a
case, use hints to instruct the optimizer to use the optimal execution
plan.
Note:
The use of hints involves extra code that must be managed, checked,
and controlled."
(http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/hintsref.htm)
There are good reasons to use hints if you've got data/situations of
which the optimizer will likely not be aware (e.g. because of
statistics only being estimated and missing some details because of
that) but on the downside you have to maintain them.
Best regards,
Robert
On Mon, Aug 15, 2011 at 7:43 AM, Orlando L <oralrnr@xxxxxxxxx> wrote:
> Hello all,
>
> Are hints in queries considered bad, if so why.
>
> Orlando.
>
>
>
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