Use of hints in query performance

Question

Hi
Please let me know actual usage of hints in query tunging, how do we write hints of increase performnace.
let me know below query will gives better performnce. if hints are not use query will degrade performance.
SELECT /*+ ORDERED INDEX (b, jl_br_balances_n1) USE_NL (j b)
USE_NL (glcc glf) USE_MERGE (gp gsb) */
b.application_id ,
b.set_of_books_id ,
b.personnel_id,
p.vendor_id Personnel,
p.segment1 PersonnelNumber,
p.vendor_name Name
FROM jl_br_journals j,
jl_br_balances b,
gl_code_combinations glcc,
fnd_flex_values_vl glf,
gl_periods gp,
gl_sets_of_books gsb,
po_vendors p

Answer 1

942919 wrote:
Please let me know actual usage of hints in query tunging, how do we write hints of increase performnace.The majority of hints would be used to diagnose a performance problem by identifying a better query plan and fixing the underlying reason that the optimizer did not select that plan automatically. Hints used in this way would be removed from the query after the cause of the performance problem was fixed.
http://docs.oracle.com/cd/E11882_01/server.112/e16638/hintsref.htm#i8327
Hints change the access paths and methods the optimizer chooses, so before using a hint, you need to understand what the optimizer does, what access methods are, when they are chosen, and what they are best used for.
To do that you need to read the Performance Tuning Guide
http://docs.oracle.com/cd/E11882_01/server.112/e16638/toc.htm
At a minimum reading and understanding these sections -
http://docs.oracle.com/cd/E11882_01/server.112/e16638/perf_overview.htm#i1006218
http://docs.oracle.com/cd/E11882_01/server.112/e16638/optimops.htm#i21299
http://docs.oracle.com/cd/E11882_01/server.112/e16638/ex_plan.htm#i19260
http://docs.oracle.com/cd/E11882_01/server.112/e16638/stats.htm#i13546
Then you should be able to use a hint safely.
let me know below query will gives better performnce. if hints are not use query will degrade performance.Not true, hints change the performance of queries they can make them slower as well as faster. Here is an example of an index hint slowing down a query
{message:id=1989089}