Explicitly using full hint

Hi
In some of codes, I see the DBA explicitly force the sql to perform a full table scan by using full hint. What should be the reason?
thanks

user8779435 wrote:
I know Anurag. But what could be the reason for DBA to believe on that ...By comparing the one with without full hint and one with full hint.
If he would be getting better response time or less consistent gets or any other stats that he fill is better for the plan.
Like sometime doing full table scan would make a query to do hash join rather than nested loop and it could be possible that full table scan with hash join is giving better stats then index scan with nested loop
Regards
Anurag

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SELECT /*+ FULL(A) */ * FROM TEST A;
In our production system, when we join two bulk tables using FULL hint and it has got indexes on the join fields,
performance is much better.
If indexes are dropped and FULL hint is removed, performance is pretty slow.
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Recently, our database got migrated to Exadata environment, and a DBA told me that using the /*+ FULL */ hint in the query increases the query performance.
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2) I read some articles and got some information that Exadata does some kind of "Smart Scan" and "Cell Offloading" which makes the query efficient. But how does FULL hint contribute here?
This links talks something about this, but not sure if correct - Some Hints for Exadata SQL Tuning - Part III - SQL Optimizer for Oracle - SQL Optimizer for Oracle - Toad World
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Ranit -
Lots of good advice given by others. A little more to add to the comments already made...
Using a full hint as a general tuning rule on Exadata would not be a good idea, just like the sometimes proposed notion of dropping all indexes on Exadata to performance is not a good idea. As Mohamed mentions, a key performance optimization for Exadata are the smart scans, which do require direct path reads. Pushing for smart scans is what drives these types of ideas; because, other than the index fast full scan, index scans will not smart scan. However, smart scanning isn't always faster. OLTP type queries that are looking for one or two rows out of many are still usually faster with an index even on Exadata. If you find using a hint like FULL does improve a query's performance, then just as with using hints in general, it's better to determine why the optimizer is not picking the better execution plan, a full table scan in this case, in the first place; and resolve the underlying issue.
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How do I use Sql hints in PreparedStatement?

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Using Oracle Hints in Selects......

Hello,
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Hi!
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<BLOCKQUOTE><font size="1" face="Verdana, Arial, Helvetica">quote:</font><HR>Originally posted by kanchana Hettiarachchi ([email protected]):
Hello,
Are there any after effects/side effects by using Oracle Hints in a SQL select ??? (hints such as Cache, NOCache, all_rows)
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Kanchi<HR></BLOCKQUOTE>
null

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Hello guys
I have a report that is running forever and I have reviewed the explain plan over and over, which makes me think that the join between these 2 tables are slowing everything down --- The fact table has 10Billion records and the Dim has 10 Millions records. Even if the report has filters on various columns of the 2 tables, it is still taking forever. The explain is showing that its doing a nested loop join of these 2 tables which takes a lot of time.
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Just an update:
I have tried a couple of join operation hints like USE_NL and USE_HASH hints, it changes the join method but didn't help with performance at all.
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Edited by: user7276913 on Nov 5, 2009 7:22 PM

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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.
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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.
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http://docs.oracle.com/cd/E11882_01/server.112/e16638/toc.htm
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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}

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How to use full qualified table names in RPD

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kmangamuri wrote:
Hi,
We are implementing the BI Financial Analytics, we have a requirement to use diffrent user accounts for DAC , ETL and OBIEE
DAC, ETL we are using user as XXOBI
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Any help in this is appreciated.
Thanks
KrisAre you saying you just need to access the database using different accounts? If that is the case, why dont you just update the connection pool settings like username and password with XXOBI_APP account which you are supposed to be using for OBIEE?

Explicitly using full hint

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