Thursday, April 26, 2007

Questions Answers and then Questions i.e etiquette

Reading Tom Kyte's   Post   and  This Post  and  This Post  . It seems to be a common Theme for the last couple of days.

I have also noticed not only  technet(OTN). but on a lot of mailing lists  this being  a common theme .

People are taking the fact that people respond for granted and try to resolve an issue by using other people's advice without even looking at the fact that the advice is sound or not.

The sheer volume of mail on a lot of mailing lists including but not limited to oracle-l seems to  on topics like can someone tell me how to export a table  or  i want to install RAC  . More how to Questions are popping up everyday.

though i do not oppose asking How-TO questions . That is how i learned  during my DBA career. But what we did was read the oracle Manuals and try ot understand and then ask a how to question.

I still believe Oracle Manuals are really well written and have more than enough information for us to find  info about  a feature or a task.

Yeah asking questions is good but i believe asking questions just to save one's self  the hassle of looking it up is just plain wrong.

A Answer is much better understood if the person who is asking the question has done  the basic analysis.



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Friday, April 06, 2007

Explain Plans

Tom Kyte has an article on his blog . which deals with explain plans .
This is really interesting since i have recently been very intigued by explain plans. I'mstill investigiating an issue where an explain plan changed between 2 idrntical systems.
and where there was less data but enough to use an index and all the columns that the join was based upon were indexed. after a routine stats gathering the explain plan changed from nested loops to a huge hash join with full tablescans of all involved tables.
whne i hinted indexes it ran in 9 secs . and when i used first_rows hint it showed a very bad explain plan but the query finished in 768 msecs.
i've put that workaround in place till i get time to figure out what is going on .
the database is 9.2.0.8 with optimizer_mode =choose and optimizer_features_enable-8.1.7
and optimizer_index_cost_adj=40
Please note it was working till stats were gathered in a routine stats gathering exercise. since we did nt backup old stats.
i have unable to get it back to where it was regardless of what types of stats i gather or indexes i rebuild.

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