HP-UX 11.0/8.1.6.2.0/Optimizer

Hi All:

Here's a strange thing. I did a reorg of a very nasty tablespace over the weekend. I broke it out into 4 new tablespaces for the large tables and the rest into a single tablespace. This database has 'optimizer_mode = rule' set in the initSID.ora file because the Cognos application can't seem to handle the CBO, so I did not compute any statistics as part of the process.

Sounds like routine maintenance, right?

Nope. It went weird. One query, which included an outer join and a sub-query went from about 2 minutes to not finishing in over two hours. All indexes and objects were back in the DB. I verified that about a dozen times, all with manglement breathing down my neck. I EXPLAINED the query till I was blue in the face. I rebuilt (again!) all the indexes. No joy.

Finally, I thought "oh heck...might as well analyze them".

Shazzam. Back to 2 minutes. Huh? But Optimizer-mode is RULE!!

How? Why? I look stupid and so does my whole DBA group. Does anybody have any insights about this behavior?

Thanks,
Mike

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Michael P. Vergara
Oracle DBA
Guidant Corporation



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Author: Vergara, Michael (TEM)
  INET: mvergara_at_guidant.com

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