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Index and statistics

for infoprovider, what is the problem to run the indicex, but not statistics them?

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  • author's profile photo Former Member
    Former Member
    Posted on Jan 05, 2005 at 01:21 PM

    Do you mean to say that you would like to drop and recreate indexes after loading but not update the statistics?

    If the statistics are updated by other means (e.g. in Oracle with brconnect), there is typically no problem. Only if the other means doesn't update statistics as frequently as is best for your InfoProvider you might have a problem.

    Regards, Klaus

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  • Posted on Jan 10, 2005 at 08:04 AM

    One activity should be connected wit the other: consider that the same SQL runs in a different way if you update statistics or not, with obvious consequences on performance.

    Hope it helps

    GFV

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  • author's profile photo Former Member
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    Posted on Jan 10, 2005 at 01:06 PM

    Statistics tell the optimizer things like how many values there, how similar or unique the values are, etc. The database optimizer uses the index and table statistics to make decisions about how best to execute the query, e.g. perform indexed reads of the table or a full table scan, or what order to read tables. The CBO (Cost Based Optimzer) is generally trying to find the execution plan that requires the fewest system resources, generally the fewest IOs (but there are other factors in the mix). It may examine hundreds or thousands of different execution plans to find wht it thinks is best.

    Without any / good statistics the CBO may make bad choices about how to execute the query, that are not the most efficient.

    When you drop and rebuild the indices, you lose the statistics which could easily result in bad choices by the CBO (Cost Based Optimizer).

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