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Statistics used by optimizer.
Posted by: Rakshit Trivedi ()
Date: August 28, 2009 07:32AM

Hi,

I wanted to know about the use of statistics by MYSQL optimizer. According to what I have followed, for estimating the number of rows to be read from a table , the optimizer probes the indexes and calculates the values. Is it true that for different constant values for a given query, the optimizer probes and accesses the indexes to estimate the rows? Or does it only use the already stored statistics of the table?

And one more question. While browsing on summaries and statistics used by MYSQL, I came across the following post:
http://forge.mysql.com/worklog/task.php?id=4816

Here, the reasons for not preferring the histograms are presented. I just wanted to know how the use of histograms leads the optimizer not to use right instructions mentioned there? And how not using histograms is beneficial to optimizer?

Thanks.

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Subject Views Written By Posted
Statistics used by optimizer. 5430 Rakshit Trivedi 08/28/2009 07:32AM
Re: Statistics used by optimizer. 2306 Rick James 08/29/2009 01:11PM
Re: Statistics used by optimizer. 2148 Rakshit Trivedi 09/01/2009 06:30AM
Re: Statistics used by optimizer. 2050 Rick James 09/01/2009 07:44AM
Re: Statistics used by optimizer. 2135 Rakshit Trivedi 09/01/2009 02:51PM
Re: Statistics used by optimizer. 2003 Rick James 09/01/2009 09:59PM
Re: Statistics used by optimizer. 2069 Rakshit Trivedi 09/04/2009 11:00AM
Re: Statistics used by optimizer. 2126 Rick James 09/04/2009 07:37PM


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